THE SKULL AND MANDIBLE OF THE STEREOSPONDYL LYDEKKERINA HUXLEYI , (TETRAPODA: TEMNOSPONDYLI) FROM THE LOWER TRIASSIC OF SOUTH AFRICA, AND A REAPPRAISAL OF THE FAMILY LYDEKKERINIDAE, ITS ORIGIN, TAXONOMIC RELATIONSHIPS AND PHYLOGENETIC IMPORTANCE

By Robin H. Hewison Oldstream Cottage, 24 Park St. Dunster, Somerset TA24 6SR [email protected] (01643 821525)

ABSTRACT. The structure of the skull and mandible of the basal stereospondyl Lydekkerina huxleyi (Lydekker) Broom 1915 , from the Lower Triassic Lystrosaurus Assemblage Zone (Middle Beaufort Group of the Karoo Basin) of South Africa, is re-described in detail on the basis of a study of the holotype skull, BMNH R 507, other previously described material, and some undescribed material, in particular, a small and relatively complete skull, UMZC T110, and an almost complete right mandible, believed to be BP/1/1373. Three new autapomorphies are proposed for Lydekkerina huxleyi : a bi-tuberculated quadrate boss; the presence of a pair of tubercles on the palatal surface of the exoccipitals; and the presence of dentary type teeth within the denticle fields on all three coronoid bones. New, composite reconstructions of the skull and mandible are given, and the genus and species are diagnosed. A reappraisal of the family Lydekkerinidae by means of a chronological review of the morphology of the skull and mandible of all the genera and species that have been assigned to the Lydekkerinidae, concludes that that the content of the family should be restricted to Lydekkerina huxleyi , Broomulus dutoiti, Limnoiketes paludinatans, Deltacephalus whitei , and Eolydekkerina magna. Putterillia platyceps is considered to be a junior synonym of L. huxleyi , and Lydekkerinia kitchingi, Lydekkerina panchetensis and Luzocephalus kochi to be nomina vana . Broomistega putterilli , formerly Lydekkerina putterilli , is adjudged to be a rhinesuchid, and ‘ Parotosuchus ’ madagascariensis (Watsonisuchus madagascariensis ) a mastodonsaurid. It is argued that Chomatobatrachus halei and Luzocephalus blomi are allied more to rhytidosteids than they are to lydekkerinids, and are sufficiently different from each other, and from other forms, to be classified within separate monotypic families. Indobenthosuchus panchetensis and Cryobatrachus kitchingi are assessed as Stereospondyli incertae sedis . The lydekkerinids are considered to be small-sized adult stereospondyls derived from Upper Permian rhinesuchid temnospondyls by the paedomorphic process of progenesis, and the family Lydekkerinidae, to be a specialised basal offshoot of an adaptive radiation of Upper Permian and Lower Triassic stereospondyls. Undoubted members of the family are confined to southern areas of Gondwana viz. South Africa, Madagascar and Australia, but fragmentary remains of ‘lydekkerinids’ have been reported from India, Russia and Brazil.

KEY WORDS: Lydekkerina , Lydekkerinidae, stereospondyls, Rhinesuchidae, mastodonsaurids, rhytidosteids, mandible, Lower Triassic, Lystrosaurus Assemblage Zone of South Africa, Permo-Triassic extinction, progenesis, adaptive radiation, Gondwana.

INTRODUCTION

Lydekkerina huxleyi (Lydekker) Broom 1915, is a small, short-faced, basal stereospondyl from the Lower Triassic Lystrosaurus Assemblage Zone of South Africa. It is by far the most commonly preserved temnospondyl within this assemblage and is known from over 200 skulls and a considerable amount of postcranial material. The holotype, BMNH R507, and two other specimens from the same locality, (R506 and R508), were originally described as Bothriceps huxleyi by Lydekker in 1889, and again in 1890, along with two additional specimens, R504 and R505. In 1915, however, Broom removed this species

1 from the genus Bothriceps (a brachyopid temnospondyl), and established for it the new genus Lydekkerina. The general structure of the skull and mandible of L. huxleyi has become well known through the researches of Watson (1912, 1913, 1919, 1951), Broom (1915), Haughton (1925), Broili & Schröder (1937), Parrington (1948), Warren & Black (1985), Jupp & Warren (1986), Shishkin, Rubidge & Kitching (1996) and Jeannot, Damiani & Rubidge (2006), yet certain important morphological features of the skull and mandible still remain unknown. The holotype skull itself remained virtually unknown until very recently, and our only previous knowledge of it comprised the two original, very brief descriptions by Lydekker (1889 and 1890), and his figure of the skull roof (1890, fig. 41), which showed merely the outline of the skull and the position and apparent sizes of the nares, orbits and otic embayments. Although Watson (1919) referred directly to the structure of the holotype skull, it is clear from his text, and a personal knowledge of the specimens he was studying, that he was referring, not to the holotype itself, but to two related specimens from the same locality, BMNH R505 and R506. Many years ago, in connection with this reappraisal of the Lydekkerinidae, the dorsal surface of the holotype skull was cleared of matrix at the British Museum of Natural History, and is described and illustrated here in as much detail as is possible. The palatal and occipital surfaces were not prepared at that time, due to the fragile nature of the skull, but improved preparation techniques have now made this possible (Jeannot et al 2006), and relevant information regarding the morphology of the palate and occiput have been incorporated into this account. A detailed study has also been made of a small, well ossified and virtually complete skull of Lydekkerina huxleyi , UMZC T110, (formerly D.M.S.Watson B.156), which consists of 10 interlocking pieces and some fragments, that enable many new features of the skull roof, palate, occiput, palatoquadrate complex, neurocranium, otic region and stapes to be studied, illustrated and described. This skull, is the ‘unnamed form’ that Cosgriff (1974) recognized as probably being conspecific with L. huxleyi , a view that is confirmed by this present study. The skull has been figured in various views and sections by Watson (1951, fig 15 A-E), but has not until now been described. A detailed study has also been made of other previously described material of L. huxleyi , as well as some undescribed material, of which an almost complete right mandible, that was once in the possession of D.M.S.Watson, and believed to be BP/1/1373 , has allowed many new features of the mandible to be described and illustrated. The new information resulting from these studies has made it possible to give a more informative diagnosis of Lydekkerina huxleyi , and to provide new and more detailed, composite reconstructions of its skull and mandible. L. huxleyi was the only member of the family Lydekkerinidae when this was established by Watson (1919), but since then, fourteen additional species have been referred to the family: Lydekkerina putterilli Broom, 1930; Putterillia platyceps Broom, 1930; Broomulus dutoiti (Broom) Romer, 1947; Limnoiketes paludinatans Parrington, 1948; Lydekkerina kitchingi Broom, 1950; Deltacephalus whitei Swinton, 1956; Lydekkerina panchetensis Tripathi, 1969; Indobenthosuchus panchetensis Tripathi, 1969; Cryobatrachus kitchingi Colbert & Cosgriff, 1974; Chomatobatrachus halei Cosgriff, 1974; Luzocephalus blomi Shiskin, 1980; Eolydekkerina magna Shishkin, Rubidge & Kitching, 1996; ‘ Parotosuchus ’ madagascariensis (cladogram of Damiani 2001); and Luzocephalus kochi Jeannot, Damiani & Rubidge, 2006. Almasaurus habbazi Dutuit (1972), was added in error by Warren & Black (1985 p323). L. huxleyi and L. kitchingi are known from an abundance of cranial and postcranial material, but the remaining species are known virtually only from isolated skulls, and for this reason, all definitions of species, genera and families that are presented here are based solely on cranial material. Watson’s original definition of the family Lydekkerinidae (Watson 1919) was based mainly upon BMNH R505 and R506, two specimens of L. huxleyi from the same locality as the holotype, but, with the growth of the family, later diagnoses of the Lydekkerinidae, came to be founded on genera, other than Lydekkerina . The diagnosis by Cosgriff (1974), for example, was based largely upon the skull structure of Chomatobatrachus halei and Cryobatrachus kitchingi , two new temnospondyls he had assigned to the family, whilst that of Shishkin et al (1996), was mainly derived from the structure of the skulls of Chomatobatrachus halei, Luzocephalus blomi and a newly described form, Eolydekkerina magna. The most recent diagnosis of the family, that of Jeannot et al (2006), was also based partly on

2 Chomatobatrachus, Luzocephalus , and Eolydekkerina , as well as Lydekkerina , and was essentially a synthesis based on previous work (eg Milner, 1991; Shishkin, et al 1996), combined with a study of the holotype skull and a large number of L. huxleyi specimens, mainly from South African collections. The content of the family Lydekkerinidae, its distribution, phylogenetic relationships and habits have been briefly summarised by Warren (2000), and dealt with in greater depth by Schoch & Milner (2000), and, although the membership of the family has been reviewed again recently by Jeannot et al (2006), there remains a great deal of uncertainty and disagreement about the content of the family, and its relationships. Apart from Lydekkerina huxleyi , only Eolydekkerina has achieved universal acceptance into the family. Of the remaining taxa, Broomulus , Putterillia , Lydekkerina putterilli and Limnoiketes , have all been considered at one time or another, to be junior synonyms of L. huxleyi , and Indobenthosuchus has been synonymised with Lydekkerina panchetensis , and both possibly with Lydekkerina huxleyi. Eight taxa have been considered incertae sedis viz. Broomulus , Putterillia , Lydekkerina putterilli , Deltacephalus, Limnoiketes, Cryobatrachus , Lydekkerina panchetensis and Indobenthosuchus , and four taxa as indeterminate: Deltacephalus, Cryobatrachus, Lydekkerina panchetensis and Indobenthosuchus . Some of the taxa have also been classified in families other than the Lydekkerinidae viz. Lydekkerina putterilli and Lydekkerina kitchingi in the Rhinesuchidae; Chomatobatrachus , Luzocephalus and Lydekkerina panchetensis in the Luzocephalidae; Deltacephalus into a new capitosauroid family, the Deltacephalidae, and Luzocephalus into a trematosaurian family. These taxonomic uncertainties may have resulted from the high number of species assigned to the Lydekkerinidae, and the wide range of morphological variation that they display, due to differences in their size, phenotypic variation, life-style and degree of paedomorphosis, and in an attempt to resolve these uncertainties, a chronological review of the morphology of the skull and mandible of all taxa that have been assigned to the family has been undertaken. This review has not only provided revised and more informative diagnoses of the Lydekkerinidae, and of the five taxa assigned to the family, but has also allowed the paedomorphic origin of the Lydekkerinidae from rhinesuchid temnospondyls to be explored, and an assessement to be made of the relationships and phylogenetic importance of the family.

The abbreviations for the various institutions where material discussed in this paper is held are as follows: AMNH, American Museum of Natural History, New York, U.S.A.; BMNH, Natural History Museum, London, U.K.; BP, Bernard Price Institute for Palaeontological Research, University of the Witwatersrand, Johannesburg, S.A.; BSP, Bayerische Staatssammlung für Palaeontologie und historische Geologie, Munich, Germany; GSI. Geological Survey of India, Kolkata; MGM, MacGregor Museum, Kimberley, S.A.; PIN, Palaeontological Institute, Academy of Science, Moscow, U.S.S.R.; TM, Transvaal Museum, Pretoria, S.A.; UMZC, University Museum of Zoology, Cambridge, U.K.; UTGD, University of Tasmania, Geology Department, Hobart, Tasmania.

SYSTEMATIC PALAEONTOLOGY TEMNOSPONDYLI Zittel, 1887-1890 STEREOSPONDYLI Zittel, 1887-1890 (sensu Yates and Warren, 2000) Family LYDEKKERINIDAE Watson, 1919

Revised diagnosis : Synapomorphic characters shared by all lydekkerinids : small paedomorphic stereospondyls of Lower Triassic age, with moderately flattened skulls which are almost as broad as they are long, and widest across the quadratojugal bones; otic notch well developed, broadly rounded and widening posteriorly; septomaxillary with an ornamented roofing portion and an unornamented, plate- like intranarial portion; supratemporal excluded from margin of otic notch; squamosal with an incipient crista falciformis represented by an outward curvature of its posterior border; anterior palatal vacuity single, of varying shape, but not deeply divided into two sections, and with little development of a palatal plate anterior to it; palatine lacking denticles, but having an elongated postero-mesial process extending

3 behind the most anterior ectopterygoid tooth; ectopterygoid lacking denticles; alar process of jugal present; palatal ramus of pterygoid shortened and less than three-quarters of the total length of the interpterygoid vacuities; anterior borders of cristae musculari lying more or less on a level with the posterior ends of the pterygoid-parasphenoid sutures; quadrate ramus of pterygoid with a shallow stapedial groove bordered mesially by a low, rounded crista obliqua; quadrate boss or tubercle present; crista tympanica of squamosal with a vertical to sub-vertical alignment; sphenethmoid large, bulky, ossified only perichondrally and pierced by an optic foramen; stapes stout with massive, expanded conical foot plate bearing a triangular antero-ventral process attaching to the stapedial facet of the crista parapterygoidea, and a postero-ventral process approaching the mesial portions of the opisthotic; stapedial foramen present; mandible with an extensive postglenoid area, bearing a median depressor groove flanked by a cylindrical retroarticular process lingually, and a very long, posterodorsally directed surangular process labially; hamate process very well developed; prominent postglenoid process; prearticular short, not reaching splenial-postsplenial suture; posterior Meckelian foramen moderately long and centred below the most anterior point of the adductor fossa; chorda tympanic foramen on the articular-prearticular suture; single symphysial tusk. Synapomorphic characters shared by a majority of lydekkerinids : ornament has conules at ridge junctions; lacrimal flexure, when present, is step-shaped to Z-shaped; orbits centrally situated and straddling mid- length of skull roof; parietal foramen close to hinder border of orbits; lacrimal terminating posteriorly a short distance from the anterior border of the orbits; antorbital projection of jugal of moderate length; tabular horn supported ventrally by a crista tabularis externa and a crista terminalis; pterygoid strongly ornamented, particularly along its palatal ramus; sub-otic notch present separating exoccipital from pterygoid; opisthotic absent from paroccipital bar.

Genus LYDEKKERINA Broom, 1915 TYPE SPECIES. Bothriceps huxleyi Lydekker 1889. Diagnosis : As for the type and only species: Lydekkerina huxleyi (Lydekker) Broom, 1915. 1889 Bothriceps huxleyi Lydekker; Lydekker: 476. 1890 Bothriceps huxleyi Lydekker; Lydekker: 172, fig. 41. 1912 ‘ Bothriceps ’ huxleyi Lydekker; Andrews: 115, unnumbered fig. 1912 Bothriceps huxleyi Lydekker; Watson: 584, fig. 6. 1913 ‘ Bothriceps ’ huxleyi Lydekker; Watson: 341. 1915 Lydekkerina huxleyi (Lydekker) Broom; Broom: 366, fig. 3. 1916 ‘ Bothriceps’ huxleyi Lydekker; Watson: 84. 1919 Lydekkerina huxleyi (Lydekker) Broom; Watson: 12, figs 4-9. 1930 Lydekkerina putterilli Broom 1930; Broom: 7, fig. 6. 1930 Putterillia platyceps Broom 1930; Broom: 8. figs 7. 9B. 1930 Lydekkerina dutoiti Broom 1930; Broom: 9, fig. 10. 1947 Broomulus dutoiti (Broom) Romer; Romer: 202, fig. 25. 1948 Limnoiketes paludinatans Parrington; Parrington: 434, figs 5-7. Revised Diagnosis . Lydekkerinid stereospondyl distinguished from all other members of the family by the following combination of characters: skull parabolic with a narrowly rounded snout and gently convex lateral margins; sensory sulci moderately well developed, partly as separate depressions and partly as grooves; lacrimal flexure slightly step-shaped to distinctly Z-shaped; parietals with deeply irregular anterior margins; postorbital with a very broad antero-lateral process; tabular horns moderately long, bluntly rounded, directed postero-laterally and terminating posterior to the postero- lateral corners of the skull roof; ventral surface of skull roof with series of thickened ridges around the orbits; anterior palatal vacuity reniform with paired, antero-dorsal projections within it, each formed from the vomer and premaxilla; anterior palatal plate short and shaped like a rounded-V; vomer with a well defined field of denticles; processus cultriformis grooved laterally over its posterior half; palatal ramus of pterygoid short and failing to meet palatine; ectopterygoid entering the border of the interpterygoid vacuity; stapedial lappets very well developed; subotic notch rounded, separating an

4 expanded subotic lamina of the exoccipital from the pterygoid; palatal surfaces of pterygoid strongly ornamented; opisthotic with a rod-like paroccipital process exposed in the paroccipital bar; quadrate boss bi-tuberculate and pitted and roughened by tiny ridges and projections; paired tubercles present on palatal surface of exoccipitals and separated from condylar processes by a transverse groove; 2-3 anterior Meckelian foramina; extensive dentition developed on all three coronoid elements, with a few dentary-type teeth present amidst the denticles on all three coronoid bones. This definition includes three new autapomorphies for L. huxleyi : a bi-tuberculate quadrate boss; paired tubercles on palatal surface of exoccipitals which are separated from the condylar processes by a transverse groove, and presence of dentary-type teeth amongst the denticles on all three coronoid bones.

A RE-DESCRIPTION OF THE STRUCTURE OF THE SKULL AND MANDIBLE OF LYDEKKERINA HUXLEYI (Text-figs 1-29; all scale bars represent 10mm)

Materials and methods Cranial material associated with specimens of L. huxleyi from the following localities has been examined: Locality 1: ? Edenburg, Free State Province, South Africa : BMNH R507 : the holotype, a skull with articulated left mandible, part of the right mandible and anterior part of the vertebral column (Lydekker 1889 and 1890; Jeannot, et al 2006). BMNH R504 : two entire skulls and the anterior half of a third, all exposed in dorsal view (Watson 1919). BMNH R505 : a skull covered by a thin crust of matrix dorsally, but clearly exposed in both palatal and occipital views (Watson 1919). BMNH R506 : a skull, largely hidden dorsally, but exposed for the most part in palatal aspect (Watson 1919). BMNH R508 : a skull exposed in patches dorsally (undescribed). Locality 2: Harrismith, Free State Province, South Africa : BSP 1934 VIII 44 : three skulls, of which 2 are exposed in dorsal and palatal view and one showing only the palate (Broili and Schröder 1937). UMZC T206 : the posterior half of a skull (Parrington 1948). UMZC T238 : a complete and well-preserved skull (Parrington 1948). UMZC T110 : a complete and well-preserved skull (figured by Watson 1951). BMNH R5482 : a skull exposed dorsally and partially ventrally (undescribed). BMNH R6850 : a large, well-preserved skull exposed in dorsal and occipital views (undescribed). BMNH R8943 : the posterior half of a large skull (undescribed). Locality 3: Van Rienen’s Pass, Drakensberg, between Natal and Free State Province, South Africa : BMNH R3909 : a well preserved skull exposed dorsally but only partially in its palatal and occipital regions (undescribed, although a photograph was published by Andrews in 1912). Mandibles studied include all those associated with the above material, together with the following material from Harrismith, Free State Province, South Africa : BH54, BH55, BH74, BH95 (Private collection of Dr Barry Hughes, 57 Snaresbrook Rd. Wanstead, London, UK). BP/1/1373 : a right mandible. The postglenoid area of the right mandible of BMNH R5482 was prepared using an abrasive air drill, whilst certain internal structures of the skull of UMZC T110 were mechanically prepared using a mounted needle, after an initial chemical treatment that involved brushing on drops of 4% acetic acid over a 2 hour period, followed by washing in running water for 2 hours and drying. The mandible BPI No1373 and the postglenoid area of the mandible BH54 were prepared both mechanically by an engraving drill and chemically by 4% acetic acid. During this chemical preparation, exposed bone was coated with dilute polybutylmethacrylate and the specimens immersed in the acid for 1 hour, followed by washing in flowing water for 4 hours and drying.

5 General features (Text-figs 1-4).

Text-fig.1. Lydekkerina huxleyi (Lydekker) Broom; Lower Triassic; South Africa. Holotype skull BMNH R507, dorsal view x 1.9.

6 Text-fig.2. Lydekkerina huxleyi (Lydekker) Broom; Lower Triassic; South Africa. Holotype skull BMNH R507, lateral (and slightly dorsal) view x 1.6

The skull of L. huxleyi is small in size, ranging from about 49-91mm in midline length in the specimens studied, and it has a rather narrowly parabolic outline when seen from above, with a rounded snout and gently convex lateral borders. The skull is moderately flattened and is almost as broad as long. The quadratojugal corners terminate approximately on a level with the posterior ends of the exoccipital condyles and some distance in front of the tips of the tabular horns. The condylar region of the quadrate is directed postero-mesially with regard to the quadratojugal corner of the skull, at a varying angle, being about 22 degrees on the left side of the skull of BMNH R505, and about 28 degrees on the right side. Skull roof (Text-figs 1-8): Unless stated otherwise, most of the details of the skull roof have been determined from the holotype, BMNH R507, despite the fact that the bone surface of the roof has been abraded in some areas and almost completely removed in others. This skull, which has a median length of nearly 59mm and a similar maximum width across the quadratojugal bones, has been somewhat flattened posterior to the right orbit and just anterior to the left otic notch, and the left side of the skull has suffered some distortion, which has heaped up the roofing bones lateral to the orbit, and pushed the quadratojugal corner of the skull ventro-posteriorly. The orbits differ slightly in outline due to post-mortem distortion and abrasion around their edges, but are essentially sub-circular in shape and are centrally placed on the roof, lying halfway between the mid-line and the lateral borders, with their centres only a short distance behind the mid-length of the roof. The preorbital region of the skull is therefore very short and only a little longer than the postorbital region. The preorbital region is somewhat depressed and there is a distinct preorbital step leading down from the orbits onto the snout. The skull is quite markedly hollowed out transversely between the orbits, this hollowing continuing anteriorly onto the facial region where it widens but becomes shallower over the frontals and nasals. The postorbital region is less depressed, and the skull table is only slightly hollowed out centrally with the cheek regions curving ventro-laterally away from it. The hinder border of the skull table is distinctly concave. The tabular horns project postero-laterally and are moderately long and relatively slender and terminate in a bluntly rounded tip that lies well posterior to both the exoccipital condyles and the quadratojugal corners of the skull; their length varies in different specimens, however, and in BMNH R508 they are exceptionally long. The roofing bones bear an ornament that consists of a network of anastomosing ridges, which separate either rounded depressions or grooves (Text-figs 1 & 2). The ridges are smoothly rounded in section and generally relatively high and thin, and at each anastomosis the uniting ridges tend to form a slight conule. The depressions vary greatly in size and outline and very large, deep, irregular

7 depressions can lie next to rather small, rounded or hexagonal ones. In the bottom of those depressions, which have been cleared of matrix, a small foramen opens, presumably for a nutritive vessel leading to the overlying skin. The grooves of the ornament are relatively deep, much longer than wide, and have a slightly irregular outline. They appear to have been formed from series of adjacent depressions, which have merged during growth, with the dividing walls between them remaining lower than the walls bordering the groove. In the region of the initial ossification centre of each bone, the ornament has a rather honeycomb like appearance, with the ridges separating small, rounded depressions. In the more peripheral areas of some of the bones, the rounded depressions are replaced by grooves, which radiate away from the ossification centre. There are, however, no indications of any region of intense growth.

Text-fig.3. Lydekkerina huxleyi (Lydekker) Broom; Lower Triassic; South Africa. Holotype skull BMNH R507, dorsal view.

8 Text-fig.4. Lydekkerina huxleyi (Lydekker) Broom; Lower Triassic; South Africa. Holotype skull BMNH R507, slightly antero-lateral view of right side.

The great majority of the interdigitating sutures that separate the roofing bones are visible and the bones are arranged in the pattern typical of that of advanced temnospondyls. Although the left premaxilla is much abraded, and the right slightly displaced, it is clear that they do not protrude markedly between the nares and have fairly simple, slightly postero-laterally directed sutures with the nasals. The nasals are large and each has a step-shaped posterior border with the prefrontal. There are no traces of septomaxillaries, as those areas of the roof immediately postero-lateral to the external nares are denuded of bone. In UMZC T110, however, where the right naris is particularly well preserved, a small septomaxillary is present and forms the postero-lateral border of the naris (Text-fig. 5), as it does also in UMZC T238 and BMNH R6850. Watson (1913) was the first worker to note the presence of a septomaxillary in Lydekkerina huxleyi, and its general form and the effect that its presence or absence has on the shape of the naris, was first commented upon by Parrington (1948), pursued further by Jeannot et al (2006), and is also dealt with in this paper. In UMZC T110, this bone has an ornamented posterior portion suturing with the nasal and maxillary bones and forming part of the skull roof, and an unornamented, thin and poorly ossified anterior portion, which dips down into the narial cavity only to rise again to the level of the surrounding roofing bones. When the septomaxillary is completely cleared of matrix, the narial cavity has a somewhat pear-shaped outline (Text-fig. 6a), whereas Text-fig.5. Lydekkerina huxleyi (Lydekker) if the lower-lying, intra-narial portion remains Broom; Lower Triassic; South Africa. UMZC covered in matrix, the outline becomes an oval T110, right naris and septomaxilla. surrounded by ornamented bone (Text-fig. 6b). If the septomaxillary has been lost from the roofing surface of the skull, as often happens with this small, vulnerable bone, then this area of denuded bone appears to form a postero-lateral extrusion to the oval

9 outline of the naris (Text-fig 6c). Jeannot et al (2006) described such a naris as being ‘notched’, and this is the condition that is seen on the right side of the holotype skull. The oval outline of this right naris clearly lies at a lower level than the surface of the matrix immediately postero-lateral to the naris from where the septomaxillary bone has been lost, and the mesial surface of this denuded area slopes down into the naris, presumably representing the proximal region of the intranarial portion of the septomaxilla. This situation is repeated on the left side of the skull, but to a lesser degree. Anterior to the roofing portion of the septomaxilla, the maxilla forms from a third to a half of the lateral margin of the naris.

Text-fig.6. Lydekkerina huxleyi (Lydekker) Broom; Lower Triassic; South Africa. Outline shape of right naris: a) septomaxilla intact and cleared of matrix; b) unornamented portion of septomaxilla hidden by matrix; c) septomaxilla lost.

In the holotype, the prefrontals are very large bones extending some two-thirds of the distance between orbit and naris, and they have their ossification centre anteriorly situated. The lacrimals are also well developed and relatively long, with their posterior ends projecting into the jugals only a short distance in front of the level of the anterior borders of the orbits. Because of their inclined position on the roof, however, the posterior portions of the lacrimals have a more lateral position than the orbits. The lacrimal, as shown in UMZC T110, is excluded from the naris by a short junction between the nasal and maxillary. In the holotype, the preorbital projection of the jugal is very short and terminates behind the level of the posterior borders of the nasals. The frontals are very much broadened anteriorly, and have very irregular asymmetrical sutures with both the nasals and parietals; they are also excluded from the orbital borders by a prefrontal-postfrontal contact. The fronto-parietal sutures lie some distance in front of the level of the posterior borders of the orbits. The postorbital has a very broad antero-lateral projection, but does not prevent the jugal from contributing considerably to the lateral border of the orbit. On the right side of the holotype, the jugal originally formed a short section of the lateral margin of the skull between the maxillary and quadratojugal (Text-figs 2 & 4), and the same situation is seen in UMZC T110. On the left side of the holotype, as it currently appears, the jugal is excluded from the margin of the skull by a very short contact between a forwardly directed tongue from the quadratojugal and a narrow posterior slip of the maxilla, a further example of the intraspecific variation that is prevalent in this species (see Jeannot et al 2006). In both the holotype and in UMZC T110, the marginal tooth row terminates posteriorly behind the level of the anterior margin of the subtemporal fossa. The supratemporals in all the skulls examined are excluded from the borders of the otic notches, and the postparietals lack the distinct lappets described by Shishkin et al (1996). A slight posterior swelling is present, however on the right postparietal of the holotype, although its extent has been exaggerated somewhat by bone loss at the postparietal-tabular suture on the rear margin of the skull. The left postparietal shows virtually no undulation at all, but the neighbouring tabular does have a slight, but wide outward curvature. Shishkin et al (1996) figured an interparietal bone in their drawing of the skull rooof of L. huxleyi , but this was an unusual variation that was found in only one particular specimen. The left squamosal of the holotype bears a distinct convex curvature on its postero-lateral border, which slightly closes off the opening of the otic notch laterally, but as this curvature is not accompanied by any inward projecting flange overhanging the cheek region, it cannot be considered as representing a true crista falciformis, but only an incipient one. In some specimens this curvature is seen to continue onto the quadratojugal laterally. The sensory openings in the holotype are well developed. The nares, enlarged by wear, are widely separated and lie far forward, close to the antero- lateral margins of the roof. They have an elongated oval outline and are inclined a little towards the

10 midline anteriorly; they are longer than broad, and narrower anteriorly than posteriorly. The orbits are large and broadly oval, with the anterior end more narrowly rounded than the posterior. They are also inclined slightly towards the mid-line anteriorly, and have their margins elevated above the surrounding ornament. They are centred slightly behind the mid-length of the roof, and lie approximately mid-way between the mid-line of the skull and its lateral borders. The parietal foramen is a relatively large, round opening lying only very slightly (2.6mm) behind the level of the posterior borders of the orbits, a position exaggerated by the wear along the posterior rims of the orbits; in life it would have had a slightly more posterior position, as it has in such skulls as BMNH R3909 and BSP 1934 VIII 44 skull B. The parietal foramen pierces the roof in the anterior half of the suture between the two parietals and is surrounded by a thick rim of smooth bone. The otic notches are well-developed U-shaped openings incised quite deeply into the squamosals. They are inclined towards the mid-line anteriorly and are widely open posteriorly, although narrowed slightly on their lateral side by the development on the squamosal of an incipient crista falciformis. The lateral-line system, as Watson (1919) noted, is extensively developed on the skull roof of the holotype, and the majority of the sulci can be seen under suitable illumination, particularly those on the right side of the skull (Text-figs 1 & 2). The sulci appear partly as series of close-set, rounded depressions, which are not always immediately distinguishable from the depressions of the surrounding ornament, and partly as distinct, moderately deep and continuous grooves. A small rounded foramen appears to open into the base of each of the sensory depressions. Six pairs of sulci are present, and many of these are visible on other specimens, even though they have not always been fully figured eg. UMZC T238 (Parrington 1948) and BSP 1934 VIII 44 (Broili & Schröder 1937). The disposition of the sulci can be seen from Text-figs 1-4. The suborbital, ethmoidal and jugal sulci are largely continuous grooves, whilst the supraorbital and postorbital sulci consist mainly of depressions. Typical supraorbital lyrae are present on the preorbital region, and such lyrae are visible on both sides of the photograph of the skull of L. huxleyi AMNH 9799 figured by Colbert & Cosgriff (Fig.16, 1974), and a lyra that closely parallels that of the holotype is also seen on the right side of the skull roof of the specimen of L. huxleyi from Australia, although referred to as the antorbital ridge (Warren, Damiani & Yates 2006, Fig 3 a,). A very slightly step-shaped to a Z-shaped lacrimal flexure occurs on the right suborbital sulcus of the holotype where it crosses the maxillary and lacrimal boundaries. The short, ventrally directed section of the flexure widens out as it passes downwards over the lateral face of the skull, and the flexure could be construed as being either slightly Z-shaped, if defined by the anterior rim of the groove, or slightly step- shaped, if defined by its posterior rim. On the left side of the skull, this flexed section is directed virtually straight downwards, as it is in BMNH R6850, but a more distinctive Z-shaped lacrimal flexure occurs in UMZC T110, and on the right side of BMNH R3909. In UMZC T110, the suborbital sulcus is slightly unusual in consisting of two overlapping sections, the first of which appears on the maxilla, mainly as a short, deep groove curving posteriorly around the septomaxillary, and the second, as a series of depressions that continues the sulcus backwards onto the lacrimal and into the Z-shaped flexure (Text-fig. 7). Otic sulci may be represented in the holotype by very short, groove-like sections, which arise from the supraorbital sulci in a more anterior position than is normal. Most of the sulci pass directly over or close to the ossification centre of the bones they cross. In UMZC Text-fig.7. Lydekkerina huxleyi (Lydekker) T110, the jugal sulcus forms a groove, which runs Broom; Lower Triassic; South Africa. posteriorly along the squamosal-quadratojugal suture, as UMZC T110. right suborbital sulcus.

11 it does in the holotype, and then curves over the posterior edge of the ornamented surface of the quadratojugal onto its occipital surface (Text-fig. 8). Here it continues ventro-laterally as a relatively narrow groove running mesial to the ornamented rim of the quadratojugal, before passing onto the smooth bone of the upper regions of the mandible via a shallow notch, lying mesial to the extreme tip of the quadratojugal. The teeth born by the maxillary and premaxillary of the holotype are numerous and close-set and there is evidence for some 9 teeth on the right premaxilla and at least 31 on the right maxilla, with gaps for more. Most of the teeth are incomplete, having been either broken off or sliced through in various ways, but they were originally relatively long, and fairly slender, and tapered distally to a sharp tip which curved slightly mesially. The outer surface of the basal portions of each tooth is ornamented with a number of narrow, shallow grooves, which taper distally. In transverse section the teeth have an oval outline and are slightly compressed antero-posteriorly. The most anterior tooth of the left maxilla measures some 3mm in length, but most of the Text-fig.8. Lydekkerina huxleyi (Lydekker) Broom; Lower Triassic; South Africa. UMZC T110, right quadratojugal remaining teeth are shorter. The teeth region, slightly postero-lateral view. vary in form along the row, some being more slender than others, but the anterior teeth are longer and stouter overall than the more posterior teeth, while those on the premaxillae appear shorter and stouter than those on the maxilla. In UMZC T110, the marginal teeth are all much the same size and shape, with the exception of a distinctly larger tooth lying on the left maxillary, immediately posterior to the position of the external naris, and a similar ‘canine-type’ tooth occurs on other skulls of L. huxleyi . Palate (Text-figs. 9 and 32): No single skull displays all features of the palate. The general features of the anterior half of the palate are best displayed in the holotype BMNH R507, in UMZC T238 and BMNH R506, and to a lesser extent in skulls A and C in BSP 1934 VIII 44. The anterior palatal vacuity is large and reniform, as originally described by Broili & Schröder (1937), and its concave anterior border is formed from a pair of moderate, posteriorly directed protrusions of the premaxillary bones. These projections form together a short Text-fig.9. Lydekkerina huxleyi (Lydekker) Broom; Lower anterior palatal plate, within which lies a Triassic; South Africa. Holotype skull BMNH R507, slight depression. palatal view of left antero-dorsal projection protruding In UMZC T238, a large mandibular into the anterior palatal vacuity. symphysial tusk enters the left antero-

12 lateral projection of the anterior palatal vacuity, suggesting that the function of the vacuity was to house such tusks rather than an intermaxillary gland, as was suggested by Parrington (1948). In the holotype BMNH R507, the symphysial tusk of the left mandible also enters the anterior palatal vacuity, curving downwards and slightly backwards as it does so, and appearing to occlude against the left member of the pair of bony projections described by Jeannot et al (2006) as projecting antero-dorsally into the cavity. This left antero-dorsal projection would seem to have two components: a longer, more horizontally orientated and smooth-faced flange directed backwards from the ventral surface of the premaxilla, and a shorter, less smooth, stubby process curving downwards and forwards from the vomer (Text-fig. 9). The former narrows slightly posteriorly towards its junction with the latter. Of the right antero-dorsal process, only the vomerine section has been preserved. If the function of these projections was to provide an occlusal surface for the symphysial tusks, then they may not be quite so delicate as Jeannot et al (2006) have suggested, and may in fact be more common than hitherto suspected, and indeed have now also been described as being present in the Australian specimen of L. huxleyi QMF 39705 (Warren, Damiani & Yates 2006, Fig 3b). That they have not been detected previously, may be due to a lack of any further preparation of the anterior palatal vacuity, once its outline had been established. Jeannot et al (2006) noted that the anterior palatal vacuity merged posteriorly into a countersunk, triangular depression, and although there is a clear demarcating rim separating the vacuity from the depression, they considered this depression to be part of the overall margin of the vacuity. A somewhat similar, shallow posterior extension of the anterior palatal vacuity has recently been described in the Australian specimen of L. huxleyi (Warren, Damiani & Yates 2006, Fig 3b). The vomers are large, and are prolonged posteriorly into a pair of moderately long processes that clasp the anterior end of the cultriform process, which nestles in a central valley between them. Broom (1915) recorded the presence of denticles on the vomers in specimens of L. huxleyi which came from the same locality as the holotype, and on the right vomer of the holotype, a cluster of denticles was noted by Jeannot et al (2006). The left vomer lacks denticles, but does bear a pair of large tusks, over 5mm long, immediately anterior to the choana. Each tusk is fluted basally for half its height, and curves posteriorly and slightly mesially towards its tip. The right vomer bears but a single tusk, followed posteriorly, by a large replacement pit. Between the two sets of vomerine tusks, four transvomerine (interchoanal) teeth have been preserved, lying in two groups of two, close behind the depressed vomerine area, and in UMZC T238, three small interchoanal teeth have been preserved out of what was almost certainly a gently curved row of six interchoanal teeth. This row is convexly curved posteriorly and, as in the holotype, lies close to the posterior border of the anterior palatal vacuity. On both sides of the holotype, there are the remains of a curved row of parachoanal teeth, three on the left and 5 on the right, which serve to link the vomerine tusks anterior to the choana with the palatine tusks lying immediately posterior to it. Such parachoanal teeth are clearly seen in skull A of BSP 1934 VIII 44, although more are present than were figured by Broili & Schröder (1937, Fig 2), and in both this specimen, and in the holotype, the row of teeth is crossed centrally by a short vomer-palatine suture. The choanae are quite large, and broadly oval in form, the right choana of the holotype being 6mm long and 3mm wide across its mid-length. The maxilla forms most of the lateral border of the choana, its suture with the vomer running into the antero-lateral border of the choana, and its suture with the palatine into its postero-lateral border. Of the palatine tusks, one tusk can be seen on the left side of the holotype, and one anterior tusk followed by a replacement pit on the right side. Immediately posterior to this replacement pit, is a row of 3-4 smaller palatine teeth and, an elongated, postero-mesial process, which extends backwards behind the level of the anterior tooth of a much more extensive ectopterygoid tooth row, which terminates only 1.5mm in front of the anterior end of the sub-temporal fossa. The suture between the palatine and ectopterygoid is not clear, although the anterior end of the ectopterygoid may be marked by a larger than normal tooth, which, although some 2mm high, is not really large enough to qualitfy for consideration as an ectopterygoid tusk. This is followed by a row of 5 slender teeth, all pushed over mesially towards the interpterygoid vacuity, and then by a further row of at least 6 more upright teeth.

13 These teeth are much the same size as the maxillary teeth, and like these are grooved basally and terminate in a slender, recurved tip. Denticles are absent from both the palatine and the ectopterygoid. The more posterior regions of the palate are best preserved in UMZC T110, particularly on the left side of the skull. Most of the bones in this specimen have a thin covering of black, perichondral bone, and certain bones also have an inner mass of cancellar, endochondral bone, and it is possible to describe in some detail the morphology of the palatoquadrate complex, neurocranium, otic region, occiput and stapes.

Text-fig.10. Lydekkerina huxleyi (Lydekker) Broom; Lower Triassic; South Africa. UMZC T110, ventral view of left palatoquadrate complex. The palatoquadrate complex (Text-figs 10-18): The pterygoids are large bones characterized ventrally by a well-developed ornamentation over the proximal portions of the quadrate ramus, the more lateral regions of the corpus and almost the whole of the palatal ramus (Text-fig.10). This ornamentation was first alluded to by Broili & Schröder (1937), and has been confirmed in other specimens by Shishkin et al (1996), and in the holotype by Jeannot et al (2006). This ornamentation is similar to that seen on the roofing bones, and is most highly developed over the base of the quadrate ramus, as a triangular area of rather angular depressions, sharply set off from the rest of the ramus. These depressions continue

14 in a less developed form on the corpus and base of the palatal ramus, but give way to grooving over the more anterior portions of the palatal ramus. A wide, shallow depression runs along the length of the palatal ramus, which also has a moderately developed postero-lateral flange protruding into the subtemporal fossa. The unornamented region of the quadrate ramus is twisted some 45 degrees out of the plane of the ornamented portion, and faces ventro-mesially. It extends postero-laterally to overlap the mesial face of the quadrate. No denticular teeth are visible on any of the palatal surfaces of the pterygoid in this very well preserved specimen, although Haughton (1925) recorded the presence of minute denticles on those portions of the pterygoid adjoining the corpus of the parasphenoid, and Jeannot et al (2006), reported the presence of denticles on the holotype, running along the antero- mesial border of the palatal ramus and even extending onto the quadrate ramus. It is quite feasible, however, that conules formed by the confluence of the ornament ridges might well, in poorly preserved and inadequately prepared material, be mistaken for denticles.

Text-fig.11. Lydekkerina huxleyi (Lydekker) Broom; Lower Triassic; South Africa. UMZC T110, dorsal view of basicranial region.

15 The dorsal surface of both the pterygoid rami are hollowed out to house the cartilaginous ventral portions of the palatoquadrate complex (Text-figs 11 & 16). On the palatal ramus, this hollowing is extensive and is bordered mesially by a thickened rim (torus medialis) and laterally by a low rim (linea marginalis). Lateral to the linea marginalis, the palatal ramus expands into a broad flange, which slopes downwards towards the subtemporal fossa, and such a flange is also seen on the right palatal ramus of the holotype. On the narrower and more distinctly curved quadrate ramus, the hollowing for the palatoquadrate cartilage is restricted to a narrow shelf drawn out ventrally along the margin of the subtemporal fossa and bordered laterally by a posterior continuation of the linea marginalis of the palatal ramus. The subtemporal fossa is large, with a broadly rounded posterior half and a narrower, bluntly rounded anterior projection, which is bordered laterally by the posterior termination of the long maxillary bone. A deep, cone-shaped recess for the reception of a cartilaginous basipterygoid process from the basisphenoid, opens antero-mesially onto the dorsal surface of the corpus of the left pterygoid (Text-fig. 12a). This recess narrows to a rounded apex directed deeply into the corpus in a postero-lateral and slightly ventral direction, much as in Benthosuchus sushkini (Bystrow & Efremov 1940). The proximal portions of the recess are bounded posteriorly by a thick ridge of parasphenoidal bone, which overlaps the more mesial portions of the pterygoid, and continues along behind the recess to terminate against the thick base of the transverse ascending lamina of the pterygoid. Overhanging the opening of the recess is the oval base of the epipterygoid (Text-fig.12b).

a) b)

Text-fig.12. Lydekkerina huxleyi (Lydekker) Broom; Lower Triassic; South Africa. UMZC. T110. a) mesial view of left pterygoid corpus, looking down into the conical recess; b) lateral view of the basicranial articulation of the left side of the skull.

Posterior to the conical recess, the corpus of the pterygoid rises up to form a thick, high transverse ascending lamina, which is directed slightly antero-laterally (Text-figs 11 & 16) and which, on the left side of the skull, contacts the supratemporal of the skull roof some 7mm anterior to the otic embayment (Text-fig. 13). This lamina arches over the conical recess and is firmly joined to both the basal column and otic process of the epipterygoid (Text-figs 12a & 13). The mesial surface of this lamina is pierced by a pair of large foramina, the posterior of which possibly corresponds with the fovea ovalis described in Benthosuchus sushkini by Bystrow & Efremov (1940). Into this foramen, a slight ventrally directed groove enters. There are indications of a third, much smaller foramen lying just above the other two.

16 Text-fig.13. Lydekkerina huxleyi (Lydekker) Broom; Lower Triassic; South Africa. UMZC. T110, slightly postero-mesial view of left palatoquadrate complex. The transverse lamina is expanded dorso-laterally into a broadly rounded ridge, which, from fragments of prootic bone adhering to it, would seem to have contacted this bone. The posterior surface of the lamina is hollowed out to form the anterior wall of an extensive tympanic cavity, which, on the right side of the skull is clearly seen to be more pronounced dorsally than it is ventrally (Text- figs 11 & 16). The wall of the tympanic cavity is slightly ornamented at its base. The transverse lamina of the pterygoid soon turns sharply posteriorly to form a long, postero-laterally directed posterior ascending lamina which, although vertical and high anteriorly, gradually decreases in height and becomes less vertical posteriorly (Text-fig. 13). This lamina is united dorsally throughout its length with a descending lamina from the squamosal, and is bounded posteriorly by the quadrate. On the left side of the skull, a portion of the ascending lamina is missing between the more anterior parts of the pterygoid and squamosal, but on the right side of the skull, an impression of the ‘missing’ part of the ascending lamina is preserved in the matrix, indicating that there was a continuous contact between the squamosal and pterygoid laminae and that a palatoquadrate fissure was not present. The mesial surface of the posterior ascending lamina is hollowed out ventrally along its length posteriorly to form a stapedial groove, which floored the posterior regions of the tympanic cavity. The mesial edge of this stapedial groove is drawn out into a shallow shelf, whose rim defines the lower postero-mesial limit of the tympanic cavity, and is therefore equivalent to what is usually referred to as the crista obliqua or oblique ridge (Text-figs 13 & 14a), although for a contrary view see Jeannot et al (2006). Bystrow & Efremov (1940) have suggested that the crista obliqua may have served as an origin for the depressor mandibulae muscle, but, on mechanical grounds, its position would not have afforded any reasonable

17 leverage to such a muscle. The low nature of the crista obliqua in L. huxleyi , is somewhat reminiscent of that seen in the juvenile skull of the rhinesuchid Broomistega putterilli , in juvenile skulls of many capitosauroids (Shishkin & Rubidge 2000), and in very young specimens of Benthosuchus sushkini , and since this crista in the adult B. sushkini , is set much more dorsally on the quadrate ramus, its low position in L. huxleyi is probably the result of the paedomorphic nature of this species. Anterior to the stapedial groove, the oblique ridge curves sharply ventrally and extends onto the corpus of the pterygoid, whilst a slight, rounded ridge continues forwards in a slightly ventro-mesial direction towards the ornamented base of the tympanic cavity (Text-fig.13). This latter ridge serves to delimit the lower mesial boundary of the more anterior parts of the tympanic cavity. a)

b)

Text-fig.14. Lydekkerina huxleyi (Lydekker) Broom; Lower Triassic; South Africa. a) UMZC T110. slightly postero-lateral view of left quadrate region; b) Holotype skull BMNH R507. slightly postero-lateral view of left quadrate boss.

18 The pterygoid corpus forms a thick, broad sheet of bone firmly joined mesially with the corpus of the parasphenoid. The junction between these two bones is of moderate length and is virtually a direct abutment, although the lateral portions of the parasphenoid extend over the more mesial portions of the pterygoid (Text-figs 12a & b & 13). A similar junction is seen in certain other small specimens of L. huxleyi , but in larger, and presumably older skulls, the suture between the pterygoid and parasphenoid shows extensive interdigitation (Watson 1919, Broili & Schröder 1937). The epipterygoid is a large, rather T-shaped bone, firmly attached to the anterior face of the transverse lamina (Text-figs 12a & 13). On the left side of the skull, it is seen to consist of a stout, pillar- like basal column, whose expanded oval base overhangs the opening of the conical recess, and a more tapered dorsal portion, which rises up almost half-way towards the skull roof before giving rise to a long, slender ascending process antero-mesially, and a less well-developed otic process postero-laterally (Text-figs 11, 12a, 13, 16, & 17a & b,). A distinct basal process is lacking. The ascending process is gently curved dorso-ventrally and is directed antero-mesially and slightly dorsally to abut against the poorly ossified lateral wall of the slender laterosphenoid region of the braincase, just below the skull roof, 4mm apart from its opposite fellow, and some 5mm posterior to the indications of the position of the parietal foramen on the dorsal surface of the sphenethmoid (Text-figs 11, 16, & 17a & b). The process is oval in cross-section, being slightly higher dorso-ventrally than broad antero-posteriorly, and it is constricted slightly at its origin where it is crossed antero-posteriorly by a shallow groove. The otic process is rod-like and arises from the dorsal end of the basal column in continuity with the ascending process, and passes slightly dorsally in a postero-lateral direction towards the skull roof. It is firmly attached to the anterior face of the transverse lamina of the pterygoid and, although its posterior parts have been broken off, does not appear to have had any osseous contact with the prootic (Text-fig. 13). The quadrate is a stout bone, well exposed on the left side of the skull. Ventrally, it forms an extensive, though poorly ossified, doubly keeled articular surface for the mandible. This surface projects a little below the level of the neighbouring pterygoid and quadratojugal bones (Text-figs 10 & 14a). The large inner keel is narrow anteriorly but much broader posteriorly and is directed postero- laterally. A broad, shallow trochlear groove separates it from the smaller outer keel, which is broadly oval in outline and tightly clasped anteriorly and posteriorly by a pair of in-turned paraquadrate laminae from the quadratojugal. The occipital surface of the quadrate rises above the inner keel as a well-ossified, triangular plate wedged firmly between the quadrate ramus mesially and the posterior paraquadrate lamina and part of the lamina descendens of the squamosal laterally (Text-fig. 14a). This surface bears a large, essentially bi-lobed tubercle or boss, which on the right side of the skull terminates in a small beak-like process projecting postero-ventrally (Text-fig. 15). The tubercle is covered by shiny, black perichondral bone, which is pitted and roughened by tiny ridges and projections, and several distinct pits occur around the base of the beak-like process. Watson (1962) noted the presence of numerous small foramina on the large quadrate boss of Wetlugasaurus magnus, and suggested that the boss had some functional significance, although it did not have the appearance of an ordinary muscle attachment. Possibly it was associated with the attachment of a ligament running up to a tuberosity lying in the grooved postero- ventral surface of the stapes, as is discussed later.

19 Text-fig.15. Lydekkerina huxleyi (Lydekker) Broom; Lower Triassic; South Africa.UMZC T110, mesial view of right quadrate ramus and quadrate.

The distinctive bi-lobed nature of the tubercle in L. huxleyi is confirmed on both sides of the holotype skull BMNH R507, especially so on the left side, where there it is seen to be composed of two, almost cylindrical ridges directed postero-laterally, separated from each other by a shallow valley, and each terminating in a bluntly rounded head (Text-fig. 14b). Anterior to the tubercle in UMZC T110, the quadrate forms the low posterior wall of the stapedial groove (Text-fig. 14a). The posterior paraquadrate lamina of the quadratojugal forms an extensive, triangular sheet of bone covering part of the posterior surface of the quadrate (Text-fig.14a). It is separated from the ornamented roofing portion of the bone by a relatively narrow and shallow paraquadrate (occipital) groove, into which leads the posterior end of the jugal sulcus. This groove is bounded mesially by a ridge, anterior to which, on the right side of the skull, there opens a small, round foramen, very much as is seen on the left side of the holotype skull. A much larger, oval paraquadrate foramen lies at the ventral end of this ridge in UMZC T110, almost directly above the outer keel, and on the left side of the skull, there is a smaller accessory foramen immediately below it (Text-fig. 14a), the two foramina, corresponding perhaps to the pair of foramina piercing the quadrate, that Haughton (1925) described. Mesial to the paraquadrate ridge, a wide, moderately shallow, quadrangular-shaped, trough, for the origin of a large depressor mandibulae muscle, runs dorsally over the lamina and neighbouring portions of the quadrate onto the occipital surface of the lamina descendens of the squamosal. This squamosal- quadratojugal trough is delimited mesially by a ridge-like crista tympanica squamosi extending ventrally from the posterior regions of the otic notch, below the incipient crista falciformis, and terminating against the apex of the triangular occipital plate of the quadrate, directly above the quadrate tubercle. This crista tympanica is very clearly delineated in occipital view on the left squamosal of the holotype. The crista tympanica, first noted by Watson (1919), not only forms the mesial boundary of the grooved area accommodating the depressor mandibulae muscle, but also defines the postero-lateral boundary of the extensive tympanic cavity. The anterior paraquadrate lamina forms, on the left side of the skull (Text-fig. 10), a deep and fairly extensive sheet of bone covering most of the anterior surface of the exposed part of the quadrate. It is unornamented and forms part of the concave posterior wall of the subtemporal fossa. A small, rounded foramen opens into its surface a short distance anterior to the outer keel, and slightly lateral to it. The parasphenoid has a broad, thick, plate-like corpus, whose ventral surface is unornamented and

20 is drawn out on the left side of the skull into a short, stout lappet, just mesial to the posterior end of the basicranial suture (Text-fig.18).

Text-fig.16. Lydekkerina huxleyi (Lydekker) Broom; Lower Triassic. South Africa. UMZC T110, lateral view of right palatoquadrate complex and sphenethmoid.

Well-developed lappets arise fully from the parasphenoid in all skulls, except UMZC T238 (Parrington 1948, Fig.1B), where in palatal view, the left lappet appears to come from the pterygoid. This bone, however, only under-plates the lappet ventrally, and the bulk of the lappet is indeed composed of parasphenoid. The lappet underlies the head of the stapes, and mesial to it in UMZC T110, the border of the corpus continues posteriorly as a distinct, crescent-shaped ridge, or crista muscularis, which forms the anterior wall of a well-developed and moderately deep pocket lying on the neighbouring ventral and ventro-lateral surfaces of the parasphenoid and exoccipital (Text-fig. 18). This pocket is wider than deep and faces mainly posteriorly. Its surface is slightly roughened to serve for the insertion of the rectus capitis muscle, which ran anteriorly towards it along a wide, shallow groove on the exoccipital, just lateral to the parasphenoid and the exoccipital condyle. The pockets lie well anterior to the exoccipital condyles and are quite widely separated from each other. Immediately lateral to the roughened muscle-insertion surface of the rectus capitis pocket, and mesial to the lappet, there appears in palatal view, a rounded embayment or notch, seemingly bordered anteriorly by a free posterior margin of the parasphenoid corpus, and posteriorly, but at a more dorsal level, by the anteriormost portion of the subotic lamina of the exoccipital. The expanded footplate of the stapes is directed into this embayment, which is visible, in varying degrees of development, in all specimens of L. huxleyi in which this area of the palate is clearly exposed in palatal view. The embayment has essentially a vertical orientation, being formed from the recessed curvature of the lateral and ventro-lateral surfaces of the exoccipital and adjacent parasphenoidal region, and this view is in agreement with those expressed by Warren (1980) and Jeannot et al (2006), but contra to those of Shishkin et al (1996). The embayment is not equivalent therefore to the deep transverse groove gouged out of the ventral surface of the parasphenoid that was described by Warren in ‘Parotosuchus’ gunganj (1980), although, like this, it lies lateral to the rectus capitis pocket, and posterior to the sulcus intercristatus on the dorsal surface of the body of the parasphenoid. This subotic embayment, was first figured by Watson (1919, Fig 5) from the

21 right side of BMNH R505 (his R.506), although it is not so well defined as he has drawn it, and it is also present on the left side of the palate of the holotype BMNH R507. An exaggerated otic embayment was figured by Parrington (1948), which approaches in extent to that depicted in Eolydekkerin a by Shishkin et al (1996). The anterior portions of the ventral surface of the body of the parasphenoid are not exposed in UMZC T110, but in the holotype and in BMNH R505, as in most other skulls of L. huxleyi , this region is covered in denticles, which are continuous with those present on the posterior regions of the processus cultriformis. The dorsal surface of the corpus parasphenoidei, on the right side of the skull in UMZC T110, displays a pair of rounded ridges which diverge posteriorly from a slightly depressed central area lying immediately posterior to the overlying basisphenoid (Text-fig. 11). The anterior ridge, or crista parapterygoidea, gradually widens posteriorly and terminates on the border of the corpus just mesial to the hinder end of the basicranial suture. The crista rises up here, and although this surface is broken across, there is little doubt that it formed a facet for the attachment of the stapes, similar to that described and figured by Watson (1962 Fig. 4) in Rhinesuchus whaitsi . A similar, but less well-preserved facet, terminates the posterior end of the left crista parapterygoidea (Text-fig.14a), and would also appear to have been present on the left side of UMZC T238. A mass of calcite seen in the unfinished surface terminating the right crista may indicate the canal for the internal carotid artery, which entered the palate here, as it does in Benthosuchus sushkini (Bystrow & Efremov 1940). The posterior ridge, or crista paraoccipitalis, is less developed and is directed more posteriorly (Text- fig. 11). It also widens and thickens posteriorly and its more posterior parts are partially overlain mesially by the exoccipital. Between these two cristae, there lies a sulcus intercristatus, which although shallow and narrow anteriorly, deepens and widens posteriorly before leading into the passage between the anterior part of the exocciptal and the mesial surface of the quadrate ramus. Mesial to the right crista paraoccipitalis, the dorsal surface of the corpus is hollowed out to form the anterior part of a basioccipital fossa, which once housed the cartilaginous anterior portions of the basioccipital. The cultriform process, partially visible on the right side of the skull, consists of a wide basal portion and a more slender, though fairly thick anterior portion, extending forwards, and supporting the overlying sphenethmoid ossification (Text-fig.17). In UMZC T238 and BSP 1934 VIII 44, the processus cultriformis is seen to have a more flattened central portion that is grooved along its sides over its basal and central portions, and unless the processus has been fully cleared of matrix, it will appear to be narrower than it actually is. The lateral grooving narrows posteriorly as it extends around onto the anterior borders of the corpus parasphenoidei and corpus pterygoidei, and eventually disappears along the anterior border of the palatal ramus of the pterygoid. Anteriorly along the processus cultriformis, this lateral grooving flattens and widens and eventually merges with the central flattened area some 5mm before the vomerine sutures. In BMNH R505, the denticulation covering the anterior portions of the corpus parasphenoidei continues forwards over the posterior half of the processus as a raised platform, and in the holotype, continues as a rounded ridge of denticles which terminates only a short distance behind the anterior end of the interpterygoid vacuities. The shape of the two large, interpterygoid vacuities that are sparated by the processus cultriformis, varies in the different specimens. They tend to have a rather elongated, flattened-oval shape with rounded ends and are widest about two-thirds of the way anteriorly along their length. They are marginally wider anteriorly than posteriorly, and in most skulls, each vacuity has a slight indentation of its antero-lateral margin adjacent to the palatine tusk. In UMZC T238, the ectopterygoid reached the vacuity with an exposure of about 4-5mm in length, and a toothless processus alaris was probably present posterior to this bone, isolating it from the subtemporal vacuity, as it does also on the right side of the holotype. The palatal ramus of the pterygoid was therefore relatively short and failed to make contact with the palatine, a condition also noted in other specimens of L. huxleyi by Jeannot et al (2006).

22 a) b)

Text-fig.17. Lydekkerina huxleyi (Lydekker) Broom; Lower Triassic; South Africa. UMZC T110. a) slightly antero-latero-dorsal view of right basicranial region; b) antero-lateral and slightly ventral view of laterosphenoid region on the right side of the skull.

Text-fig.18. Lydekkerina huxleyi (Lydekker) Broom; Lower Triassic; South Africa. UMZC T110, ventral view of parasphenoid and posterior part of left side of skull.

Neurocranium (Text-figs 16-17): The sphenethmoid in UMZC T110 (Text-fig.16) is a large, bulky element resting upon the processus cultriformis, and extending anteriorly in the mid-line of the skull from the region of the parietal foramen to a short distance anterior to the orbits. Anteriorly, the sphenethmoid appears to be slightly displaced towards the right. Dorsally, it supported the mesial portions of most of the frontals and the anterior parts of the parietals, probably via a very thin layer of soft tissue now replaced by an equally thin layer of matrix, which bears impressions of the striated ventral surface of the roofing bones (Text-fig. 11). The sphenethmoid was held in place by a pair of ridges on the ventral surface of the roofing bones, which abutted against the lateral edges of the dorsal

23 surface of the sphenethmoid. These stabilising ridges are quite different from the series of elongated, smooth ridges on the ventral surface of the roofing bones in the orbital region that Jeannot et al (2006) described, and which possibly provided additional mechanical support to this region of the roof. The sphenethmoid is ossified only perichondrally. Its dorsal surface is a long, rectangular and essentially flat sheet of bone, but its lateral surfaces have a more complex topography (Text-fig.16). Anteriorly, the sphenethmoid is broad dorsally, but not very high, and its inwardly curving lateral surfaces soon reach a narrow ventral surface resting on a broader cultriform process. Posterior to this, however, the sphenethmoid becomes progressively deeper and more bulky as the dorsal broadening gradually shifts ventrally until eventually the whole of the last quarter of the bone is broad and bulky and overhangs the now relatively narrower processus cultriformis. The broader regions of the sphenethmoid are separated from the narrower regions by a well-defined rounded ridge, which curves posteriorly and then ventrally over the lateral surface of the bone. This ridge has been considered by some workers to be the site of attachment of the m. levator bulbi. A large, rounded optic foramen opens low down on the broad posterior part of the sphenethmoid. It is greatly overhung by the almost flattened lateral surface of the sphenethmoid in this region, and leads into a short, wide and shallow groove which runs anteriorly and slightly dorsally over the surface of the bone. The basisphenoid is a poorly ossified, transverse strip of bone resting upon the dorsal surface of the parasphenoid corpus between the two epipterygoids. Anteriorly, where it is best ossified, the dorsal surface of its more mesial portions is hollowed out into an extensive pituitary fossa which leads forwards onto the smooth dorsal surface of the most anterior parts of the parasphenoid corpus, and is backed by a high, nearly vertical wall representing the anterior parts of an otherwise poorly ossified dorsum sellae (Text-fig. 17a). Posterior to this, the basisphenoid slopes abruptly ventrally and is represented only by isolated patches of bone (Text-fig.11). Lateral to the pituitary fossa, the basisphenoid on the right side of the skull forms a thick wedge of largely perichondral bone extending outwards and slightly backwards parallel to, but below, the ascending process of the epipterygoid. The dorsum sellae diminishes in height laterally and eventually fades away into the dorsal surface of this wedge, which itself thins out laterally where it reaches the basal column of the epipterygoid. Due to disturbance on this side of the skull, the parasphenoid together with the overlying basisphenoid has been lifted up so that it now lies on top of the more mesial portions of the pterygoid corpus. The wedge of basisphenoid bone continued as a cartilaginous basipterygoid process into the conical recess of the pterygoid, and a cross-section through the basipterygoid process prior to its entry into the conical recess on the left side of the skull shows the decayed basipterygoid core, now replaced by matrix, to be basically triangular in outline (Text-fig. 12b). It is surrounded by the pterygoid anteriorly and ventrally, the parasphenoid posteriorly and the base of the basal column of the epipterygoid dorsally. The basisphenoid, when viewed anteriorly on the right side of the skull, is seen to rise up mesially and become continuous with a small sheet of black, perichondral bone, which faces ventro-laterally and probably represents an ossification lying in the otherwise unossified side wall of the bulging latero- sphenoid region of the braincase (Text-fig.17b). Near to this ossification, a small foramen, possibly for the intracranial branch of the internal carotid artery, pierces the dorsal surface of the basisphenoid a short distance behind its anterior margin. Otic region (Text-figs 18 and 19-22): The prootic in UMZC T110 (Text-figs 19 & 20) is well ossified and is relatively undisturbed on the left side of the skull. It has a bulky antero-lateral portion, thickened by endochondral bone, which projects far laterally beyond the head of the stapes to contact the upper parts of the transverse ascending lamina of the pterygoid. Above this contact, a small gap is left below the skull roof.

24 Text-fig.19. Lydekkerina huxleyi (Lydekker) Broom; Lower Triassic; South Africa. UMZC T110, slightly antero-mesial view of left prootic and stapes.

Mesial to this thickened corner of the prootic, two thin sheets of perichondral bone diverge from each other, one horizontally to form part of the roof of the prootic, some 1.5-2.0mm below the roofing bones, the other vertically inwards to form the anterior surface of the prootic. This surface is pierced ventrally by a number of small foramina, and is hollowed out centrally by a wide, shallow groove, which runs ventrally from a low semi-circular opening notching its dorsal margin. On either side of this opening, a wide, bony projection rises up to the skull roof, presumably to assist in the attachment of the braincase to the skull roof.

a) b)

Text-fig.20. Lydekkerina huxleyi (Lydekker) Broom; Lower Triassic; South Africa. UMZC T110, lateral view of left otic capsule and stapes; b) Holotype skull BMNH R507, palatal view of footplate of left stapes connecting to dorsal surface of crista pterygoidea.

25 a)

b)

Text-fig.21. Lydekkerina huxleyi (Lydekker) Broom; Lower Triassic; South Africa. UMZC T110. a) posterior view of left side of occipital region; b) slightly postero-mesial view of left occipital region.

The opisthotic is a comparatively large ossification that is well exposed on the left side of the skull (Text-figs 20a & 21a). Mesially, it forms a high and relatively thin, vertical lamina that is concave anteriorly and is overlain posteriorly by the parotic process of the exoccipital (Text-fig.20a). This portion of the opisthotic forms part of the posterior margin of the fenestra ovalis, but further laterally, it thickens into a solid, rod-like paroccipital process that is firmly clasped distally by a well-developed occipital process from the tabular, which wraps itself around its posterior, ventral and anterior surfaces. Such a rod-like paroccipital process is also clearly seen in (Warren, Damiani & Yates 2006, Fig 3a), arising anteriorly and antero-laterally to the left exoccipital. The opisthotic therefore forms, between the tabular and the exoccipital, the central portion of a stout paroccipital bar, above which lies a moderately well developed posttemporal fossa which, is large and triangular with rounded corners, and deeper mesially and shallower laterally (Text-fig. 21a). The presence of an ossified opisthotic forming the central portions of the paroccipital bar, was first noted by Watson (1919), and is confirmed by all those skulls in which the appropriate regions have been preserved, including the holotype ( contra

26 Jeannot et al (2006), where its disposition is very similar to that seen in UMZC T 110, being wrapped around by the paroccipital process of the tabular a short distance from the base of the tabular horn, and extending mesially anterior to the parotic process of the exoccipital where it forms a curved flange extending anteriorly and slightly dorsally into the posttemporal fossa. The posterior edge of the occipital process of the tabular continues onto the underside of the tabular as a crista tabularis externa, where it provides support for the base of the tabular horn. Further support is provided by a less-well developed, broadly rounded crista terminalis, which is separated laterally from the former crista by a wide, shallow groove (Text-figs 18 & 21a), as is also seen in UMZC T238. The right otic region, although somewhat crushed, shows what appears to be an additional thick ossification, almost continuous with the thin mesial end of the right paroccipital process and possibly forming the postero-mesial corner of the capsule (Text-fig.22). It lies anterior to the supraoccipital process of the exoccipital and postero-mesial to the head of the stapes and consists of a pair of laminae, almost at right angles to each other, one facing dorso-mesially and the other ventro-mesially.

Text-fig.22. Lydekkerina huxleyi (Lydekker) Broom; Lower Triassic; South Africa. UMZC T110, mesial view of right otic region.

Occiput (Text-figs 18 and 20-21): The occipital region of the holotype has been somewhat compacted and is partially hidden by the associated anterior end of the vertrbral column, but the exoccipital bones, which form the major component of the occiput, are well displayed in UMZC T110, where they are large and well-ossified elements (Text-figs 18 & 21a & b). The better preserved left exoccipital rises up dorsally as a stout, columnar processus lamellosus which projects inwards to partially roof the medullary region of the foramen magnum (Text-fig.21a). It expands dorsally into a flattened top, which may have supported a cartilaginous supraoccipital lying in what is now a moderately wide and narrowly rectangular space. Anterior to the procesus lamellosus, a large vagal fissure leaves the cranial cavity in a postero-lateral direction, and mesial to this, the exoccipital is drawn out into a narrow but long, almost horizontal sheet of bone, the most anterior portions of which form a thin basal process which partially floors the medullary region (Text-fig.21b). The two basal processes almost meet in the mid-line and overlie a small space for the basioccipital cartilage. On the left side of the skull, the exoccipital appears to extend forwards in front of the vagal fissure as a triangular sheet of bone which rises up to form the anterior wall of the fissure. This fissure narrows considerably away from the cranial cavity, and a further thin

27 vertical plate of bone can be seen forming the anterior wall of the more lateral portions of the fissure. Immediately lateral to the processus lamellosus, and separated from it by a very narrow fissure, a wide occipital process extends downwards from the ventral surface of the postparietal (Text-fig.21a). This process narrows into a thick, rod-like structure, which then spreads out over the posterior surface of the exoccipital and also extends along the upper edge of its parotic process. The parotic process or lamina of the exoccipital is a thickly built, fan-shaped lateral expansion, which wraps around the dorsal, posterior and ventral surfaces of the mesial portions of the stout paroccipital bar and forms a part of the ventral margin of the large posttemporal fossa (Text-fig. 21a). Mesially, the parotic lamina is pitted and roughened in places, for muscle attachment, and somewhat ventrally, about half way along its lateral extension, it is pierced by a large, oval vagal foramen, overhung by a broadly rounded ridge of bone. A small, rounded hypoglossal foramen lies posteriorly and ventro-mesially to the vagal foramen, in a slight valley between the parotic lamina and the condyle. Below the vagal foramen, the parotic lamaina curves quite sharply forwards around the postero-ventral portions of the otic capsule to form an extensive, fan-shaped subotic lamina. This lamina is broadly expanded posteriorly, where it forms the ventral component of the paroccipital bar (Text-fig.18), and mesially overlaps the ventral surface of the corpus of the parasphenoid to meet its opposite fellow to form the posterior margin of the palate in the mid-line. Anteriorly, the subotic lamina narrows and thins out, and comes to underlie the lower edge of the inner end of the stapes, and, as is clearly shown in UMZC T238, sutures with the parasphenoid, the suture crossing the floor of the rectus capitis pocket. Lateral to this suture, there can be seen the small, rounded subotic embayment discussed earlier. The exoccipital has no contact with the pterygoid. From the posterior face of the exoccipital, a short, stout condylar process extends posteriorly, lateral to a much-reduced basioccipital (Text-figs 18 & 21a). This process is strongly drawn out laterally and expanded distally to form an almost rectangular, unfinished surface for a cartilaginous condyle, which is directed postero-mesially and slightly ventrally. The well-separated condyles are formed entirely from the exoccipitals and, as in the holotype, BMNH R507, UMZC T238, BMNH R6850, R504, R505, and BSP VIII 1934 44 skull B, they are visible in dorsal view, projecting backwards from an occipital surface, which slopes gently downwards posteriorly. The postero-lateral edges of the condyles terminate some 5mm posterior to the hinder margin of the overlying skull roof. The occipital surface is gently vaulted in posterior view and the exoccipital condyles lie above the horizontal plane of the quadrate condyles, as they also appear to do in the holotype. Related perhaps to this vaulting of the occipital surface, the cheek margins are quite steeply curved in occipital view, as has been noted to occur in small individuals of L. huxleyi by Shishkin et al (1996), and in agreement with the figures produced by Watson (1919, 1951) and Parrington (1948, 1952) but contra Shishkin et al (1996, Fig. 7) and Jeannot et al (2006), where the cheek margin is considered to be straight in occipital view. In the holotype skull, both cheek regions are more curved than straight, despite the flattening that these regions have suffered. Towards the base of each condylar process, the palatal surface of the exoccipital bears a distinct, irregular tubercle (Text-fig.18), separated from the condylar process by a transversely running groove, features that are also seen in BMNH R505 and UMZC T238, but not in the holotype, where the bones in this region have been somewhat disrupted. The basioccipital is a poorly ossified, spongy mass of endochondral bone fused to the exoccipitals and lying in the mid-ventral line between them (Text-fig.21a). It did not extend very far anteriorly and is absent from the dorsal surface of the most posteriorly preserved part of the parasphenoid. It is deeply hollowed out posteriorly, and appears mainly as a pair of rough, unfinished surfaces, which slope obliquely away from each other posteriorly. Dorsally, it is almost completely overlain by the pair of thin basal processes of the exoccipitals, retaining only a slit-like communication with the foramen magnum. Ventrally it is completely underlain by the exoccipitals (Text-fig.18). Stapes (Text-figs 14, 18-20): Both stapes are moderately well preserved, but that on the left is the better exposed and lies fairly close to its natural position (Text-figs 14a, 18, 19 & 20a). The stapes is a stout bone, some 15mm long, consisting of a massively expanded, conical footplate seemingly filling the

28 fenestra ovalis, and a more slender, elongate rod-like shaft, extending dorsally and postero-laterally from the footplate, and lying freely within a tympanic cavity formed by the conjoined laminae from the pterygoid and squamosal laterally, the stapedial groove and crista obliqua ventrally, and the paroccipital process mesially. It terminates in an unfinished surface in the more anterior parts of the otic notch, some 2mm below the level of the roofing bones, indicating perhaps that a cartilaginous extra-stapes was present attaching it to a tympanic membrane. The footplate is longer antero-posteriorly than it is deep, and is drawn out antero-ventrally into a well- developed triangular process which extends downwards, inwards and slightly forwards towards the posterior end of the crista parapterygoidea to whose stapedial facet it would seem to have been attached, even though the distal end of this process has not been fully preserved (Text-figs 18 & 20a). This attachment could well have been an articulated one, like that seen in Rhinesuchus whaitsi (Watson 1962 Fig. 4), thereby allowing vibratory movements of the stapes to be transmitted from the tympanic membrane to the fenestra ovalis. The footplate of the left stapes of the holotype, BMNH R507, also gives the appearance of having been attached to the dorsal surface of the crista parapterygoidea, although the precise details of this attachment are not clear (Text-fig. 20b). The head of the stapes may also possibly have rested upon, or been closely associated with the subotic lamina of the exoccipital, which would appear to have formed a part of the margin of the fenestra ovalis. A large foramen for the stapedial artery pierces the hollowed out ventral surface of the stapes just posterior and lateral to the origin of the antero-ventral process. The footplate of the stapes is also drawn out posteriorly into a deep and even more extensive process, which extends posteriorly towards the dorsal parts of the proximal end of the expanded lamina of the opisthotic (Text-fig. 20a), diagonally opposite to its contact with the stapedial facet. This latter process would seem, from its position, to be equivalent to the expansive processs of the stapedial footplate that Parrington referred to as the antero-dorsal process (1948, Fig.3 B & C), the stapes in this specimen, however, having been somewhat disturbed and rotated in an anti-clockwise position within the tympanic cavity. A contact between this posterior process and the opisthotic is unlikely, however, as this would have provided the stapes with a two-pronged osseous attachment around the rim of the fenestra ovalis, and would have seriously affected the functioning of the stapes as a sound-conducting element activated by the tympanum. Separating these two processes on the ventral surface of the stapes is a wide, shallow groove, which extends along the shaft of the stapes almost to its tip and narrowing as it goes (Text-figs 14a & 20a). Proximally, this groove is bounded by a pair of distinct ridges running along the antero- ventral and postero-ventral edges of the bone (Text-figs 14a & 20a). The shaft is here broadly oval in cross-section, and slightly flattened dorso-ventrally, with rounded, convex surfaces except for the groove, which faces slightly posteriorly as well as ventrally. Distal to the foramen for the stapedial artery, about a third of the way along the shaft, this groove is roughened over an elongated, almost oval- shaped area bounded by the two ridges. This roughening includes several sharp ridges of bone, and within this area there also arises a tuberosity, which is directed towards the quadrate tubercle (Text-fig. 18). In UMZC T206, this roughened tuberosity is replaced by a small, ventral process, and it is possible that both structures represent the origin of a cartilaginous, or perhaps even ligamentous, quadrate process, that once connected the shaft of the stapes with the quadrate tubercle. Watson (1926) argued for the presence of such a quadrate process in the embolomere Orthosaurus , as has Olson (1941) for Trematops , and Westoll (1943) for labyrinthodonts in general, with the additional presence of a cartilaginous connection from this to the hyoid. Parrington (1952, Fig.4a), figured both cartilages as being hypothetically present in Lydekkerina . Such a process may have existed in order to support the stapes within the tympanic cavity, or possibly to act as an additional sound-transmitting mechanism, carrying vibrations from the articular region of the mandible to the fenestra ovalis. The footplate of the stapes is greatly overhung by the prootic bone and the large fenestra ovalis must have been well sunk into the ventro-lateral parts of the otic capsule, with its borders formed largely of cartilage (Text-figs.19 & 20a). The distal end of the stapes narrows as it approaches the otic notch and becomes relatively slender and oval in cross-section. The left squamosal, where it borders the notch, is produced postero-laterally into a slightly projecting rim, or incipient crista falciformis, which, as stated

29 earlier, very slightly closes in the area behind the otic notch. Immediately anterior to this, a shallow recess runs around the notch, just below the ornamented roof and separated from it by a rim. This groove and rim probably represent the area of attachment of the tympanic membrane in the otic notch. Mandible (Text-figs 23-29): The mandible of L. huxleyi has been figured and partially described by Watson (1912), Broili & Schröder (1937), Parrington (1948), Warren & Black (1985), Jupp & Warren (1986), and Jeannot et al (2006), and briefly alluded to by Watson (1913) and Broom (1915). Recent interpretations of certain of its features by Warren & Black (1985) and Jupp & Warren (1986), differ from those of some of the earlier authors and from those given here, and the following account of the mandible concentrates on these particular features, and upon certain features which have not been described or illustrated before. The mandible of L. huxleyi is characterised by an unusually elongate and complex postglenoid area (PGA), and although this has been broken off in the majority of specimens examined, it has been partially preserved in BMNH R505, R506, R508, R3909 and R8943, is well preserved in the holotype BMNH R507, and in BP/1/1373 (Text-figs 24 & 25), and is virtually complete in BMNH R5482 (Text- figs 23a & b). The PGA was considered to be of considerable diagnostic importance in temnospondyls by Warren & Black (1985) and by Jupp & Warren (1986), who also proposed a terminology for the PGA, based largely upon the mandible of the ‘rhytidosteid’ Arcadia myriadens . In this paper, their terms ‘arcadian groove’ and ‘arcadian process’ are substituted by the less species-orientated terms, depressor groove and surangular process.

a)

b)

Text-fig.23. Lydekkerina huxleyi (Lydekker) Broom; Lower Triassic; South Africa. BMNH R5482, a) dorsal view and b) posterior view of the postglenoid area of the right mandble, with the skull roof held horizontally.

30 Text-fig.24. (above) Lydekkerina huxleyi (Lydekker) Broom; Lower Triassic; South Africa. BP/1/1373, dorsal view of posterior end of right mandible.

Text-fig.25. Lydekkerina huxleyi (Lydekker) Broom; Lower Triassic; South Africa. BPI No 1373, lingual view of posterior end of right mandible.

31 The mandible of L. huxleyi has a type 1 PGA, as defined by Jupp & Warren (1986), and this is dominated by a long, postero-dorsally directed surangular process, which is separated mesially from a shorter retroarticular process, by a well-developed depressor groove, for the accommodation of the insertion tendon of a powerful depressor mandibulae muscle (Text-fig. 24). The posterior end of the mandible has therefore a distinctive bifid appearance. The PGA is composed of the surangular and articular, and these are virtually fused together, although a partial, hairline suture between them can be discerned on both BMNH R5482 and BP/1/1373 (Text-figs 23b & 25), and a much more distinctive suture on the left mandible of the holotype BMNH R507. This suture extends dorsally over the depressor groove, and in BPI No1373 continues anteriorly towards a moderately large foramen on the dorsal surface of the PGA, a short distance behind the postglenoid ridge. A similar foramen is also visible in UMZC T238, mesial to the postglenoid process of the surangular, in the region where the depressor groove begins on the dorsal surface of the PGA. The surangular forms the major part of the PGA, and all of the extensive surangular process. In BP/1/1373 , this process projects postero-dorsally for some 11mm behind the glenoid fossa, which represents some 12% of the mandibular length, whilst in BMNH R506, the PGA of the right mandible is over 13% of the length of the jaw. The surangular process is comparatively narrow when viewed from above and has a rather flat, strongly ornamented labial surface, whose lower border continues backwards the postero-dorsal curvature of the ornamented angular part of the jaw (Text-fig. 26a). This ornamented surface bears proximally a conspicuous dorsal swelling, recognisable as the postglenoid process of Jupp & Warren (1986), and immediately posterior to this there is the origin of a deeply grooved mandibular sulcus (Text-fig. 26a &b).

Text-fig.26a. Lydekkerina huxleyi (Lydekker) Broom; Lower Triassic; South Africa. BMNH R8943, labial view of posterior end of right mandible.

32 Text-fig.26b. Lydekkerina huxleyi (Lydekker) Broom; Lower Triassic; South Africa. BMNH R5482, ventro-lateral view of postglenoid area of the right mandible. The remaining surfaces of the surangular process are unornamented and convexly curved, with the dorsal and mesial surfaces bearing several nutrient foramina, to nourish those muscle fibres of the depressor mandibulae muscle, which inserted upon them (Text-fig. 23a & b). Mesial to the base of the surangular process, and lying at a somewhat lower level, there juts posteriorly, a solid, squat and almost cylindrical retroarticular process of the articular (Text-figs 23a & b, 24, 25). This terminates in an unfinished surface, which is separated from the surangular process on the posterior face of the PGA by the deep and wide depressor groove. This groove forms an extensive pulley-like surface, which curves ventrally over the posterior surface of the PGA and passes below the strongly projecting surangular process onto the labial face of the mandible. Here it continues anteriorly below the ornamented portions of the surangular and angular, becoming narrower and shallower, and eventually merging with the mandibular sulcus just posterior to where the surangular-angular suture crosses the groove (Text-fig 26a & b). This merger between the depressor groove and the mandibular sulcus is present in all those specimens in which this part of the mandible has been preserved. This groove then slips below the rim of the angular onto its lingual surface, and continues anteriorly just above the lower border of the angular as an even shallower groove, almost to the level of the most posterior of the three anterior Meckelian foramina. This latter groove is believed by Maryanska & Shishkin (1996), to have housed the internal mandibular vein. The pulley-like surface on the posterior face of the PGA is particularly well preserved in BH54 (Text-fig. 27), where it continues dorsally and anteriorly onto the dorsal surface of the PGA, over which it spreads out and gradually fades away. The lateral-line system is well developed on the surangular process and is most clearly displayed on the right ramus of BMNH R8943 (Text-fig.26a). The mandibular sulcus originates on the surangular immediately posterior to the postglenoid process and runs antero-ventrally below this prominence as a very deep groove, which then continues along the surangular until it merges with the depressor groove. The accessory sulcus is a very wide but short groove, arising from the anterior edge of the mandibular sulcus some distance below the postglenoid process, and passing antero-dorsally for a short distance before fading away on the unornamented dorsal portions of the surangular. The oral sulcus arises more anteriorly along the mandibular sulcus, and consists proximally of two very large depressions running in a line antero-dorsally, before continuing as a groove which passes in a more anterior direction along the

33 Text-fig.27. Lydekkerina huxleyi (Lydekker) Broom; Lower Triassic; South Africa. BH54, dorsal view of the postglenoid area of the left mandible. dorsal portions of the surangular. On the right mandible of UMZC T238, both the accessory and oral sulcus are present, but only as short series of discrete depressions. In UMZC T110, however, the oral sulcus on the left mandible is entirely a groove, and in other specimens this sulcus can often be seen over the more anterior parts of the dentary as a narrow groove running forwards a short distance below the tooth-bearing margin (Text-fig. 29a). The PGA of L. huxleyi , as described here, differs considerably from the simpler conical projection illustrated by Jupp & Warren (1986, Fig. 5), and from the PGA figured by Warren & Black (1985, Fig. 12), which gives no real indication of the extensiveness of the PGA. The unusual length of the postglenoid area of the mandible of L. huxleyi was first observed by Watson (1912, Fig. 6), and confirmed by him in 1919 (Fig. 9, p18). Parrington (1948) described L. huxleyi as having a ‘retroarticular process (ie PGA), which is remarkable for its length’, a view that has recently been endorsed by Jeannot et al (2006). The articular, the second bone contributing to the PGA, forms all of the retroarticular process, the lingual parts of the dorsal surface of the PGA and by far the greater part of the glenoid fossa. The latter lies high up on the jaw, immediately behind the adductor fossa, well above the level of the dorsal surface of the dentary. It is sub-divided into two shallow, elliptical condylar surfaces, the inner of which is more extensive than the outer, and ascends anteriorly onto a very prominent hamate process (Text-figs 24 & 27). The glenoid fossa is bordered posteriorly by a postglenoid ridge which is high and thick mesially, but becomes lower and thinner laterally. Anterior to the glenoid fossa, the articular forms a smooth surface lining the curved, posterior border of the adductor fossa, and rises up antero-mesially to suture with the prearticular and to form the greater part of the hamate process (Text-fig. 28) The arrangement of the bones around the adductor fossa is best seen in BPI No1373 (Text-fig 24). The posterior coronoid here extends posteriorly along the labial border of the adductor fossa, capping the surangular for about a third of the length of the fossa, and preventing the dentary from entering the fossa. The rounded surface of this capping is strongly ornamented with longitudinal ridges, as is the narrow strip of surangular flanking it laterally, and it is also raised into a slight hummock, perhaps for the attachment of adductor musculature. The posterior end of the dentary in BPI No1373 and in BH55

34 Text-fig.28. Lydekkerina huxleyi (Lydekker) Broom; Lower Triassic; South Africa. BPI NO1373, labial view of posterior region of right mandible. terminates in a pointed wedge lying in a groove between the surangular and the angular, just above where the oral sulcus crosses onto the dentary at the apex of the angular. The posterior coronoid in BP/1/1373 bears dorsally an irregular scattering of conical and rounded denticles of varying sizes, mostly represented by their abraded bases, and on the left mandible of the holotype, BMNH R507, these denticles cover a raised, and almost horizontal platform extending over the whole length of the posterior coronoid, with their abraded bases showing an inner pulp cavity surrounded by a thin rim of bone. There is no sign of any coronoid process. The remainder of the coronoid region in BP/1/1373 is poorly preserved, but there are indications of the presence of a distinct ridge running along the middle coronoid and forming a parapet on the lingual side of the tooth-bearing area of the dentary (Text-fig. 29b), much as Watson (1912) described as being present in Eryop s, Anaschisma and Labyrinthodon, and this is confirmed by the holotype, where the denticulated platform on the posterior coronoid is continued forwards, although its preservation is poor. The middle coronoid in the holotype also bears a distinct tooth amidst its coronoid denticles with their rounded domes, some 5mm in front of the suture between the middle and posterior coronoid, and 5mm behind the tip of a large downwardly and posteriorly directed palatal tusk. The anterior coronoid in BP/1/1373, appears to have a broad dorso-lingual surface, which subtended the whole of the symphysial area of the dentary when seen in dorsal view, and although it has not been possible to confirm the presence of any denticles on this bone, nor on the anterior coronoid of the holotype, the latter does display two large teeth, positioned about 2.7mm behind the pair of vomerine tusks. In other specimens of L. huxleyi , Jeannot et al (2006), have confirmed the presence of a dentition on all three coronoids, with the teeth on the posterior and middle coronoids appearing as scattered, tiny, rounded domes, in contrast to those on the anterior coronoid, where they comprise a short row of large, pointed denticles that approach the size of the marginal teeth. On the posterior coronoids of QMF 39705, the dentition comprised uneven rows of large denticles, with individual denticles approaching the size of adjacent maxillary teeth. The enlargement of some denticular teeth on the coronoid bones to the size of the marginal teeth has previously been observed in another stereospondyl, Arcadia myriadens by Warren & Black (1985). The adductor fossa is elongated, with a narrowly rounded anterior border, and a much broader posterior border which lies obliquely across the jaw with the lingual end more anterior than the labial (Text-fig. 24). The mesial border of the fossa is shorter and has a more thinly rounded rim than the lateral border. The chorda tympani foramen, as in other type 1 PGA’s, lies between the prearticular and the articular,

35 a) b)

Text-fig.29. Lydekkerina huxleyi (Lydekker) Broom; Lower Triassic; South Africa. BH95 a) labial view of anterior end of right mandible, b) posterior view of c) dentary tooth of right mandible, c) UMZC T110, lingual view of posterior end of the right mandible. the suture between these two bones running into its upper border, and leaving via its posterior border. It is best displayed on the right ramus of UMZC T110, where it is a moderately large, rounded opening lying for the most part in the hollowed out postero-dorsal parts of the mesial face of the prearticular (the fossa subglenoidalis) (Text-fig. 29c). Jeannot et al (2006) also recorded the presence of this foramen on the dislocated right mandible of the holotype BMNH R507, as lying ‘between the prearticular-articular suture’. In UMZC T110, a distinct groove, probably housing the chorda tympani nerve, curves ventrally towards the foramen over the articular. Above the foramen, the prearticular sheathes mesially the large, pyramidal hamate process, and wraps around its anterior face (Text-fig.25), from which it descends rather steeply to form the lingual border of the adductor fossa. The prearticular then extends forwards to a suture with the middle coronoid, as it also does in the holotype BMNH R507. Ventral to the chorda tympani foramen, the angular, in both BPI No1373 and in UMZC T238, tapers posteriorly to form a shallow, narrow, keel-shaped splint of bone that terminates ventral to the proximal end of the retroarticular process (Text-fig. 25). Three anterior Meckelian foramina of varying shape and size open low down on the mesial face of the anterior half of the postsplenial on the right ramus of BMNH R5482 and on the left ramus of UMZC T238. In R5482, the two hinder foramina lie very close to each other near the central portions of the postsplenial, not far above it’s ornamented border, whilst the anterior foramen lies nearer the suture between the two splenial bones. Two anterior Meckelian foramina are visible on the left mandible of the holotype BMNH R507, a larger oval anterior one, 1.5mm long, and a smaller, oval posterior one. The moderately large, oval, posterior Meckelian fenestra, most clearly seen in R, 54582, lies mid-way between the adductor fossa and the ornamented ventral rim of the mandible with its centre-point lying below the anterior edge of the adductor fossa. It is broadly rounded posteriorly but has a more narrowly rounded anterior end from which a shallow groove extends forwards for a short distance before fading away in the region of the suture between the postsplenial and prearticular. A post-symphysial foramen is also present on the left ramus of BMNH R548, piercing the smooth lingual surface of the splenial immediately posterior to the symphysial area, just where the bone begins to splay out and curve towards the symphysis. Into this foramen there enters the deep portions of a groove, which passes anteriorly over the surface of the splenial. The symphysial region is extensive and deep and is formed from expanded, shelf-like laminae from the dentary and splenial, which may have

36 served for the origin of anterior depressor muscles. The symphysial region in the holotype BMNH R507, and in BH74 and in BP/1/1373 bears a single, large, posteriorly curved tusk, which in BH74 is some 4mm long. This tusk, as described earlier, is accommodated during occlusion within the antero- lateral projection of the anterior palatal vacuity. Apart from the marginal tooth row, this tusk is the only additional tooth present on the symphysial area. The numerous dentary teeth are set close together in a deep, broad groove which runs along the outer edge of the jaw, and this is bordered laterally by a narrow, rounded rim of bone, and mesially by a much thicker, broader ridge. The bases of the teeth splay out and fuse with the roughened bony surface of the dentary groove (Text-fig. 29b) and with the narrow lateral rim. The complete tooth row extends from the symphysis to just behind the anterior end of the adductor fossa. The teeth are as described in the holotype, BMNH R 507.

RECONSTRUCTIONS OF THE SKULL AND MANDIBLE OF LYDEKKERINA HUXLEYI (Text-figs 30-34) No single skull or mandible of the many specimens of Lydekkerina huxleyi that have been examined is adequately enough preserved in all aspects of its structure to provide the sole basis for a total reconstruction, and the reconstructions shown here, are of necessity composite. All the skulls and mandibles that have been studied display morphological variation due to their individuality, age, state of preservation and amount of distortion (see also Jeannot et al (2006), but, as far as possible, the holotype BMNH R507 has been used as the basis for the reconstructions of the dermal roof of the skull and the anterior regions of the palate, and UMZC T110 for the reconstructions of the posterior half of the palate, the palatoquadrate complex, neurocranium, otic region and stapes. The reconstructions of the mandible have been based upon a much wider range of specimens, as is detailed in the text. Any problem that has arisen, regarding the reconstruction of a particular morphological feature has been resolved by using either the best-preserved specimens available, or those specimens that display the maximum amount of agreement. The reconstruction of the skull in lateral view shows a skull that is rather deeper in the region of the angular curvature than is apparent in the holotype skull BMNH R507, which, as described earlier, has suffered a certain amount of dorso-ventral compression. It does closely resemble, however, the left lateral view of the skull drawn by Pawley & Warren 2005 Fig.4c, and is also comparable in proportions to that figured by Parrington 1948 Fig.2. This lateral reconstruction differs slightly from the ‘lateral view’ shown in Text-figs 2 and 4, since the latter are very slightly antero- lateral views, and the tabular horn in these figures therefore does not appear to extend quite so far posteriorly behind the squamosal. The right tabular horn also appears shorter in these two figures because its tip was broken off during the later stages of preparation. Lydekkerina huxleyi is the most widely distributed temnospondyl within the Lystrosaurus Assemblage

37 Text-fig.30. Lydekkerina huxleyi . Reconstruction of skull in dorsal view.

Text-fig.31. Lydekkerina huxleyi . Reconstruction of skull and mandible in right lateral view.

38 Text-fig.32. Lydekkerina huxleyi . Reconstruction of skull in palatal view.

Text-fig.33. Lydekkerina huxleyi . Reconstruction of skull in occipital view.

39 a)

b)

c)

Text-fig.34. Lydekkerina huxleyi . a) Reconstruction of mandible in labial view; b) lingual view; c) dorsal view.

Zone, and due to the climatic conditions within the Karoo Basin during the Lower Triassic, may well have been distributed throughout virtually the whole of the region as rather isolated demes that would have encouraged genetic differentiation, and led to the considerable range of morphological variation that L. huxleyi displays (Jeannot et al (2006). Any areas of disagreement with the views of other authors,

40 regarding certain morphological features, may well have arisen as a result of this morphological variation, and the different suites of specimens that these authors have studied.

CHRONOLOGICAL REVIEW OF THE MORPHOLOGY OF THE SKULL AND MANDIBLE OF THE REMAINING GENERA AND SPECIES PREVIOUSLY ASSIGNED TO THE FAMILY LYDEKKERINIDAE

LYDEKKERINA PUTTERILLI BROOM 1930 (= BROOMISTEGA PUTTERILLI (Broom) Shishkin & Rubidge 2000, comb. nov.) (Text-fig. 35) Lydekkerina huxleyi (Lydekker) Broom, 1915. Broomistega putterilli (Broom) Shishkin & Rubidge, 2000, comb. nov. Holotype. TM 184, the post-orbital regions of a skull in the Transvaal Museum, Pretoria, with a mid-roof length estimated to be about 100mm, together with a small, disarticulated fragment of mandible. Locality and horizon . Harrismith, Free State Province, South Africa, upper part of the Lystrosaurus Assemblage Zone, Middle Beaufort Group, Lower Triassic. This species was established by Broom (1930) for an incomplete and poorly preserved skull found associated with material of L. huxleyi . It was considered a nomen dubium by Kitching (1978), incertae sedis by Colbert & Cosgriff (1974), Cosgriff (1974) and Hewison (1996), and as a distorted specimen of L. huxleyi by Cosgriff & Zawiskie (1979) and Cosgriff (1984). Shishkin et al (1996) considered it to be a rhinesuchid, although not a juvenile form of Uranocentrodon , as had been suggested earlier by Parrington (1948), as this latter taxon came most probably from the earlier Upper Permian Dicynodon zone and not from the Lower Triassic Lystrosaurus zone. Although this skull resembles that of L. huxleyi in the outline and disposition on the roof of the parietals, with their narrowed and highly indented anterior borders, and the presence of wide, U-shaped otic notches, it is more reminiscent of rhinesuchids in Text-fig.35. ‘ Lydekkerina ’ putterilli now having supratemporals that enter into the border of the Broomistega putterilli (Broom) Shishkin& otic notches, and occipital flanges from the tabulars and Rubidge; Lower Triassic; South Africa. postparietals that slope backwards to partially roof over Holotype TM 184. Skull in a) dorsal view; b) the posttemporal fossae. Other features suggestive of occipital view (both after Shishkin & rhinesuchids, include its coarse ornamentation and the Rubidge 2000). lack of any terminal projection of the tabular horn above the paroccipital process. Shishkin & Rubidge (2000), prepared the holotype material further, and demonstrated that the paroccipital bar, the posttemporal fenestra and cristae musculari were likewise rhinesuchid in nature. Having made a detailed comparison of this skull with two previously undescribed, immature specimens of the same species from the Lystrosaurus Assemblage Zone, BP/1/5058 and BP/1/3241, they concluded that all three specimens were successive growth stages of a relict paedomorphic rhinesuchid, quite distinct from other known forms. They redescribed this form as Broomistega putterilli, and the validity of this taxon, and its rhinesuchid nature are accepted here.

41 PUTTERILLIA PLATYCEPS BROOM 1930 (Text-fig. 36) Lydekkerina huxleyi (Lydekker) Broom 1915. Holotype TM 168, a poorly preserved skull in the Transvaal Museum, displaying only the inter-orbital regions of the roof and the basicranial regions of the palate, and TM 88, an imperfectly preserved dermal shoulder girdle and mandible in the same Museum. Locality and horizon . Harrismith, Free State Province, South Africa, upper part of the Lystrosaurus Assemblage Zone, Middle Beaufort Group, Lower Triassic. Both specimens were found associated with material of L. huxleyi . Putterillia platyceps was established by Broom (1930), who considered it to be Text-fig.36. Putterillia platyceps Broom; Lower Triassic; related to Lydekkerina . Romer (1947) was South Africa. Holotype TM 168. Skull in a) dorsal view; the first worker to classify it within the b) palatal view (both after Broom 1930) family Lydekkerinidae, and he also suggested that it might be generically identical with Broomulus . Kitching (1978) considered Putterillia platyceps to be a nomen dubium , and Colbert & Cosgriff (1974), Cosgriff (1974) and Hewison (1996) to be incertae sedis. Cosgriff & Zawiskie (1979) and Cosgriff (1984), on the other hand, believed it to be a distorted specimen of L. huxleyi, and this latter view was given some credence, following a re- examination of the holotype by Shishkin et al (1996). They revealed that Broom’s figure of the basicranial region was inaccurate in many respects, and that it resembled L. huxleyi , in the presence of ornamentation ridges on the more anterior parts of the palatal ramus of the pterygoid, the palatal exposure of a broad subotic process from the exoccipital, and the separation of this process from the pterygoid by a subotic notch. The few details of the skull roof that are known are also reminiscent of L. huxleyi , and Shishkin et al (1996), concluded that Putterilli platyceps was a junior synonym of L. huxleyi , a view that is accepted here. The unusually broad dermal shoulder girdle, that was tentatively associated by Broom with the type skull, and utilised by him to support his argument that Putterillia was a new and unusual genus and species, was also re-examined by Shishkin et al (1966). They confirmed Broom’s description of the unusual long median contact between the two clavicles, but noted that such a contact also occurred in certain specimens of L. huxleyi that they had examined.

BROOMULUS DUTOITI (BROOM) ROMER 1947 (Text-fig. 37) Lydekkerina huxleyi (Lydekker) Broom, 1915. Lydekkerina dutoiti Broom, 1930. Holotype, and only specimen . MGM 4285, a broad and somewhat crushed skull in the Kimberley Museum, associated with its Text-fig.37. Broomulus dutoiti (Broom) Romer; mandibles, the anterior portion of the Lower Triassic; South Africa. Holotype MGM 4285. vertebral column and the pectoral girdle. Skull in a) dorsal view;

42 Locality and horizon . Harrismith, Free State Province, South Africa, upper part of the Lystrosaurus Assemblage Zone, Middle Beaufort Group, Lower Triassic. Revised diagnosis: Lydekkerinid stereospondyl distinguished from other lydekkerinids by the following combination of characters: quadratojugal corners lie distinctly posterior to the level of the occipital condyles; sensory sulci absent; ornament finely pitted and lacking conules at ridge junctions; orbits relatively close together; lacrimal contacting septomaxilla, preventing a maxillary-nasal contact; anterior margins of frontals much wider than posterior margins; palatal ramus of pterygoid denticulated with little or no ornament, and with only a very slight flange; subotic lamina of exoccipital not expanded; subotic notch absent; anterior Meckelian foramina absent from the mandible. Discussion : Broomulus dutoiti was originally described by Broom (1930) as Lydekkerina dutoiti , a new species of lydekkerinid, characterised mainly by the broad nature of its skull, its round orbits which are set fairly close together, the presence of short, broad parietals, and a coarse dermal ornament. Romer (1947) considered it to represent a new genus of lydekkerinid, which he named Broomulus , noting that its skull differed from that of Lydekkerina in the marked shortening of the facial region, its unusual breadth, and in having lacrimals that formed part of the narial border, orbits that were relatively close together, frontals that only just entered the orbital margins, jugals that were broadly expanded, and the very unusual presence of a postorbital-parietal contact. The distinctive generic nature of Broomulus has been accepted by Swinton (1956), Carroll & Winer (1977), Shishkin et al (1996), Schoch & Milner (2000), Damiani & Rubidge (2003) and Stayton & Ruta (2006), but not by Colbert & Cosgriff (1974), Cosgriff (1974), Kitching (1978), and Hewison (1996), all of whom considered it to be incertae sedis , nor by Cosgriff (1984) and Jeannot et al (2006), who believed it to be a distorted specimen of L. huxleyi. A re-investigation and further preparation of the type skull, by Shishkin et al (1996), led to a more accurate interpretation of the skull roof, and yielded additional information regarding the palate and mandible. The very unusual postorbital-parietal suture noted by Romer was shown to be absent, as were sensory grooves, but most of the new information emphasised a considerable similarity between Broomulus and Lydekkerina. Despite this similarity, Shishkin et al (1996) concluded that Broomulus dutoiti was nonetheless a valid lydekkerinid taxon, distinguished by a finely pitted ornamentation, the lack of ornament conules, the presence of small, round orbits, a conspicuous antero-lateral projection of the postorbital, a broad lacrimal that lay well anterior to the orbit, and a long ‘retroarticular process’ on the mandible. Jeannot et al (2006), prepared the holotype skull still further, and revealed several additional features that Broomulus shared with Lydekkerina huxleyi . These included an incipient crista falciformis of the squamosal; rectus capitis pockets lying moderately far apart on the parasphenoid and lateral wall of the exoccipital, and each bordered anteriorly and mesially by a crescentic crista muscularis whose anterior border lies more or less on a level with the posterior end of the pterygo-parasphenoid suture; an ossified sphenethmoid; and a chorda tympani foramen that opened on the suture between the articular and the prearticular. They argued that Broomulus dutoiti should be considered to be a subjective junior synonym of Lydekkerina huxleyi , and not a separate taxon, and argued further that several of the skull’s previously accepted diagnostic features, which had served to distinguish it from L. huxleyi , almost certainly resulted from the severe dorso-ventral crushing and post-mortem distortion that the skull had suffered. They believed that the skull was not as broad as had been previously emphasised, and neither were the lacrimal, jugal, postorbital and postparietal bones, and that the orbits were probably sub-circular in shape rather than rounded. The close similarity in the structure of the skull and mandible of Broomulus and Lydekkerina huxleyi , clearly demonstrated by Shishkin et al (1996) and Jeannot et al (2006), indicate that Broomulus is an undoubted member of the Lydekkerinidae, and although Jeannot et al (2006), argued that this similarity is so great that B. dutoiti should be considered as a subjective synonym of L. huxleyi , the the lack of many distinctive features that are characteristic of L. huxleyi , such as a conulated ornament, the presence of sensory sulci, a broadly expanded subotic lamina of the exoccipital, a sub-otic notch, a bi-tuberculated quadrate boss and the presence of several anterior Meckelian foramina on the mandible, combined with

43 the presence of other diagnostic features, listed in the revised diagnosis of Broomulus dutoiti given above, strongly suggest that Broomulus is a valid lydekkerinid taxon, distinct from all other members of the family.

LIMNOIKETES PALUDINATANS PARRINGTON 1948 (Text-fig. 38) Lydekkerina huxleyi (Lydekker) Broom 1915 Holotype, and only specimen . UMZC T214, a small skull and its mandibles, together with the shoulder girdle and proximal end of the right humerus, in the University Museum of Zoology, Cambridge. Locality and Horizon . Harrismith, Free State Province, South Africa, upper part of the Lystrosaurus Assemblage Zone, Middle Beaufort Group, Lower Triassic. Revised diagnosis: Lydekkerinid stereospondyl distinguished from all other members of the family by the following combination of characters: skull with a broadly rounded snout and irregular lateral margins; posterior border of skull table very shallowly curved; interorbital hollowing slight; orbits face more laterally and lack elevated rims and preorbtital step; Text-fig.38. Limoiketes paludinatans Parrington; Lower Triassic; sensory sulci weakly developed; South Africa Holotype UMZC T214. Skull in a) dorsal view; lacrimal flexure sinuous; anterior b) palatal view; c) labial view; and d) occipital view (after margins of parietals lack indentations; Parrington 1948 and Jeannot et al (2006). pre-orbital projection of jugal extremely short; tabular horns moderately long triangular structures that terminate on a level anterior to the postero-lateral corners of the skull roof; parietal foramen set in raised, domed-area of roof; skull unusually deep in its orbital and postorbital regions, with the quadratojugal and jugal bones much developed; pair of nasolacrimal ducts open at hind end of lacrimal bones; processus cultriformis non-denticulated and terminating on a level with the anterior ends of the interpterygoid vacuities; palatal ramus with a pronounced flange; basicranial suture relatively short; rectus capitis pockets deeper and wider than usual and set closer together; subotic process of exoccipital not broadly expanded but subotic notch present; occipital flanges of postparietals and tabulars flattened and sloping backwards and visible in dorsal view; paroccipital process directed in a more dorsal direction; cheeks steeply curved in occipital view; partial palatoquadrate fissure present. Discussion : Limnoiketes paludinatans , was first figured and described by Parrington (1948), who believed this new genus and species to differ considerably from L. huxleyi , yet to be closely related to the main stem of temnospondyls between Rhinesuchus and the Triassic capitosaurs. It was first classified as a lydekkerinid by Cosgriff (1974), and has been accepted as such by a majority of later workers. Shishkin et al (1996), and Jeannot et al (2006), however, have considered it to be a subjective junior synonym of L. huxleyi, with the former authors believing it to be a juvenile form, and the latter an adult. Schoch & Milner (2000), on the other hand, were uncertain as to whether it was a distorted form of L. huxleyi , or a genuine lydekkerinid in its own right. A re-examination of the skull of Limnoiketes , which has a median length of only 55mm, indicates that it does display a large number of features that are also found in L. huxleyi and other lydekkerinids.

44 Some of these features, such as the presence of an interorbital hollowing, stapedial lappets, squamosal- quadratojugal trough etc. are plesiomorphies, but others are paedomorphic in nature. These include the small size of the skull, which is as broad as it is long, quadratojugal corners that lie more or less on a level with the exoccipital condyles, the large size of the nares, orbits and parietal foramen, the central positioning of the orbits on the skull roof, the closeness of the parietal foramen to the orbits, the elongated lacrimal, the short, broad otic notches that widen posteriorly, the presence of a low, sub- horizontal oblique ridge, and the curvature of the cheek regions, when seen in occipital view. Certain other features, however, are synapomorphies that are shared with other lydekkerinids, and these include the presence of a septomaxilla which has both an ornamented roofing component, and an unornamented portion flooring much of the naris; the presence of an incipient crista falciformis; the loss of ectopterygoid tusks; the positioning of the rectus capitis pockets on a level with the hind end of the basicranical sutures; the presence of a subotic notch the ornamentation of the pterygoid; the buttressing of the tabular horn; a sub-vertical tympanic crest, and on the mandible, the presence of a large hamate process, an elongated, postero-dorsally directed surangular process, and a deep depressor groove, which labially, runs anteriorly along the lower border of the surangular and merges with the mandibular sulcus. Despite the many similarities that Limnoiketes shares with other lydekkerinids, it also possesses many original features of its own that serve to distinguish it as a separate and distinctive taxon within the Lydekkerinidae. The skull has a broadly rounded snout, irregular lateral margins, and a skull table whose posterior border is only very shallowly curved. The interorbital hollowing is only slight, and the orbits face more laterally than in other lydekkerinids, and lack the characteristic elevated rims and preorbital step. The sensory sulci, although present partly as grooves and partly as disconnected pits, as in L. huxleyi , are weakly developed and include a lacrimal flexure that is sinuous, and not Z-shaped or step-shaped. Roofing bone differences include nasals that lack distinct step-shaped posterior borders on both sides of the skull, frontals that are unusually wide, and whose anterior margins are only slightly wider than its posterior margins; postorbitals that have no antero-lateral process; parietals whose anterior margins lack indentations, and tabular horns that are moderately long, triangular structures Uniquely, the parietal foramen is set in a raised, domed-area of the roof, and the skull is unusually deep in its orbital and postorbital regions, with the quadratojugal and jugal bones much developed, and the jugal forming a large portion of the lateral skull border. An extremely rare feature is the presence of a pair of small openings on the roof at the hind end of the lacrimal bones, which may represent the posterior termination of nasolacrimal ducts. Jeannot et al (2006) suggested that certain of these features, namely the depth of the skull, the shape of the orbits, the flaring of the cheeks, the flattening of the interorbital region and the foreshortening of the facial region may have resulted from an unusual, explosive deformation of the skull, possibly caused by post-mortem mineral growth within the cranium. Whether or not all of these diverse effects on the skull could have resulted from one and the same deformation process, this would fail to explain the presence of the many other characteristic features that Limnoiketes possesses that serve to distinguish it from other lydekkerinids. Further differences can be seen on the palate, where the cultriform process terminates more or less on a level with the anterior ends of the interpterygoid vacuities and is flanked by long postero-mesial processes from the vomers. A long row of more than six palatine teeth is present and the interpterygoid vacuities are relatively larger and much broader openings than they are in Lydekkerina and Broomulus , whilst the cultriform process of the parasphenoid is narrower, non-denticulated and lacking in lateral grooving. The palatal ramus has a pronounced flange; the basicranial suture is relatively short and the rectus capitis pockets, which are more crescentic than shown in Parrington’s figure, are deeper and wider than usual, and also set closer together. The subotic process of the exoccipital does not appear to be as broadly expanded as it is in other lydekkerinids, although a distinctive subotic notch is present. On the occiput, the occipital flanges of the postparietals and tabulars are seen to be flattened and sloping backwards in rhinesuchid fashion, and are therefore visible in dorsal view, as are the exoccipital condyles which lie slightly in front of the plane of the quadrates. The paroccipital process is directed

45 in a decidedly more dorsal direction than is seen in other lydekkerinids, and it has no opisthotic component, the tabular suturing with the exoccipital. The unusually deep cheek regions are steeply curved in occipital view, yet the palate is only gently vaulted. A partial palatoquadrate fissure is present, which Parrington (1948) considered to be a juvenile characteristic, with the fissure being filled in the adult skull. Other juvenile features noted included the large size of the orbits, parietal foramen, and posttemporal fenestrae, the poorly ossified exoccipital processes and the absence of a quadrate tubercle. Parrington also argued however, that the unexpected small size of the choanae suggested that the skull had almost reached adult size. The skull of Limnoiketes , with its domed up parietal area and the great depth of its orbital and postorbital regions, has an extremely solid and bulky appearance, and this, with the less well developed lateral line system and the more laterally facing orbits, suggests that this form may have been adapted to a more terrestrial way of life than the other lydekkerinids. The lack of elevated rims to the orbits and the absence of a preorbital step, which are adaptations to provide vision during sub-surface swimming in lydekkerinids, support this view. Possibly associated with this way of life is the presence of the pair of small openings on the skull roof in the posterior regions of the lacrimal, which lead forwards and downwards into the lacrimal bones and which may be a part of a nasolacrimal duct system maintaining the moisture of the eyes and keeping them free of dust. Parrington (1948) suggested that the more posterior section of this duct system lay in a more superficial position. Similar openings occur at the posterior borders of the lacrimals in the small dissorophoid Micropholis stowi , another Lystrosaurus Assemblage Zone temnospondyl that is considered to be a terrestrial form, although here the openings are located within the anterior borders of the orbits, as the lacrimals extend backwards into these openings. Some doubt, however, must be cast upon a purely terrestrial explanation for these nasolacrimal openings, as a similar pair of openings occur in Indobrachyops panchetensis , an undoubted aquatic form, although here they lie well in advance of the orbits, on the lacrimal-nasal sutures (Huene & Sahni, 1958. Fig. 2). Similarly, in a specimen of another aquatic form, Batrachosuchus , (later made the type of B. watsoni by Haughton, 1925), Watson (1919) described a canal-like ductus naso-lachrymalis, that began in the prefrontal-maxillary suture on the orbital margin, perforated the maxilla, and terminated in a small foramen just behind the meeting place of the nasal, lacrimal and maxilla. Limnoiketes paludinatans is much closer to L. huxleyi , in the morphology of its skull and mandible, than Parrington believed, so close in fact that Shishkin et al (1996) and Jeannot et al (2006) have separately considered it to be a subjective junior synonym of Lydekkerina huxleyi . However, the numerous morphological features, noted above, that differentiate it from all other lydekkerinids, indicates strongly that the two forms are not synonymous, and in aggreement with the majority of other workers, it is concluded here that Limnoiketes , is a valid lydekkerinid taxon.

LYDEKKERINA KITCHINGI BROOM 1950 (Text-fig. 39) (now Mucocephalus kitchingi (Watson) Schoch & Milner comb.nov. 2000) Muchocephalus muchos Watson, 1962. Mucocephalus kitchingi (Watson) Schoch & Milner comb.nov. 2000. Material . The type, BPI/1/214, a poorly preserved Text-fig.39. Lydekkerina kitchingi ’ Broom, now skull with its mandibles; a number of undescribed Muchocephalus kitchingi (Watson) Schoch & specimens, and 92 additional skulls and associated Milner. Upper Permian; South Africa. skeletal remains, all in the Bernard Price Institute, Holotype BP/1/214. Skull in dorsal view (after Witwatersrand, Republic of South Africa. Shishkin et al 1996).

46 Locality and horizon . The type and undescribed specimens were discovered on the farm Ringsfontein, Murraysburg District, Cape Province, South Africa, and are from the upper part of the Dicynodon Assemblage Zone, Beaufort Series, Upper Permian, whilst the 92 additional skulls, which were found on the adjoining farm Beeldhouersfontein, are from the underlying Cistecephalus Zone, Upper Permian (Kitching 1978; Shishkin, et al 1996). Broom’s original description of Lydekkerina kitchingi, and his figure of the skull roof of the type, indicated that this skull, in its size, general shape, and in the disposition of its roofing bones, showed some similarity to L. huxleyi . The skull, however, has a much more elongated snout region and more posteriorly situated orbits, and these features, along with the more posterior position of the parietal foramen, are characteristics of rhinesuschids rather than lydekkerinids. No information about the occipital and palatal regions was given by Broom, except for the presence of denticles on the pterygoid. Shishkin et al (1996) re-figured the skull in dorsal view (their Fig. 8b), and showed that the supratemporal bone entered into the border of the otic notch, another feature that is characteristic of rhinesuchids, but not of lydekkerinids. The type, and a paratype, are of Dicynodon Assemblage Zone age, and were found in close association with the rhinesuchid Muchocephalus muchos , and many more specimens were recovered from earlier Cistecephalus Assemblage Zone deposits. Shishkin et al (1996) made a detailed comparison of all these forms, and, following Kitching (1978), suggested that Lydekkerina kitchingi represented a growth stage of the rhinesuchid Muchocephalus muchos , being either a juvenile or a semi-adult form. This view has been generally accepted, and Lydekkerina kitchingi has become a nomen vanum . Schoch & Milner (2000) pointed out that the senior species name of this form is kitchingi, and they re- named it as Muchocephalus kitchingi . comb. nov. More recently, Damiani and Rubidge (2003) have considered that both ‘L’ kitchingi and M. muchos are junior synonyms of the Upper Permian rhinesuchid Laccosaurus watsoni Haughton 1925. Whether this prediction a) turns out to be correct or not, this form is clearly rhinesuchid in nature and is not a lydekkerinid.

DELTACEPHALUS WHITEI SWINTON 1956 (Text-fig.40) Parotosuchus madagascariensis (Lehman, 1961) comb. nov. Warren & Hutchinson b) 1988. Text-fig.40. Deltacephalus whitei Swinton; Lower Triassic; Watsonisuchus madagascariensis Madagascar. Restoration of the skull in a) dorsal view; (Lehman, 1961), comb. nov. Steyer 2003. b) left lateral view

47 Holotype, and only specimen : BMNH R6695, a small ironstone concretion enclosing the natural mould of a single skull, in the British Museum of Natural History. Locality and horizon : Ambarakaraka, 8 km north of Anaborano, north-west Madagascar; Middle Sakamena Formation, Induan, Lower Triassic. Revised diagnosis : Lydekkerinid stereospondyl distinguished from all other members of the family by the following combination of characters: parabolic skull with a broadly rounded snout and gently curved lateral margins; tabular c) horns long and curved, directed posteriorly and terminating far behind the postero-lateral corners of the roof; parietal foramen transversely oval; lateral line system exceptionally well developed with almost all d) the sulci deeply grooved; a Text-fig.40. Deltacephalus whitei Swinton; Lower Triassic; Madagascar. preorbital zone of intensive Restoration of the skull in c) palatal view; growth resulting in a greater d) occipital view (all after Hewison 1996). grooving of the ornament over the posterior third of the nasals and the neighbouring portions of the frontals and prefrontals; lacrimal flexure distinctly Z- shaped; frontals relatively long and narrow; parietals relatively short and broad; cultriform process striated ventrally with a weak keel; palatal ramus of pterygoid with a long convexly-curved flange; parasphenoid body ornamented with radiating, conulated ridges and bearing slight, broad lappets; rectus capitis pockets very far apart and situated more posteriorly than is usual, slightly behind the posterior ends of the basicranial sutures; interpterygoid vacuities, occipital openings and subtemporal fossae very large and separated by slender struts of bone, with the subtemporal fossa extending far in front of the hinder borders of the interpterygoid vacuities; quadrate condyles positioned a short distance in front of the horizontal level of the occipital condyles; basioccipital unossified. Discussion : The concretion enclosing the skull is broken into three closely fitting pieces, two larger fragments bearing impressions of the skull roof and palate respectively, and a smaller third piece bearing an impression of the occipital surface. A study of these impressions, in conjunction with a series of plaster casts made from them, led Swinton (1956) to recognise that they represented a new genus of rhinesuchoid temnospondyl, which he named Deltacephalus whitei . He believed Deltacephalus to be related to Broomulus dutoiti and assigned it to the Lydekkerinidae. Although some authors believed Deltacephalus to be unclassifiable (Colbert & Cosgriff, 1974; Cosgriff, 1974, 1984; Milner, 1990;

48 Jeannot et al , 2006), some new casts in flexible, coloured welvic made at the Natural History Museum, London, permitted Hewison (1996) to give a more extensive description and figuration of the specimen (his Figs, 2,3,5,6,7.8), which he believed confirmed its lydekkerinid status, a view supported by Schoch & Milner (2000), and seemingly by Damiani (2001), who noted 6 characteristic lydekkerinid features of Deltacephalus , and clustered it with Lydekkerina , Chomatobatrachus and ‘ P’ madagascariensis in his cladogram of mastodonsauroid temnospondyls. Despite this association, he preferred to consider it as Lydekkerinidae incertae sedis . Deltacephalus is a rather small form with a median skull roof length of only 48mm and a maximum width of 49mm across the quadratojugal bones. The form and proportions of its skull, sensory openings, and the openings of its palate and occiput resemble those of other lydekkerinids, as do the nature and relationships of the bones of the roof, palate and occiput, and the possession of such characteristic lydekkerinid features as a stapedial groove bordered by a low, crista obliqua, a quadrate boss, and stapedial lappets. Maryanska & Shishkin (1996), however, tentatively proposed that Deltacephalus should be refered to a new “capitosaurid” lineage, the Deltacephalidae, within the “Capitosauroidea”, along with a range of small juvenile to adult temnospondyls from the Lower Triassic (Middle Sakamena Group) of Madagascar, that were originally described as Benthosuchus madagascariensis and Wetlugasaurus milloti by Lehman (1961), but later re-designated as Parotosuchus madagascariensis by Warren and Hutchinson (1988), and most recently as Watsonisuchus madagascariensis (Steyer 2003). Support for this proposal, has been given by Shishkin et al (1996), and it has been further suggested that all of this material should be referred to the single genus Deltacephalus. Damiani (2001), however, noted that those specimens in Lehman’s material in which the frontal was included in the orbital margin, could not be referable to Deltacephalus, and further considered that all this material was stereospondyli incertae sedis . Certain similarities do exist between the type skulls of P. madagascariensis (Warren & Hutchinson 1988), and Deltacephalus whitei , due to some extent to their comparable size and the shortness of their preorbital regions, and it may be partly because of these similarities, that Damiani (2001), in his cladogram, depicts ‘P’ madagascariensis as being the sister group to Deltacephalus within a cluster of taxa that could be interpreted as representing the Lydekkerinidae. Despite these similarities, there are nonetheless crucial differences between these two forms which prevent them being placed in the same genus. The skull has a more triangular outline in P. madagascariensis , and a narrower snout, and on the skull roof, the frontals enter the orbital margin, and the supratemporals the dorsal margin of the otic embayments. The lacrimals are also much longer, and a moderately developed crista falciformis is present. Palatal differences include the presence in P. madagascariensis of ectopterygoid tusks and a distinct pair of notches on the posterior border of the parasphenoid body immediately lateral to rather more mesially situated and transverse cristae musculari. The ornamentation on the palatal ramus of the pterygoid of P. madagascariensis is not as well developed as that on Deltacephalus , and on the occiput, it is distinguished from this form by the much smaller size of the posttemporal fossae and a much stouter development of the exoccipital bone and paroccipital bar. The arguments forwarded by Maryanska & Shishkin (1996) and Shishkin et al (1996) to support their view that Deltacephalus was “capitosaurid” rather than lydekkerinid are discussed below: 1). The lacrimal flexure is very sharp : The Z-shaped lacrimal flexure seen in Deltacephalus also occurs in specimens of Lydekkerina huxleyi . 2) The lacrimal is short and broad and far removed from both naris and orbit : the lacrimal of Broomulus , described and considered by Shishkin et al (1996) to be a lydekkerinid , has, according to the amended reconstruction by Jeannot et al (2006) much the same shape as that of Deltacephalus , and furthermore, the lacrimal in Deltacephalus approaches much more closely to the orbits than it does to the nares, which is the normal condition that is found in lydekkerinids, and the opposite to that found in the “capitosaurids”. 3) The jugal extends forwards well beyond the anterior orbital rim : the jugal extends just as far forwards in Broomulus , which Shishkin et al (1996) recognise as a valid lydekkerinid genus, yet does not extend so

49 far forwards as in “capitosaurids”. 4) The parietal and frontal have more or less pointed anterior ends : the frontals in the holotype of L. huxleyi also have pointed anterior ends, and although the anterior ends of the parietals are only slightly irregular in Deltacephalus , this is also the case in the lydekkerinid Broomulus as described by Shishkin et al (1996). 5) The preorbital sensory grooves are well developed : although this is a feature of certain “capitosaurids”, the remaining sulci of the lateral-line system of Deltacephalus are equally well developed, a condition more reflective perhaps of the aquatic nature of Deltacephalus than its taxonomic status. 6) The parasphenoid corpus shows a radiate pattern of shagreen denticulation : the radiate ornamentation present on the parasphenoid corpus of Deltacephalus, consists of slightly conulated ornament ridges, and not of discrete denticles, whereas the denticles on the type specimen of P. madagascariensis are randomly distributed and not arranged in any radiate pattern. These morphological arguments, and those presented earlier, indicate that Deltacephalus should be retained within the family Lydekkerinidae, rather than within a new “capitosaurid”-like lineage that has advanced beyond the lydekkerinid level.

LYDEKKERINA PANCHETENSIS TRIPATHI 1969 (Text-fig.41) Bothriceps panchetensis Tripathi, 1961 Indobenthosuchus panchetensis Tripathi, 1969 Holotype and only specimen . GSI Type No. 17890, a poorly preserved and incomplete skull roof in the Geological Survey of India, Kolkata. Locality and horizon . Talkunri village, about three miles south-east of Asansol, Damodar Valley, India; Deoli stage, Upper Panchet Series, Induan, Lower Triassic. The holotype skull of L. panchetensis is considerably weathered and incomplete, and the skull roof, which has a calculated length of about 100mm, has been preserved face downwards so that its bones are viewed from their ventral surfaces. Despite Tripathi’s Text-fig.41. Lydekkerina panchetensis identification of this specimen as a new species of Lydekkerina , and Tripathi 1969; Lower Triassic; India the first record of a lydekkerinid from the Indian sub-continent, Reconstruction of the skull roof the few features of L. panchetensis that have been preserved show (after Tripathi 1969). little resemblance to the corresponding features of the skulls of known lydekkerinids, except in the central position of the orbits on the roof, the very short preorbital region (preorbital index of 39)*, the very long lacrimals, the frontals failing to reach the orbital margins and the premaxillae not extending backwards between the two nares. Tripathi himself pointed out that L. panchetensis showed a marked resemblance in the width of its interorbital space and in the shape, size and disposition of its orbits, to the brachyopid Bothriceps australis, and this comparison can be extended, for in both forms the parietal foramen lies well posterior to the level of the hinder borders of the orbits and in the posterior half of the suture between two very large parietals, and the nasals are very reduced in size. Unlike Bothriceps australis , however, the frontals are exceedingly long, as are the prefrontals and lacrimals, and the latter are most unusual in apparently extending from the nares to well back behind the level of the anterior margins of the orbits. In none of these features does L. panchetensis resemble lydekkerinids, nor does it in its finely pitted ornamentation, the pointed anterior ends of the frontals and parietals, and in the presence of a well- defined median furrow which runs over the postorbital parts of the skull roof and fades away in the interorbital space. Furthermore, the nasals are minute and lack any step-like posterior border; there is no antero-lateral process on the postorbitals; the frontals are narrow anteriorly and the supratemporals appear to enter the otic notches. Although this specimen is of Lower Triassic age, and the locality at which it was found has yielded up

* for this and all otherindices see Appendix 2

50 some two dozen skulls of Lystrosaurus , a common associate of L. huxleyi in the Lystrosaurus Assemblage Zone deposits of South Africa, there is no convincing morphological evidence to suggest that the Indian form belongs to the genus Lydekkerina , or indeed is a lydekkerinid. In view of the lack of information regarding the rest of the skull of this specimen, and even its true shape, the apparent similarities it shares with B. australis may only be superficial, and although Cosgriff 1984, and Shishkin et al (1996) considered that this form may be a lydekkerinid, and, according to the latter authors, possibly congeneric with Indobenthosuchus panchetensis , its true affinities, as Jeannot et al (2006) have earlier pointed out, remain obscure. The name Lydekkerina panchetensis should therefore be considered a nomen vanum .

INDOBENTHOSUCHUS PANCHETENSIS TRIPATHI 1969 (Text-fig. 42) Lydekkerina panchetensis Tripathi 1969. Holotype . G.S.I. Type No. 17888, a poorly preserved and badly weathered skull in the Geological Survey of India, Kolkata. Locality and Horizon . Dihika village, Damodar Valley, India, Deoli stage, Upper Panchet Series, Lower Triassic. A further specimen, G.S.I. No 17889, is an incomplete left mandible from the same locality. Most of the bones of the skull roof of the holotype have been weathered away, but the left half of the palate is sufficiently well preserved. There is some discrepancy between the text given by Tripathi, and his figure of the skull roof, but Tripathi judged this form to be most closely allied to Benthosuchus . Shishkin et al (1996), however, suggested that it might be a lydekkerinid, and synonymous with Lydekkerina panchetensis, because of the outline of the skull, its apparent short pre-orbital index (c.36)*, the presence of a step-like lacrimal Text-fig.42. Indobenthosuchus panchetensis flexure, (although described by Tripathi as Z-shaped, Tripathi 1969; Lower Triassic; India and figured as sinuous), the lack of a preorbital jugal Reconstruction of the skull roof and projection, the slightly reniform shape of the anterior palate (after Tripathi 1969). palatal vacuity and the pattern of the palatal dentition. The interchoanal teeth, however, have a deep, V-shaped alignment that is far removed from the palatal vacuity, features that are not found in any lydekkerinid, and the skull also differs markedly from those of lydekkerinids in having a narrowly triangular outline, orbits that lie well in front of the middle of the skull, and a parietal foramen that is situated far behind the level of the orbits. The mandible resembles that of lydekkerinids in having two small anterior Meckelian foramina, but differs in having two symphysial tusks, instead of one, and, according to Tripathi, a prominent coronoid process, a feature that is never found in lydekkerinids. Tripathi’s text, however, would seem to indicate that this coronoid process is in fact a denticulated ridge that runs along the coronoid, intercoronoid and posterior regions of the precoronoid, and as such, does resemble the condition seen in the holotype skull of L. huxleyi , and in the related rhinesuchids. Indobenthosuchus displays a mix of features, some of which are reminiscent of rhinesuchids, some of lydekkerinids, and some of benthosuchids, and at present there is insufficient information from either the skull or mandible to be certain of the precise taxonomic affinities of this form, a view already expressed by Schoch & Milner (2000), and Damiani (2001). Indobenthosuchus , therefore is not considered in this paper to belong to the Lydekkerinidae.

51 CRYOBATRACHUS KITCHINGI COLBERT AND COSGRIFF 197 4 (Text-fig. 43) Material. The type, AMNH 9503, a small skull embedded in rock showing only the ventral surface of its roofing bones, and a paratype, AMNH 9556, an impression of the right postero-lateral regions of a skull roof, both in the American Museum of Natural History, New York. Additional fragmentary skull and postcranial material, mainly from Coalsack Bluff, were tentatively referred to the species, as was later, a partial interclavicle with a pitted sculpture (Cosgriff and Hammer 1984). Localities and horizon . The Transantarctic Mountains, Antarctica, the type coming from Kitching Ridge, Shackleton Glacier and the paratype from Mount Kenyon, McGregor Glacier; Lower Fremouw Formation, Lower Triassic. Discussion : Colbert and Cosgriff (1974) described these remains as belonging to a lydekkerinid because of the entirely pitted ornament on the roofing bones, the central position of the orbits on the skull roof, and the rudimentary and incomplete state of the lateral-line sulci, which are much interrupted and obscured by the dermal ornament, and entirely absent in some areas. Although the central position of the orbits, is a valid lydekkerinid feature, the evidence that the lateral-line sulci were rudimentary and incomplete, and that the ornament was entirely pitted is far from convincing, for the ventral surface of the skull roof of the type does not yield any information about surface ornamentation or the lateral-line system, and the fragmentary paratype has neither the size nor the appropriate position on the skull roof from which to deduce the overall nature of these two characteristics. The ornament shown by this fragment is indeed entirely pitted but this does not Text-fig 43. Cryobatrachus kitchingi Colbert and justify the assumption that the remainder of the roof Cosgriff 1974); Lower Triassic, Antarctica. was similarly pitted, for the bones presumed to be Restoration of the skull of Cryobatrachus present, ie portions of the squamosal, kitchingi in a) dorsal view after Colbert and supratemporal, postorbital and postfrontal, are Cosgriff 1974; b) dorsal view after the text and precisely those bones in lydekkerinids that show the fig. 14 of Colbert and Cosgriff 1974. least amount of grooving. Grooving tends to occur in lydekkerinid species only on the peripheral areas of some of the larger bones such as the jugal and quadratojugal, and these have not been preserved in the paratype. As regards the lateral-line system, the fragmentary paratype could only be expected to show portions of the supraorbital and postorbital sulci, and possibly the otic sulcus, and, although none of these sulci are clearly visible in the published photograph, Colbert and Cosgriff did record the preservation of a section of the right supraorbital sulcus just mesial to the orbit. This sulcus is invaded in places by depressions of the surrounding ornament, but this also occurs in the corresponding portion of this sulcus in the type specimens of L. huxleyi and Deltacephalus , and it cannot be argued from this, that the rest of the sulci are similarly developed, for in L. huxleyi every sulcus of the type skull has at least one grooved

52 section, and in Deltacephalus the majority of the remaining sulci are deeply grooved. The skull of Cryobatrachus, as preserved, is small, narrowly parabolic in outline and has a midline roofing length of about 45mm. It resembles lydekkerinids in that the skull is almost as broad across the quadratojugals as it is long, and has a conulated ornament, orbits that straddle the mid-length of the skull roof, a short preorbital region, a parietal foramen that lies level with the posterior borders of the orbits, and supratemporals that do not form part of the otic notch (Text-fig. 43a). In Cryobatrachus , however, the orbits are closer together than in any of the lydekkerinids considered so far, the external nares are relatively large, the parietal foramen has an elongated oval outline, the septomaxillaries are very large, the supratemporals are far removed from the otic notches and the tabular horns are long and narrowly pointed. Moreover the skull displays several unusual features, which appear at first sight to set it apart from other lydekkerinids (Colbert & Cosgriff 1974 Fig. 15). Most of these features, except for the most unusual anterior extension of the postfrontal, occur in the postorbital half of the skull, and include unusually small supratemporals; very long, narrow and anteriorly-curving, crescentic otic notches, which have a sharply pointed antero-medial border; lateral skull margins which curve inwards posteriorly to give the skull an unusual oval outline from above; and a much narrower width across the quadratojugals than occurs in lydekkerinids. The quadratojugals also terminate a long way behind the posterior edge of the midpoint of the markedly concave posterior margin of the skull table, so that, as in rhinesuchids, the quadrate condyles lie well behind the level of the occipital condyles, and not as Colbert & Cosgriff (1974) argued, on the same level. The published photograph of Cryobatrachus shows the type skull to be both incomplete and poorly preserved, and indicates that the interpretation of the skull roof given by Colbert & Cosgriff (1974 Fig. 15) was based upon the left side of the skull as regards the more unusual postorbital features of the skull. There are, however, certain discrepancies between the restoration and the photograph. The tabular horns, although seen on the photograph and described as narrow and quite pointed, are nevertheless reconstructed as stubby structures with rounded ends, and the otic notches are figured with much wider anterior ends. It would also seem from the specimen that certain areas of bone are missing, including some from the anterior end of the otic notch, and this opening may not be as elongated or as unusual as figured. Colbert & Cosgriff (1974) asserted that the type specimen is only slightly crushed and that the distortion is so minor that the skull fairly approximates to its original shape, yet the right side of the skull roof is wider than the left side by anything up to 36%. It appears therefore that the skull has either been flattened along its right side or, as is more likely, constricted along its left side. Such a constriction, particularly over the quadratojugal regions, could account for some of the more unusual features of Cryobatrachus , such as the incurving hinder regions of the lateral skull margins, the narrowness across the quadratojugal region, the very long quadratojugal corners and the narrow, crescentic form of the otic notches. This suggests that in life Cryobatrachus might have had a skull that was parabolic in outline in dorsal view, with more gently convex lateral margins, a quadratojugal width that was rather broader than figured, otic notches that were wider, more U-shaped, and not so deeply incised into the squamosals, and quadratojugal corners that were more on a level with the exoccipital condyles (Text-fig.43 b). Cryobatrachus has been tentatively included within the family Lydekkerinidae by Colbert & Cosgriff (1974), Cosgriff (1974, 1983), Cosgriff & Hammer (1984) and Shishkin et al (1996), but has been considered to be of uncertain affinity by Hewison (1996), Schoch & Milner (2000), and Jeannot et al (2006). Schoch & Milner (2000), although accepting that fragmentary material from several localities in the Fremouw Formation was certainly lydekkerinid, were not convinced that Cryobatrachus itself was a lydekkerinid, and that it might equally well have been a juvenile parotosuchid or benthosuchid. The few lydekkerinid features of the skull roof that Cryobatrachus displays, do also occur in juvenile stereospondyls from families other than the Lydekkerinidae, and, in the absence of any additional diagnostic information from the palatal and occipital regions of this taxon, it’s precise taxonomic position is unresolved, and it is concluded here that C ryobatrachus should not be included within the family Lydekkerinidae, but considered to be Stereospondyli incertae sedis .

53 CHOMATOBATRACHUS HALEI COSGRIFF 1974 (Text-figs 44 & 45)

Text-fig 44. Chomatobatrachus halei Cosgriff 1974; Lower Triassic; Australia Reconstruction of the skull in a) dorsal view; b) palatal view; c) occipital view (all after Warren, Damiani & Yates 2006).

Material. The holotype UTGD 80738, in the University of Tasmania, Geology Department, Hobart, Tasmania, is a virtually complete skull, whose internal structure is partially known. Numerous paratypes include one complete and one incomplete mandible; fragments of skulls and mandibles; and an incomplete clavicle. Localities and horizon . The holotype came from Meadowbank Dam, southeastern Tasmania and the

54 paratypes from numerous localities in southwestern Tasmania (Midway Point, Old Beach, Conningham, Crisp and Gunn Quarry and Milford); Knocklofty Formation, Induan-Olenekian, Lower Triassic. Discussion : Chomatobatrachus was originally described by Cosgriff (1974) as a new form of lydekkerinid, on account of the short, broad nature of the skull, its centrally placed orbits, U-shaped otic embayments, well developed, bluntly-rounded tabular horns, and the nature of the frontal, supratemporal, lacrimal and jugal bones. He has been supported in this by a majority of authors: Colbert & Cosgriff (1974); Cosgriff & Hammer (1983); Cosgriff (1984); Warren & Black (1985-although also classifying it as a rhytidosteid); Milner (1991); Shishkin et al (1996); Maryansky & Shishkin (1996); Marsicano & Warren (1998); Schoch & Milner (2000), Dias-Da-Silva, Marsicano & Schultz (2006), Jeannot et al (2006), Stayton and Ruta (2006), and Warren, Damiani & Yates (2006). Warren & Hutchinson (1988), Milner (1990) and Hewison (1996), however, have not accepted that Chomatobatrachus was a lydekkerinid, and Damiani (2001), despite having Chomatobatrachus and Lydekkerina as sister groups in his cladogram, could find no synapomorphies uniting them. Following the discovery of a specimen of Lydekkerina huxleyi in Australia, Warren. Damiani & Yates (2006) re-examined the holotype skull of Chomatobatrachus halei , which they considered to represent the only other lydekkerinid from Australia, and listed eight important morphological differences between the two forms. Their account of C. halei , also differed in several important ways from that given originally by Cosgriff (1974), such as the premaxillae having much shorter posteror extensions between the nares, the lacrimal not reaching the narial border, the supratemporal not being isolated from the postfrontal by a parietal-postorbital contact, the nature of the tabular horns being unknown, a less developed lateral line system, and a longer parasphenoid plate. These updated features of Chomatobatrachus have been taken into account here, as have certain features they recorded of the juvenile condition of this stereospondyl. Strong support for the exclusion of Chomatobatrachus from the Lydekkerinidae, comes from many morphological features of its skull and mandible. Unlike lydekkerinids, the dermal ornament of its roofing bones is entirely pitted and lacking in conules; the central portions of the skull roof are flattened, and the orbits lack elevated orbital rims and a preorbital step. Palatal differences (Text-fig. 44b) include an almost V-shaped interchoanal tooth row that in the adult, lies well posterior to a large, pear-shaped anterior palatal vacuity; the lack of any antero-dorsal projections into the anterior palatal vacuity; a more elongated choana, whose lateral margin is formed to a much greater extent by both the vomer and palatine, and, on one isolated skull fragment, an unusual narial tooth row inserted on the maxilla between the naris and the maxillary tooth row, although Jeannot et al (2006), have suggested that this unusual rooth row may represent the broken tips of mandibular teeth that were once in occlusion with the skull. An alar process is lacking; the processus cultriformis is narrow; and there is a deep, narrow palatal trough along the mesial margin of the ectopterygoid tooth row. Sub-otic notches are lacking, and there appears to be no ornamentation on the pterygoid corpus and rami. The sub-otic process of the exoccipital, although broadly displayed ventrally, is so extensive as to suture anteriorly with the postero-mesial edge of a lengthened pterygoid corpus (Cosgriff 1974, p.53), and associated with this is the lack of the subotic notch. The prootic is smaller and less strongly ossified than in L. huxleyi , and the epipterygoid of Chomatobatrachus , as described, is most unusual. The main body of this bone resembles that of Lydekkerina in being columnar in form, but differs in having a small, ridge-like mesial process directed inwards from its base, and in lacking an otic process. The ascending process, as described by Cosgriff, has the very unusual form of a rather meagre, horizontal sheet of bone from which a peg-like projection arises dorsally to contact the skull roof. This apparently unique epipterygoid is poorly preserved, however, and somewhat displaced, and it is possible that what Cosgriff regarded as the ascending process was in fact part of the prootic, which in Lydekkerina does have a horizontal component with projections reaching up to the cranial roof. The conical recess is partially hollowed out of the mesial face of the body of the epipterygoid (Cosgriff 1974, Fig. 38b), whereas in Lydekkerina, as in rhinesuchids, the epipterygoid has withdrawn away from this position and the recess is hollowed out entirely from the body of the pterygoid, leaving the base of the epipterygoid to roof over the more proximal portions of

55 the basipterygoid process. On the occiput of Chomatobatrachus (Text-fig. 44c), the quadrate ramus of the pterygoid does not possess a stapedial groove or crista obliqua, and the quadrate lacks both a tubercle and a dorsal process. The mandible of Chomatobatrachus (Text-fig. 45) lacks anterior Meckelian foramina, where two or three are present in Lydekkerina, and it has a small oval posterior Meckelian foramen, which lies in a more posterior position than does the more extensive, oval fenestra seen in Lydekkerina. Furthermore, the prearticular of Chomatobatrachus is sufficiently elongated to extend beyond the splenial-postsplenial suture, and there is a denticulated symphysial area with two symphysial tusks, and possibly an extra row of small outer dentary teeth. The posterior region of the mandible, however, does bear a striking resemblance to that of Lydekkerina, Broomulus and Limnoiketes , for it has a large hamate process, a very extensive PGA, and, as in Lydekkerina and Limnoiketes, a long depressor groove, which curves across the dorsal, lingual and ventral surfaces of the postglenoid area, and forms a groove-like, pulley surface between a short retroarticular process lingually and a much more extensive backwardly-projecting surangular process labially. This process, however, is not so well defined as it is in Lydekkerina , nor is it directed dorso- posteriorly in what is a mechanically more efficient direction for the action of that part of the depressor mandibulae muscle, which ran ventro- posteriorly to it from the squamosal- quadratojugal trough. Such an extensive PGA, however, also occurs outside of the Lydekkerinidae in Arcadia myriadens , which also possesses a large hamate process, and there is little doubt that the presence of these structures are independent developments in all these divergent forms. In both Chomatobatrachus and Lydekkerina the mandible lacks a coronoid process, and the anterior coronoid occupies all the dorsal surface of the mandible lingual to the dentary, and has a wide contact with its symphysial plate. Warren & Black (1985), Jupp & Warren (1986) and Shishkin (1994) have argued that the Chomatobatrachus mandible described by Cosgriff really belonged to a rhytidosteid (since retracted by Warren, Damiani & Yates 2006), but Text-fig.45. Chomatobatrachus halei Cosgriff 1974; Lower Cosgriff himself, believed it to be identical Triassic; Australia The right mandible in a) lingual view; to another ramus that was closely b) labial view; c) dorsal view (all after Cosgriff 1974). associated with the skull material of Chomatobatrachus (Cosgriff 1974, and personal communication 1966). The fact that the symphysial plate of Chomatobatrachus lacks the mid-symphysial constriction and expanded anterior portion that is so characteristic of the rhytidosteid symphysial plate (Shishkin 1994), gives further support to Cosgriff’s argument. Chomatobatrachus displays a mosaic of features, some of which are rhinesuchid, some lydekkerinid (of which several are paedomorphic), but most of which are unique to itself, and the overall structure of its skull and mandible strongly argue for its exclusion from the Lydekkerinidae . Chomatobatrachus has been allied closely with Luzocephalus blomi by many authors, and its taxonomic position is discussed at the end of the following account of Luzocephalus blomi .

LUZOCEPHALUS BLOMI SHISHKIN 1980 (Text-fig.46)

56 Holotype, and only specimen. PIN 3784/1, an incomplete skull in the Palaeontological Institute, Academy of Science, Moscow, Russia.

Text-fig.46. Luzocephalus blom Shishkin 1980; Lower Triassic, Russia. Reconstruction of the skull in a) dorsal view; b) palatal view; c) occipital view (all after Shishkin 1980).

Locality and Horizon . Left valley slope of the Luza River, facing the southeastern end of Luza Town, Kirov Province, Northern Russia, Vetluga series, Krasnyye Baki Horizon, Induan, Lower Triassic. Discussion : Luzocephalus blomi was originally described by Shishkin (1980) as an aberrant early capitosaurid, and placed it in its own family the Luzocephalidae. Many authors have argued that Luzocephalus is closely allied to Chomatobatrachus , and both forms have sometimes been classified within the Luzocephalidae (Warren & Hutchinson 1988, Milner 1990), but more often within the Lydekkerinidae (Cosgriff 1984, Warren & Black 1985, Milner 1991, Maryanska & Shishkin 1996, Shishkin, et al 1996, Warren 2000, Schoch & Milner 2000, Damiani & Rubidge (2003), Dias-Da-Silva, Marsicano & Schultz 2006, Jeannot et al , 2006, and Stayton and Ruta (2006). Shishkin (1980) equated some material from the Lower Triassic of East Greenland, described by Save- Soderbergh (1935) as ‘ Lyrocephalus’ kochi , ‘ L’ rapax and ‘ L’ johannsoni , to the genus Luzocephalus , and

57 this material has recently been considered by Jeannot et al (1996), to belong to a new lydekkerinid species Luzocephalus kochi. Bjerring (1999), on the other hand, re-described these Greenland forms as an entirely new genus, Aquiloniferus kochi, which differed in many important ways from both Luzocephalus and from Lydekkerina, and concluded that it was capitosauroid in nature, and not a lydekkerinid. Both of these views are accepted here. The holotype skull of Luzocephalus blomi , which is wedge-shaped rather than parabolic, is very much larger and relatively narrower than the skull of any lydekkerinid, having a midline length of 172mm and a maximum width of 150mm, and although it does share certain characteristics of its skull roof, palate and occiput with lydekkerinids, many of these features are plesiomorphies, and some of them are paedomorphic. In contrast to these features, Luzocephalus possesses a very large number of important, derived characters that clearly separate it from lydekkerinids. The skull for example, has a distinctly triangular outline in dorsal view and has a wide skull table whose cheek regions are greatly developed (Text-fig.46a). The squamosal and quadratojugal bones extend postero-ventrally to such an extent that the quadratojugal corners of the skull lie well posterior to the exoccipital condyles and the basicranial regions of the palate are deeply vaulted in occipital view. The nares lie more posteriorly than is normal in lydekkerinids, as do the orbits, which are located entirely behind the mid-length of the skull roof. The parietal foramen also lies very far back behind the orbits and is located in the posterior half of the interparietal suture. The orbits are more widely separated than in lydekkerinids and lack both an inter- orbital hollowing between them and a pre-orbital step. Other features in which Luzocephalus differs from lydekkerinids include a lacrimal flexure that is only gently curved; narrower nasals, which have postero-laterally directed sutures with the premaxillae; jugals with an extremely short antorbital projection, that is very much shorter than its postorbital projection; tabular horns that are short, rounded, triangular, and unbuttressed, and which terminate anterior to the postero-lateral corners of the skull; and squamosals with a nearly straight occipital edge. On the palate, significant differences from lydekkerinids include an anterior palatal vacuity that is large and cordiform, and well separated from the premaxillary tooth row by an extensive anterior palatal plate; choanae that are broadly oval, and lie closer together; and interpterygoid vacuities and a processsus cultriformis that are narrower. The palatal tooth row is longer, as is the basicranial suture, and more importantly, according to Shishkin, (1980), there do not appear to be any rectus capitis pockets bordered by cristae musculari, nor any stapedial lappets. Ornamentation is lacking from the palatal ramus of the pterygoid, and denticles on the parasphenoid corpus are confined to its medial parts. The occiput of Luzocephalus is strikingly different from that of lydekkerinids in the straightness of the cheek borders (excepting Eolydekkerina ); the very deep vaulting of the palatal plate; the presence of a large, palatoquadrate fissure, and, possibly, according to Shishkin, the absence of any stapedial groove and oblique ridge, although his figure of the occiput (Fig. 2b. p 92, 1980), would seem to indicate that a low, sub-horizontal, rounded ridge bordering the equivalent of a stapedial groove, was present on the quadrate ramus of the pterygoid, at least over its proximal regions. The tympanic crest is more mesially situated and more obliquely orientated than it is in Lydekkerina, and the quadrate, although displaying a very large dorsal process, would appear to lack a tubercle. Shishkin et al (1996) appeared to have no doubt about the lydekkerinid status of Luzocephalus , but they recorded only one derived character that it shared with Lydekkerina viz. that the anterior palatal vacuity is bordered anteriorly by a premaxillary palatal shelf. At the same time, they enumerated many differences between Luzocephalus and another lydekkerinid, Eolydekkerina, and this observation, in conjunction with the numerous and important differences between Luzocephalus and the lydekkerinids summarised above, indicates that Luzocephalus cannot be classified satisfactorily within the Lydekkerinidae. As stated earlier, Chomatobatrachus has been closely allied with Luzocephalus by many authors, but the morphological differences between the skulls of these two taxa strongly argue against such an alliance. The skull of Luzocephalus is not only much larger than that of Chomatobatrachus , but in its general features, differs from it in many ways. It is much more triangular in outline, and has straighter

58 lateral margins, a wider table region and quadratojugal corners that lie markedly posterior to the occipital condyles. The snout is longer and narrower, and there is a much more elongated postorbital region due to the roofing bones in both these regions being relatively much longer than they are in Chomatobatrachus . The nares are further from the tip of the snout; the orbits are further apart and more posterior in position, and the otic notches are less well developed, with the notches being only slightly incised into the squamosals. The tabular horns terminate anterior to the postero-lateral corners of the skull roof and the parietal foramen lies more posteriorly to the orbits in Luzocephalus and the lateral-line system is less well developed, and includes a lacrimal flexure that is only gently curved. The ornament is of depressions and grooves, separated by conulated ridges and is not entirely pitted. The proportions of the frontals, parietals and jugals are different in the two taxa, although the relationships of the septomaxillae, lacrimals and frontals, are similar, as is the absence of any interorbital hollowing and pre-orbital step. The palate of Luzocephalus, resembles that of Chomatobatrachus in the form of its anterior palatal vacuity, interpterygoid vacuities and vomerine teeth, yet it lacks the palatal troughs, and the postulated additional tooth row lateral to the choanae that characterises Chomatobatrachus, and neither does it have cristae musculari or rectus capitis pockets. It also differs in having a more extensive anterior palatal plate, long palatal extensions to the premaxillae, longer and narrower choanae, a much shorter processus cultriformis, that terminates in a rounded end, the presence of pterygoid ornamentation, and a fissure separating the pterygoid from the exoccipital. The occipital surface of Luzocephalus is distinguished from that of Chomatobatrachus in having a much more extensive palatoquadrate fissure, a very extensive squamosal-quadratojugal trough, a stapedial groove and a low, rounded, sub-horizontal crista obliqua. Luzocephalus is clearly not closely related to Chomatobatrachus , and should be retained within a family of its own, the Luzocephalidae, as originally suggested by Shishkin (1980). Chomatobatrachus , which cannot be satisfactorily classified within either the Luzocephalidae or the Lydekkerinidae, would seem, in the view of many recent authors, to be morphologically and phylogenetically, somewhat intermediate between lydekkerinids and rhytidosteids, although alliled more to rhytidosteids than to lydekkerinids (Milner 1990 & 1991; Marsicano & Warren, 1998). These views have been reinforced by a new detailed cladistic analysis of lydekkerinids and related forms, that will be presented shortly in a follow-up paper to this one. Milner (1990) separated both Chomatobatrachus and Luzocephalus from Lydekkerina and Limnoiketes and placed them within the family Luzocephalidae, as a sister taxon to the Rhytidosteidae, and in 1991, he showd the Lydekkerinidae to be the stem, and the Rhytidosteidae to be the crown, of a single, rapid adaptive radiation, with Chomatobatrachus occupying an intermediate position between Lydekkerina + Limnoiketes, and a sister grouping of Luzocephalus -Rhytidosteidae. Marsicano & Warren (1998) have similarly placed Chomatobatrachus in an intermediate position between Lydekkerina and the Rhytidosteids, and Shishkin et al (1996), increasingly distanced Chomatobatrachus and Luzocephalus from the lydekkerinids Eolydekkerina , Broomulus and Lydekkerina. These authors argued that Luzocephalus was strikingly divergent from the Gondwanan lydekkerinids, and even “capitosauroids” in general, due to a great number of autapomorphies (both paedomorphic and non-paedomorphic) that are unknown among these forms. As with Luzocephalus , Chomatobatrachus is probably best accommodated within a monotypic family of its own, the Chomatobatrachidae.

59 EOLYDEKKERINA MAGNA SHISHKIN, RUBIDGE & KITCHING 1996 (Text-fig. 47)

Text-fig.47. Eolydekkerina magna Shishkin, Rubidge & Kitching 1996; Lower Triassic; South Africa. Reconstruction of the skull in a) dorsal view; b) palatal view; c) right lateral view; d) occipital view (all after Shishkin et al 1996).

Holotype. BP/1/5079, an almost complete skull without its lower jaw, in the Bernard Price Institute for Palaeontological Research, University of the Witwatersrand, Johannesburg, Republic of South Africa. Locality and Horizon . Fairydale Farm, Bethulie District, Free State Province, South Africa; upper part of the Balfour Formation, lower part of the Lystrosaurus Assemblage Zone, Middle Beaufort Group, Lower Triassic. A separate poorly preserved lower jaw from the same locality may also belong to Eolydekkerina. Revised diagnosis : Large lydekkerinid stereospondyl differing from all other lydekkerinids by the following combination of features: skull with almost straight lateral margins, and a median longitudinal depression; orbits in posterior half of skull roof, giving the skull a much longer than usual preorbital index (52)*; parietal foramen well posterior to orbits; quadratojugal corners distinctly posterior to occipital condyles, but terminating on a level with the ends of the tabular horns; supraorbital and jugal sensory sulci lacking; premaxillae with extensive roofing portions; lacrimal short and terminating well in front of the orbits; postorbital with well developed antero-lateral projection; moderate preorbital

60 projection of the jugal; non-buttressed tabular horns; postparietals with short occipital projections; occipital edge of squamosal sigmoid; anterior palatal vacuity large and rounded, with indented postero- lateral sides; no premaxillary palatal extensions; choanae pear-shaped; interchoanal tooth row straight; long row of more than 6 palatal teeth; processus cultriformis heavily denticulated centrally; pterygoids with denticles and ornamentation, but ornamentation lacking from the palatal ramus; palatal ramus sutures with palatine; subotic notch a deep and rather narrow, transverse opening; cheek borders more or less straight; quadrate condyles more or less on the same horizontal level as the occipital condyles; tympanic crest less vertically orientated; small posttemporal fenestrae; poorly developed processus lamellosus and processus basalis; quadrate tubercle a buttress-like surface borne largely by the pterygoid; stapedial groove flat and step-shaped in cross section; stapedial lappets formed from adjacent elevated triangular areas of the parasphenoid and pterygoid. Discussion: Eolydekkerina magna was described by Shishkin et al (1996) as a new lydekkerinid genus, and was visualised as a possible ancestor to Lydekkerina . The general structure of its skull roof, palate, occiput and stapes exhibit virtually all of the synapomorphic features shared by all lydekkerinids, listed earlier, where they are known, and all workers, without exception, have accepted Eolydekkerina as a member of the Lydekkerinidae. Pawley and Warren (2005) have suggested that Eolydekkerina may represent a large individual of L. huxleyi , and not a separate taxon, but the recent study, and additional preparation of the type specimen by Jeannot et al (2006), indicates that, although Eolydekkerina is much closer morphologically to Lydekkerina huxleyi than had previously been suggested, it is nonetheless a distinct taxon, a view that is strongly supported by the many distinctive morphological characteristics that Eolydekkerina possesses, and which were summarised in the diagnosis given earlier. Some of these characteristics are unique to Eolydekkerina itself, but many can be related to the paedomorphic origin of the family from rhinesuchid-like ancestral forms, as is discussed in more detail later. Eolydekkerina is the least paedomorphic of all the lydekkerinids, and in some respects, appears to be somewhat intermediate in form between rhinesuchids and lydekkerinids. Thus it is larger than any of the other lydekkerinids, and has orbits that are located in the posterior half of the skull roof, a parietal foramen that is positioned well behind the orbits, quadratojugal corners that lie distinctly posterior to the occipital condyles, and non-buttressed tabular horns. These features, together with its slightly earlier geological age, appear to provide some support to the proposal by Shishkin et al (1996), that it is an ancestral form of Lydekkerina , a proposal, however, that is not accepted here, as is explained later. ‘PAROTOSUCHUS’ MADAGASCARIENSIS DAMIANI 2001 (Text-fig. 48) Benthosuchus madagascariensis Lehman, 1961. Parotosuchus madagascariensis Warren & Hutchinson, 1988. Deltacephalus sp. Maryanska & Shishkin, 1996. Watsonisuchus madagascariensis Steyer 2003. The holotype of Benthosuchus madagascariensis was included in a phylogenetic analysis of mastodonsauroids by Damiani (2001), and appeared in the resulting cladogram within the family Lydekkerinidae, as ‘Parotosuchus’ madagascariensis, and as a sister group to Deltacephalus whitei. In his text, however, Damiani noted that B. madagascariensis could not be referred to as a lydekkerinid because its frontal bone entered into the margin of the orbit, and he further argued that, along with the rest of Lehman’s material, it should be considered as Stereospondyli incertae sedis . The earlier claims by Maryanska & Shishkin (1996) and Shishkin et al (1996), that all this material should be referred to a

61 Text-fig.48. ‘ Parotosuchus’ madagascariensis Damiani 2001; Lower Triassic; Madagascar. Skull in a) dorsal view; b) palatal view; c) occipital view (all after Warren & Hutchinson 1988). new “capitosaurid” lineage, the Deltacephalidae within the “Capitosauroidea” have been discussed and countered earlier. Since Damiani (2001), all of Lehman’s material has been redescribed as the mastodonsaurid Watsonisuchus madagascariensis.

LUZOCEPHALUS KOCHI JEANNOT, DAMIANI & RUBIDGE 2006 The species Lyrocephalus kochi , L. rapax and L. johannsoni (Save-Soderbergh, 1935), from the Lower Triassic of East Greenland, were considered by Shishkin (1980) to belong to the aberrant early capitosaurid genus Luzocephalus , but have recently been regarded by Jeannot et al (2006) as all pertaining to a new lydekkerinid species, Luzocephalus kochi . As explained earlier, I take the view that this species is a nomen vanum , and that this material belongs to Aquiloniferus kochi (Bjerring 1999), a ‘capitosauroid’ taxon and not a lydekkerinid, and in consequence it is not discussed further. It is concluded from this morphological review of all the genera and species that have been assigned to the Lydekkerinidae, that only Lydekkerina huxleyi , Broomulus dutoiti , Limnoiketes paludinatans , Deltacephalus whitei , and Eolydekkerina magna should be included within the family Lydekkerinidae. It has been argued that Putterillia platyceps is a junior synonym of L. huxleyi , and that Lydekkerinia kitchingi and Lydekkerina panchetensis are nomina vana . Broomistega putterilli , formerly Lydekkerina putterilli , is undoubtedly a rhinesuchid, and ‘ Parotosuchus ’ madagascariensis , now referred to as Watsonisuchus madagascariensis , a mastodonsaurid. Chomatobatrachus halei and Luzocephalus blomi are allied more to rhytidosteids than they are to lydekkerinids, and are sufficiently different from each other, and from other forms, to be each given a monotypic family of their own. The taxonomic position of Indobenthosuchus panchetensis and Cryobatrachus kitchingi remain uncertain. Of the five taxa regarded here as belonging to the Lydekkerinidae, four of them, Lydekkerina , Broomulus , Limnoiketes and Eolydekkerin a have also been recognised as lydekkerinids by the most recent workers on the family viz. Jeannot et al (2006), Stayton & Ruta (2006) and Shishkin et al (1996), although, Broomulus (Jeannot et al , 2006), and Limnoiketes (Jeannot et al , 2006 & Shishkin et al 1996), were only included in the family by these authors as synonyms for L. huxleyi . The lydekkerinid status of Deltacephalus , however, has found little support, except by Stayton & Ruta (2006), and similarly, the proposal that Chomatobatrachus and Luzocephalus should be omitted from the family altogether, has also found little favour with such recent workers as Jeannot et al (2006), Stayton & Ruta (2006), and Shishkin et al (1996), or indeed with the majority of earlier workers. It should be emphasised, however, that Shishkin et al (1996), and Warren (2000), have both made a clear distinction between Chomatobatrachus and Luzocephalus on the one hand , and the remaining lydekkerinids on the

62 other, with Chomatobatrachus and Luzocephalus being conceived as larger forms, belonging to assemblages dominated by amphibians, and the remaining lydekkerinids ( Lydekkerina (including Limnoiketes ), Broomulus , Cryobatrachus and Eolydekkererina ) as smaller, more obviously paedomorphic forms, associated with reptile-rich faunas. This concept has found additional support in the morphometric analysis by Stayton & Ruta (2006), who also recognised these two groups and described them as ‘derived lydekkerinids’ and ‘basal lydekkerinids’ respectively.

THE ORIGIN OF THE LYDEKKERINIDAE The Lydekkerinidae was originally erected by Watson (1919) as one of the 12 families within his Grade Rachitomi, but the precise relationships between this family and other temnospondyl families, lacked any concensus until 1947, when Romer, in his review of all temnospondyls, postulated that the Lydekkerinidae was related to the Rhinesuchidae and Uranocentrodontidae within the Rhinesuchoidea, one of two Superfamilies into which he divided the majority of the Upper Permian and Triassic temnospondyls. This rhinesuchid-uranocentrodontid relationship of the lydekkerinids has been broadly accepted by the vast majority of later workers, although not by Warren & Black (1985) nor by Milner (1990). The Rhinesuchidae and Uranocentrodontidae have been considered as separate families by Romer (1947), Cosgriff (1965), Ochev (1966), Kitching (1978), Shishkin (1980), Warren & Black (1985), Milner (1990) and Maryanska & Shishkin (1996), but not by Watson (1919), Carroll & Winer (1977), Cosgriff (1984) and Shishkin et al (1996), all of whom have classified the uranocentrodontids within the Rhinesuchidae. The most recent study involving rhinesuchoid morphology (Yates & Warren 2000) supports this latter view, which is also the view adopted here as there appears to be no valid character states of sufficient importance at a family level to warrant separating rhinesuchids from uranocentrodontids. The Lydekkerinidae, was believed by Cosgriff & Hammer (1983) and Cosgriff (1984) to be descended from the Rhinesuchidae, and to be part of an adaptive radiation of temnospondyls that also included the Rhytidosteidae, Capitosauridae, Benthosuchidae, Trematosauridae and Indobrachyopidae. Milner (1990 and 1991) has likewise shown the Lydekkerinidae to be derived from the Rhinesuchidae, and to be part of an adaptive radiation, but one that involved Lydekkerina , Limnoiketes , Chomatobatrachus , Luzocephalus , the Rhytidosteidae, the Derwentia group and the Chigutisauridae. This derivation of the Lydekkerinidae from the Rhinesuchidae has been supported by Shishkin & Rubidge (2000), but not by Shishkin et al , (1996), who argued that the Lydekkerinidae originated not from the Rhinesuchidae directly, but from forms that were rhinesuchid-like in their morphology, nor by Ochev (1966), who believed that the Lydekkerinidae and the Rhinesuchidae had shared a common ancestor. The Rhinesuchidae was the dominant temnospondyl family in the Upper Permian deposits pertaining to the Tapinocephalus , Cistecephalus and Dicynodon Assemblage Zones of the Karoo System of South Africa, and from the rhinesuchid nature of Broomistega putterilli , the family would appear to have lingered on into the Lower Triassic Lystrosaurus Assemblage Zone. The Rhinesuchidae is known elsewhere from the Upper Permian Chiweta Beds of Malawi ( Rhineceps nyasaensis , Watson 1962), a Rhinesuchus -like form from the Upper Permian levels of the Parana basin of Brazil (Barberena & Dias 1998), a possible rhinesuchid mandible from the Lower Triassic Sakamena Formation of southwest Madagascar (Piveteau 1926; Steyer 2003), and isolated remains recently reported from India and Russia (Warren 2000). Over a dozen species of rhinesuchid have been described, and although the great majority of the specimens are either fragmentary, incomplete, distorted or inadequately prepared (Kitching 1978), sufficient morphological information can be obtained from specimens of Rhinesuchus whaitsi , Rhinesuchoides tenuiceps , Muchocephalus kitchingi , Laccosaurus watsoni , Laccocephalus insperatus , and in particular, Uranocentrodon senekalensis , and Rhineceps nyasaensis , to enable the taxonomic relationships between the rhinesuchids and the lydekkerinids, to be discussed in a critical way. Shishkin & Rubidge (2000) considered the Rhinesuchidae and the Lydekkerinidae to be closely related, and the great majority of the rhinesuchids listed above certainly share a number of characteristic morphological features with lydekkerinids. On the skull roof, these include: nares close

63 to the tip of the snout; parietal foramen in the anterior half of the interparietal suture; premaxillae with short roofing portions and a more or less transverse and simple suture with the nasals; nasal with a step- shaped posterior border and a nasal-maxilla contact; septomaxilla with intranarial process; frontals excluded from orbital borders. On the palate in both groups, the choanae are oval and moderately far apart, and have a vomer-maxillary suture anterior to them and a parachoanal tooth row mesially. An ectopterygoid tooth row is also present but lacks tusks. Rectus capitis pockets, cristae musculari and stapedial lappets all occur, as do paired exoccipital condyles, and the basioccipital is usually small and not visible in palatal view. Other shared features include a conical recess excavated entirely out of the body of the pterygoid, and an epipterygoid with a bulky basal column and a more slender, rod-shaped ascending process which abuts against the unossified latero-sphenoid region of the braincase, just below the parietal bones and a short distance behind the parietal foramen. Shared features present on the occiput include the presence of a squamosal-quadratojugal trough; stapedial groove and crista obliqua; opisthotic usually absent from the paroccipital process and cheek contours curved in occipital view. On the mandible of both rhinesuchids and lydekkerinds, the PGA bears a depressor groove separating a retroarticular process lingually from a surangular process labially; the anterior coronoid is large and broad, and sutures with the dentary along the whole of the symphysial plate, hiding the splenial in dorsal view Adult rhinesuchids are large, long-snouted temnospondyls of mainly Upper Permian age with a skull roof length often greater than 300mm. The otic notches are usually deep and relatively narrow, and do not widen out appreciably posteriorly. The orbits are located entirely behind the mid-length of the skull roof, giving a preorbital region that is relatively long, and a postorbital region that is relatively short. The parietal foramen lies far behind the level of the posterior borders of the orbits, and the quadrate condyles lie well posterior to the level of the occipital condyle or condyles. The posterior border of the skull table tends to be moderately curved. On the skull roof, the ornament normally lacks conules, the septomaxilla has a spine-like intranarial portion, the lacrimal is moderately long and usually terminates posteriorly well in advance of the level of the anterior borders of the orbits, and the lacrimal flexure is gently curved. The preorbital projection of the jugal is normally well developed and considerably longer than the postorbital projection, and the maxilla sutures with the quadratojugal on the lower border of the lateral margin of the skull roof. The supratemporal forms part of the border of the otic notch, and the occipital flanges of the postparietals and tabulars are usually flattened, slope backwards and are visible in dorsal view. On the palate, an extensive anterior palatal plate is present anterior to a palatal fossa or vacuity, which comprises either a pair of rounded openings or a conjoined pair. Denticles are usually present on the vomers, palatines, ectopterygoids, parasphenoid and pterygoid. The interchoanal tooth row, when present, is straight, and there is a long row of more than 6 palatine teeth. The palatal ramus of the pterygoid is long, extending more than three-quarters of the length of the relatively broad interpterygoid vacuities, meeting the palatine and isolating the ectopterygoid from the vacuity. The rectus capitis pockets and cristae musculari normally lie fairly close together, but at varying distances behind the hinder ends of the basicranial sutures, and the subotic process of the exoccipital in palatal view is seen to be expanded antero-laterally to some extent. On the occiput, the posttemporal fossa is often narrow and slit-like, and the paroccipital process terminates with a tabular that is normally expanded, blade-like and curved ventrally, and bears an unsupported tabular horn. The stapedial groove is set high upon the quadrate ramus of the pterygoid and is bordered by a sharp-edged crista obliqua, and the tympanic crest of the squamosal, bordering the squamosal-quadratojugal trough mesially, is rather obliquely orientated. A quadrate tubercle is normally absent, but a dorsal process is present, as is a small, ossified basioccipital. Palatal vaulting is shallow with the quadrate condyles positioned on much the same horizontal plane as the occipital condyle(s). The mandible is characterised by a short PGA, which is cleft by a depressor groove separating a small, rounded retroarticular process lingually from an equally small, or only slightly longer surangular process labially. The prearticular is unusually long and extends beyond the splenial-postsplenial suture, and a

64 long posterior Meckelian fenestra is also present. A continuous, broad, denticulated ridge runs along all three coronoid bones mesial to the tooth row, and a coronoid process is usually present. The lydekkerinids, despite sharing numerous morphological features with the rhinesuchids, mark a significant departure from rhinesuchid morphology. The skull has become much smaller, and has centrally placed orbits, resulting in a considerably shortened preorbital region and a relatively longer postorbital region. The otic notches are now broad, widely open embayments, from which the supratemporals are excluded, and the quadratojugal corners lie further forwards, and in extreme cases, lie approximately on a level with the exoccipital condyles. On the shortened facial region, the lacrimal has become relatively longer and terminates posteriorly closer to the level of the anterior margins of the orbits, whilst the preorbital projection of the jugal has shortened and is now considerably shorter than the postorbital projection. The parietal foramen lies in a more anterior position, usually only a short distance behind the level of the posterior margins of the orbits. The anterior portions of the frontals have generally become broader, the dermal ornament has developed conules, and the lacrimal flexure has become step-shaped to Z-shaped. On the palate, there is now a short anterior palatal plate and a single anterior palatal vacuity, which is not deeply divided into two sections, and posterior to this there is usually a curved interchoanal tooth row. Denticles have been lost from the palatines and ectopterygoids, and the palatal tooth row has become shorter, with usually less than 6 teeth, and is now braced posteriorly by an alar process from the jugal. Anteriorly, the palatine has developed an elongated posteromedial process that extends behind the most anterior ectopterygoid tooth. There is an extremely well developed dermal ornamentation on parts of the body of the pterygoid and its rami, and a subotic embayment or notch has developed separating the broadly expanded subotic lamina of the exoccipital from the pterygoid, and this is visible in palatal view, lying directly dorsal to a free portion of the posterior border of the parasphenoid lying mesial to the stapedial lappet. The pockets and cristae now tend to lie on a level with the hinder ends of the basicranial sutures, possibly as a result of the backward extension of these sutures (Ochev, 1966) or by a forward shift of the cristae (Shishkin & Rubidge, 2000) On the occiput, the paroccipital bar has become more vertically orientated, and its tabular component is no longer expanded ventrally. The tabular horn has become supported from below by a crista tabularis externa and a crista terminalis, and the stapedial groove which now lies low on the quadrate ramus of the pterygoid, has become bordered by a low, sub-horizontal, rounded, oblique ridge. Other morphological advances within the Lydekkerinidae have involved the jaw mechanism. With the shortening of the otic embayment, the tympanic crest has become sub-vertical, and the squamosal- quadratojugal trough more extensive to allow for the origin of an enlarged cranial component of the depressor mandibulae muscle. At the rear of the mandible, an extensive PGA has evolved, with a greatly elongated surangular process for the insertion of the fleshy parts of this depressor muscle, and there is now a deep depressor groove between the surangular and retroarticular processes, to house a tendon from the depressor muscle, and to enable it to insert far anteriorly on the ventral surface of the mandible, well below the glenoid, thereby greatly extending its line of action. The postglenoid process has become conspicuous, and may have functioned as a ‘stop’ to absorb the kinetic energy of a more rapidly closing jaw, and a very large hamate process has developed to provide an increased insertion area for the adductor musculature. Other mandibular differences from the rhinesuchids include a shorter prearticular, a smaller posterior Meckelian foramen and the presence of isolated groupings of denticles on all three coronoid bones, and the appearance within these groupings of a few large teeth resembling those on the dentary. The current view generally held, that the lydekkerinids were descendents of rhinesuchids, or rhinesuchid-like forms, has been given further support recently by Pawley & Warren (2005), who noted the similarity of the postcranial skeleton of L. huxleyi to that of the rhinesuchid Uranocentrodon. The morphological changes that led eventually to the evolution of the lydekkerinids, may have been evoked by profound climatic changes that took place in the Karoo Basin during Permo-Triassic times. Smith (1995), in his recent detailed studies on the sedimentology, vertebrate taphonomy and biostratigraphy of the rocks of the boundary sequence between the Permian Dicynodon zone and the

65 Triassic Lystrosaurus zone in the Karoo Basin, has argued that by the end of the Permian and the beginning of the Triassic, the regional climate had become progressively warmer and more arid, with a more pronounced seasonality and less reliable rainfall, a view that was in direct opposition to that forwarded much earlier by Parrington (1948). In this drought-susceptible environment, large areas within the Karoo Basin had been converted from wet floodplains with a high water table and a seasonally dry period, into predominantly dry, semi-arid floodplains. This resulted in a great reduction in the areal distribution of aquatic and marshy habitats and the elimination of some 86% of the Upper Permian Dicynodon Assemblage Zone fauna, (mainly the large herbivorous dicynodonts, the carnivorous gorgonopsians and the large rhinesuchid temnospondyls), and their replacement in the succeeding Lower Triassic Lystrosaurus Assemblage Zone by a new fauna, still dominated by reptiles, but comprised of relatively small to moderately sized tetrapods, of which the medium-sized, dry-adapted dicynodont Lystrosaurus was the dominant reptile, and the small, semi-aquatic temnospondyl Lydekkerina, the commonest amphibian. In somewhat similar fashion, the medium to large sized rhinesuchids of the Upper Permian beds of the Parana Basin, Brazil, were replaced during the Lower Triassic by small temnospondyls, in this case, however, mainly rhytidosteids (Dias-Da-Silva, Marsicano & Schultz 2005). Lydekkerina was almost certainly largely confined to small, transient lakes, pools and shallow outlying pockets of larger stretches of water, maintained by a highly seasonal rainfall, and to the marshy areas of land surrounding these habitats. An aquatic or semi-aquatic lifestyle is evidenced by the presence of sensory canals on the skull and the lateral surface of the mandibles, and adaptations of the snout region for sub-surface swimming, eg the presence of an interorbital hollowing, raised orbital margins and a pre- orbital step. At the same time, the well-ossified postcranial skeleton of Lydekkerina , with large processes for muscle attachment and well-developed articulation surfaces (Pawley and Warren, 2005), also suggests that it was well able to support itself and to hunt for food on drier land away from water. Whilst these climatic changes were taking place towards the close of the Permian, certain members of the rhinesuchid dominated population appear to have initiated a process of progenetic dwarfing that enabled them to become precociously sexually mature whilst in a relatively small and morphologically juvenile stage. This progenetic dwarfing may have been an adaptive response to selection pressures for small size, as it results in the early and rapid production of large, breeding populations of small individuals which could exploit the small areas of freshwater and ephemeral food resources resulting from the severe, and unpredictable environmental fluctuations that were taking place within the Karoo Basin at this time. There may well have been also a selection pressure, in these increasingly arid times, to retain a fully ossified skeleton suitable for terrestrial locomotion (Pawley & Warren 2005), and this, combined with the progenetic dwarfing, could have ensured the survival of these forms in scattered areas within the Basin, despite the undoubted temporary nature of many of these freshwater habitats. This process of progenetic dwarfing is seen to some extent in the relic rhinesuchid Broomistega putterilli , but was taken to extremes by the lydekkerinids (Milner 1990, 1991), hence the abundance in these forms of the many paedomorphic characters, which characterise the family. These features have been discussed in some detail by Shishkin et al (1996), and include the small size of the skulls; the large size of the orbits, external nares, parietal foramen and vagal foramen; the central position of the orbits on the skull roof and the low preorbital index; the elongated lacrimal that terminates posteriorly relatively close to the level of the anterior margins of the orbits; the short preorbital projection of the jugal; the broadening of the anterior portions of the frontals; the positioning of the parietal foramen close to the level of the posterior borders of the orbits; the short, broad otic embayments that widen posteriorly, and from which the supratemporal is excluded; a sub-vertical tympanic crest; quadratojugal corners that lie more or less on a level with the exoccipital condyles; the presence of a lowly positioned stapedial groove bordered by a sub-horizontal, rounded crista obliqua, and the curved slope of the cheek in occipital view. Warren (2000) has also noted that a parabolic skull shape was a further characteristic feature of juvenile temnospondyls. A comparison of the adult features of Lydekkerina, Limnoiketes, Deltacephalus, Eolydekkerina and Broomulus, with corresponding features shown by eight juvenile and one semi-grown rhinesuchid of comparable size recorded by Shishkin et al (1996) from a single locality in the Cistecephalus zone,

66 confirm the paedomorphic nature of these particular features, and additional support for this view comes from measurements taken from a sample of 29 skulls of L. huxleyi, 14 examined by the author, and 15 additional ones studied by Shishkin et al (Table 1). These comparative studies, particularly

TABLE 1. Preorbital indices, midline lengths and preorbital lengths of the skull roof in a sample of 29 skulls of Lydekkerina huxleyi . Measurements are from original specimens (Hewison) or from Table 1 of Shishkin et al 1996. those related to the nature of the lacrimal and the position of the parietal foramen, suggest that the process of paedomorphosis initially occurred in juvenile rhinesuchids as small as, or even smaller, than 55mm in mid-roof length. Support is also given to Milner’s view that the ontogenetic development of the lydekkerinid skull involved a reduced allometric growth of the snout, for although preorbital elongation begins in rhinesuchid skulls with a mid-roof length of about 70mm, little elongation occurs

GRAPH 1. Graph showing the relationship between the preorbital indices and the midline lengths of skull roofs in a sample of 29 skulls of Lydekkerina huxleyi (Table 1).

67 in lydekkerinids and the unusually low preorbital indices shown by the sample of L. huxleyi skulls remains fairly constant in skulls that range in mid-roof length from 49mm right up to 91mm (graph 1). Within the Lydekkerinidae, the most highly developed paedomorphic forms are Lydekkerina and Limnoiketes, and the least paedomorphic forms Eolydekkerina and Broomulus . Shishkin & Rubidge (2000) had earlier emphasised that whereas Lydekkerina was strongly paedomorphic, Eolydekkerina was only moderately so, and as shown below, some of the paedomorphic features seen in Eolydekkerinai tend to be intermediate in nature between the conditions seen in the other lydekkerinids and those in rhinesuchids. Such intermediate paedomorphic features include: (1) The small size of the skull : The type skull of Eolydekkerina has a mid-roof length of 130mm,which is well above that of the remaining lydekkerinids, which range from 91mm down to 48mm, but is still far below that of the skulls of adult rhinesuchids, which tend to have a mid-roof length of over 300mm. (2) The short preorbital region and central position of the orbits on the roof : In Eolydekkerina , the orbits, like those of rhinesuchids, are located entirely behind the mid-length of the skull roof, giving it a preorbital index of 52*, which is only just short of the index of 54* for the rhinesuchid Muchocephalus kitchingi , whereas in all other lydekkerinids, the orbits straddle the mid length of the skull roof, giving them indices ranging from 42-44*. (3) Posterior termination of the lacrimals : In Eolydekkerina the lacrimals terminate posteriorly much further in advance of the level of the anterior borders of the orbits (index of 23*) than they do in Deltacephalus (12), Broomulus (11), Limnoiketes & L. huxleyi (4), and they terminate only slightly more posteriorly than in rhinesuchids which have indices of 27-30. (4) Position of the parietal foramen relative to orbits : In Eolydekkerina (and in Broomulus ), the parietal foramen is positioned much further posteriorly to the hinder borders of the orbits (both with an index of 23*), than in the remaining lydekkerinids (indices 13-5) , and are rhinesuchid-like in this respect (19- 25). (5) Posterior position of the quadratojugal corners : The quadratojugal corners of Eolydekkerina (and Broomulus) , lie further forwards with respect to the occipital condyles than they do in rhinesuchids, but not so far forwards as to lie on much the same level as the condyles as in the remaining lydekkerinids. The precocious sexual maturation associated with progenesis is usually accompanied by the ontogenetic development of certain adult features associated with maturity (Gould 1977), such as the heavily ossified postcranial skeleton that L. huxleyi possesses (Pawley and Warren 2005), and also by the acquisition of certain rapidly evolving adaptive features, such as the elongated postglenoid area, and such a mix of juvenile, adult and derived features is most clearly evident in Lydekkerina huxleyi. The evolution of a rapid, snapping action of the jaws, that resulted from the shortening of the facial regions and changes to the occiput and mandible, combined with the retention of a fully ossified skeleton, enabled these small, semi-aquatic temnospondyls to become active and successful predators, both in and out of the water. The rapid bringing together of opposing rows of relatively long, curved, sharply- pointed marginal teeth, would have proved very beneficial in enabling the Lydekkerina to feed, as do young crocodiles and alligators today, on a diverse range of small animal prey such as fish, crustaceans, insects etc, either at the water surface, just below it, on the marshy fringes of the small bodies of water in which it lived, and even on small prey on drier land away from the water. The denticulate and associated dentary-type teeth on the coronoids would have assisted in gripping prey as the jaws began to snap together, and those on the posterior coronoid, would be in a favourable mechanical position to exert the most powerful gripping effect, lying as they do, immediately anterior to the fulcrum of the jaw. The fusion of the articular and surangular components of the PGA that has been observed in certain specimens, would have helped to cope with the greater stresses imposed upon this region of the mandible during the opening and closure of the jaws, and other changes that may have been related to the altered method of predation, include the extra bracing of the palatal tooth equipment by the development of an alar process from the jugal posteriorly, and by a posteromesial extension from the palatine anteriorly. The advanced PGA present in lydekkerinids could have evolved from an earlier and simpler condition such as that retained in rhinesuchids eg Rhineceps (Text-fig.49A, B, C).

68 Text-fig.49. The postglenoid area of the mandible of (a). Rhineceps nyasaensis in A) lingual, B) posterior and C) dorsal view; (b) Peltobatrachus pustulatus in D) lingual, and E) dorsal view; © Arcadia myriadens in F) lingual, G) posterior and H) dorsal view. x = retroarticular process of the articular; y = depressor groove; z = surangular process.

Here the PGA, although extremely short, has a depressor groove which forms a vertically long, but shallow and quite narrow groove running down the deep hinder surface of the PGA, flanked by a very short, rounded retroarticular process lingually and by an equally short, but deeper, surangular process labially. The depressor groove leads downwards from a shallow, rounded depression on the upper surface of the articular immediately behind the glenoid cavity, and in dorsal view is seen as a notch lying between two very slight protuberances. Two other Upper Permian rhinesuchids that show such an early state in the development of the more extensive, bifid PGA seen in later forms, are Rhinesuchus (Watson 1962), which has a short, notched hinder end, and Rhinesuchoides , in which the extreme hinder end of the PGA is reminiscent of that of Rhineceps . The rhytidosteid Arcadia , also has a specialized, elongate bifid PGA, that is strikingly similar to that

69 seen in both Lydekkerina and Chomatobatrachu s, having a depressor groove separating extensive retroarticular and surangular processes, a large hamate process and an adductor fossa that is only slightly exposed in lingual view (Text-fig.49F, G, H). It is argued here, that this elongated, bifid PGA evolved independently in these three diverse forms rather than having been inherited from a common rhinesuchid-like ancestor. Information regarding the PGA is unfortunately lacking in many genera belonging to the Mastodonsauroidea and Rhytidosteomorpha (rhytidosteids and chigutisaurs), but such an elongated, bifid PGA is certainly not present in the mastodonsauroids Kupferzellia or Benthosuchus, nor in the rhytidosteomorph Deltasaurus , and the PGA of the rhytidosteomorph Compsocerops is of a very different design. Furthermore, the morphological evidence from all those forms in which the PGA is known, suggest that the elongated PGA of Arcadia , evolved not from the simple condition seen in an ancestral rhinesuchid, but independently, from an equally simple condition of the PGA seen in such rhytidosteids as Rhytidosteus and Deltasaurus , where it is short, broad-based and triangular. In Deltasaurus, this PGA terminates in a pointed apex, but in Rhytidosteus , it is notched posteriorly for the depressor mandibulae muscle, much as it is in Rhineceps . The mandible of Arcadia itself lends further support to the argument for an independent evolution of the rhytidosteid mandible, since it differs from virtually all the mandibles discussed so far in having a distinct coronoid process (a slight one may be present in Rhinesuchoides ), a chorda tympani foramen that is entirely enclosed within the prearticular, and in having several symphysial tusks. The elongate, bifid PGA of the non-lydekkerinid Chomatobatrachus, would also appear to have evolved independently, and the similarity in design of the elongated PGA’s of the mandibles of lydekkerinids, Chomatobatrachus and Arcadia , reflects a similar solution to the same biomechanical problem of efficiently and rapidly opening the jaws. In the ancestors of the forms under discussion, the depressor mandibulae muscle inserted on a simple, rounded or triangular fossa on the dorsal surface of the PGA immediately behind the glenoid fossa, and the simplest way to improve the mechanical efficiency of jaw opening would be by extending the insertion area backwards over the posterior end of the mandible, even onto its ventral surface, and forming a groove for the tendon of the insertion muscle between the retroarticular process and the surangular process. Jupp & Warren (1986) noted a similar parallel evolution between the unusual type II PGA of the Metoposauridae and the more conventional type II PGA of the brachyopoid-plagiosaurid group, and the initiation of a similar trend also occurs in Peltobatrachus pustulatus (Panchen 1959), where the condition of the PGA is somewhat intermediate between Rhineceps and the more advanced forms (Text- fig.49D, E). The depressor groove in Peltobatrachus remains shallow and narrow and flanked by only slightly protruding retroarticular and surangular processes, but it is only very short, since the hinder end of the PGA is no longer deep dorso-ventrally as in Rhineceps, but terminates, as in the later forms, in a long, slender projection formed by the extension backwards of both processes behind the glenoid area. The initial stages in the evolution of the many changes that affected the skull and mandible of lydekkerinids can be observed in certain rhinesuchids that lived in the Karoo Basin during the closing stages of the Permian, and one such rhinesuchid, Muchocephalus kitchingi , has already been proposed as a possible ancestor of the lydekkerinids (Cosgriff 1974). The type skull of this form, BPI/1/214, (Text- fig.39), comes from the Dicynodon Assemblage Zone, and is large, with a mid-roof length of about 240mm. It is typically rhinesuchid in most of its features, yet nonetheless displays certain paedomorphic features characteristic of lydekkerinids, such as the moderately deep, U-shaped otic embayments that are widely open behind. It also shares certain identical or near identical paedomorphic indices with Eolydekkerina magna, namely preorbital index (54*) and postorbital index (31*). It also departs from rhinesuchids and approaches lydekkerinids in a broadening of the anterior border of the frontals, an increased orbital size, a loss of palatal denticulation, and a more anterior positioning of its pockets and cristae. This skull of Muchocephalus , however, has certain specialisations that prevent it from being directly ancestral to lydekkerinids, such as external nares that lie very close to the tip of the snout; frontals that enter the borders of the orbits; orbits which lack raised rims and a preorbital step; absence of interorbital hollowing; an anterior palatal vacuity that is deeply divided and separated from the

70 premaxillary tooth row by a lengthy anterior palatal plate; an essentially flat and high occipital condyle with a large basioccipital component; unusually deep, hemispherical rectus capitis pockets, which are relatively close together and sunk directly into the ventral surface of the parasphenoid. It is also possible that an interchoanal tooth row and parachoanal tooth rows were lacking. The medium-sized Muchocephalus, although not directly ancestral to lydekkerinids , can nonetheless be recognized as a rhinesuchid form that was progressing towards the fully progenetic lydekkerinid condition, and provides an indicator of the manner in which the lydekkerinids emerged from juvenile ancestral forms during the Upper Permian. Shishkin et al (1996) has suggested that Lydekkerina evolved from a less paedomorphic ancestor such as Eolydekkerina , and although it has been shown above that Eolydekkerina is the least paedomorphic lydekkerinid known, and comes from a slightly lower horizon within the Lystrosaurus Zone Assemblage than does Lydekkerina , it is nonetheless already a lydekkerinid with unique features of its own that would bar it from being itself ancestral to Lydekkerina . The small size of L. huxleyi , not only favoured its survival within the prevailing ecological conditions, but may also have assisted in its preservation in large numbers. Many of the fossils of L. huxleyi , occur in small groups, clustered closely together with little distortion or disruption of their skeletons, and they are very often preserved in calcareous concretions resembling the hardened remains of a small pool of drying sediment eg BSP 1934 VIII 44 (Broili & Schröder 1937, plates 4 and 5), and BMNH R504. The articulated and often curled-up skeletons of these individuals indicate that they died in the actual habitat in which they were living, perhaps as a result of being trapped in drying, shrinking shallow pools that eventually dried out, after they had sought protection against high temperatures or predators scouring the drying ponds. Pawley and Warren (2005) have suggested that the fully articulated nature of the skeletons resulted from the carcasses being mummified before burial, but alternatively, these clusters of articulated remains may have resulted from a deliberate act of aestivation, for L. huxleyi , like certain amphibians living today in areas where seasonal droughts occur, may well have collected in small ponds at the onset of the dry season in order to burrow into the mud and begin a period of aestivation that would enable them to survive the drought. If the rains failed to arrive and soften the soil, then the clusters of aestivating lydekkerinids would have perished and become entombed as fossils, and at the same time remained relatively free from any disturbance by predators and scavengers. The bacterial decay of any cluster of buried lydekkerinids would have produced reducing conditions favouring the deposition of lime around them from the surrounding ground water, thereby creating a calcareous concretion. The lack of fish and invertebrate remains within these concretions would be an expected outcome if the lydekkerinids had deliberately burrowed deep into the mud, rather than perishing at the surface. This would also explain the lack of deep cracking or marked sub-periosteal flaking of the preserved bone, which as Kitching (1978) has noted, so often occurs when skeletons are exposed on the surface during hot, drying conditions. There is an absence of juvenile forms from these clusters of L. huxleyi specimens, however, which suggests that the behavioural activity that resulted in these congregations of L. huxleyi specimens, may have been sexually related and confined to adults. If, on the other hand, these clusters of adult forms were entirely the result of aestivation, then either the young forms were physically unable to burrow into the mud in order to aestivate, or that if they did manage to do so, their skeletons were too delicate for preservation. There is also the possibility, that as in the English frog Rana temporaria , it was only adult males of L. huxleyi , and not females or young forms, that burrowed into the mud during the unfavourable season. The view presented here that the lydekkerinids were small-sized, fully-grown adult temnospondyls, is supported by three lines of indirect evidence: 1) Uniformity in the size of the skulls of L. huxleyi : Over 200 skulls of L. huxleyi have been collected from numerous localities scattered throughout the large area of deposition of the Lystrosaurus Assemblage Zone, yet there are none that are very small nor any that might reasonably be considered as even moderately large, the majority, according to Shishkin et al (1996), having a skull length of 60- 80mm, and a rather stable generic pattern. This does suggest that we are dealing with the mature forms of a small-sized temnospondyl, although occasionally such uniformity in size can prove to be deceptive,

71 (see Welles & Cosgriff 1965, p.13). Jeannot et al (2006) concluded that the holotype of L. huxleyi, which has a median skull length of nearly 60mm, was already a small adult, as its proportions were similar to those of larger individuals. 2) Growth studies on related temnospondyls : Studies on the growth stages of temnospondyl species in which small immature stages and larger adults are known, support the idea that the preorbital index is a valid criterion by which to distinguish small-sized adult lydekkerinids, as has been suggested by Colbert & Cosgriff (1974). In the benthosuchid Benthosuchus sushkini for example, a graph (graph 2) plotted of the preorbital indices of all the figured skulls of B. sushkini , which range in size from 27.5mm to 576mm (Table 2), shows that a skull of a size comparable to that of an average lydekkerinid in the large sample (66mm), would have a preorbital index of around 51*, which is well above the average index of 44 shown by the lydekkerinid sample. Just as certain characteristic adult features are already stamped upon the skulls of immature, post-metamorphic stages, such as the development of a crista falciformis on the squamosal, frontals entering the orbits and a hamate process on the mandible (Warren & Hutchinson 1988a), so also is the future nature of the snout region, ie whether it is going to remain short as in lydekkerinids or whether it is going to become longer as in benthosuchids and capitosaurids.

TABLE 2. Preorbital indices and midline lengths of the skull roof of 5 specimens of Benthosuchus sushkini . From Bystrow and Efremov 1940. The same general conclusion regarding snout length can be drawn from the recent study on the changes in skull roof proportions seen in a growth series of skulls of the mastodonsaurid Watsonisuchus madagascariensis ranging in length from 46mm (juvenile) to 129mm (adult), and which clearly shows “an allometric trend from juvenile semirostry to adult longirostry” (Steyer 2003). An analysis of the skulls of juvenile rhinesuchids, a semi-grown stage of the rhinesuchid Muchocephalus kitchingi and the adult skull of M. kitching i by Shishkin et al (1996), shows that in the two juvenile skulls in which this index can be calculated, the preorbital index is the same as that found in similar-sized Lydekkerina skulls . The semi-grown stage, on the other hand, which has a skull length of 84mm, and is therefore equivalent to a large Lydekkerina in size, has a preorbital index of 50*, which is above that found in any Lydekkerina skull. Since the adult M.

GRAPH 2. Graph showing the relationship between the preorbital indices and midline lengths of the skull roofs of 5 specimens of Benthosuchus sushkini (Table 2).

72 kitchingi skull, has a mid-line length of 236mm, yet a preorbital index of only 55, this would seem to indicate that in this rhinesuchid at least, positive allometric growth of the snout region has already begun in the largest juvenile skull, and that, as in “capitosaurids”, the skull attained almost adult proportions by the time it had a skull length of 60-70mm (Warren & Hutchinson, 1988a). The similarity between the preorbital indices of small, juvenile rhinesuchids and adult skulls of L. huxleyi , lends further support to the hypothesis that Lydekkerina arose via a process of progenesis from juvenile forms prior to the growth stage at which any positive allometric growth of the snout had begun. 3) Ontogeny of the temnospondyl skull : In Benthosuchus sushkini (Bystrow & Efremov 1940), the cartilage bones of the skull ossify in a sequence beginning with the exoccipital, followed by the quadrate, epipterygoid, sphenethmoid (which ossifies very late in life, ‘almost at the boundary of middle age’), followed finally by the prootic. In the skull of L. huxleyi , UMZC T110, which has an estimated mid-line length of only about 62mm, and is therefore slightly below the average size calculated from the large sample of L. huxleyi skulls, the sphenethmoid, basisphenoid, epipterygoid, opisthotic and prootic are all ossified, the exoccipital has a well-developed processus submedularis and processus lamellosus, and the quadrate a prominent tubercle, all indicating that this is a mature, adult skull, in which ossification and the cessation of major growth took place at an early stage in ontogeny. The lack of a palatoquadrate fissure confirms the skull’s maturity. The high degree of ossification of the cranial skeleton of Lydekkerina extended also to its post-cranial skeleton (Pawley & Warren 2005), and this has been confirmed by Hewison (in press), who has described and figured the presence of large, well-ossified pleurocentra in Lydekkerina . Deltacephalus, with its midline roofing length of only 48mm and its relatively larger sensory, palatal and occipital openings than those of other lydekkerinids, is the most juvenile looking of all the lydekkerinds. Its roofing bones, particularly in the preorbital region, are weakly sutured together, and it is the only lydekkerinid showing the presence of a preorbital zone of intensive growth and a considerable degree of grooving of the ornament over the posterior third of the nasals and the neighbouring regions of the frontals and prefrontals. Such extensive grooving and a zone of intensive growth are characteristic of juvenile temnospondyls, and they are absent from the larger holotypes of both Broomulus dutoiti (84mm midline length) and L. huxleyi (60mm midline length), which suggests that in these forms, allometric growth of the snout region has virtually ceased. Limnoiketes , another paedomorphic lydekkerinid, has a skull with a median length of 55mm, and consonant with this, displays an intermediate condition in the degree of grooving over the nasal, frontal and prefrontal bones.

THE PHYLOGENETIC IMPORTANCE OF THE LYDEKKERINDAE There would seem little doubt that the lydekkerinids evolved within the Karoo Basin from rhinesuchid ancestors that lived within this Basin during Upper Permian times, and that the paedomorphic pathway that they followed served to isolate them as a rather specialized off-shoot of a widespread and highly successful adaptive radiation of new forms that arose at the close of the Permian in this area. This radiation began prior to the extinction of the rhinesuchids, and the new, advanced, paedomorphic forms within this radiation, replaced the rhinesuchids in the Karoo Basin in the Lower Triassic Lystrosaurus Assemblage Zone, although it is probable that they occupied new ecological niches created by the changing climatic and habitat conditions, rather than taking over those once inhabited by the rhinesuchids. The more dramatic climatic changes that were responsible for the final faunal change over may have taken place in the geologically short space of time of about 500,000 years, for there was a brief transitional period when both Dicynodon and Lystrosaurus lived side by side (Smith 1995). The mastodonsauroid and rhytidosteomorph complexes that originated in the Upper Permian of the Karoo region appear to have spread rapidly overland from one freshwater habitat to another during the latest stages of the Upper Permian and the very earliest stages of the Lower Triassic, a view that supports the more generalised suggestion by Marsicano & Warren (1998) and Warren (2000), that the apparent radiation of temnospondyl taxa in the Early Triassic was an extension of a Late Permian event, which probably took place in Gondwana. Cosgriff & Hammer (1983) have argued that there was at the southern end of Pangaea at the beginning of the Lower Triassic the right mix of conditions to favour

73 these rapid radiations ie a close similarity in climatic-ecologic conditions, open migration routes for the dispersal of the fauna and a proximity of the land masses involved, particularly between South Africa, East Antarctica and Tasmania. Cox (1973) and Cosgriff (1984), on the other hand, have argued that the whole of the Triassic world was open to the movements of terrestrial animals. The Lydekkerinidae appear to have originated in South Africa, but are known also from Madagascar (Deltacephalus ) and Australia ( L. huxleyi (Warren, Damiani & Yates 2006)) and possibly Antarctica (Cryobatrachus ), and Brazil (Lavina & Barberena 1985) and are therefore a wholly Gondwanan group. The rhytidosteomorphs, on the other hand, were more widely dispersed throughout Pangaea, extending from South Africa and Madagascar into Tasmania and Australia, westwards into Brazil (Dias-Da-Silva, Marsicano & Schultz 2006) and into more northerly regions such as India, Russia and Spitsbergen. All four genera of the Derwentia group, however, are confined to either Australia or in neighbouring Tasmania, and may reflect a more or less isolated and separate endemic radiation of these particular rhytidosteomorphs. The lydekkerinids were small to modest-sized paedomorphic forms that, apart from the Madagascan form Deltacephalus , were from dry-adapted, reptile dominated assemblages in which Lystrosaurus was abundant. The rhytidosteomorphs, on the other hand, comprised larger forms, which belonged to amphibian-dominated assemblages in which Lystrosaurus is absent or rare (Shishkin, et al ( 1986). This suggests that the arid conditions driving paedomorphosis in the Karoo Basin, may have been to some extent localised, and were not so widespread or drastic in the more remote regions of Pangaea, and could have been caused by a pulse of tectonism along the southern margin of the Basin as suggested by Smith (1995). The recent discovery of a skull of L. huxleyi in the early Triassic Rewan Formation of the Galilee Basin, central Queensland, Australia, however, suggests that the arid conditions prevalent in the Karoo Basin were possibly much more extensive (Warren, Damiani & Yates 2006). The Lydekkerinidae appear to have had no direct phylogenetic role to play in the evolution of Triassic temnospondyl groups, and neither do they appear, on current evidence, to have had the worldwide distribution that some authors have credited them with (Milner 1991, Shishkin & Ochev 1993, Shishkin et al 1996). Although they became the most abundant and widespread temnospondyl family throughout the Karoo Basin in the Lystrosaurus Assemblage zone, the Lydekkerinidae was a relatively short-lived family that was largely a localised opportunistic product of the habitat changes taking place in and around the Karoo Basin of South Africa during the Upper Permian and Lower Triassic. The family in South Africa became extinct by Cynognathus zone times, when less arid conditions returned, and along with other Lystrosaurus Assemblage Zone temnospondyl families, viz. the Rhinesuchidae, Micropholidae and Rhytidosteidae, although not the Brachyopidae, they were replaced by a host of new families, the Trematosauridae, Laidleridae, and Mastodonsauridae, perhaps as a result of a southward migration of Euramerican taxa (Shishkin, Rubidge & Hancox (1995), or alternatively an eastward migration of taxa from other areas of Gondwana such as Australia (Shishkin et al (1996).

ACKNOWLEDGEMENTS I thank Professor C. Barry Cox (former Division of Biosphere Sciences, King’s College London) and the late Dr Pamela Lamplugh-Robinson for their assistance and guidance during the early stages of my work on the Lydekkerinidae, and more recently to Dr A. R. Milner (Birkbeck college, London), Dr Smith (Natural History Museum, London) Dr.Ian Corfe and Dr Marcello Ruta (Life Sciences, Bristol University) for their advice and encouragement. I am grateful to Dr Angela Milner, Sandra Chapman, and previous to that, to Dr W. E. Swinton (The Natural History Museum London) for permission to study material in their care and for the production of casts, peels and photographs of Deltacephalus whitei and photographs of Lydekkerina huxleyi . I further thank Dr Adrian Friday of the Department of Zoology, University of Cambridge, for permission to re-study material of Lydekkerina , and Limnoiketes , and to Dr Barry Hughes for the loan of material of L. huxleyi . I am much indebted to Mia Stanley for help with the final production of some of the Figs. And to Toni Sherrin of Friday Print, Minehead, for her excellent Art Work associated with the designing and printing of this paper.

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APPENDIX 1: LIST OF ANATOMICAL ABBREVIATIONS acc. f , accessory foramen; acc. s , accessory sulcus; add. fos , adductor fossa; ANG , angular; ant. pal. vac , anterior palatal vacuity; ant. pqd. r , anterior paraquadrate ramus; ant. wall tym. cav , anterior wall tympanic cavity; ART, articular; BOCC, basioccipital; bocc. fos, basioccipital fossa; BSPH, basisphenoid; cond. pr, condylar process of exoccipital; cor. dent, coronoid denticles; cor. teeth, coronoid teeth; c. int. car. a , canal for internal carotid artery; c. rec, conical recess; cr. m, crista muscularis; cr. ob, crista obliqua; cr. parapt, c rista parapterygoidea; cr. tym. sq , crista tympanica squamosi; c. tym. f , chordae tympani foramen; DENT, dentary; dpr. gr, depressor groove; d. sel, dorsum sellae; EPIPT, epipterygoid; epipt. as. pr , ascending process of epipterygoid; epipt. b. col, basal column of epipterygoid; epipt. ot. pr, otic process of epipterygoid; eth. s, ethmoidal sulcus; EX , exoccipital; ex. b. pr , basal process of exoccipital; ex. cond , exoccipital condyle; ex. cond. pr, condylar process of exoccipital; ex. par. pr, parotic process of exoccipital; ex. pr. l , processus lamellosus of exoccipital; ex. subot. l , subotic lamina of exoccipital; ex. supr. pr, supraoccipital process of exoccipital; ex. tr. gr, transverse groove of exoccipital; ex. tub, exoccipital tubercle; ext. n, external naris; F, frontal; fl. pal. r, flange of palatal ramus of pterygoid; f. m, foramen magnum; for , foramen; fr. imp, impressions of frontal bones; gl. fos, glenoid fossa; ham pr, hamate process; h. for, hypoglossal foramen; inc. cr. f , incipient crista falciformis; J, jugal; jug. s, jugal sulcus; in. keel, inner condylar keel; L, lacrimal ; l.mar, linea marginalis; LATSPH, laterosphenoid; mnd. s , mandibular sulcus; MX , maxilla; N, nasal; op. for, optic foramen; opisth. v.l, vertical lamina of opisthotic; orb, orbit; or. s , oral sulcus; ot. em, otic embayment ; ot. fl , otic flange; ot. s, otic sulcus; out. keel, outer condylar keel; P, parietal; par. pr, paroccipital process ; pit. f, pituitary fossa ; PF, postfrontal; PF, postfrontal; p. for, parietal foramen; PMX, premaxilla; PO , postorbital; po. s, postorbital sulcus; post. cor, posterior coronoid; post. gl. pr, postglenoid process; post. gl. r, postglenoid ridge; post. pq. l, posterior paraquadrate lamina; post. t. fos, posttemporal fossa ; PP, postparietal; pp. occ. pr, occipital process of postparietal; pqd. dpr, palatoquadrate depression; pq. for, paraquadrate foramen; pq. gr , paraquadrate groove; PRF , prefrontal; PR.OT, prootic; PSPH, parasphenoid; psph. cp, corpus/body of parasphenoid; psph. cul. pr, cultriform process of parasphenoid; psph. l , parasphenoid lappet; PT , pterygoid; pt. cp, corpus/body of pterygoid; pt. pal. r, palatal ramus of pterygoid; pt. post. as. l, posterior ascending lamina of pterygoid; pt. qd. r , quadrate ramus of pterygoid; pt. tr. as. l, t ransverse ascending lamina of pterygoid; QD , quadrate; qd. tub, quadrate tubercle; QJ, quadratojugal; r.c.gr, groove for rectus capitis muscle; r.c. pkt, pocket for rectus capitis muscle; retr. pr, retroarticular process; SANG , surangular; sang. pr, surangular process; SMX, septomaxilla; SPH, sphenethmoid; sph. obl. r, oblique ridge of sphenethmoid; SQ , squamosal; sq. ds. l , descending lamina of squamosal; sq. qj. tr , squamosal-quadratojugal trough; ST, supratemporal; stp , stapes; stp. a. for, arterial foramen of stapes; stp. fpl, footplate of stapes; stp. a.v. pr, antero-ventral process of stapes; stp. fac, stapedial facet; stp. gr, stapedial groove ; stp. lpt, stapedial lappet; stp. rgs, stapedial ridges; stp. tub, stapedial tuberosity; stp. p.v.pr, postero-ventral process of stapes; sub. f , subtemporal fossa; sub. ot. emb , sub otic embayment; sub. s, suborbital sulcus; sul. int, sulcus intercristatus; sup. s, supraorbital sulcus; supr. sp, supraoccipital space; symph. tsk , symphysial tusk; T, tabular; t. cr. ext, crista tabularis externa; t. cr. t, crista terminalis of tabular; t. med, torus medialis ; t. occ. fl ; occipital flange of tabular; trans.v. teeth , transvomerine teeth; troch. gr, trochlear groove; tym. cav , tympanic cavity; V, vomer; v. for , vagal foramen; v. tsk , vomer tusks; v. fs, vagal fissure; vn. grt.s, groove in ventral surface of stapes.

79 APPENDIX 2: MEASUREMENTS FOR INDICES:

1) Preorbital index: b/a x 100 2) Postorbital index: c/a x 100 3) Parietal foramen position relative to orbits: d/c x 100 4) Lacrimal posterior termination relative to orbits: e/f x 100

80