89
Palaeont. afr., 18, 89- 131 (1975)
THE MORPHOLOGY AND RELATIONSHIPS OF YOUNGINA CAPENSIS BROOM AND PROLACERTA BROOMI PARRINGTON
by C. E. Gow
ABSTRACT
Comprchcnsive descriptions o f the osteology of Youngina capensis Broom and Prolacerla broomi P
CONTENTS Page INTRODUCTION .... 89 YOUNG INA M INTRODUCTION are notas generalised as has until now been believed. The Eosuchia are an order within the Subclass The Permian eosuchians, typified by Youngina, are Lepidosauria and in the light ofthe present study must generally considered the hub oflater diapsid reptilian be added to Romer's (1956 ) otherwise satisfactory diversification (e .g. Romer, 1956 ). definition that dorsal dermal armour was present. The Youngina is relatively poorly known ; thus part of the genera comprising Romer's family Younginidae are a present study will describe the anatomy of this animal reasonably homogeneous group, with the exception in detail. To begin with it will be necessary to decide of Noteosuchus, which shows rhynchocephalian af just what we mean by Eosuchia and to try to decide finities (Carroll, pers. com.). Of the rest the best what is to be understood as comprising the genus material in existence is that of Youngina (with its tax You ngina. Here it is necessary to be very explicit as it is onomic variants), and these with their smooth peg becoming clear that the Upper Permian was a crucial like marginal dentition can be distinguished from period in sauropsid evolution and that relationships H eleosaurus (Carroll, in press) which has serrated 90 marginal dentition and certain other features which Material referable to Youngina capensis Broom 1914. put it more closely in line with the Archosaurs. A.M. N.H. 5561: Younginacapensis Broom 1914. Skull Broom (1914 et seq.) was responsible for the three and vertebrae, in American Museum of Natural generic and five specific names with which what is History. mani festly one form (Youngina capensis) is presently en Locality: New Bethesda, Graaff- Reinet. cumbered. This string of names is misleading; all the Collected: R. Broom. specimens come from the same horizon, differing only u.c. 1528: Youngoides romeri Olson and Broom 1937. in size, state of preservation and preparation, and Skull in University of Chicago. nature of deformation, which factors adequately ac Locality:Towerwater, Murraysburg. count for all supposed taxonomic differences. One R. C. 90: Y oungopsis rubidgei Broom and Robinson can have no doubts about synonymising them all un 1948. Very good skull. der Youngina capensis to stress the probability that this Locality: Doornkloof, Graaff- Reinet. was a single monospecific genus. This work will pre Collected:J. W. Kitching, 1939. sent a detailed description of this animal based on all R. C. 91: Youngoides minor Broomand Robinson 1948. useful material. A poor partial skull. A second undescribed Pro lacerta (Parrington, 1935), on the basis of its in specimen with the same number is also Youngina. complete lower temporal bar, has been considered to Locality: New Bethesda, Graaff- Reinet. represent a stage between the Eosuchia and the Collected: Kitching Bros., 1940. Squamata, but this concept must be reject~d. Acritical T.M. 1490: Youngopsis kitchingi Broom 1937. A very re-examination of the true position of Prolacerta is poor skull. necessary. Until now Pro lacerta (which includes Pricea) Locality: New Bethesda, Graaff- Reinet. has been known from a few skulls and some cervical Collected:J. W. Kitching. vertebrae. Largely on the basis ofan incomplete lower T.M. 200: Younginacapensis Broom 1922. Fragments of temporal bar it has been regarded as ancestral to the postcranial skeleton, now even fewer than when Squamata. The present study describes the whole described by Broom, but certainly ofYoung ina. skeleton and the animal is shown to be Archosaurian Locality: New Bethesda, Graaff- Reinet. in almost every respect. Collected: I. Venter, circa 1920. The braincase ofProterosuchus is here re-described in T.M. 3603: Posterior half of a large skull, now acid some detail for comparative purposes. prepared. No catalogue data. R. C. 625 and 626: Two poorly preserved skulls. YOUNGINA Locality : Well wood , Graaff- Reinet. Collected: S. H. Rubidge, 1936 -45. MATERIAL AND METHODS R.C. 714: Incomplete skull. The descriptions of Youngina are based on Locality: Ganora, New Bethesda, Graaff-Reinet. material in the Bernard Price Institute (BPI) and one Collected: S. H. Rubidge, 1940. partial skull from the Transvaal Museum (TM). The K. 106: Badly flattened skull in the collections of the several specimens in the Rubidge Collection (RC) Geological Survey, Pretoria. - were examined. Professor Crompton kindly provid Locality: Blaaukranz. ed copies of his unpublished drawings of Youngina Collected: A. W. Keyser. rubidgei; these, though useful, have not been used B.P.1.375:Skull. here, and there are one or two points where we Locality: von der Waltzhoek, Graaff- Reinet. differ. These points of difference are those which it Collected:J. W. Kitching, 1946. has been possible to prepare more fully. A cast and B.P.1.2459: Small flattened partial skull. photographs of the Chicago specimen (Youngoides Locality: Klipplaat, Richmond. romeri ) were made available to the author. Collected:J. W. Kitching, 1951. All Youngina material comes from the Dap B.P.1.2871 : Skull. tocephalus zone of the Karroo. The state of preserva tion is rather different from that of the millerettids Locality: Beeldhouersfontein, Murraysburg. (Gow, 1972) of the same age, which might imply Collected:J. W. Kitching, 1958. some ecological differences in life. While the B. P.1. 2859: Skull and skeleton. millercttids are articulated and distortion free, the Locality: Doornplaas, Graaff- Reinet. younginids are disarticulated and the skulls are dis Collected:J. W. Kitching, 1964. torted. Most of the Youngina material has in the past been OSTEOLOGY OF YOUNGINA subjected to mechanical preparation which had caused some damage and also restricted the scope of The Skull further work. Fortunately it was possible to prepare Dnma/ bonf'1 of the skull roof a good braincase and skeleton in formic acid; other details were pieced together from mechanical PTf'1llaxil/a (Figures 1 and 6). The premaxilla is preparation of selected areas of different skulls. fairly well represented only in B.P.I. 2871. There 91 N ------t. 2cm Figure I. Youngina capensis B.P.I. 287 J. appear to have been three premaxillary teeth. The Parietal (Figures 2, 4, 5 and 6). The parietals enclose a important feature of the premaxilla is its medial ex large pineal opening and send out posterolaterally tent in the palate: the premaxillae run well back in directed wings. The area bordering the upper tem side the maxillae in a strong contact and meet in the poral opening is deep and has a shallow pocket in the midline. posterior corner affording a strong area of origin for Maxilla (Most Figures). The maxilla sheaths most of the part of the jaw adductor muscle complex. The wings slender, rather shallow snout, and has an extensive are joined by a slight ridge between skull table and oc contact with the palatine. The teeth are conical, sharply ciput. Each lateral wing forms important at pointed and not serrated; they thicken lingually at the tachments; anteriorly there is an extensive firm con base much as described for Milleretta (Cow , 1972); they are tact with the squamosal (Figures 4 and 6): applied to sub-thecodont and become firmly ankylosed in deep pi ts. the posterior surface are a post-parietal and tabular, An exact count is not possible but there are about30 tooth while the tip is sheathed by a supratemporal whose ex positions with alternate replacement so that one gets a act relationships will be discussed separately. The count of about 20 functional teeth of different ages. An lateral wings roof large post-temporal fossae and important aspect of the maxillary tooth row is that it there is no firm contactwith the supraoccipital. extends back to below the postorbital bar (c.f. Postfrontal. The postfrontal is firmly sutured Proterosuchus Cruickshank, 1972, and crocodilians, but between frontal and postorbital. not lizards) . Postorbital. The postorbital is overlapped above by SeptomaxiLla. Detailsofthis bone are totally lacking. the post-frontal (this region, the anterior border of Nasal (Figures 1 and 6). The relationships of the th e upper temporal opening, is deep); ventrally it has a nasals are clear except anteriorly where there is some rigid sloping contact with the jugal, and posteriorly a doubt as to the exact position of the sutures with the broad flat sheet has an extensive overlap onto th e premaxillae, but this is oflittle consequence. squamosal. Lacrimal (Figures 1 and 6). The lateral exposure of Jugal (Figures 2, 5 and 6). This is a straightforward the lacrimal is reduced to a short distance in front of elementhavinga longslopingcontactwith the maxilla the orbit. A single foramen runs the full antorbital ex and short rigid connections with post-orbital and tent of the bone (as seen in section in R. C. 625 ). quadratojugal. Where it forms the anterior border of . Prefrontal. As figured, requires no special descrip the lower temporal opening there is a distinctive tIO n. depression (indicated in Figure 6, lateral view). Inter Frontal (Figures 2 and 6). The frontals are the only nally the jugal has the ectopterygoid abutting against .skull roofing elements which have roughened sur it. It has not been possible to expose the inner surface faces, notably between the postfrontals and above the ofthis region ofthe jugal. orbits. The frontals are rigidly sutured to theparietals. Q.uadratojugal (Figures 2 and 6). This is an element 92 A B c lCffi _ C ___",2iij l'::ffi====-_ . BPI. 3859. FIgur. e 2 . Youngma. capenslS. . tvIX N L --+:177/r-.. ! PRF :J--v \ F PTGD PO PSP P PP ST -~~'/I SQ 2cm FIgure. 3 . Youngma. capensls . B ...PI375. 93 (A) (C) (0) pp T SO ST par. proc. SQ EO Q q.ra. pt. 2cm Figure 4. Youngina capensis T.M. 3603. A, Dorsal ; B, Ventral; C, Occipital ; D, Internal detail of frontoparietal region. critical to phylogenetic discussion. The contact with Sclera. These are present in B.P. I. 2871 and suggesta the jugal presents no problem; itis the relationships to ring of ± 12 flat plates. squamosal and quadrate which are important. With The palate. The palate of Youngina has to date been B. P. I. 3859 (Figure 2) it was possible to remove part of poorly known and imaginatively drawn. Olson's the squamosal to reveal the full extent of the (1936) reconstruction is poor and has been used by quadratojugal beneath it. T.M. 3603 provides a check Romer (1956): in this, the anterior ofthe palate is quite in that the upper two-thirds of the inner surface of the wrong as is the epipterygoid stuck in the basal articula squamosal are clean and there is no sign of any dorsal tion. continuation of the quadratojugal. Unfortunately no Vomer (Fi gures 2 and 6). The vomers are fused in specimen shows the contact of quadrate and the midline. Anteriorly they disappear above the quadratojugal. palatal extensions of the premaxillae which are also Squamosal (Figures 2, 4, 5 and 6). The squamosal united in the m idline. Relationships with palatine overlies part of the quadratojugal below, then rises up and pterygoid are clear. Median and lateral borders in contact with the quadrate, finally turning inwards to of each vomer bear a row of small teeth: the median cap the quadrate, running under a facet of the post row divides into two along the posterior third of its orbital and lapping against the parietal wing. length . Medial to the tooth rows where the vomers Postparie tal, Tabular and Supratemporal (Figures 4, 5 meet they are upturned to form what in palatal view and 6). There is reasonable certainty regarding the is a narrow smoothly rounded trough. There are presence of these three elements. Postparietal and two or three larger teeth grouped at the tip of each tabular are simply applied against the back of the vo mer. parietal. The supratemporal on the other hand is more Palatine (Fi gure 2). The relationships of the complex; it lies against the back of the parietal wing palatine are clear; it bears four rows of teeth, one a and extends beyond its tip, turning down and continuation of the lateral row on the vomer, the forwards to form a hook which lies against the top of others of corresponding rows on the palatine. The the pterygoid flange of the quadrate. This hooked foot in contact with the maxilla projects downwards supratemporal possibly supported a cartilaginous somewhat from the level of the palate. pad which could rotate against the paroccipital EctojJter.Yf!,oid (Figures 2 and 6). The ectopterygoid process. overlaps onto the palatal surface of the pterygoid, 94 extending well down the pterygoid flange. This ele POF ment is poorly known in more primitive reptiles, but by analogy with Millerettids it appears that the in fraorbital fenestra in Youngina is formed by reduc tion of the ectopterygoid. The extent of the surface abutting against the jugal is not clear. pterygoid (Figures 2, 3, 4, 5 and 6). The palatal por tion of the pterygoid bears a double row ofteeth on the mesial edge continuous with a double row on the vomer. Three rows of teeth fan out from near the basal 2cm articulation and continue onto the palatine. The (D) (El strongly down-turned flange of the pterygoid bears a row of 6 or 7 robust teeth. The articulation with the basisphenoid is freely movable. The quadrate ramus of the pterygoid is a rigid triradiate structure with its edges directed laterally, mesially and dorsally, enclos ing a dorso-mesial depression (for the protractor pterygoideus). There is a considerable overlap between pterygoid and quadrate, and a marked sup portingridge on the quadrate. The palatoquadrate Epipterygoid (Figure 5 E). Both epipterygoids are par tially exposed in T.M. 3603. The upper portio!, of the lcm shaft is missing; there is no sign of an attachment area on the parietal. A broad footplate rests on the pterygoid very much as illustrated for Milleretta (Cow, 1972, Figure 8) and, by analogy, probably caps the basal articulation. Figure 5. Youngina capensis T.M. 3603. A, Lateral view; B. Mesial Quadrate (Figures 3, 4, 5 and 6). The quadrate isheld view of quadrate and cheek region; C, Saggital section laterally and dorsally by the squamosal and internally through braincase; D, Braincase dorsal view; E, by parietal and supratemporal above and the Braincase lateral view. pterygoid below. Anteriorly it is braced by the quadratojugal. l'his is a rigid system. The pterygoid specimen), so that the prootic appears susp~nded ramus is a tall flat sheet. The ridge supporting the from astrong suture with the supraoccipital whileven quadrate ramus of the pterygoid extends to the back of trally it rests on the basisphenoid. The system of inner the quadrate, as is clear from Figures 3, 5 and 6; lateral ear canals converging at the fenestra ovalis from to this and sloping in from the back of the outer con supraoccipital, opisthosthotic and prootic is well dis dyle is an abrupt depression. The stapes would have played in the specimen. passed across this region. As is plain from the Basisphenoid (Figures 3, 4, 5 and 6). Basisphenoid reconstructed lateral view the quadrate is held ver material is poor. The nature of the basipterygoid ticallyand the term "otic notch" hardlyapplies. processes is clear and the articulation possible here is very similar to that described for millerettids (Cow, The braincase (Figure 5) 1972); the low clinoid processes too are very similar. Supraoccipital. The relationships of this element are Parasphenoid (Figures 3, 4, 5 and 6). The largely evident from the figures. The supraoccip~al parasphenoid is edentulous. It overlaps the basioc runs in under the parietals, this area being bridged by cipital extensively and has a pronounced semicircular the postparietals. The bone slopes obliquely down lip posteroventrally (seen in section in Figure 5 C). and backwards. Stapes (Figure 6). The stapes is a thin rod pierced Opisthotic. The structure and relationships of the near the proximal end by a stapedial foramen. The opisthotic are clear from the figures. The point to note foramen is bounded by an extremely thin bridge here is that the paroccipital process articulates in a which is bowed slightly outwards; such a foramen pocket formed by the supratemporal (Figure 5 E). could well disappear in later forms. Exoccipitals and Basioccipital (Figures 4, 5 and 6). These form a fused unit. The exoccipitals almost meet The lower jaw (Figure 6) above the foramen magnum behind the supraoc There is no good lower jaw material: the region of cipital. The overlap between parasphenoid and the retroarticular process is eroded off in all basioccipital is clear from Figure 5 C. specimens. The tooth~bearing rami are rather slender Prootic (Figure 5C, 0 and E). The region of the while the region of the adductor fossa is considerably fenestra ovalis is poorly ossified (and this is a large deeper. .. ". . ." ." -." .. - ' - •• "; 0" . . 95 · PMX ...... ". ". '. . . . . " , .' . . . -H>--' ...... · MX . II---~-' . MX··.. ----f. . -- - . " . . " , .. :. ~,,-'r'---,-,-, PRF .' '. POF P . ,.". Figure 6. Youngina capensis . Composite skull reconstruction. ThepostcranialskeletonOfYOUNGINA . The first sacral is missing; in the second the ribs are The skeleton ofB.P:1. 2859 was jumbled together in directed forwards and the distal ends. bifurcate, the a tight bundle behind the skufl and part of it had more anterior branch articulating with the iliumand already rotted away. Before acid preparation could the posterior branch forming a continuation of the commence the skull which had been extensively caudal transverse processes and a site of attachment mechanically prepared had to be removed along a for caudal musculature. The caudal vertebrae with natural joint. The forelimb too was prepared their strong transverse processes and deep haemaL mechanically and removed. The remainder was then arches indicate a deep ' and powerful tail. A small. disentangled by the repeated use of formic acid. The number of symmetrical middorsal scines are preserv skeleton comprises a nearly complete set of presacral . ed (Figure 8), sufficient to indicate that there was one to vertebrae apparently lacking only the atlas, axis and each vertebra but there is no indication as to the extent first sacral. The second sacral and first caudal are at ofthe row. tached and there are two other caudals and two haemal arches (thought absent by Broom, 1922). Girdles and limbs (Figures 9and 31) There are several plates of middorsal armour. There The pectoral girdle comprises a T-shaped In are several ribs. All elements of both girdles are terclavicle (with anteroventral notches for the represented. The left forelimb is complete, also the clavicles), and a scapulocoracoid anteriorly notched right humerus. The left femur and the proximal end of to leave a gap between it and the clavicle. The ends of the tibia and a presumed fourth metatarsal are all that the humerus are rotated at 900 to each other. There is remain of the hind limb. Thus it is only the hind limb an entepicondylar foramen and a pronounced which is incomplete. ectepicondylar groove. Radius and ulna require no additional description. The wrist is practically intact: Vertebrae (Figure 7) and ribs there is a large ulnare and a rather small radiale, an in The neural arches are broad and flat with moderate termedium, lateral and medial centrales, and five dis ly tall spines. The zygapophyses are horizontal, the tal carpals. The digits are complete and bear powerful, transverse processes are pronounced, slanted, and laterally compressed, curved claws. The pelvic girdle is have facets for single rib heads. The centra are rather similar to that ofHowesia(Broom, 1906). The il amphicoelous and notochordal and invisibly fused to ium has a short, almost vertical blade, the pubis a the neural arches. Intercentra are present. pronounced thickened outturned antero-ventral 96 (A) lcm (el OJ . "... .: .:.. ;; (F 1 (Gl (E 1 Figure 7. Youngina capensis B.P.1. 3859. A, Cervical vertebra; B, Anterior dorsal vertebra; C, Se cond sacral and first caudal vertebrae; D, Proximal caudal vertebra; E, Proximal haemal arch; F, Distal caudal vertebra; G, Distal haemal arch. (Cross hatching of neural spines and articular facets does not indicate damaged surfaces.) 97 (8) - lcm \lI 2cm I I I I '. .... ",: )~:;;: .. .' .'. ' ---' \!%).< : ... '\. I I 1!f!rI I Figure 8. Youngina capensis B.P.I. 3859. Mid-dorsal scutes. "\ I " process, and the ischium extends well back. The Figure 9. Youngina capensis B.P.!' 3859. A, Left forelimb ; B, Femur, tibia and fourth metatarsal in anterior view; proximal and to acetabulum is confined the ilium. The notch distal ends of femur; C, Right aspect of pectoral girdle; D, between pubis and ischium would, according to Ri ght pelvic girdle. Romer (1956, p. 318), indicate incomplete ossification and notan incipient thyroid fenestra. The femur is primitive, though with a marked cur impression are the apparently unspecialised terminal ~a ture which seems natural. The tibia is unfortunately nares. Incomplete. There is a single metatarsal which is Broom (1922) figured the humerus and tibia of almost certainly the fourth. Youngina; combining measurements from these with The following are the limb element measurements data available from the present study we can conclude In mm: with a fair degree of certainty that the tibia was shorter Humerus 23 than the femur, but not dramatically so-this points Ulna 16 Radius 18 towards a terrestrial quadrupedal existence. Femur 34 The tail is important, but as the interpretation oftail The skeletal fragments described by Broom (1922) function is important with Prolacerta as well, and as this were alm Scm ' . -.' Figure 10 .. Youngina capensis. ·Reconstruction of the skeleton. parisoris we find .that in Sphenodonthe chevrons are YOUNGINARELATIONSHIPS substantial but balanced . by tall neural spines. While the skull of Youngina is essentially Permian Something dosely approaching the Youngina condi (braincase, palatal dentitiOn} it exhibits certain ad tion is seen in one of our local lizards, Cordylus vances which foreshadow the Triassic early thecodont giganteus , a fairly large spiky armoured lizard of the grade (considerable palatal .extent of premaxillae, grassveld. Pairs live in burrows of their own making, suborbital vacuity, and slender stapes). This should and judging by the even distribution of burrows are not be construed to imply a direct relationship strongly territorial. In this animal neural spines·are between Youngina and a possible Prolerosuchus-Prolacer very poorly developed throughout and the chevrons ta ancestor. These are simply time grades of reptilian are comparable iii size to those of Young ina. This evolution, and while it is useful to know what the similarity of tail structure, however, may be just that "Eosuchian" skull looks like there are other small lit and no more, anditis interestingthatSphenodonandC. tie known U . .Permian eosuchians which rria y prove to giganteuswhich have moreor less the same way oflife in be more directly· on specific lines to the Triassic several respects should have such different tails. C. Thecodonts (e .g.Hel eosaurus) . giganteus would probably fare poorly as a swimmer. One must concede that the diapsid upper temporal This may be a case where it is not possible roexplain opening is a rigid distinctive feature shared by the observed differences in functional terms. Youngina and its kin plus all later diapsids. The one It should be noted that in swimming reptiles (e.g. serious drawback to Youngina as a thecodont ancestor crocodiles, monitors) the distal caudal vertebrae have is in the structure and relationships of the quadrato tall neural spines which balance longchevrons in sup jugal. Both the tall "archosaurian" quadratojugal ot porting a flattened, moreor less symmetrical, tail. e.g. Proterosuchus and the small articulating slip of a There can be little doubt that Youngina was a bone inProlacerta are readily derivable from the sort of terrestrial animal. Girdle measurements relating to condition seen in millerettids (Gow, 1972, Figures 8 body sections are given in Table 1. and 22 ) but not from the arrangement in Youngina. Table I . " . Crocodylus Youngina Sphenodon Chamaeleo Prolace rta niloticus capensis punctatus dilepis parringtoni Measurements in mm. Intergleno id width IGW 241 28 34 II 32 Interacetabula r width lAW 127 19 28 9 30 P",o" 1 } girdle depth 17 8 18 33 18 50 Pe lvi c girdle depth Taken together as girdle depth GO 17 8 22 34 16 46 Rati os IGW : IAW 2 :1 3 :2 1:1 1 :1 1:1 IGW :GD 4 :3 3 :2 1 :1 1 :2 3 :5 IAW :GD 2:3 1 :1 1 :1 1 :2 3 :5 Bo dy Shape Do rsoventra II y Round La tera ll y compressed bodied compressed 99 ' . This is notto suggest arelatio'nship between milleret- ·.· . has undescribed material. of equivaleni:;ige. collecred tids and thecodonts. Thisquadratojugalobjection . by Kitchirig. in Antarctica.l Pro[acerta.broomfwasfirsr does not (lpply to-rhynchocephalian derivation from ' described ' by Pairing-ton .' inT935. parr-jng-ton' s . Youngina, but it does rejecra too Close relationship specimen lacks ,the posterior spur of t~ejug ...... • -.; .. - ~ .. 100 jaws with a saw cut between upper and lower teeth and maxilla which is extremely thin walled. so to prepare mechanically the anterior of the Marginal dentition (Figures 13, 13A and 32). It is es palate- notably the premaxillae and tips of the sential that the marginal dentition be described in vomers. This material then yields the complete os full detail. Thecodont teeth are known in only one teology ofProlacerta. group of lizards, the Cretaceous mosasaurs (Ed mund, 1967; Russel, D. A., 1967) : these teeth are OSTEO LO GY O F PROLACERTA distinguished by having enamel-coated crowns one The skull third the length of the dentine base; resorption pits Though the fo llowing description refers to B.P.1. affect the tooth base and the adjoining bone and 2675, points of difference with the interpretations of arise in the posterior half of the lingual surface of other workers are noted. the tooth. Dermal bones ofthe skull roof By contrast the teeth of Prolacerta appear entirely Premaxilla (Figures 11 and 12 ). In lateral aspect the coated by enamel and are held in deep alveoli by bone premaxilla is somewhat downturned. There appear to of attachment; resorption pits are medially situated in be five tooth positions. The premaxillae extend back the lingual base of each tooth, and do not affect the beyond the tips of the maxillae in the palate and unite adjoining bone of the mandible. In Figure 32A the in the midline beneath the ti ps of the vomers. g:oove for the dental lamina can be seen clearly, M axilla (Figures 11, 12, 13, 13A and 32 ). Figure 13 Figure 13A supplements the photographs, giving the clearly shows the structure of the maxilla with its pattern of resorption pits and replacement teeth. thickened tooth-bearing margin dropping away inter Among known dentitions this is typical only of the nally to an extremely delicate vertical sheet with inter Archosauria. nal thickening behind the nasal capsule. The maxilla is Nasal (Figures 11 and 14). Little can be added to excluded from the nasal opening by the premaxilla. ~amp's description. The nasal is overlapped con There are 25 ( + 2?) maxillary tooth positions and ac Siderably by the maxilla . A clear suture with the tive alternate replacement. The thecodont teeth are frontal is seen in Figure 14A. laterally compressed, with sharp unserrated edges Lacrimal (Figures 11 and 12). The lacrimal is ex and are recurved ; they are deep rooted, extending the posed as a narrow strip on the side of the snout. full depth of the thickened alveolar portion of the There are two lacrimal foramina as indicated. PMX MX :..+,....;-q- --- N 2cm roo psp. ------t'; 1.'P.fr---- PRF J'~a---- L PAL F EPT POF PTGD PO PSP P Q SQ ST Figure II . Prolacerta broomi B.P.I. 2675 . Skull in palatal.and dorsal views . lOl QJ 2cm Figure 12 . Prolacerta broomi B.P.1. 2675. Skull in lateral and occipital views. ~--- ... , , , ~~-~" -\ .. I ) ., I I . I , , ,...... __ ! . / I' I I / I \ ,. . \ ,/ , I ,/ , I / I . I' , . f I /. f . , / ./ E I I u I . I , . , '/ 0. " . / , ' 1 I ' ' . 1 I . / , . / . / " . , " . ,"'1' " I ' , " I ./ I ' . ' .. , I . '. ~'-'J' I , I I· ' 1 I '- ";:~ Figure 13 . Pro lacerta broomi B.P.1. 2675. Maxillae in external and internal aspects. ... '-' ~ . . . ,...... :- .., .. ' ...... 1 em '. '''<~''~ '~ ~ ;'-:'', -« ~ ! ., - __II::::!I __ . = .::JiI ..-=: ' ===i -' - . Figure 13A. PreJfQfltaLjFigure~ 11 .~ 12 aria ·.14J.·. ·Thisis :an exc . . ·.·Poslfront~1(FigUre~11, 12 and 14). This . li~s againsta .' tremdy thin walled eiernenfrirnming pan of the or~ .···.· suhstantialfacet fQrmedby frOhtaJand . parietal. .' .' .. bitand~arPjng r'o~nd ' ontcithe sI;lout;- .' •...... •... .' . '.' Posteriotly it has adeepcontact wi th ibe postorbital, ". Frontal (Fig~re 14}: The.t:elati6nships ofthefmn- which latter runs right up ::agairist 'the parietal" ex- . .ta~ar~clear . frQ[l1' the ' figure ~ supraOrqital thickening . chiding the postfrontal from thetemporal fossa. · . lsmdicated riYC; - ... ' . .. . .' ...... ;" ' ...•.•. " . Postorbital{Figures 12and15G). The contact with the Parietar . (Figure -14); S:P.L ·2675 is the . only postfrontal is describedabove. The vemraJprong in- Pro lacerta skullwi'th .' asubstantialpinealopening ' serts ina gnjove.inthejugal (Figures 15Hand I ), while ' midway along the . parietal suture;· in. the 'other -' ' the posterior tip is received into a depression on the desciibedspecirnensthere is no sign of this opening; -squamosal (Figure 15 i2:.) , . .' . .. .. this'mustbetakentobeavariablethaiacter. Dorsal- Jugal {Figures 12 and 15). The right jugal is present ly the_paiietalscutve ' laterally .over the · brai~ . area. intactwhich clears up all doubt regarding the extentof '. PosteroJateraIry . vertically . flattened wings . run out the· posteriorspur.Theportion rimming the orbit is and back, and these are connected in the occipital . substantial butthe spur and the area above it behind .. pio:nebY:I: thin bridgn,vhichslides' ciyerthe :s\.Ipraoc- . thepos torbi tal are extremely thin. . .'. . cipitaLThesupratemporalliesalongthe top 'of the . Quadratojugal (Figures 12 and 15). The quadrato pari.etalwing .,mdis heIdproximaUyin a small . jugal is a small bemand flattened rod articulating . notch: " '.' . - . between facets on the quadrate (Figure lSA) aild the · squam6~al (Figures ·15£ and F), with af6ramen-- " betweenitand thequadr<.lte. . . .' ..•.. '. .'. . . ,Squamo.s2zl(Figures 11,12 arid 15 ),Facetsforpostor- . bital and quadratojugalhave·alreadybeendescribed: Posteriorly thereisa mesiaUydirectedhemispherical . . . facet in .· which the head .ofthequadratearticulates . . · Above thisis a long concave facet which receives the paroccipital process; (this i~alm6st ventrallydirecte.d . ." . and It seems likely that squamosal; quadrate, and ' .. par-occipita:! process meetat this pOint-thisexplana tionlends perspective to Figure 15F), Thesquamosal is held againsttheparietalaridsupratemporal.by a,fifth facet· which is vertical and follows the curve of the ' .. supratemporal. '. '. '. '. . Supratemporal (Figures>: n, . 12 and - 14 ). The · supratemporal is a thin, cUrved Fad notched into the · top of the parietal wing and extending beyond it: it is exposed indorsaland 'occipitaLview but entirely · obscured laterally by the squamosal. '.' . . .' Sclera1platei Scleroti'cs are absent in this specimen. Camp gives acountonl~12 forhis; . . . .. ' ' . . Thepalate{Figures 11 ; 16and 17 ) '. '. '.' . '.' .' Vomer. The left varner is (omplete (Figure 16A) but . - .: wasi)'ing out ofpositiori.It bearsthreedistinctrows of· teeth .It is 'dear that the vomers would be . united . .-.. anteriorly for about half their length, - a~shown by : .. : lcm·· . Camp. Posteriorly the vomer 'slightlyoverlaps the _ ...... 0 ·.. . Fi gure 14 . Pfoldceri'abrl)omi B:P .1.2615 ~ Nasal s, frontalS ,parietals . . pterygoid and palatine; alsofiHing the' gap between .and supratemporaIS.A; Dorsal (inCludesprefronra1); the tips of these:eh ;ments (Camp illustrates a gap here '· 8 , Left latetal; C,Vemral; D,OtcipitaL . . . · butthisisimprcibablel. - '. _ .. : . . 103 P (El (Fl - --Icm (Hl :: ...... '.~ .. (() Fi'gure IS. Prolacerta broomi B.P.I.2675. A-D, Quadrate; A, Lateral; B, Mesial; C, Ventral ; D, Dorsal; E, Squamosal, quadrate and quadratojugal; F, Squamosal in internal aspect and quadratojugal; G, Postorbital; Hand J, Jugal ; J , K and L, Epipterygoid in lateral, mesial and ventral views. ,,'\ A B E Icm I,, I "V Figure 16. Pro lacerta broomi B.P.I. 2675. A, Vomer; B, Palatine; C, Palatine in lateral view; D, Dorsal view of palatine foot; E, Palatal extent of premaxilla. S.P . _ H 104 t\ I I I • , I Figure 17 . Proiacerta broomi B. P. I. 2675. Pterygoid and Ectopterygoid: palatal, dorsal, mesial and lateral views (last slightly rotated). Palatine. The mesial portion of the palatine is an ex directed obliquely posteriad. The quadrate ramus is tremely thin sheet; laterally the bone thickens and deeply concave on its mesial surface with a pit situated turns downwards, this thickened edge bearing a single anteriorly. The ornate margins of this process (Figure · row of teeth continuous with those of pterygoid and 17) are genuine. The area of origin of the pterygoman vomer. The foot of the palatine is applied against the dibularis is marked by a ridge on the inwardly sloping alveolar border of the maxilla and has a small dorsal lower portion ofthe quadrate ramus. process which rests on top of the alveolar ledge (Figure Epipterygoid. The lower half of each epipterygoid is 16B and D). Above this latter process is the palatine preserved. It is very similar to that of Youngina, in groove which transmits the maxillary artery and cluding a facet capping the basal articulation. Camp's superior alveolar nerve (Figure 16C)which then enter description and figure of a thin quadrate process is a foramen in the maxilla (Figure 13), branches also clearly an artifact. possibly running forward in a groove behind the alveolar ledge to enter the more anterior foramen. Quadrate (Figures 11, 12 and 15). The articular sur Ectopterygoid. Only part of the left ectopterygoid is face of the quadrate comprises inner and outer con present, the process abutting against the jugal having dyles with a facet above the outer condyle for attach been lost. However, this element is present in Camp's ment of the quadratojugal (Figure 15A). The specimen and well illustrated by him. It is also present pterygoid ramus is extensive, with a depressed area of in Crompton's specimen, whose drawing agrees with articulation with the pterygoid (Figure 15B). Figure that of Camp. This element overlaps the pterygoid 15 D indicates the areas of cartilaginous attachment to. from above (not from below as shown by Camp); it squamosal and paroccipital process. curves gently forward and outwards, continuing the The braincase (Figures 12 , 18, 19,34 and 35). edge of the pterygoid flange, and terminates in a sub Supraoccipital. The supraoccipital (Figure 18A-D) is stantial footincontactwith the jugal. broad, as in Youngina. There is no suggestion ofcontact pterygoid. The palatal portion of the pterygoid is ex with the parietals; post-temporal fossae were present. tremely thin, except where it turns up into a ridge Opisthotic. The opisthotic is firmly united to bordering the interpterygoid vacuity. On the mesial supraoccipital and prootic. Its ventral ramus borders border there is a continuous row of teeth, while from the foramen ovale anteriorly and the jugal foramen just anterior to the basal articulation a double row mesially: Above the jugal foramen is a facet for the runs towards those of the palatine; the flange is also reception of the exoccipital. The ventral ramus has a toothed. A notch on the lateral edge of the pterygoid loose mesial contact with a ventrally directed process receives the palatine. The articulation for the ofthe basioccipital. The paroccipital process is flatten basi pterygoid process is deep, hemicylindrical, and ed, as in Varanus, but meets the squamosal/quadrate 105 A lcm- -- B B ;;;;::::,.-5 o c l c m Figure 19. Prolacerta broomi B.P.1. 2675 . A, Lateral view of brain case ; B, Dorsal view of para-basispheno id; C, Ven D tral view of para-basisphenoid; D, Anterior view of para -basisphenoid. Before leaving the occiput it should be noted that Camp's ( 1945) reconstruction of this area is complete . '...... F ··· ... G lywrong. Robinson's (I 966 )is better, butthe tips ofth e • ... ,j, c\.. .• < paroccipital processes are out of position, the tops of ~ '!;, the exoccipitals are the wrong shape and do not meet, 8 . the top of the quadratojugal is shown touching the outer surface of the squamosal instead of the inner, Figure 18 . Prolacerta broomi B.P.1. 267 5. A - D, Supraoccipital, and the quadrate squamosal contact is too low. prootic and opisthotic; A, Dorsal ; B, Ventral; C, Prootic( Figures 18 and 19). The prootic has extensive Anterior; D, Posterior; E-G, Basi- and exoccipitals; E, Anterior; F, Posterior; G, Lateral; H, Dorsal (ex sutural contact with supraoccipital and opisthotic. occipital ring removed). The pila antotica contacts the dorsum sella of the basisphenOid and there is an additional ventral con tact with a delicate posterior ridge ofparasphenoid (cf. description ofProterosu chus braincase to follow). There joint more or less horizontally, and not vertically as is a deep trigeminal notch and a pronounced crista does that of Va ran us. prootica which continues on to the opisthotic; within, Exoccipital and basioccipital (Figure 18E-H). These the recess formed by the crista and somewhat elements are fused and they completely ring the posterior of the trigeminal notch is a small foramen foramen magnum. The braincase is difficult to assem for the facial (VII) nerve. This is the earliest known ble as so many joints involved cartilage, and this is par appearance of the crista prootica s.s. (see Youngina ) ticularly true of the basioccipital/parasphenoid which is particularly significant as a point of origin for relationship (Figure 11 ). These bones separated freely, the protractor pterygoideus . (Internal canals in sU{Jraoc though it seems the medial prong of the parasphenoid cipital, opisthotic and prootic are clearly dlspIay was applied beneath the basioccipital. The lateral ed-should comparison prove necessary.) Medial prongs of the parasphenoid, however, span the same to the crista prootica is a further depression above the width as the ventral tips of the opisthotics and it seems foramen ovale (involving prootic and opisthotic) for very likely that parasphenoid, basioccipital, and the anterior semicircular canal (Oelrich, 1956, p . 15 ). opisthotics were held together in cartilage at this Para/Basisphenoid (Figures 11 and 19 ). This element point, the basioccipital contributing reasonably dis is completely edentulous. The parasphenoid rostrum, crete basal tubera. V-shaped in cross section, extends a little farther 106 forward than the pterygoids. Posteromedially there is Between this point of contact and the alar process a light overlapping contact with the basioccipital, there is a sharp smooth edge of parasphenoid; bycon while posterolaterally a gap exists which, when closed trast the corresponding edge of the prootic is broad by cartilage, would connect basisphenoid and and channelled, indicating the presence of a connec opisthotic. Prominent basi pterygoid processes ting membranous sheet. (orientation Figure 190) correspond with deep Stapes (Figures 12 and 18). The stapes is a thin rod, pockets in the pterygoids already described. The vi the stapedial foramen having been lost. dian (parabasal) canal is a deep groove. Ceratobranchial. A long thin ceratobranchial I is The only foramina are those for the internal present - this has been described by Camp. carotids. The course of the abducens (VI) is marked by The lowerjaw (Figure 20). a groove on the posterior dorsal surface between alar The elements of the lower jaw, like those ofthe skull, process and dorsum sella. The alar process meets the are rather delicate. The Meckelian canal runs to the tip pila antotica, its lateral edge continuous with the crista of the dentary. There is a large Meckelian fossa on the prootica. Behind the dorsum sella the bony sheet lingual surface. The glenoid, with two distinct facets, (parasphenoid) is W-shaped in cross section, with tall was probably reinforced anteriorly by a wad of car lateral walls. tilage. The large broad retroarticular process bears The posterolateral extremities of the parasphertoid muscle attachment scars (pterygomandibularis). Twenty do not contact the ventral processes of the opisthotics seven tooth positions are indicated, the teeth being in the region where the sternohyoideus muscles would somewhat smaller than the maxillary teeth. The attach. This area would have been filled in by cartilage . symphysis is extremely light and was probably A distinctive ridge on the posterolateral wall of the movable. Therelationshipsofthe bones are clear from parasphenoid terminates in a knob which meets the the figures, though some notes are in order. The sur prootic below and in front of the lagena recess. angular contributes the lateral glenoid facet, and 2em (A) SA A~. ~ ·.• ·••• . ~·Zl$·~"J\bhl)~ SPL PR ART A Iem (8) - -- Figure 20. Prolacerta broomi B. P.1. 2675. A, Reconstructions ot the lower jaw; B, Dorsal view of posterior half of left ra ITIUS . 107 sends a projection mesially to contact the prearticular. Axial5keleton The angular, which forms the postero-ventral There are 26 presacral vertebrae, including border ofthe jaw, terminates beneath the glenoid. The proatlas, deeply amphicoelous but not notochordal. tip of the coronoid is barely raised above the dorsal sur There are two sacrals and a string of 13 proximal faceofthejaw. caudals plus several isolated more terminal caudals. The articular contributes the mesial glenoid facet; its Intercentra are present only as far back as between the recurved tip forms the site of attachment for the first two caudals, after which they are succeeded by depre550r mandibulari5. There is good evidence for a very long, flat haemal arches. The vertebrae are very tympanic crest on the lateral border. The chorda tym lightly constructed: there is no sign of separation pani/posterior condylar artery foramen is present. between centrum and neural arch; the centra are There is an incipient angular process. hollow with an intricate system of internal supporting The p05tcranial5keleton struts. The nearly complete articulated skeleton, B.P.1. Atla5 and axi5 (Figure 21). The atlas complex is 2676, lacks the first three cervicals and ofthe forelimbs primitive. The proatlas connects the atlas arch to the only the proximal ends of the humeri are present. exoccipital above the foramen magnum. The paired B. P. I. 2675 which contains the forelimbs and skull is atlas arch elements just meet in the midline anteriorly truncated anterior to the pelvis. The overlap between and rest on a large pleurocentrum. The atlas intercen these two specimens then is only in the vertebral trum articulates between the occipital condyle and the column and the scapulocoracoids. axis intercentrum. This gives the appearance of being It must be stated at the outset that scales in the a highly mobile joint. The axis has a long neural spine typical of this bone, and it has a facet for the first drawings are true for the smaller specimen C~.P.1. 2675) while the larger specimen has been reduced by cervical rib. 1I6th to bring it to the same size: this figure was arrived Cervical5 (Figure 21 , (7)). The following six vertebrae at by measuring the scapulocoracoids and this reduc may be termed cervicals; they are greatly elongated. tion produced a very good fit of the vertebrae. While The last three cervicals and first three dorsals have this appears to be satisfactory it is unfortunate that an thickened neural spines -clearly points ofattachment approximation was necessary, though the critical for important neck muscles. In the neck region proportions of the skeleton are ofa far greater order of capitular facets are all on the centra and do not involve magnitude than any error of scale which may have the intercentra. Rather long, slightly inclined resulted. zygapophyses would permit great freedom of move B. P. I. 4005 yielded additional information on the ment, both lateral and dorsoventral. hindlimb, and here there is no problem of equating Anterior dorsal5. A lateral ridge leading towards the size with undistorted tibiae for comparison. tubercular facet becomes increasingly pronounced Camp has described the first six cervical vertebrae posteriad until the first dorsal, which is characterized and suggested they might indicate aquatic habits-a by transverse processes with their leading edges almost significant remark in view of the close affinity of at right angles to the column (Figure 21, (l0)). The bipedal lizards for water (Neill, 1971). Prolacerta was length of the neural spines decreases to a minimum on clearly a bipedal runner with a large tail to counter 10 before picking up again over the back. This is also balance the weight of the body. That the head and neck the pointatwhich the rib facets start to merge, forming were highly manoeuvrable is shown by thickening of a continuous articular region. This process is com the tips of the neural spines in the shoulder region. plete by 15. Like the skull, the skeleton is extremely light, with P05terior dorsal5. Here there is a slight but distinct hollow limb bones, and centra thin walled but sup alternation in the length of the neural spines. By 19 ported by a delicate web of internal bony struts (there all trace of two rib facets has gone leaving a single is no sign of pneumatopores). The ankle and hooked circular facet (Figure 22, (21)). fifi:h metatarsal are similar to those of rhyncho Sacral5 (Figure 22). The narrow-necked transverse cephalians and Protero5uchu5, yet not much different processes (or pleurapophyses) widen into substantial from those ofEuparkeria. Intercentra are one primitive facets which touch and interlock slightly as shown. The character in an otherwise very advanced, typically transverse processes of the second sacral bifurcate into Triassic, skeleton. two functionally distinct processes; the anterior -The whole animal is so I closely comparable to process is thick and broad and abuts against the ilium. MacrocnemUJ (Peyer, 1937; Kuhn Schyder, 1962) as to The posterior process is thin and narrow and does not assure very close relationship. It seems ridiculous to touch the ilium; it in fact constitutes an additional think of these distinctive thecodonts as lizards: they caudal transverse process and would no doubt are yet another group which has dispensed with the strengthen the attachment of tail muscles, helping to lower temporal arcade. Glevo5auru5 hud50ni (Robinson, support and control the large powerful tail which is 1973) is an undoubted sphenodontid which has an in such an important organ to a bipedal lizard-like ::omplete lower temporal arcade. Clearly this feature animal. (This seems to be a rather different arrange evolved independently in squamates, thecodonts and ment from that described for Protero5uchu5 by rhynchocephalia. Cruickshank, though I am not convinced that the 108 1-3 7 10 15 2cm Figure 21. Prolacerta broomi B. P.1. 2675. Vertebrae as numbered. posterior process contacts the ilium as he has shown.) rather weak with expanded circular attachment facets, The beginnings of a Prolacerta-like condition can be shafts very slender proximally, expanding a little dis seen in Y oungina, and several modern lizards trend the tally. same way (Hoffsetter and Gasc, 1969, p.265). Caudals (Figures 22 and 27). The string of 13 prox Pectoral girdle andJorelimb (Figures 23 and 30). The imal caudals all have strong transverse processes scapulocoracoid is extremely delicate, particularly diminishing gradually in size in the same way as do the that portion of the scapula anterior to the shaded line neural spines and haemal arches. The chevron bones in the figure, which is paper thin. The posterior third or haemal arches are laterally compressed and of the suture between the two elements can be seen on anteroposteriorly broadened: they are extremely long the mesial surface. A coracoid foramen is present im (1t x the depth of the preceding vertebra). The enor mediately in frontof the screw-shaped glenoid. mously powerful tail indicated by the osteology Clavicles appear to elaborate with age (F is larger almost certainly relates purely to the animal's bipedal than G and therefore probably older, or possibly a mode oflocomotion and active feeding movements of male); unfortunately most of the medial shaft is miss the head and neck, though the possible importance of ing. The vertical shaft is grooved on the inner surface lateral threatdisplaycannot be overlooked. where it would lie against the scapula. A prominent Ribs (Figure 22 ). The cervical ribs have extremely anteriorly directed boss appears to form with age in slender shafts tapering to fine points; they have two the angle between the two shafts. distinct articular facets and an anterior dorsal process. The interclavicle is somewhat damaged though its Ribs 10 and 11 (in the pectoral region) are rather stout essential structure is clear-it has a narrow medial proximally; here the two rib heads have merged into a shaft and a broad crosspiece notched anteriorly and single articular facet. For the rest the ribs have slender with depressed facets on the ventral surface which shafts circular in section. From 19 to 26 the ribs are receive the clavicles. J09 21 2cm Figure 22. Pro lacerta broomi B.P.I. 2675. 21st Vertebra; Sacrum and two proximal caudals in lateral and ventral aspect; Ribs as numbered. The humerus is primitive and simple, though the trochanter, with intertrochanteric fossa, very much entepicondylar foramen has been lost; there is a deep restricted to the head. The shaft is devoid of muscle at ectepicondylar groove. tachment protruberances and scars. The tibia is large Radius and ulna are long and slender. The small and robust, particularly at the proximal articulation; wrist elements preserved are as shown, but as they are the distal end is concave and poorly ossified, somewhat disarticulated nothing definite can be said suggesting the involvement of cartilage at this point. regarding the missing elements. The phalangeal count The fibula is rather slender and is laterally com for the hand is the standard reptilian one. pressed. Pelvic girdle and hindlimb (Figures 24, 31 and 33 l. All The ankle comprises a proximal assemblage of the elements of the pelvic girdle have smoothly round astragalus and calcaneum in loose articulation with a ed margins. All three contribute to the acetabulum large foramen between them, and a centrale in firm which has no upper rim as such (though it is rimmed contact with the mesial surface ofthe astragalus. There anteriorly by a ridge angled towards the posterior tip are four distal elements of which the first three are of the iliac bladel-this could be to allow the femur to small and featureless while the fourth is large with a be raised rather high during bipedal locomotion. The lateral facet for the fifth metatarsal and a terminal facet pubo-ischiadic plate is broad; the central area is ex for the fourth; it lies in the junction between astragalus tremely thin. There is a thickened out-turned antero and calcaneum. ventral process of the pubis, with the obturator There is a standard phalangeal count of 2:3:4: foramen immediately behind it. Girdle measurements . 5 : 4. The fifth metatarsal is hooked with a ven relating to body sections are given in Table 1. p. 98. trolateral scar indicating the insertion of the gas The femur has marked posteriad curvature at the trocnemius. distal end. The head is concave and would thus have The astragalus has a large proximal facet which been capped by an epiphysis which would effectively receives the tibia; this is followed by a smooth narrow increase the length of the femur. There is an internal neck before a second facet at right angles to the first. 110 A B c F . ':.;-"',:,' : ' .• • 1 .J E G Figure 230 Prolacerta broomio (A - E and G, BoPoi. 2675; F, BoPoi. 2676 0) A, Scapulocoracoid; B, Humerus mesial view; C, Right forelimb ; D, Humerus in lateral view; E, Interclavi cle ventral view; F, Dorsal limb of clavicle, mesial and lateral views: G, Dorsal limb of clavicle, mesial and lateral viewso A c F ~ B H 2cm Figure 240 Prolacerta broomi BoPoi. 26760 A, Right pelvic girdle lateral aspect; B, Left pelvic girdle internal aspect; C - F, Left femur ; C, lateral view; D, Posterior view; E, Mesial view; F, Proximal end; G, Right hind limb flat; H, Ankle flexed o 111 The calcaneum below this is of equivalent thickness, the pituitary fossa. This sheet is continuous with the thinninga little from here towards its lateral edge. One dorsum sella; the exit for the VIth cranial nerve can be can thus envisage a mass ofcartilage here for reception clearly seen (Figure 26A) between them. This of the fibula. The astragalus bears a marked depres condition also occurs in Euparkeria. The sion in its dorsal surface as indicated. basisphenoid has several notable features. In lateral view Figure 24G shows the hind-foot in one plane while in H a natural positioning has been attempted with the so ankle flexed at the meso tarsal joint. al. pro pro. Some of the more important length measurements are as follows in mm: s:::::::2+-- OP V Skull (occipital condyle to snout) 67 7=-=------P a. Neck (condyle through ninth vertebra) 100 Vl----,~ ---al. pro bsp. Trunk (glenoid to acetabulum) 130 Femur 54 Tibia 58 ~--bpt.pr. Humerus 42 Radius . 37 (A) PROTEROSUCHUS BRAINCASE The braincase in B.P.1. 3993 (Figures 25, 26, 36 and 37) has suffered from the vertical compression which has affected the whole skull; no corrections have been made in the drawings except in Figure 26B bpt.pr. which has been restored to symmetry. V. C. p. pr. pro. al. pr pro. ~*---b.t. OP---ffl~ p.a. al. pro bsp. I-----BO Figure 26 . Proterosuchus vanhoepeni B.P.1. 3993, (Braincase); A, Anterior view; B, Ventral view. bpt. pro ------' CAl (Figure 25A) can be seen the prominent process com ing in behind the ventral process of the prootic; and thin bone behind it is folded inwards, as indicated also in Figure 25B. This arrangement floors the foramen ovale. The large postero-Iateral processes of the basisphenoid bearing the grooves of muscle attach f.m.--~ ment scars run out beyond and below the ventral processes of the opisthotics -this is indicated in BO----'i'~ Figure 25B, a somewhat oblique view. In ventral bt.-----'I aspect (Figure 26B) the basisphenoid runs anterior to and closely applied against the prominent basal tubera otthe basioccipital, while just anterior to this is (8) a deep depression. The open videan canals lie mesial to Figure 25 . Proterosuchus vanhoepeni B.P,1. 3993, (Braincase); A, the posterior edge of the basipterygoid processes, Lateral view; B, Somewhat oblique occipital view. while immediately in front of them are a pair of foramina (present also in Prolacerta) which possibly The prootic has an open trigeminal notch between transmitted a branch ofthe palatine artery. well developed alar process and pila antotica: it has a The ear region poses a problem. The foramen ovale long posterior process running along the paroccipital is very small. A stapes if present would have been process of the opisthotic. A distinct ventral process restricted to a channel between opisthotic and prootic meets the alar process ofthe basisphenoid; behind this and would thus have run obliquely backwards to the a second process from the basisphenoid contacts the head of the quadrate, indicating a tympanum in the prootic. Anteriorly the prootics are united position postulated by Ewer (1965) for Euparkeria. in the midline by a substantial sheet of bone, stretch There is in any case no room for the attachment of a ing from one pita antotica to the other, which roofs tympanum on the retro-articular process. 112 Palatine Cruickshank ( 1972) shows the palatine forming the entire lateral margin of the suborbital fenestra. In fact itonlyrunshalfwayback. (B.P.1. 3993 andP.fergusi.) Streptostyly Cruickshank suggested that the quadrate of Proterosuchus might be movable. This is clearly not possible in an animal with a solid lower temporal bar. Variations in the position of the quadrate are ap parently due solely to post-mortem distortion just as in Youngina . PROLACTERTA FUNCTION (a) Cranial kinesis. It is well known that most if not all predatory squamates have kinetic skills. These are generally speaking small animals which swallow their prey whole. Prolacerta, though not a squamate, is func tionally similar. A small, lightly built predator, it is the epitome of the sort of animal to which cranial kinesis is of advantage. In Prolacerta the skull can move in a ver tical plane relative to the braincase, pivoting on the paroccipital processes, the palate being guided by the basal articulations of the basisphenoid. The quadrate is free to move anteroposteriorly as a result of the loss of the lower temporal bar; this is the only accep table explanation for the retention of the quadrato jugal as a delicate strut articulating between squamosal and quadrate. (One can readily accept that slight refinement to the quadrate controlling mechanism in a more advanced form would render the quadratojugal superfluous, but there is no reason to believe that this type of quadratojugal mechanism formed part ofthe lizard evolutionary story.) Certain less obvious movements are also possible. These involve the jugal and postorbital, and may be connected with either streptostyly (fore and aft movements or quadrate spreading) or muzzle movements, or both. Some lateral movement of the postorbital along its vertical contact with the postfrontal would have been possible though slight. The postorbital! squamosal contact is loose and would allow free movement in anteroposterior and dorsoventral planes. The tongue and groove contact between postorbital and jugal would allow sliding movement, and itseems logical to assume a fair degree of the same sort of sliding at the long curving jugal-maxillary junc tion. The great reduction ofjugal and postorbital in re cent lizards and the loss of contact between them, as for example in Varanus, would suggest thatjugallpostorbital sliding is necessary in the early stages of the development ofmesokinesis. Movements at the upper extremities ofthe postorbital in Prolacerta might be related more to quadrate movements. Although there is no mesokinetic joint as such, yet the bones ofthe snout are extremely thin and the fenestrae exochoanis very long, so that muzzle flexure by actual bending of particularly the nasals almost certainly occurred. Figure 27 . Prolacerta broomi, Reconstruction of the skeleton. 113 It is interesting to note the movable joints present in BDrepresents the lowerjaw, hingingat B. lizard skulls (Frazzetta, 1962) which are not present in CF represents the extent of posteriad movement of Prolacerta. In all lizards which have a mesokinetic lower teeth relative to upper in an akinetic skull. (fronto-parietal) joint, the skull roofis broadest at the Protraction of the quadrate during jaw opening straight transverse fronto-parietal suture. In results in the tip of the jaw moving to position E. As millerosaurs, younginids and Prolacerta this marked the jaws close and the quadrate is retracted E moves broadening is lacking and the fronto-parietal suture is through an arc to C, as would D in an akinetic W -shaped, effectively preventing flexure at this point. system. In this context the keuhneosaurs are intermediate in Clearly the teeth and the bite force move upward morphology, though apparently not yet mesokinetic through an arc. Representing the bite force as a (Robinson, 1966). Associated with mesokinesis in chord on this arc it is clear that in the akinetic system lizards is antero-posterior movement of the this force CD has a forward as well as an upward pterygoids. This is reflected in a sliding basal articula component. In the kinetic system CE moves tion and a rod-like epipterygoid which pivots at both posteriad throughout the closing cycle. This cir ends. In Prolacerta there is no suggestion that the basal cumstance is governed by two variables, the angle of articulation is moving in this direction and the . the jaw opening e and the extent of protrusion DE. epipterygoid has an antero-posteriorly elongated e as used above is greater than any angle of jaw footplate which could not conceivably have pivoted. depression illustrated by Frazzetta, but it is still Relative movement between pterygoid and quadrate necessary to determine DE for live lizards to decide certainly occurred. whether natural movements fall within the limits set Slight spreading of the pterygoids and hence of the by these variables. It certainly seems plausible to quadrates and lower jaw rami is a possibility, but until suggest that there could be an advantage in having both the movements and their functional importance the teeth and the bite force directed backwards dur can be convincingly demonstrated in living lizards, ing jaw closing for an animal capturing active prey. there is no purpose served by discussion at this stage. It is surely more than coincidental too that ECD is Frazzetta (op. cit. ) has shown that the lizard quadrate the shape of a generalised carnivorous thecodont moves forward as the jaws open; it would thus be tooth. reasonable to assume that the same is true ofProlacerta. Compare the akinetic system (A) with the kinetic system Now while kinesis in Prolacerta is not as complexas that (8) p. 114 . In both the muscles contract from length ACto described by Frazzetta for lizards, there appears to be a length AE. In both a decreases to ~ . But, whereas in A the very simple explanation for quadrate protrusion. direction of pull shifts from AC to AE, in B AE and AC lie Upward movement of the skull on the braincase as the on the same line, with C moving to E as B moves to Bl. jaws open is slight, and any upward movement of the Note that in B quadrate retraction B B' = adductor whole head will not alter the fact that the lower jaws are shortening CE = degree of jaw protrusion D D'. As any dropped through a considerable arc relative to the up biological system can be expected to represent a com per. promise between conflicting ideals, B B' is probably too This means that without protrusion of the quadrate short to allow perfection ofsy stem B though the system yet the lower teeth move posteriad relative to the upper, holds considerable advantage by virtue of the extra and consequently move forward during the bite, as linkage and more nearly constant line ofaction ofthe ad shown in the following diagram. ductors. A Streptostyly seems to hold an irresistible fascination which has led to some curious statements in the literature. Some of these merit brief consideration. Walker (1961 ) suggested that the quadrate of Stagonolepis (a pseudosuchian) might have been movable and have played a part in that animal's shovel-snouted foraging mechanism. Ewer (1965) B suggested that some movement of the quadrate may have been possible in Euparkeria, a thecodont, and suggested the presence of an additional wholly un necessary and improbable protractor muscle at taching to the mesial surface of the quadrate ramus of the pterygoid, i.e. that portion which lines the throat. Cruickshank (1972 ) has suggested that the E Proterosuchus quadrate may _~ave been movable-this to account for the variaoility in the slope of the ABC represents the skull. The snout moves upwards quadrate exhibited by several skulls. The fact remains hinging at A. This movement is slight and for present that Proterosuchus has a solid lower temporal bar and purposes can be ignored. the quadrate always bears the same relationship to it; it 114 A B A o therefore seems more reasonable to attribute this relative lengths of femur and tibia: in a terrestrial variability to distortion of the specimens. It would be quadruped these are subequal in length, in aquatic unexpected to find a streptostylic quadrate in any animals the tibia is markedly shorter and in bipedal diapsid, as meaningful movement is only possible animals the tibia is the longer bone. Hence we can say once the lower temporal arcade has been breached as that Prolacerta, on the basis of limb proportion, was in Prolacerta. bipedal (at least at speed). This, however, is the only There is merit in Robinson's (1966 ) suggestion that immediately apparent indicator ofbipedality; there is the quadrate (of lizards) might rock back and forth no indication, particularly in the pelvic girdle, of sup during chewing movements thus aiding swallowing. porting modifications for this mode oflocomotion. Whether this is true of any lizards will require ex perimental determination. In particular it is necessary Looking for comparisons then we can look first at to determine what sequence of muscle actions is the lizards. Several lizards are known to adopt a responsible for quadrate retraction and to what extent bipedal stance and/or gait at times. This subject has these movements are independent ofjaw adduction. been well covered in a delightful chapter by Neill (b) The post cranial skeleton. It is no exaggeration to say (1971 ), whose main thesis it is that bipedality arose in that the combination of characters which make arboreal lizards as a predator confrontation and es up. the skeleton of Pro lacerta (a nd Macrocnemus) is cape mechanism and is only employed by them as unIque. such. The bipedal lizards are characterized by long This is a small, very light-boned animal, un slender tails which are important in counterbalancing questionably built for speed and/or agility. Limb dis the weight of the head and trunk during this rather un parity per se is a vague and misleading term. What is gainly gait (described by Snyder, 1949, 1954, 1962). important as a clue as to whether an animal was One aspect of this crude bipedal gait which has terrestrial quadrupedal, aquatic or bipedal, is the seemingly escaped notice is the rotation which occurs 115 at the foot in contact with the ground as the opposite of the locomotor musculature for bipedal locomotion limb is swung forward in stiff-legged fashion: this can it is quite likely that the main femoral retractor, the easily be seen in the scratch marks of the toe im caudiJemoralis longus, would be considerably enlarged pressions left by a basilisc chased across a damp clay in an animal of this size (the size limit of bipedal surface. This is worth recording for the implications it lizards). Femur morphology shows that the may have for ankle structure, though Prolacerta itself caudifemoralis inserted near its proximal end, an has a typical early thecodont ankle and itis remarkable arrangement which sacrifices power for speed. that very little osteological modification, limb dispari tyexcepted, is seen in the early stages ofbipedalism. The shape of caudal chevrons in reptiles is rather A disconcerting aspect of bipedal lizard variable; as this is an aspect largely ignored one can morphology from the point of view of this discussion find little help in the literature, but comparison with is that they all have short necks and trunks; however, the incipiently bipedal dinosaurs is striking, in that the we can immediately remark that perhaps the deep chevrons are rather large and ·lateraffy compressed-: rooted tail of Prolacerta is designed in part to while these prosauropods have long necks, there is not counteract the added weight of the long neck. There much skull weight to counterbalance, and in any case are at least two other factors to consider here. one cannot compare locomotion in early thecodonts Leaving the lizards for the moment it is pertinent at and dinosaurs too closely. It is instructive to note, this stage to introduce another tentative comparison. however, that inSaltoposuchus, a bipedal dinosaur with Both the long neck and the large flattened chevrons of large head and carnivorous dentition, the cervical Pro lacerta invite comparison with the incipiently vertebrae are extremely short. bipedal prosauropod dinosaurs. We are now at the stage where we can embark on A deep tail must inevitably raise the possibility of its detailed argument on the function of the Prolacerta being an adaptation to swimming. Fortunately that skeleton. To start with the tail. The bipedallizards have possibility is easy to discount in this case. In the long slender tails with rather insignificant chevrons; crocodile which is adapted to an aquatic existence the one aspect of the function of this tail has been chevrons are of more moderate size, narrow, and cir overlooked. While it is clear from Snyder's (op. cit.) cular in section; the tail is dorso-ventrally symmetrical drawings and photographs that the distal part of the with tall neural spines extending almost to the tip. In tail is flung out to counterbalance the body, itisequal Pro lacerta the neural spines become insignificant in the ly clear that the base of the tail is held in line with the distal half of the tail. In the extinct marine reptiles pelvis and both it and the trunk are thrown over to the caudal chevrons become very small and insignificant. same side as the limb executing the powerstroke. This A piece of circumstantial evidence against an aquatic probably ensures that the direction of pull of the existence is worth mention. Macrocnemus occurs in femoral retractors places the arc of travel of the femur association with a highly adapted aquatic fauna which in the required plane, and it also helps distribute the tends to underpin the non-aquatic nature of necessary weight over the sacral region (weight against M acrocnemus. which the limb is pushing). As far as the use ofthe tail as a counterbalance to the weigh t of the body is concern The long neck of Pro lacerta may account in part for ed this is something which requires further explana the extra weight at therootofthetail. The long neck isa tion as we are dealing with a state of dynamic typically thecodont specialisation common to equilibrium in which weight distribution clearly Proterosuchians, certain dinosaurs and birds. This is a changes considerably through the stride sequence. specialisation which considerably enhances the The above remarks serve to highlight the impor predatory capability of the animal. The thickened tance of the second sacral rib ofPro lacerta doubling as a neural spines at the base of the neck and in the pectoral caudal transverse process tending to lock the base of region are sites of attachment for powerful, quick the tail to the sacral region; this also suggests a reason acting muscles concerned with raising the head and for the impression of relative rigidity conveyed by the neck and wi th lateral movements. Pro lacerta chevrons (one may note by way of contrast that in the varanids which use their tails as lashes the With regard to the limbs and girdles the latter are chevrons are centrally situated on the centra, thus not extraordinarily primitive for such an advanced impeding flexure in anyway). animal, conveying no hint of the animal's obviously The caudal chevrons of Prolacerta, in proportion, rapid, often bipedal, gait. Though the hind limb is must beamongthe largest on record. Atthe base ofthe long with tibia longer than femur, yet it shares a tail they are 1,5 times as long as the depth of the primitive ankle pattern with Proterosuchus and preceding vertebra and this ratio gradually decreases rhynchocephalians. The hammate process of the fifth to unity. The only acceptable explanation for this is metatarsal shows no sign of turning inwards un that of concentrating the bulk of the muscle mass ven derneath as is the case in bipedal lizards (Snyder, trally at the proximal end of the tail. There is almost 1954). The forelimb is not reduced and probably func certainly more than a simple weight factor involved tioned during slow locomotion, basking (Figure 27 ) here; as the pelvis shows no evidence of improvement and tree climbing. 116 ECOLOGY mian and Triassic forms. Areoscelis merits attention as the only fairly well known protorosaurian. Possible environment and habits Relationship to Pro lacerta has been argued by Camp The Lystrosaurus zone presents many problems ofin (1945 ), Romer (1947) and Vaughn (1955). The only terpretation of ecology of its fauna. A regional striking parallel is in the elongation of the cervical sedimentological study is an essential prerequisite as a vertebrae, but this feature is common to several un framework in which to place the fauna, but this is as yet related groups. Areoscelis has in fact a curious specialis lacking. This is a zone notable for its omissions ; ed postcranial skeleton (e.g. the elongate limbs) there is, for instance, little evidence of vegetation. behind a primitive Skull-certainly not a good Another notable omission is the total absence offish to generalised ancestor. The double coracoid is another date, though these must have been present in an en point against it. vironment which supported labyrinthodonts. Of the One animal which must be revived in this discussion many invertebrates, including insects which must have is the Russian Permian M esenosaurus. Here is an animal been present, only millipedes have so far been record with powerful carnivorous dentition (mode of im ed. plantation unknown), a lower temporal opening with Considering its early thecodont ancestry it is pos lower temporal bar, several primitive characters such sible that sharp blade-Ilke teeth were the only option as the maxilla entering the external naris, which available to Prolacerta; these are small in relation to the should merit consideration with early thecodonts, but size of the skull, compared with the teeth of, for exam about which too little is known. ple, Euparkeria. (This applies as well to Proterosuchus. ) An early Permian diapsid is Mesosaurus, a curious, Unfortunately no living reptiles have comparable little known, highly specialised form, but which with dentitions with the possible exception of Varanus Petrolacosaurus stands as a caution that diapsid saurop komodoensis . Prolacerta might be envisaged as feeding on sids became established early on. Hopefully, the small prey which it would grab, kill, and swallow Brazilian material, reputedly of excellent potential, whole, such as the young of the many small synapsids, will yield a good account ofthis animal. procolophonids and labyrinthodonts known from the One arrives then at the Eosuchia, the millerosaurs, Lystrosaurus zone, as well as insects. It seems very likely younginids, rhynchocephalians (sphenodontids), that the prolacertids were replaced by true squamates and archosaurs (Thecodontia) for present (pleurodont) lizards. purposes, and the problem of relationships of these The rather larger Proterosuchus on the other hand groups. probably fed by tearing pieces of meat off a carcass The millerosaurs, which mayor may not have direct much as does Varanus komodoensis, as the teeth of these bearing on later phylogenies, nevertheless exhibit cer two animals are closely comparable in size relative to tain morphological details which are not shown by, for the skull, in shape, and in ' having finely serrated instance, the younginids but which go a long way to posterior edges. Prolacerta lacks serrations on the teeth explain the derivation of early fhecodont characters and as these are present in H eleosaurus and Proterosuchus (particularly one may mention the quadratojugal and they have presumably been secondarily lost in its relationships). Prolacerta. Among the younginids, Youngina as described Stealth more than agility would be required in hun above gives an apparently satisfactory rhyncho ting. Why then this light, swift creature? Presumably cephalian ancestor, but it is necessary to note here that no contemporaries could match Prolacerta for speed, all the known rhynchocephalians have basically though some Galesaurids and Therocephalians crushing dentitions and virtually akinetic skulls. would certainly have eaten them, given a chance. The H eleosaurus (to be described by Carroll) is a good most likely explanation is that it was to an extent ar thecodont ancestor with its blade-like marginal denti boreal-here lightness and agility are of advantage. tion and advanced femur indicating bipedality. This would support Neill's (op. cit. ) argument for a Much use has been made here of the term close link between an arboreal existence and the "thecodont" as Pro lacerta is so obviously a thecodont evolution ofbipedality (in animals ofthis size). while the squamates are typically acrodont or more commonly pleurodont (Edmund, 1969). This applies RELATIONSHIPS OF PROLACERTA to the earliest recognised true lizards, the Comparisons of all the possibly significant keuneosaurids, which are defined as having sub features' of Pro lacerta cover a very wide field indeed. pleurodont teeth. Some of them are rapidly discountable, most Paliguana, contemporaneous with Prolacerta, is a flounder on inadequate knowledge of many forms, poor specimen, yet it has very much the morphology but in the end the reasonable options are few and a and proportions of the keuneosaurids. One or two stable picture seems to emerge. probable lizard skeletons are known from the Permian Some of the earlier Permian diapsids should be of South Africa, of which Palaeagama (Broom, 1926 ) mentioned. Petrolacosaurus is a Pennsylvanian form has been described; unfortunately the temporal technically diapsid but remote in time and lacking the region is badly damaged. Carroll believes he can strong morphological features which link the late Per- reconstruct it to look much like the keuneosaurids. 117 The lizard-like animals mentioned in this paragraph astragalus intermedium when it is really a compoun are to be described by Carroll. There is thus some ding of intermedium and tibiale, and the centrale he evidence to suggest that the Squamata had evolved calls astragalus. Names aside, the feet ofProlacerta and before the end ofthe Permian, though more collecting Proterosuchus are identical down to the hooked fifth is needed to strengthen this. metatarsal. To place Pro lacerta then weare left with two options. The vertebral columns are very similar, though Detailed comparisons with primitive thecodonts Proterosuchus does not have such elongate cervicals. This prove instructive, as do comparisons to the similarity extends to the large blade-like caudal chevrons, Protorosauria (sensu Romer, 1956). Comparisons though these are only two-thirds the length in between Prolacerta and M acrqcnemus are so close there Proterosuchus . can be little doubt of a dose relationship. Other All the above gave sufficient grounds for expecting Protorosaurs are so poorly known that they cannot be to find an explanation for the braincase ofProla certa in drawn into this relationship with certainty. Proterosuchus. One may expect braincases to be fairly Proterosuchus (Cruickshank, 1972) is the one animal conservative at this level; also, while that of Prolacerta is close to Pro lacerta known in sufficient detail for poorly ossified in places, this is consistent with a lil?ht meaningful comparison. Much of the material has kinetic skull, while in the larger Proterosuchus the bram also been available to the writer when additional in case is well ossified. This comparison, detailed formation was required. Proterosuchus occurs con elsewhere, is so striking in every detail as to put the seal sistently lower in the Lystrosaurus zone than does ona very close relationship. Prolacerta, but this probably does no more than The quadratojugal may be one of the more impor reflect an ecological separation. Proterosuchus is a tant elements in deciding lizardlrhyncho larger, more heavily built, and quadrupedal animal, cephalian/archosaurian relationships. Gow (1972) while Prolacerta is small, light and bipedal. has described the relationships of this bone in Proterosuchus has an antorbital fenestra which puts it millerosaurs in detail, and this pattern could veryeasi among the Archosauria, but Cruickshank has ly give rise to what we see in Prolacerta and Proterosuchus suggested with some justification the derivation of and the later archosaurs, e.g. Euparkeria (Ewer, 1965) Proterosuchus from a "rhynchocephalian" ancestor; where the quadratojugal rests on a facet on the lateral such an animal would be required not to possess art condyle of the quadrate running up to meet the antorbital fenestra, and this step would not have squamosal above, lateral to a quadrate foramen. been far back in time. From the reduced condition in Pro lacerta it is of little Strip Proterosuchus of its archosaurian label and consequence whether this bone is lost or retained by compare with Prolacerta. The skull morphology and M acrocnemus. It is difficult to see how this quadrato detailed relationships of the bones are remarkably jugal arrangement could be derived from Youngina. close. The writer does not accept Cruickshank's inter The Triassic reptiles of Monte San Giorgio (Kuhn parietal, nor the jugal process of the quadratojugal Schnyder, 1963 and others) are a diverse collection which he shows. The palatine does not form the entire mostly of specialised marine forms; it is thus sur lateral margin of the suborbital vacuity as he shows, prising to find amongst them an animal very close in bl.lt only runs halfway back. Cruickshank failed to note deed to Pro lacerta, namely M aero en emus bassanii that the teeth of Proterosuchus are serrated on their Nopsca. Owing to their poor mode of occurrence posteriormargins. these fossils are not as well known as one would like, Having disposed of these points the dlITerences are particularly in details of skull structure. Nonetheless now only of degree and quite consistent with the basic Kuhn- Schnyder (1963) described a skull of differences ofsize and build. M acrocnemus in sufficient detail to conclude con Proterosuchus has apparently a proportionately vincingly that this animal is closely allied to longer snout, achieved by compressing the orbit, with Prolacerta. In that paper he suggested the possibility a more downturned premaxilla; it has a very odd that the lower temporal opening of diapsids evolved retroarticular process (for which a functional inter before the upper. The writer has suggested (Gow, pretation is required). It is difficult to accept 1972) this might apply in the origin of squamates. In Cruickshank's assertion that the quadrate was strep view of the standard morphology of upper temporal tostylic. Surely this can only occur once the lower tem openings of younginids and early thecodonts and poral bar has been breached? bearing in mind the presence of two temporal The postcranial skeletons of the two animals pre openings in the upper Carboniferous Petrolacosaurus sent a very similar morphological grade. The girdles of these suggestions are open to doubt. It seems likely Proterosuchus are heavier, interclavicle and ilium hav that the lower temporal bar has been lost (along with ing distinctive shapes. The bifurcations of the sacral the quadratojugal?) in Macrocnemus and Tanystropheus . processes were one of the first points of strong Prolacerta constitutes the ideal starting point for the similarity noted in this study. derivation ofthese forms. Similarity extends to the hind foot and ankle, In Kuhn-Schnyder's 1963 paper there is an ex though there is some doubt regarding the phalangeal cellent photograph of an almost complete skeleton of count of Proterosuchus. Cruickshank has called the Macrocnemus. The resemblance to Prolacerta is so close liS as hardly to bear detailing and should dispel all doubt Lower Triassic prolacertids from the Lystrosaurus regarding the close relationship of these animals. zone of South Africa. Girdles large, unfenestrated, Further checks against Peyer's (1937) original detailed plate-like structures. Jugal spur and quadratojugal description of Macrocnemus with its many excellent present. ph~tographs also serve as a good standard of com M acrocnemus bassanii N opcsa 1930 panson. European Middle Triassic prolacertids. Girdles Size, proportion and morphology are closely com reduced. Posterior border of jugal smooth, parable in the two animals. The few concrete quadratojugal absent. differences are predictable and only slight advances Family Tanystropheidae Romer 1956. occur in M acrocnemus. Tanystropheus longobardicus Meyer 1852. As far as the M acrocnemus skull is known it is very Skull very similar to that of Prolacertidae but with similar to that of Pro lacerta. Doubt exists as to the heterodonty in juveniles, in which the teeth in the nature of the snout and the position of the external posterior half of both jaws are tricuspid. Greatly nares. The hind margin of the jugal is not known with elongate neck with longest neck vertebra five times as certainty, nor can the presence of a quadratojugal be long as the longest trunk vertebra. Considerably shown, though it seems certain that no lower temporal larger than Prolacertidae-in excess oHour metres in bar was present. Details of squamosal, quadrate and length. upper temporal fenestra are identical to the condition in Prolacerta. Dentitions are very similar in the two DISCUSSION animals. What can be seen of the palate ofMacrocnemus agrees well, and the shape of the basisphenoid is iden The reptilian braincase tical. Although it is now known that the incomplete The vertebrae and ribs agree very closely, even to lower temporal bar is not confined to lizards but is the divided second sacral transverse process and the present also in the sphenodontid Glevosaurus large flattened caudal chevrons. (Robinson, 1973) and certain millerettids (Gow, Ossification of the girdles in M acrocnemus shows a 1972), and in spite of the fact that Pro lacerta has considerable reduction over that in Pro lacerta but blade-like carnivorous theodont dentition, it seems this is almost universal in middle Triassic reptiles desirable to establish the differences between and to be expected and involves just those areas that squamates and archosaurs on as many features as are extremely thin in the girdles of Prolacerta. The il possible, particularly those of a predictably conser ium and inter-clavicle are still virtually in vative nature. Clear differences in braincase terchangeable between the two animals. Limb morphology would provide this additional distinc proportions are the same in both animals, both have tion. Here good comparative information is scarce, hooked fifth metatarsals and the same digital for particularly as regards good illustrations, but this mulae. Slight differences in ankle morphology situation is starting to change and new work on rep reflect only the time gap. tilian braincases can be expected to appear in the It is thus clear that Pro lacerta is representative of near future. There is enough material available for an as yet poorly known group of early Triassic certain trends to be discernible and putting these prearchosaurian thecodonts which in all probability forward at this stage may provide guidelines and ideas gave rise to the later M acrocnemus and Tanystropheus. for future work. These can then be regarded as a sterile group which A problem is that several strong features of typical paralleled the Squamata in the loss of the lower tem lizard braincases tend to lose significance the farther poral arcade. one goes back in time, and in any case squamate history below the upper Triassic is vague at the least. To illustrate the point, take the foramen rotundum PROLACERTA-SYNONYMY AND DIAGNOSIS found in lizards; this is lacking in Youngina, milleret Subclass: Incertae sedis tids and Sphenodon; it is lacking in archosaurs, some of Probably most workers would favour which develop a foramen pseudo-rotundum. Ap retention in the Leeidosauria parently the Kuehneosaur braincase is still Permian in Order Parathecodontia nov. thisrespect(Robinson, 1973). Thecodont reptiles of diapsid origin in which the The ventral process of the opisthotic thought by lower temporal arcade has been breached. Very close Robinson (1967) to be a unique character linking ly allied to proterosuchian thecodonts in most aspects Pro lacerta and Kuehneosaurus is in fact typical of the of skeletal morphology but precluded from the lower Triassic proterosuchians and were it not for the Subclass Archosauria by the almost certainly primitive fusion of opisthotic and exoccipitals in later forms it absence ofantorbital fenestrae. might be possible to extend this to modern lizards and Family Prolacertidae Parrington 1935. the sauropod dinosaurs at least. Small agile light-boned bipedal animals. Quadrate However, the negation of the usefulness of the streptostylic and quadratojugal reduced or absent. above points notwithstanding, there does seem to be a Pro lacerta broomi Parrington 1935. concrete basis for separation on braincase features. = Pricealongiceps Broom and Robinson, 1948. The millerettid-younginid grade braincase could lead 119 anywhere, but approaching the problem from the similar condition is indicated for Youngina (Figure 5 C) . other end a clear difference between lizard and The millerettid parasphenoid is characterized by a archosaur is in the extent of participation of the toothed rostrum plus two teeth on either side of t~e parasphenoid (basisphenoid when the two are no base of the rostral row; this is very similar to the condI longer distinguishable) in the sidewall of the brain tion in Petrolacosaurus (Figure 30). In I carosaurus case. In Pro lacerta, Proterosuchus, Euparkeria and (Colbert, 1970) and Kuehneosaurus (privileged data Stagonolepis this is extensive, while in lizards the brain from P. L. Robinson) these parasphenoid teeth are case is walled completely by prootic and the retained. In recent lizards, typified by Varanus (Figure basisphenoid terminates abruptly much farther 30), the parasphenoid seems to be reduced to the car forward (e.g. Varanus, Figure 28). Onthis basis it seems tilaginous rostrum, leaving only basisphenoid floor there can be no ambiguity regarding the correct ing the braincase anteriorly. assignment of Triassic fossils, though it appears at this stage that the archosaurian condition became firmly A established earlier than that of lizards. B c Figure 29. A & B, Ma.I.lOsjJondylus. From photographs of the specimen KI314 in the South African Museum; C, DromaeoJauTUJ. From a photograph in Colbert and Ostrom (1958 ). Figure 28. Varanus, Braincase in occipital, latt;ral and ventral views. Note particularly the restricted extent of the basisphenoid, On the thecodont line the picture is somewhat both laterally and posteriorly. different. The Youngina parasphenoid is a rather different shape from that of M illeropsis; it too could be The above suggestions are now considered in derived from that of Petrolacosaurus. In both animals greater detail. there is a pair of parabolic depressions in the ventral At the level ofYounginaandM illeretta the braincase is surface of the parasphenoid plate, and this pattern essentially captorhinid (Milleretta has an odd stapes tends to persist through the Proterosuchia to some of while that of Young ina is more like the slender rod seen the dinosaurs, a possible inference being that the in later reptiles, but this does not affect braincase parasphenoid as such tends to be retained in these morphology). Perhaps the braincase in these animals archosaurs. The depressions in the parasphenoids of could be said to represent an upper. Permian level of Kuehneosaurus and Icarosaurus would tend to reinforce development, just prior to considerable changes tak the identity ofthis element based on the teeth. ing place, but it is necessary to bridge the middle Per Figure 29 shows two dinosaur braincases which mian gap in the reptile story before this can be stated look to be extraordinarily primitive in their closeness with certainty. A feature of this braincase is the nature to the proterosuchian condition. A and B are of of the parasphenoid. Cow (op. cit., Figure 9C and p. M assospondylus, an upper Triassic Prosauropod, drawn 239) was able to demonstrate that the parasphenoid in from photograrhs ofthe specimen (S. A. Museum No. millerettids runs right back beneath the basioccipital KI314). Cis 0 Dromaeosaurus (Colbert and Ostrom, almost to the condyle. The basisphenoid, comprising 1958), an upper Cretaceous theropod (drawn from the basi pterygoid processess, sella turcica and published photograph). Camarasaurus (Ostrom and dorsum sellae lies on top of the parasphenoid, while Mcintosh, 1966), a Jurassic to Cretaceous sauropod, between basisphenoid and basioccipital is an exten also conforms to this primitive pattern. What is not sive gap bridged only by parasphenoid. An exactly clear in these seemingly primitive dinosaur braincases 120 THE C ODONTS 5 UAMATES C REl;. " Dromaeosaurus ~ : " to ," . REC ENT ~ UPPER TRIAS. Ku ehneosaurus Icarosaurus LOWER TRIAS. Prolacerta Proterosuc hu s UPPER PERM . UPPER FIG 30 CARR Petrolacosaurus Figure 30. An attempted separation of thecodonts and squamates through time based solely on ventral views of the para-basisphenoid. The several possible interpretations of the posi tion of Milleropsis do not affect the overall picture. H eleosaurus is a better archosaur ancestor than Youngina but there is no difference in the parasphenoids of the two. The lack oj P{'mlO-TnasslC" li zards is cl ear. 121 is the extent of participation of the basisphenoid in the Proterosuchus contact between parasphenoid and sidewall of the braincase, but with good material inex prootic is complete. An extension of this condition can istence this information should soon become be seen in for example Stagonolepis (Walker, 1961 ) and available. Euparkeria (Cruickshank, 1970). By contrast it appears In the present context the position of Euparkeria is that in lizards the basisphenoid remains essentially a still not clear. Ewer's (I965) drawing of the flooring plate giving no significant contribution to the basisphenoid seems open to question. sidewall of the braincase, which is formed entirely of Another area where one might expect to be able to prootic and opisthotic-this is true of Varanus (Bahl, make meaningful comparisons is the middle ear 1937 and personal observation) and Ctenosaurus (an region. In Milleretta and Youngina the region of the Iguanid, Oelrich, 1956). A crista lateroventralis in fenestra ovale is a large irregular opening bordered by some lizards gives an impression of lateral depth of good edges of prootic, opisthotic, basioccipital, para basisphenoid, but this is simply a downwardly projeL and basisphenoid. The pattern of exits for cranial ting ridge (Save Saderbergh, 1947, Figure 9A). The nerves IX to XII is primitive; in M illeretta IX - XI and question of changes in the ventral extent of the jugular vein emerge between exoccipital and opisthotic becomes difficult due to fusion of that bone opisthotic, XII through the opisthotic( Cow, op. cit. ). with exoccipital; hence para/basisphenoid Youngina is similar except that the foramen for XI I dis morphology is possibly the best indicator of reptilian charges externally into that which transmits IX to XI relationships in the lower Triassic particularly. and jugular. The stapes of Milleretta is peculiar, but The order Thecodontia is considered basal to all that of Youngina has the typical rod shape of later later archosaurian radiation. A spate of recent work sauropsids and runs out under the paroccipital on the classification of these animals is brought process towards the back of the head ofthe quadrate. together by Romer (I972c). In Romer's tentative Typical lizards are characterized by the presence classification we have a suborder Proterosuchia con below the foramen ovale of a foramen rotundum, the taining four families. Now it is striking that in the former bordered anteriorly by prootic, the latter pier Proterosuchidae the archosaurian antorbital fenestra cing the opisthotic alone. In iguanids these formina is rather poorly defined (having formed in a thin are separated by the crista interfenestralis of the boned minimum stress area) and does not yet show the opisthotic, in varanids both are anterior to that sheet strengthened outlines of more advanced forms. In the of bone. The footplate of the stapes is applied against light of the above it seems reasonable to assume that the foramen ovale while a membrane at the foramen the earliest thecodonts lacked the antorbital fenestra rotundum compensates for vibrations of the stapes and possibly to include a fifth family, the Pro lacer (Romer, 1956; Robinson, 1973 ). According to Robin tidae. son the required physical effect is attained in Sphenodon To do this purely on the basis of dermal bones might as follows : never prove entirely convincing, but reinforced by "an unossified portion of the inner wall of the otic what is now known about braincases such an arrange capsule, and the large vagus foramen, serve to allow ment could make sense. The braincase is well known in compensatory movements of the fluids of the inner Pro lacerta and Proterosuchus, it is reasonably well ear, and probably Kuehneosaurus had a condition figured and described in ventral view for Chanaresuchus similarto Sphenodon in these respects." (Romer, 1971 ) which seems reasonably primitive This leads to consideration of the fact that in a (further description ofthis braincase is necessary). Vir typical lizard the otic capsule is encased in bone and tually nothing is known of the braincase in this is what makes the foramen rotundum necessary. Erythrosuchids and Prestosuchids, with genera like In Milleretta, Youngina, and the early thecodonts listed M andasuchus being little more than words on paper. above the otic capsule is either known, or can safely be The braincase of phytosaurs (Camp, 1930) and inferred, to be open internally. aetosaurs (Walker, 1961 ) is well known; these are fairly In crocodiles and birds in which the middle ear is advanced in several respects, notably in the presence of enclosed in bone a foramen pseudorotundum is a laterosphenoid. developed to perform the necessary compensatory Of Romer.'s Pseudosuchia the braincase of movements (Romer, 1956; Baird, 1970; Walker, Euparkeria (Cruickshank, 1970) is fairly well known, 1972). In this context the importance ofWalker's work and considerably more primitive than that of on Sphenosuchus is that he was able to demonstrate the Phytosaurs and Aetosaurs though somewhat ad presence of a foramen pseudorotundum in an upper vanced over that of the Proterosuchids. Of the Or Triassic pseudosuchian. nithosuchidae the braincase is very inadequately Another feature which distinguishes lizards from known, though the close proximity of the basal ar archosaurs is the extent of the contribution of the ticulations of the pterygoids in Gracilisuchus (Romer, parasphenoid/basisphenoid to the sidewall of the 1972a) and Ornithosuchus (Walker, 1964) suggest braincase. In Milleretta the parasphenoid plate is flat, in similar specialisations which might be reflected in Youngina the lateral edges are slightly upturned. In several other aspects of braincase morphology. Prolacerta this upturning is pronounced, with a lateral Among Romer's miscellaneous Pseudosuchia is ridge of parasphenoid contacting the prootic, while in Lewisuchus. Romer's (I 972b) figure and description of 122 the braincase of this animal seem open to a different are derivable only from the Proterosuchia. A little interpretation: the possibility exists that there is no more work on existing material will establish this laterosphenoid, that the notch for Vin the pro6tichas point. closed and that Romer's V should be VI I. Nothing can be said at this stage about the Or As far as other later groups of archosaurs are con nithischia, though here again good material exists cerned there is a certain amount of information on and awaits only description. the braincase in the Crocodilia (fossil and recent) The foregoing is a tentative outline of the impor and birds (Walker, 1972), but one wonders whether tance of archosaur braincases in phylogeny and is discussion of this material, in vacuo as it were, need offered here in the hope of stimulating further work be taken too seriously. Little is known about of this nature. These are deep structures well dinosaur origins or of the braincase in the different obscured by other bones, but they can be removed lines. There is enough to suggest that the successfully and the suggestion is made that where Prosauropod braincase was exceedingly primitive possible braincases be illustrated in lateral, ventral, (Figure 29A and B), so much so that it is probably occipital and saggital and frontal views. derivable only from the Proterosuchian level. The NOTE: I have recently had the opportunity to ex same may be true of theropods based on what little amine a good braincase of Euparkeria. The similarity information there is on the braincase in the upper between the pr06tics and the foramen for VI in Cretaceous Dromaeo5auru5 (Figure 29C). It seems anterior view between Protero5uchu5 and Euparkeria is reasonable to suggest from this that the Saurischia clear from Figure 26 and Figure 37. 1lcm Fil'lIre 3 1 depicts the girdles of Youngina (left) and Prolacerta (right); all but the pectoral girdle or Prolacerta in anterior view, the latter as seen from behind. This gives a cfear impression of dorsoventral flattening in Y oungina and lateral flattening in Prolacerta. In order to see how body shape relates to way of life the fossil forms are compared in Table I (page 98 ) with a selected number of extant forms; when girdle measurements are converted to ratios the animals form an interesting series. This lends itself to misinterpretation as the broad pec toral girdle of crocodiles and Youngina is associated with vertical carriage ofthe humerus and probably does not as such relate to aquatic habits. Bakker's (pers. comm.) thoughts on this aspect are far advanced so it will not be pursued here. Likewise it is misleading to compare the agile Pro lacerta and slow moving chamaeleon too closely, though the more closely spaced glenoids clearly afford climbers better balance. 123 SUMMARY EDMUND, A. G. (1969). Dentition. In: Gans, c., Ed., 1. The osteology of Youngina capensis is described in Biology of the Reptila 1 : Chapt. 4. London and New detail. There is every indication that this was a York, Academic Press. terrestrial animal. Youngopsis and Youngoides are EWER, R. F. (1965). The anatomy of the thecodont relegated to junior synonyms . No tidy reptile Euparkeria capensis Broom. Phil. Trans. R. phylogenetic associations are proposed either Soc., (B)248(75 1), 379 -435. backwards or forwards in time; there are objec FRAZZETTA, T . H. (1962). A functional considera tions to close association with Prolacerta, squamates tion of cranial kinensis in lizards.]. Morph., III, and archosaurs. 287 -320. 2. The complete osteology of Pro lacerta is described. A GOW, C. E. (1972). The osteology and relationships of description of the braincase of Proterosuchus is in the Millerettidae (Reptilia: Cotylosauria).]. Zool., cluded for comparison. It is shown that Prolacerta Lond., 167,219 -264. was a swift bipedal animal morphologically very HOFFSETTER, R. and CASe,J. P. (1969). Vertebrae close to the proterosuchian thecodonts, which was and ribs of modern reptiles. In: Gans, C., Ed., probably on a direct line to Macrocnemus at least Biology of the Reptilia 1 : Chapt. 4. London and New among the lizard-like forms of the European mid York, Academic Press. dle Triassic. Pricea is relegated to a synonym of KUHN-SCHNYDER, E. (1963). I Sauridel Monte San Prolacerta. Giorgio. Archivio Storico Ticinese, 16, 811-854. 3. Discussion of sauropsid braincases suggest fun NEILL, W. T. (1971). The last of the Ruling Reptiles. damental differences exist between those oflizards Columbia University Press, New York and London. and thecodonts-a situation which helps to dispel OELRICH, T. M. (1956). The anatomy of the head of the concept ofProlacertaas an ancestral squamate. Ctenosaura pectinata Oguanidae). Misc. Publ. Mus. Zool. U. Mich. , 94,1-122. REFERENCES OLSON, E. c. (1936). Notes on the skull of Young ina BAIRD, I. L. (1970). 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On a nearly complete skeleton ofa a Pennsylvanian reptile from Kansas. Vertebrata new eosuchian. (Palaeagama vielhaueri, gen. et sp. (University of Kansas), 1, 1-41. nov.)Proc. zool. Soc. Lond., 1926,487 -49l. ---- (1937). A further contribution to our PEYER, B. (1937). Die Triasfauna der Tessiner knowledge of the fossil reptiles of the Karroo. Proc. Kalkalpen XII. Macrocnemus bassanii Nopsca. Abh. zool. Soc. Lond. B, 107,299 -318. Schweizer Palaeontol. Ces., 54, 1-139. ---- and ROBINSON, J. T. (1947). Some new ROBINSON, P. L. (1967). The evolution of the Lacer fossil reptiles from the Karroo beds of South Africa. tilia. Collog. into Cent. Matn. Rech: Scient., 163, Proc. zool. Soc. Lond. B, 118(11),392 -407. 395-407. CAMP, C. L. (1930). A study of the phytosaurs. Mem. ---- (1973). A problematic reptile from the Univ. California, 10, 1-16l. British Upper Trias.]. Ceol. Soc., 129,457 -479. ---- (1945). Prolacerta and the Protorosaurian ROMER, A. S. (1956). 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Anat., 95,1-45. - - '- - (1962). Adaptations for bipedal locomotion - - - - (1972). New light on the origin of birds and of lizards. Amer. Zool., 2, 191-203. crocodiles. Nature, 237, 257 -263. 125 A B c Figure32. Stereo-photographs ofleft maxilla ofPro lacerta broom B.P.1. 2675. A, labial oblique; B, Straight occlusal; .C, Lingual oblique. Scale is I em long. 126 A B c D E Figure 33. Stereo-photographs of ankle of Prolacerta broomi B. P. I. 2675. A, Ventral ; B, Dorsal ; C, Normal to tibial facet; D, Normal to fibial facet on astragulus; E, Both facets obli que. Scale is I cm long. 127 A Figure 34. Stereo-photographs of brain ease of Prolacerta broomi B.P.1. 2675. A, Left lateral view; B, Posterior view. Seale is 1 em long. 128 A B Figure 35. Stereo-photographs of braincase of Prolacerta broomi B.P.1. 2675. A, Ventral view; B, Dorsal view. Scale is 1 em long. 129 A B c Figure 36. Stereo photographs of braincase of Protero5uchu5 fergu5i B. P.1. 3993. A, Left lateral; B, Posterior; C, Ventral. Scale is I cm long. 130 A B Figure 37 . Stereo-photographs of: A, Braincase oiProterosuchusJergusi B. P.l. 3993, anterior view ; B, Braincase ofEuparkeriacapensis S.A.M. 7696,anteriorview. Scale is 1 cm long. 131 ABBREVIATIONS A. -angular POF. - postfrontal al.pr.bsp. -alar process of basisphenoid PP. -postparietal al.pr.pro. -alar process of prootic PRF. - prefrontal ART. -articular PRO. - prootic BO. - basioccipital PR.ART. -prearticular BSP. - basisphenoid PSP. -parasphenoid bpt.pr. - basipterygoid process PTDG. - pterygoid b.t. -basaltubera P. - parietal facet cpr. -crista prootica p.a. - pila antotica ds. -dorsum sella par.proc. - paroccipital process EO. -exoccipital p.pr.pro. -posterior process of prootic EPT. - epipterygoid Q. -quadrate F. -frontal QJ. - quadratojugal f.o. -foramen ovale q.ra.pt. -quadrate ramus of pterygoid f.m . -foramen magnum ro.psp. -parasphenoid rostrum J. -jugal S. -stapes j.f. -jugular foramen SA -surangular L. -lacrimal SO. -supraoccipital MX. -maxilla SPL -splenial N. -nasal SQ. -squamosal OP. -opisthotic ST. -supratemporal P. -parietal T. - tabular PAL. -palatine V. -vomer PMX. -premaxilla V.c. - vidian canal PO. -postorbital