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FROM the CYNOGNATHUS ZONE of SOUTH AFRICA By Palaeont. afr., 31, 39-49 (1994) A NEW FIND OF TREMATOSUCHUS (AMPHIBIA, TEMNOSPONDYLI) FROM THE CYNOGNATHUS ZONE OF SOUTH AFRICA by ~A. Shishkin1 and J. Welman2 J Bernard Price Institute for Palaeontological Research, University of the Witwatersrand, Private Bag 3, Wits 2050, South Africa 2 National Museum P.O. Box 266 Bloemfontein 9300 ABSTRACT Some aspects of the cranial morphology of Trematosuchus sobeyi, a temnospondylous trematosaurid amphibian from the South African Cynognathus Zone, are described in detail for the first time from a new fossil find referred to this form. The new specimen is similar in size to that of the Holotype of Trematosuchus sobeyi but differs in the more moderate elongation of the snout. Apart from the presence of the septomaxilla, the validity of the genus Trematosuchus is reconfirmed inter alia by its much larger size and the position of the supraorbital sensory groove alongside the lachrymal margin rather than crossing this bone. This last characteristic differentiates Trematosuchus from all other trematosauroids. T. sobeyi is of particular importance since it represents the only purely freshwater Gondwanan form closely comparable to the European Trematosaurus. The presence of T. sobeyi in the lowermost strata of the Cynognathus Zone in South Africa, in association with some other forms related to the Upper Olenekian (Middle Buntsandstein) tetrapod assemblage of Europe, indicates that these strata belong to the Scythian in contrast to the higher strata of the Cynognathus Zone which are Anisian. KEYWORDS: Trematosauridae, Biostratigraphy, Cynognathus Zone. INTRODUCTION Benthosuchidae(Shishkin 1968, 1980; Getmanov 1989). Trematosauroid amphibians, characterised by their The Trematosauridae are one of only a few amphibian wedge-shaped skull sand paired anterior palatal vacuities, groups which succeeded in spreading to the nearshore comprise one of the most common groups of Triassic habitats as seen from their particular abundance in the temnospondyls. They stem from the family coastal marine facies of the Lower Olenekian of Benthosuchidae (Shishkin 1968, 1980; Getmanov 1989) Spitsbergen and also in Madagascar. which also gave rise to other more advancedlineages such Trematosaurids are most common in Europe and rare as the Heylerosauridae (Shishkin 1980) and the poorly in the Gondwanan continents which may suggest that known Yarengiidae (Shishkin 1964; Novikov 1990). they dispersed fromLaurasia to the south, most probably The Benthosuchidae are recorded only from the via the coastal or borderland routes (Lehman 1979; early Lower Triassic (Induan - Lower Olenekian) of Cosgriff 1984). This idea is complicated by the fact that eastern Europe and northeastern Asia (Shishkin & most of the Gondwanan trematosaurid finds belong to Lozovsky 1979). Heylerosauridae are endemic to the the specialized needle-snouted forms, which first Euroamerican province; they appear in the upper appeared in both hemispheres in the lowermost Lower Lower Triassic (Upper Olenekian) and become very Triassic (Induan), i.e. before the typical benthosuchid­ common in the Anisian (Morales 1987; Ochev & derived trematosaurids which are first recorded in the Shishkin 1989; Shishkin & Ochev 1993; Milner 1990). Lower Olenekian (as exemplified by the Spitsbergen The Yarengiidae are known only from eastern Europe assemblage). The earliest Indian long-snouted forms (Upper Olenekian). In contrast, members of the family are known from the Panchet Series of India Trematosauridae are recorded from all the continents (Gonioglyptus, Panchetosaurus; Tripathi 1969), the except for South America and Antarctica. marine Prionolobus Beds of the Salt Range in Pakistan The majority of trematosaurids come from the (Halobatrachus kokeni; Huene 1920; Hammer 1987) Lower Triassic. Middle Triassic finds reported from and from the Vokhmian horizon of the Cis-Urals North Africa, India (Lehman 1971; Chatterjee & (undescribed form; Shishkin & Ochev 1993). This Hotton 1986; Welles 1993) and Canada (Baird 1986) seems to reinforce the suggestion that theassemblage of are rare and poorly known. The Upper Triassic forms currently termed Trematosauridae may well prove trematosaurids are known from a single find from to be diphyletic in origin (cf. Bystrow and Efremov western Europe (Hellrung 1987). 1940 p 143; Shishkin 1964). The subdivision of the A number of transitional forms from the Lower Trematosauridae into two (or three) subfamilies has Olenekian of eastern Europe suggest that been suggested by Efremov (1933) Save-Soderberg Trematosauridae can be derived from the Laurasian (1935), Hammer (1987) and Welles (1993). ", 40 A sso ----na 10 CM 1 ---orb pb Pmx 30 CM pd Figure 1. Trematosuchus sobeyi SAM 2979 (Holotype) A. Dorsal view of the skull, B. dorsal view of the snout, C. ventral view of the palate, D. ventral view of the anterior part of the palate. 41 Apart from the finds from Madagascar, India and SYSTEMATIC PALAEONTOLOGY Pakistan mentioned above, Gondwanan trematosaurids Trematosuchus sobeyi (Haughton 1915) are known only from Australia and South Africa. All Trematosaurus sobeyi: Haughton 1915, p.47, pI. VIII, IX the Australian finds belong to the long-snouted forms Trematosuchus sobeyi: Watson 1919, p.41 and include the type of Erythrobatrachus from the Trematosaurus sobeyi: Huene 1920, p.443 Blina Shale (Cosgriff & Garbutt 1972) and Trematosuchus sobeyi: Haughton 1925, p.250, fig.15 unidentifiable fragments from the Arcadia Formation and the lower part of the overlying Glenidaliormation Holotype (Warren 1985), the former two stratigraphic units being SAM 2979, a nearly complete skull; Queenstown, most probably lower Olenekian (Smithian) in age. Cape Province, Upper Beaufort (Cynognathus Zone). In South Africa trematosaurids were first recovered (Figure 1). in the early part of this century and are represented by two Triassic forms from the Beaufort Group, Referred specimens under description "Trematosaurus" kannemeyeri and Trematosuchus NMQR 3263 A & B (two fragments of the same sobeyi (Broom 1909; Haughton 1915, 1925; Huene skull) Verdun Farm, Paul Roux District, Orange Free 1920). The former is a poorly known long-snouted State, Cynognathus Zone (Figures 2-5). Aphaneramma-like form described from a fragment of skull (Broom 1909), the provenance of which is Generic and specific diagnosis uncertain. Kitching (1978) considers it to come from Large form (skull about 420mm in midline length); the Cynognathus Zone (Upper Beaufort Group) which orbits extremely small and round; septomaxilla and is variously considered to be Upper Olenekian interfrontal present; parietals not narrowed anteriorly; (Spathian) to Anisian in age (Ochev & Shishkin 1989). supraorbital sensory groove alongside the medial Trematosuchus sobeyi, is of particular importance lachrymal margin rather than crossing the lachrymal. since it represents the only instance in Gondwana where a complete trematosaurid skull (Figure 1) PRESERV ATION AND METHODS is recorded from a purely fresh water environment NMQR 3263 (Figures 2-5) consists of Block A: the (fluvial-lacustrine deposits of the Upper Beaufort snout broken off obliquely behind the nasochoanal Group). Furthermore, it is the only Gondwanan area, and Block B: a part of the right side of the palate form which is comparable with the European Trematosaurus. immediately in front of the subtemporal fossa, together Both the type (Figure 1) and referred specimen of with the dorsal portion of the jugal. Both blocks, obviously from a fine-grained grey T. sobeyi described by Haughton (1915, 1925) were obtained from a sandstone quarry of the Cynognathus sandstone lens, were found lying close together on the Zone in the Queenstown area, Cape Province. surface but not in situ. According to Kitching (pers. comm.) the fossil-bearing They exhibit the same type of mineralization and sandstone belongs to the lower part of the Cynognathus weathering (the surface of the bones being brown and Zone. No further finds of this genus have been reported glossy) and are consistent in size. There seems to be no until recently when another specimen (Figures 2-5) was doubt that both fragments belong to the same recovered in theCynognathus Zone of the northeastern individual, in spite of the lack of immediate contact Orange Free State (Weiman et al. 1991). The new between them. The fresh fracture surfaces of the Trematosuchus find (NMQR 3263) includes two specimen indicate that fragmentation of the skull fragments of the same skull collected at Verdun Farm, almost certainly occurred only after it weathered out of Paul Roux district. The narrowness of the snout the embedding rock. The good preservation of sharp fragment combined with paired elongated anterior edges on the specimen suggests that the skull was palatal vacuities and strong reduction of the neither transported over any long distance prior to interchoanal tooth row immediately suggest the burial nor did it suffer post depositional sedimentary trematosaurid affinity of the specimen. Although no reworking. more fossils were discovered from this site, the faunal NMQR 3263 was mechanically prepared under a assemblage of this stratigraphic unit includes stereo microscope with a pneumatic engraver. The Cynognathus, trirachodontid cynodonts, an engraver was fitted with a sharpened, round tungsten­ erythrosuchid thecodontian and Parotosuchus-like carbide tip. Exposed bone was covered with a Glyptal capitosauroid amphibians (WeIman et al. 1991). cement solution, diluted with lacquer thinners. Hancox et al. (in press)
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