The First Complete Vertebral Column of a Basal Tapinocephalid Dinocephalian

Research Letters Soutti African Journal of Science 98, July/August 2002 391

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deposited sandstone body of the Eodicynodon Assemblage zone The first complete vertebral on the farm Modderdrift, Prince Albert." Five skulls were described by Rubidge,'' who recognized a new genus and column of a basal species, Tapinocaninus pamelae (NMQR 2987), which has been tapinocephalid dinocephalian identified as the most basal tapinocephalid dinocephalian.'*"" Over the past 17 years, the postcranium of the holotype"* has (Synapsida: Therapsida) been prepared systematically to reveal a specimen of scientific importance. All the vertebrae (from the first cervical to the last caudal) are preserved in articulation, enabling us confidently to Romala Govender*, Bruce S. Rubidge* and determine that Tnpitiocariintii has 36 vertebrae. These comprise 8 Alain J. Renaut* cervicals, 16 dorsals, 5 lumbars, 2 sacrals and 7 caudals. The only other tapin(Kephalid with a relatively complete postcranial skeleton is a mounted specimen of Moschops (AMNH 5552), in the American Museum of Natural History in New York. That Non-mammalian therapsids ('mammal-like reptiles') were the most specimen has been reconstructed as having a vertebral column common continental vertebrates during Permo-Triassic times. A consisting of 6 or 7 cervical vertebrae, 21 or 22 dorsal and lumbar rich fossil record from several continents documents the acquisi- vertebrae, 3 sacral vertebrae,'- and of the 29 caudal vertebrae tion of mammalian characteristics among advanced therapsids. In only five are genuine. It is uncertain that all the bones attributed contrast, the record of the early and most basal therapsids is poorly to this specimen actually belong to it, as it was found in associa- known and restricted to only a few countries. Dinocephalians are a tion with seven other conspecific individuals.'^ major subgroup of basal therapsids and are impressive because of The cervical vertebrae of Tapinocaninus have caudally curved their large size. They were the first terrestrial tetrapods to attain neural spines (Fig. 2), and are taller and anteroposteriorly body lengths in excess oi three metres. Members of this group are narrower than those of the other vertebrae. The pre- known predominantly from Russia, South Africa, Zimbabwe and /.ygapophyses are positioned in front of the cranial margin of the recently China and Brazil. Although dinocephalians are relatively abundant, most genera are represented by very fragmentary cranial neural spine (except the axis) and are directed dorsally (except and postcranial materiai. This paper reports on the first completely those of the axis, which are directed laterally). All the articulated dinocephaiian vertebral column with associated limbs, postzygaphophyscs project beyond the caudal margin of the a find that has significance for the understanding of the morphology neural spine and are directed ventrally. Cervical transverse and palaeobiology of this important group of extinct tetrapods. processes are directed ventrally and the distal ends point cranially. In the dorsal region the prezygapophyses face dorsomedially, whereas the ventrolaterally facing postzygapo- physes do not extend beyond the caudal margin of the neural Dinocephalians comprise four families, of which the most abun- spine. The laterally directed transverse processes of the dorsal dant are the carnivorous Anteosauridae and the herbivorous vertebrae are shorter and stouter than those of the cervical Tapinocephalidae. Anteosaurids are represented by genera region. The prezygapophysial articulation surfaces of the from Russia,' Brazil/ China^ and South Africa,' whereas the lumbar vertebrae are directed anterodorsally, whereas those of Tapinocephalidae are represented by genera from South Africa the postzygapophyses point posteroventrally. The short trans- and Russia.' Anteosauridae is considered to be the most basal verse processes are ankylosed to the short lumbar ribs. dinocephalian family, whereas Tapinocephalidae is the most The caudal series is the least well preserved, but it is evident derived.'"^ In 1984, John Nyaphuli di.scovered the skulls and when compared to the rest of the other vertebrae that the associated skeletons of two dinocephalians (Fig. 1) in a fluvially neural spine is elongated and the dorsomedially directed 'Bernard Price Institute tor Palaeontological Researct!, University of the Witwatersrand, prezygapophyses are situated well in front of the neural spine. Private Bag 3, WITS 2050, South Africa. Caudal postzygapophyses project beyond the caudal margin of *Auttiorbr correspondence. E-mail: [email protected] the neural spine and are directed ventrolaterally. Only seven 392 South African Journal ol Science 98, July/August 2002 Research Letters

Titanophoneus,^^ a primitive anteosaurid dinocephalian from Russia. Since this feature is present in the least derived taxa, we consider it to be primitive for therapsids. An additional pleisomorphic feature of the vertebral column of Tapinocaninus is the presence of intercentra between all the cervical vertebrae (Fig. 3) and extending posteriorly at least as far as the fourth dorsal vertebra. Among the tapinocephalids intercentra are de- scribed only in the anterior cervical region of Struthiocephalus,'^ and in the atlas-axis complex oi Moschops, ^^ NMQR 2987 has the only completely articulated dinocepha- lian vertebral column known. It is of importance in establishing dinocephalian vertebral counts and to understanding the degree of vertebral specialization achieved in this group of therapsids. In addition, this specimen suggests that, in contrast with anteosaurids, which had long tails, tapinocephaiids had very short tails similar to anomodonts. Another important feature of Tapinocaninus is a suite of pleisomorphic characteristics exhibited in the vertebral column. The significance of this may become apparent by more extensive morphological and phylo- genetic research currently under way.

Fig. 1. Skull and complete skeleton of the hoiotype of Tapinocaninus pamelae We are indebted to John Nyapliuli, who discovered and helped collect the speci- (NMQR 2987) as seen in oblique dorsal view, with their discoverer, John Nyaphuli. men, as wefl as to the numerous preparators who have worked on the specimen over the past 17 years. They are Petrus Chalatsi, Charlton Dube, Caiphus vertebrae are preserved, with the last being very small and is Hlatswayao, Joel Mohoi, John Mothama, Jimmy Ndmande, Cfiristian Nyaphuli, thus probably the terminal member of the series. This caudal Joseph Sithole, Sam Tschabalala, and Amos and Enoch Zondi. Johann Welman and count is much less than the 29 reconstructed caudal vertebrae in Chris Engelbecht of the National Museum, Bloemfontein, are thanked for permis- the Moschops specimen (AMNH 5552), and the approximately 60 sion to work, on the specimen over an extended period. B.S.R. is grateful to Mark Morell, Chris Collins and Judy Calkin for their kind hospitality and assistance while caudals of the Russian anteosaurid Titanophoneus,'^ Watson'* on a research visit to study the Moschops specimens in the American Museum of considered Tapinocephalus to have had a short tail, and the five Natural History. The National Research Foundation and the University of the preserved caudals in the American Museum of Natural History Witwatersrand are acknowledged for financial support. We greatly appreciate the specimen corresponds closely with that of Tapinocaninus, time and effort of Sean Modesto and an anonymous referee for their constructive suggesting that tapinocephalids probably had short tails. comments. A distinguishing feature of the vertebrae of Tapinocaninus is the Rtfceived 18 October 2001. Accepted 10 July 2002 presence of a laterally facing fovea situated at the base of the neural spine of the cervical vertebrae (Fig. 2). Such a feature is 1. 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