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Geological Survey, PB112, Pretoria Rhachiocephalus, Aulacephalodon

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Geological Survey, PB112, Pretoria Rhachiocephalus, Aulacephalodon 15 Palaeont. afr., 14. 15-16. 1972 A RE-EVALUATION OF THE SYSTEMATICS AND MORPHOLOGY OF CERTAIN ANOMODONT THERAPSIDA by A. W. Keyser Geological Survey, P.B.112, Pretoria The cranial morphology of a number of O. marlothi Broili and Schroder, Dicynodon specimens assigned to the genera Oudenodon, wellwoodensis Broom, D. alla m' Broom, D. mac­ Rhachiocephalus, Aulacephalodon and Pelano­ cabei Broom, D. glaucops Broom, D. moutonae modon was investigated (Keyser, 1969). It was Broom, D. brachyrhynchus Broom, and D. robertsi found that the internal morphology and the Broom'. general structure of the skulls show great agree­ The following species from the Upper Madu­ ment. Many of the differences between the genera mabisa Mudstone of Zambia are also placed in the can be associated with the size of the skull. The genus Oudenodon, viz. Dicynodon luangwaensis main differences between the genera lie in the Boonstra, D. helenae Boonstra, D. euryceps Boon­ specialisation of the biting mechanism and in the stra and D. parabreviceps Boonstra. relative size and shape of the nasal and prefrontal Examination of a series of 20 specimens bosses. It is suggested that the genera Oudenodon collected in a delimi ted area north of Graaff-Reinet and Rhachiocephalus bit off their food with the from Cistecephalus-bearing strata showed that the sides of the horn-covered jaws while the broad­ characters used to distinguish the various species nosed genera Aulacep halodon and Pelanomodon are subject to individual variation and deforma tion. bit with the transverse anterior tips of the jaws. I t was found that all the types listed above are This difference in the morphology of the jaws is wi~hin the range of variation exhibited by this probably indicative of a fundamental dichotomy senes. between the two groups of genera. A similar Attention is drawn to the fact that all the dichotomy has been suggested for Triassic dicyn­ species previously assigned to Oudenodon from the odonts by Cox (1965). Karroo basin are very similar indeed and that most The skulls of Oudenodon and Rhachiocepha­ of the species mentioned above could be syno­ Ius have much in common and many of the nyms. The Zambian species are possibly all differences between them can be attributed to synonymous but differ from the South African differences in the relative sizes of the animals. species in having broader skulls. Rhachiocephalus has a large boss surrounding the parietal foramen and a very small fenestra ovalis. Dicynodon huenei Broili and Schroder The snouts of these two genera are p.ointed and the (Oudenodon huenei), a small species from the lower jaws do not have very pronounced shovel­ Tapinocephalus zone of Beaufort West, is tusked, like tips. These two features indicate that most of unlike all the species listed above and accordingly the biting took place at the sides of the jaws. will be placed in a new genus, of which a diagnosis All the available type-specimens of this group will be given in due course. of Anomodontia of which Oudenodon kolbei is the The genera Rhachiocephalus, Eocyclops, Neo­ best known representative, were examined. megacyclops, PIa ty cy clops, Pelorocyclops and Oudenodon baini Owen (1855) is the type species Kitchingia appear to be indistinguishable because of the genus. The following South African species of similarities in structure which are discussed. The are placed in the genus Oudenodon: Oudenodon genera were originally distinguished from one baini Owen, 0. prognathus Owen, O. greyi Owen, another on the structure and relationship of the 0. brevirostris Owen, O. strigiceps Owen, O. preparietal, which was found to be highly variable megalops Owen, 0. truncatus Broom, O. gracilis in a group of specimens from a single locality. Broom, O. bolorhinus Broom, O. kolbei Broom, There is some doubt about this as the variation of Dicynodon lutriceps Broom, D. planus Broom, D. the interpterygoid vacuity has not been studied platyceps Broom, D. haIti Watson, D. mustonis sufficiently. Haughton, D. breviceps Haughton, D. cyclops The skull of Aulacephalodon is fairly short Haughton, D. grandis Haughton, D. corstorphinei and broad. The transverse anterior tip of the short Broom and Haughton, Chelyrhynchus lachrymalis snout is reinforced by anterior longitudinal palatal Haughton, Dicynodon schwarzi Broom, D. curtus ridges and ridges on the external surface of the Broom, D. andrewsi Broom, D. milletti Broom, D. snout. This indicates that most of the biting action vanderbyli Broom, D. wilmanae Broom, D. lati­ of the jaws was restricted to the tips of the jaws. rostris Broom, Oudenodon margaritae van Hoepen, The great widening of the zygomatic arches c 16 posterior to the postorbital bars and the formation COX, C. B., (1965). New Triassic dicynodonts of bosses on the zygomatic arches can be attri­ from South America, their origins and rela­ buted to this biting mechanism. It was found that tionships: Phil. Trans. R. Soc., B, 248, the characters used to distinguish the various 457-516. species of Aulacephalodon depend greatly on the CROMPTON, A. W. & HOTTON, N., (1967). size and consequently the age of the individual. Functional morphology of the masticatory Because of this, the 16 named species of apparatus of two dicynodonts (Reptilia The­ Aulacephalodon are found to be indistinguishable rapsida): Postilla, 109, 1-51. and the possibility that they are all synonyms HAUGHTON, S. H. & BRINK, A. S., (1954). A deserves consideration. Bibliographic list of Reptilia from the Karroo The skull of Pelanomodon is very similar to beds of Africa: Palaeont. afr., 2,3--187. that of Aulacephalodon but is tuskless. The KEYSER, A. W., (1969). Re-evaluation of the similarity is probably the result of the similar systematics and morphology of certain ano­ biting mechanism. The very large nasal and modont Therapsida. Ph.D. Thesis, University prefrontal bosses, the presence of two lacrimal of the Witwatersrand, Johannesburg. foramina in each orbit and the high placement of OWEN, R., (1855). Description of certain fossil the orbits and nares in the skull indicate that the crania, discovered by A. G. Bain, Esq., in animal could have fed amongst vegetation in sandstone rocks at the south-eastern extremity shallow water. of Africa, referable to different species of an The taxonomy of the Pelanomodon-like ano­ extinct genus of Reptilia (Dicynodon), and modonts was investigated. It was found that indicative of a new tribe or sub-order of Pelanomodon rubidgei and P. kitchingi are prob­ Sauria: Trans. geol. Soc. Lond., 7, 59- 84. ably synonymous. P. haIti was found to be very - --- , (1856). On the description of the skull of a different from the above 2 species and very similar large species of Dicynodon (D. tigriceps, Ow.), to P. moschops (Broom). P. wesselsi is placed in transmitted from South Africa by A. G. Bain, the genus Rhachiocephalus. Propelanomodon de­ Esq.: Trans. geol. Soc. Lond., 7,233- 239. villiersi Toerien (1955b) was found to be synony­ ---- , (1860). On some reptilian fossils from mous with Dicynodon tylorhinus Broom. This South Africa: Q. Jf. geol. Soc. Lond., 16-63. species should therefore be called Propelanomodon - ---, (1876). Descriptive and illustrated cata­ tylorhinus (Broom). The genus Propelanomodon logue of the fossil reptilia of South Africa in is related to Oudenodon rather than to Pelano­ the collection of the British Museum: British modon. Museum (Natural History), London. The possibility is that all the genera treated in TOERIEN, M. J., (1953). The evolution of the this paper are descended from a Robertia broom­ palate in South African Anomodontia and its iana-like ancestor. classificatory significance: Palaeont. afr., 1, 49- 115. SELECTED REFERENCES --- -, (1955a). Convergent trends in Anomo­ BROIL!, F. & SCHRODER, J., (1937). Uber dontia: Evolution, 9, 152-156. einige neue Anomodontier aus der Tapino­ ---- , (1955b). Important new Anomodontia: cephalus-Zone: Sber. bayer. Akad. Wiss., Palaeont. afr., 3,65-72. 118-163. VAN HOEPEN, E. C. N., (1934). Oor die indeling BROOM, R., (1932). The Mammal-like Reptiles of van die Dicynodontidae na aanleiding van South Africa and the origin of mammals: H. F. nuwe vorme: Palaeont. Navors. nas. Mus. and G. Witherby, London. Bloemfontein: 2, 67-101. 17 Palaeont. afr., 14. 17. 1972 A NOTE ON THE GENUS PROPLACERIAS CRUICKSHANK, 1970. Since writing the review of the genus Kanne­ ridge, nor are the maxillary flanges as well meyeria (Cruickshank 1970, pp. 47- 55) a cast of developed as in Kannemeyeria simocephalus. The the type of Proplacerias vanhoepeni (Camp) has relevance of the horizontal jaw-tip in the type of been received for examination as part of the K. wilsoni, as opposed to the normal, upturned tip programme in the Bernard Price Institute for in this specimen must be re-assessed. Palaeontological Research for making types of Therefore as all the distinguishing characters South African fossils available for study here of the genus Proplacerias are false, it must be (Camp 1956, p. 311). placed into synonymy with the genus Kanne­ Even a superficial glance at the cast shows that meyeria Seeley. Nonetheless, it is clear that the it is unmistakeably a member of the genus major conclusions reached on p. 51 and in figure 4 Kannemeyeria, and probably another specimen of (Cruickshank 1970) are still valid and that the the hitherto monotypic species K. wilsoni (Broom evolutionary lines leading to Placerias and Kanne­ 1937). In the review of the genus Kannemeyeria, meyeria are distinct. K. wilsoni was recognised as probably being distinct from K. simocephalus (Weit.) but the possibility exists that it is the female of K. simocephalus (Cruickshank 1970, p. 51). REFERENCES The side of the skull which is visible in dorsal BROOM, R., (1937). A further contribution to our view in Camp's figures is dorso-ventrally crushed knowledge of the fossil reptiles of the Karroo. and the orbital border has been extensively Proc.
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