Palaeontologia africana
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ISSN (print): 0078-8554
ISSN (electronic): 2410-4418
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Item Cranial morphology and phylogenetic relationship of the enigmatic dinocephalian Styracocephalus platyrhynchus from the Karoo Supergroup, South Africa(Evolutionary Studies Institute, 2019-09) Fraser-King, Simon W.; Benoit, Julien; Day, Michael O.; Rubidge, Bruces S.Styracocephalus platyrhynchus is an unusual dinocephalian therapsid, known only from a handful of specimens from the Tapinocephalus Assemblage Zone of South Africa. It has had a chequered taxonomic history, largely because it is characterized by cranial pachyostosis and the presence of horn-like structures that project posteriorly from the temporal region; these features are found in the clades Burnetiamorpha and Dinocephalia. Its affinities have been further obfuscated by a lack of well-preserved material. This paper presents a description of a well-preserved skull referable to Styracocephalus from the western Karoo Basin and provides a revised generic diagnosis for the genus. This study – incorporating comparative anatomy,CT scanning, and cladistic analysis – reveals new character information that was not evident from pre-existing Styracocephalus material, and incorporates this into a new phylogenetic analysis. Our analysis recovers Styracocephalidae as a well-supported, monotypic family within Tapinocephalia, which is characterized by: prominent pachyostotic nasal and supraorbital bosses; two posteriorly projecting crest-like protuberances comprising contributions by the postorbital, squamosal and tabular bones; weak lingual heels on the incisor and postcanine dentition present with a moderate upper and lower canine. As Styracocephalus is restricted to the upper part of the Tapinocephalus Assemblage Zone, it may be a useful biostratigraphic index taxon in future.Item The first skeletal evidence of a dicynodont from the lower Elliot Formation of South Africa(Evolutionary Studies Institute, 2018) Kammerer, Christian F.Historical fossil specimens from the lower Elliot Formation are identified as representing a large-bodied dicynodont, the first known from skeletal material in the Late Triassic of South Africa. Although fragmentary, these fossils differ from all other known Triassic dicynodonts and are here described as a new taxon, Pentasaurus goggai gen. et sp. nov. Pentasaurus can be distinguished from other Triassic dicynodonts by a number of mandibular characters, most importantly the well-developed, unusually anteriorly-positioned lateral dentary shelf. Phylogenetic analysis indicates that Pentasaurus is a placeriine stahleckeriid. Placeriines include the latestsurviving dicynodonts but their remains are primarily known from the Northern Hemisphere, with their only previously-known Southern Hemisphere representative being the Middle Triassic Zambian taxon Zambiasaurus. The discovery of a placeriine in the Late Triassic of SouthAfrica supports recent proposals that local climatic conditions, not broad-scale biogeographic patterns, best explain the observed distribution of Triassic tetrapods. The tetrapod fauna of the lower Elliot Formation is highly unusual among Triassic assemblages in combining ‘relictual’ taxa like dicynodonts and gomphodont cynodonts with abundant, diverse sauropodomorph dinosaurs.Item Rediscovery of the holotype of Clelandina major Broom, 1948 (Gorgonopsia: Rubidgeinae) with implications for the identity of this species(Evolutionary Studies Institute, 2017-12) Kammerer, Christian F.No specimen number was given for the holotype of the rubidgeine gorgonopsian species Clelandina major Broom, 1948 in its original description. Historically, a specimen in the Rubidge Collection (RC 94) was considered to represent Broom’s type specimen for C. major. However, recent study has revealed that the holotype of C. major is in fact a different specimen in the McGregor Museum in Kimberley (MMK 5031). The morphology of this specimen is consistent with the genus Clelandina, contra work based on RC 94 that considered C. major referable toAelurognathus. Clelandina major is here considered synonymous with the type species Clelandina rubidgei.MMK5031 represents only the fifth known specimen of this rare and unusual gorgonopsian.Item The bony labyrinth of late Permian Biarmosuchia: palaeobiology and diversity in non-mammalian Therapsida(2017-07) Benoit, Julien; Manger, Paul R; Fernandez, Vincent; Rubidge, Bruce SBiarmosuchia, as the basalmost group of Therapsida (the stem group of mammals), are important for understanding mammalian origins and evolution. Unlike other therapsid groups, the bony labyrinth of biarmosuchians has not yet been studied, despite insightful clues that bony labyrinth morphology can provide to address palaeobiology and phylogeny of extinct animals. Here, using CT scanning, surface reconstruction and a 3D geometric-morphometric protocol of 60 semi-landmarks on the bony labyrinth of 30 therapsids (including three Mammaliaformes), it is demonstrated that bony labyrinth morphology of biarmosuchians is very distinctive compared to that of other therapsids. Despite the primitive nature of their cranial morphology, biarmosuchians display highly derived traits in the structure of the bony labyrinth. The most noticeable are the presence of a long and slender canal linking the vestibule to the fenestra vestibuli, an enlarged and dorsally expanded anterior canal, and the absence of a secondary common crus (except for one specimen), which sets them apart from other non-mammalian therapsids. These characters provide additional support for the monophyly of Biarmosuchia, the most recently recognized major therapsid subclade. Although implications of the derived morphology of the biarmosuchian bony labyrinth are discussed, definitive interpretations are dependent on the discovery of well-preserved postcranial material. It nevertheless sheds light on a previously overlooked diversity of bony labyrinth morphology in non-mammalian therapsids.Item Two unrecognised burnetiamorph specimens from historic Karoo collections(2016-03) Kammerer, Christian F.Two historical specimens from Permian rocks of the Karoo Basin represent previously unrecognised members of the rare therapsid group Burnetiamorpha. These specimens cannot be referred to any existing burnetiamorph species, but are left in open nomenclature because of their incompleteness (both are isolated skull roofs). The first specimen is from the Tapinocephalus Assemblage Zone (AZ) and is characterized by heavily pachyostosed supraorbital bosses and a low nasal crest. The second specimen is from the Tropidostoma AZ and is generally similar to the Malawian taxon Lende, but is unique among described burnetiamorphs in having a frontoparietal ‘dome’ that surrounds the pineal foramen. Phylogenetic analysis of burnetiamorphs recovers support for a split between Proburnetia and Burnetia-like burnetiids, here named Proburnetiinae subfam. nov. and Burnetiinae Broom, 1923.Item A partial skeleton of the tritheledontid Pachygenelus (Therapsida: Cynodontia)(Bernard Price Institute for Palaeontological Research, 2001) Gow, Chris ETritheledontids are advanced cynodonts that are considered the sister group of Mammalia. To date the postcranial skeleton has remained largely unknown, so that cladistic analyses are based on cranial characters only. This paper describes a specimen of the tritheledontid Pachygenelus which has most of the skull and vertebral column, a complete shoulder girdle, and most of the forelimb. The girdle and limb are closely comparable to those of Massetognathusand Eozostrodon, and unlike these elements in tritylodontids, which are more derived for fossorial specialisations.Item New find of Diarthrognathus (Therapsida: Cynodontia) after seventy years(Bernard Price Institute for Palaeontological Research, 1994) Gow, Chris EDiarthrognathus is arguably South Africa's most famous therapsid fossil. Since its discovery seventy years ago no new material had come to light until now. This paper records the recovery, from the Elliot Formation of South Africa, of a partial left lower dentary with most of its dentition preserved.Item A detailed description of the internal structure of the skull of Emydops (Therapsida: Dicynodontia)(Bernard Price Institute for Palaeontological Research, 1993) Fourie, HeidiA detailed morphological study of two skulls of Emydops was undertaken by using the serial grinding technique. Graphic reconstructions of various aspects of the skulls were made. The internal structures are described in detail and compared to other small dicynodonts such as Eodicynodon, Pristerodon, Cistecephalus and Diictodon. Emydops and Cistecephalus show more advanced features in common with each other than with other dicynodonts. The structure of the skull of Emydops conforms within the limits of variation known for this genus, to descriptions given in the literature. It was found that Emydops differs from other dicynodonts in that the parasphenoid has a definite suture with the pterygoid anterior to the pterygoid-basisphenoid suture, instead of passing between the pterygoids without contacting them, as reported by Olson (1944).Item Phylogenetic interrelationships and pattern of evolution of the therapsids: testing for polytomy(Bernard Price Institute for Palaeontological Research, University of the Witwatersrand, 2009-12) Kemp, Tom S.There is little agreement on the interrelationships of the major therapsid subtaxa because none of the variously proposed sister-group relationships are supported by clearly defined, unambiguously distributed morphological characters. Rather than pursue a new cladistic analysis here, the hypothesis is explored that the lack of an agreed cladogram is because there was a polytomy at the base of the therapsid radiation that is not amenable to positive testing by conventional morphological cladistics, but that can be tested in four ways. The virtually simultaneous appearance of all the lineages except Cynodontia in the Middle Permian stratigraphic record supports the hypothesis. The palaeogeographic record, which shows a combination of taxa with first occurrences in different parts of Pangaea also supports it, though this is not strong evidence. The palaeoenvironmental record supports the polytomous hypothesis strongly by providing evidence of a coincidence between the start of the therapsid radiation and the appearance of a new suite of ecological opportunities for diversification within higher latitudes. Finally, a functional correlation analysis of the characters associated with feeding, and the reconstruction of lineages of functionally integrated organisms offers strong support by indicating that no two of the four respective lineages, Dinocephalia, Gorgonopsia, Anomodontia and Therocephalia, could have shared a functionally feasible common ancestral stage subsequent to a hypothetical ancestor at a biarmosuchian grade. The exception is Cynodontia and Therocephalia, which are inferred to have shared such a more recent common ancestral stage, and therefore to be sister-groups in the taxon Eutheriodonta.