Two Dicynodont Papers

A New Species of Emydops (Synapsida, Anomodontia) and a Discussion of Dental Variability and Pathology in Dicynodonts

Jörg Fröbisch and Robert R. Reisz

Department of Biology, University of Toronto at Mississauga, 3359 Mississauga Rd., Mississagua, Ontario, L5L 1C6, Canada, E-mail: jorg.frobisch@utoronto.ca, E-mail: robert.reisz@utoronto.ca

An enigmatic dicynodont specimen from Tweefontein in Graaff-Reinet, South Africa, represents a new species of the Middle to Late Permian genus Emydops, E. oweni. Taxonomic revision of the genus reveals that, of the thirteen previously described species, only E. arctatus is valid. The holotype of E. oweni, SAM-PK-3721 is unusual in that it bears two tusks on each side of the skull, a symmetrically developed double-tusked condition being a very rare if not unique case in the dicynodont fossil record. The possible pathological causes for this occurrence are discussed and the production of the supernumerary teeth by mutation is considered to be the most likely explanation. Phylogenetic analysis supports the sister-taxon relationship of the two species of Emydops and their position at the base of Emydopidae. Emydops oweni shares a number of derived characters with E. arctatus, including its small size, wide temporal region, prominent lateral dentary shelf, embayment on the medial surface of the palatal rim, and squared-off profile of occiput. In addition to its aberrant dentition, SAM-PK-3721 can be distinguished from the type species by a number of autapomorphies, including the absence of the small maxillary foramen lateral to the postcaniniform keel, the presence of a distinct ventrolaterally projecting pterygoid flange, and the diagnostic shape of the lateral dentary shelf. The identification of two additional tuskless specimens referable to the new species excludes the possibility that the autapomorphic characters are associated with the double-tusked condition, allowing us to conclude that E. oweni has both tusked and tuskless morphs.

Full paper here.

Diictodon Feliceps (Owen, 1876), A Dicynodont (Therapsida, Anomodontia) Species with a Pangaean Distribution

Kenneth D. AngielczykA and Corwin SullivanB

A. Department of Geology, The Field Museum, 1400 South Lake Shore Drive, Chicago, IL 60605, USA, E-mail: kangielczyk@fieldmuseum.org, B. Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences, P.O. Box 643, Beijing 100044, China, E-mail: csullivan@ivpp.ac.cn

Dicynodont therapsids were cosmopolitan members of Middle and Late Permian terrestrial ecosystems. Despite occurring in nearly all places where tetrapod fossils of these ages are found, it is unclear whether any individual dicynodont species ever achieved a Pangaean distribution, with populations located in both Gondwana and Laurasia. Diictodon feliceps (Owen, 1876) is perhaps the best candidate for a species with such a broad distribution, but this depends on whether D. tienshanensis (Sun, 1973) from the Junggur Basin of China is a valid species. We use qualitative morphological characters, as well as linear measurement- and landmark-based morphometric techniques, to demonstrate that IVPP V.3260 (the type and only known specimen of D. tienshanensis) falls well within the range of variation displayed by D. feliceps, implying that D. tienshanensis is not a valid species. The occurrence of D. feliceps in China poses a biogeographic puzzle, since this species is otherwise known only from southern Africa. We predict that D. feliceps will be discovered in areas between southern Africa and China. However, if its absence persists in the face of continued exploration and collecting efforts, it may imply that a dispersal route and/or intervening populations of D. feliceps existed in areas in which an Upper Permian terrestrial fossil record was not preserved. Finally, if dicynodonts were adapted to exploiting components of the Gondwanan flora, the presence of D. feliceps in Gondwana and Laurasia indicates that such trophic interactions were not an insurmountable barrier to their dispersal.

Full Paper here.

Sweetness. Anything Permian Therapsid-ish is tres kewl as far as I am concerned.