A new endothiodont dicynodont (Therapsida, Anomodontia) from the Permian Ruhuhu Formation (Songea Group) of Tanzania and its feeding system

ABSTRACTCranial material of the dicynodont <i>Endothiodon</i> from the middle fossiliferous horizon of the Permian Ruhuhu Formation (Ruhuhu Basin, Tanzania) is described as a new species, <i>E. tolani</i>. <i>Endothiodon tolani</i> is distinguished from other <i>Endothiodon</i> species by the absence of a pineal boss and the presence of tusks in most specimens. Although some parts of the Ruhuhu Formation probably correlate with the <i>Eodicynodon</i> or <i>Tapinocephalus</i> assemblage zones of the South African Karoo Basin, it is uncertain whether <i>E. tolani</i> is older than <i>E. bathystoma</i> or <i>E. mahalanobisi</i>. There is less evidence for extensive anteroposterior translation of the mandible in <i>E. tolani</i> than in other dicynodonts. The jaw joint is specialized for allowing some medial-lateral motion. Mastication involved unilateral chewing. Flexure of the postdentary bones relative to the fused dentaries permitted the posterolaterally directed rows of teeth on one side of the skull and mandible to move past one another. The long tooth rows and prominent horn-covered ridges and grooves on the palate and mandible of <i>Endothiodon</i> are unique among dicynodonts. Comparisons with other taxa suggest that its feeding system may have been specialized for cutting three-dimensional objects such as stems or rhizomes. The dicynodont feeding system is very stereotyped throughout the clade's history, but <i>Endothiodon</i> escaped the constraints that affected other dicynodonts, allowing it to evolve a unique skull morphology. This evolutionary flexibility did not translate into high taxonomic richness (we recognize only three species of <i>Endothiodon</i>), but <i>Endothiodon</i> was able to achieve high levels of relative abundance in some basins.http://zoobank.org/urn:lsid:zoobank.org:pub:9686F708-2E6E-40EB-956F-05659889684FSUPPLEMENTAL DATA—Supplemental materials are available for this article for free at www.tandfonline.com/UJVP