A Basal Nonmammaliaform Cynodont from the Permian of Zambia and the Origins of Mammalian Endocranial and Postcranial Anatomy

Nonmammaliaform cynodonts were a diverse group of Permo-Triassic synapsids whose morphological evolution documented the beginning of many classic mammalian traits. Here, we describe a new basal cynodont from the upper Permian Madumabisa Mudstone Formation of Zambia’s Luangwa Basin as <i>Nshimbodon muchingaensis</i> gen. et sp. nov. The holotype, a relatively complete and undistorted cranium and articulated mandible with associated postcranial elements, is interpreted as the most complete and well-preserved example of a charassognathid cynodont, and preserves hitherto unknown details of charassognathid endocranial and postcranial anatomy. A phylogenetic analysis of 111 morphological characters from 25 therapsid taxa (including 15 Permo-Triassic cynodonts) supports a sister-taxon relationship between <i>Nshimbodon</i> and <i>Abdalodon</i>, including them with <i>Charassognathus</i> in a monophyletic Charassognathidae, and placing the family near the base of Cynodontia. In addition to its phylogenetic importance, <i>Nshimbodon</i> provides evidence of correlated transformations in the feeding system, neck, and shoulder, which are consistent with novel mammal-like locomotor and feeding mechanics in the earliest cynodonts. Lastly, given previous reports of charassognathids in the Karoo Basin of South Africa, the occurrence of <i>Nshimbodon</i> indicates that charassognathids, like the basal cynodont <i>Procynosuchus</i>, were geographically widespread in southern Pangea by Lopingian times. Continued collecting in the Madumabisa Mudstone Formation will lead to a better understanding of the formation’s Permian cynodont diversity and biostratigraphy, as well as the biogeographic structure of southern Pangean vertebrate assemblages prior to the Permo-Triassic mass extinction. http://zoobank.org/urn:lsid:zoobank.org:pub:143CE9D3-5742-4E92-B48F-164685F0907C