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 Nshimbodon muchingaensis 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 Nshimbodon and Abdalodon, including them with Charassognathus in a monophyletic Charassognathidae, and placing the family near the base of Cynodontia. In addition to its phylogenetic importance, Nshimbodon 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 Nshimbodon indicates that charassognathids, like the basal cynodont Procynosuchus, 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

非哺乳形犬齿兽类（Nonmammaliaform cynodonts）是一类多样性丰富的二叠纪-三叠纪合弓类（synapsids）类群，其形态演化记录了诸多经典哺乳动物特征的起源。本文记述了一件采自赞比亚卢安瓜盆地二叠纪上部马杜马比萨泥岩组的基干犬齿兽类新属新种：*Nshimbodon muchingaensis* gen. et sp. nov.，其正模标本为一件相对完整且未受变形的颅骨、关联下颌骨及相关颅后骨骼。该正模标本被认为是目前已知最完整、保存最完好的叉颌兽科（Charassognathidae）犬齿兽类标本，且保留了此前未知的叉颌兽科颅腔解剖学与颅后解剖学细节。针对25个兽孔类（therapsid）类群（包含15个二叠纪-三叠纪犬齿兽类）的111个形态特征开展的系统发育分析显示，*Nshimbodon* 与阿贝达龙属（*Abdalodon*）构成姊妹群关系，二者与叉颌兽属（*Charassognathus*）一同归入单系的叉颌兽科，且该科位于犬齿兽亚目（Cynodontia）的基干位置。除系统发育学意义外，*Nshimbodon* 还为取食系统、颈部与肩部的协同演化提供了证据，这与最早犬齿兽类中新颖的类哺乳动物运动与取食力学特征相契合。此外，鉴于此前在南非卡鲁盆地（Karoo Basin）已有叉颌兽科的报道，*Nshimbodon* 的发现表明，叉颌兽科与基干犬齿兽类原犬鳄龙属（*Procynosuchus*）一样，在乐平世就已广泛分布于泛大陆南部。对马杜马比萨泥岩组的持续野外采集工作，将有助于我们进一步明晰该地层中二叠纪犬齿兽类的多样性与生物地层学特征，以及二叠纪-三叠纪大灭绝之前泛大陆南部脊椎动物群的生物地理结构。
http://zoobank.org/urn:lsid:zoobank.org:pub:143CE9D3-5742-4E92-B48F-164685F0907C