ABSTRACT

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

摘要

非哺乳动物的犬齿类是由一群不同的Permo-Triassic突触构成的，它们的形态演变证明了许多经典哺乳动物性状的开始。在这里，我们描述了来自赞比亚卢安瓜盆地上二叠纪马杜马比萨泥岩组的一种新的基底犬齿，为Nshimbodon muchingaensis gen。等。十一月 完整型颅骨，相对完整且未变形的颅骨，下颌关节清晰，并伴有相关的颅后元件，被解释为charassognathid cynodont的最完整且保存最完好的例子，并保留了charassognathid颅内和颅后解剖结构迄今未知的细节。对来自25个节肢动物类群（包括15个Permo-Triassic犬齿类）的111个形态特征进行系统发育分析，支持了它们之间的姐妹-类群关系Nshimbodon和Abdalodon，包括他们与Charassognathus一起生活在一个单一的Charassognathidae中，并将这个家庭安置在Cynodontia的附近。除了在系统发育上的重要性外，Nshimbodon还提供了饲喂系统，颈部和肩部相关转化的证据，这与最早的犬齿类的新型哺乳动物样运动和饲喂机制是一致的。最后，鉴于以前在南非卡鲁盆地中发现的charassognathids，Nshimbodon的出现表明charassognathids像基底犬齿Procynosuchus，在Lopingian时代在Pangea南部分布广泛。在Madumabisa泥岩组中继续收集将有助于人们更好地了解该组的二叠纪犬齿多样性和生物地层学，以及在二叠纪—三叠纪大规模灭绝之前南部庞氏脊椎动物组合的生物地理结构。

http://zoobank.org/urn:lsid:zoobank.org:pub:143CE9D3-5742-4E92-B48F-164685F0907C