Novel Endocranial Data on the Early Therocephalian Lycosuchus vanderrieti Underpin High Character Variability in Early Theriodont Evolution
Novel Endocranial Data on the Early Therocephalian Lycosuchus vanderrieti Underpin High Character Variability in Early Theriodont Evolution
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DOI：
10.3389/fevo.2019.00464
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发表时间：
2020-01-23
影响因子：
3
通讯作者：
Froebisch, Joerg
中科院分区：
文献类型：
--
作者：
Pusch, Luisa C.;Ponstein, Jasper;Froebisch, Joerg
Therocephalia是Therapsid的主要分支之一，分布于中二叠世至中三叠世。最早的兽头类是体型庞大的掠食者，其化石在南非中二叠世的岩石中很常见，但很少有人研究。在这里，我们提出了一个重新描述的头骨的早期兽头类狼鳄的标本的基础上，从中二叠世Tapinocephalus组合区的南非卡鲁盆地。通过使用这个标本的计算机断层扫描（CT）重建，我们第一次描述了这个分类群的几个颅内特征，包括高度分叉的上颌管和内耳，其特征是延长的外侧半规管，以前只知道从非哺乳动物兽孔目动物中的异齿龙Kawingasaurus的特征，以及耳蜗隐窝的存在，到目前为止，在兽头目中只知道来自高度特化的三叠纪分类群Microgomphodon。我们还提供了新的见解，在狼鳄类，这已被证明是有争议的taxon.Craniodental字符的牙齿更换模式一般支持的位置狼鳄作为最基本的分类群在therocephalian的brachogeny。上颌管和内耳的形态揭示了马赛克的功能，表明一个复杂的历史的字符收购和损失的兽头类，可比的犬齿。
Therocephalia is one of the major therapsid clades and ranges from the middle Permian to Middle Triassic. The earliest therocephalians were large-bodied predators whose fossils are common in middle Permian rocks of South Africa, but have received little study. Here we present a redescription of the skull of the early therocephalian Lycosuchus based on a specimen from the middle Permian Tapinocephalus Assemblage Zone of the South African Karoo Basin. By using a computed tomographic (CT) reconstruction of this specimen, we describe for the first time several endocranial characters of this taxon including a highly ramified maxillary canal and the inner ear, which is characterized by a lengthened lateral semicircular canal, a feature previously only known from the anomodont Kawingasaurus among non-mammalian therapsids, and the presence of a cochlear recess, so far only known within Therocephalia from the highly specialized Triassic taxon Microgomphodon. We also provide new insights into patterns of tooth replacement in lycosuchids, which have proven controversial for this taxon. Craniodental characters generally support the placement of Lycosuchus as the most basal taxon in therocephalian phylogeny. The morphology of the maxillary canal and inner ear reveal a mosaic of features indicating a complex history of character acquisition and loss in Therocephalia, comparable to that of cynodonts.