ABSTRACT

Probainognathian cynodonts are well represented in the fossil record from the Middle and Upper Triassic of South America, especially in Brazil and Argentina. In this contribution, we describe a new genus and species of non-mammaliaform prozostrodontian cynodont from southern Brazil. The new taxon comes from the Niemeyer Site, a locality in which the traversodontid cynodont Siriusgnathus niemeyerorum is numerically dominant, whereas probainognathians and other tetrapods are comparatively scarce. The fauna from the Niemeyer Site was putatively assigned to the Riograndia Assemblage Zone (Norian age) recently, although none of the index fossils for that biozone (e.g., Riograndia, Clevosaurus, Jachaleria) have so far been discovered at this locality. The new cynodont taxon is based on a left lower jaw with the canine and six (pc2–pc7) well-preserved postcanines (CAPPA/UFSM 0262, holotype), and a second referred specimen (CAPPA/UFSM 0208, paratype), which includes a right lower jaw with incisors, canine, and seven (pc1–pc7) postcanines, with pc6–pc7 being the best preserved. These specimens have a robust dentary, a long and dorsoventrally tall Meckelian groove, unserrated canines, and unserrated, sectorial postcanine teeth with posteriorly inclined cusps and a poorly developed lingual cingulum. This combination of features is unknown in other Carnian and Norian non-mammaliaform cynodonts. The new taxon contributes to our knowledge of the evolutionary radiation of small prozostrodonts that occurred in western Gondwana during the Late Triassic and led to the emergence of several important cynodont groups, including Mammaliaformes.

http://zoobank.org/urn:lsid:zoobank.org:pub:FDC21881-532B-490A-96A1-A65EA5F62737

摘要

南美白三叠纪中，上三叠统的化石记录中很好地体现了Probainognathian犬齿类动物，特别是在巴西和阿根廷。在此贡献中，我们描述了来自巴西南部的非哺乳动物类原口齿犬齿犬齿科的新属和种。新的分类单元来自尼迈耶（Niemeyer）站点，该地区在数量上占优势的是横纹齿犬齿天狼星（Siriusgnathus niemeyerorum），而白藻和其他四足动物则相对稀少。从尼迈耶网站上的动物被推定分配到里奥格兰德兽属组合带（诺利岁）最近，尽管没有索引化石为BIOZONE（例如，里奥格兰德兽属，Clevosaurus，哈查尔兽属）迄今已在该地区被发现。新的犬齿类群基于左下颌，犬和六个（pc2-pc7）保存完好的犬齿（CAPPA / UFSM 0262，完整型），以及第二个参照标本（CAPPA / UFSM 0208，同型），包括右下颌上有门牙，犬齿和七个（pc1-pc7）犬齿，其中pc6-pc7是保存最完好的。这些标本具有健壮的牙齿，长而高的背侧Meckelian沟，不锯齿的犬齿，不锯齿的扇形后犬齿，后牙尖倾斜，舌舌扣带发育不良。在其他Carnian和Norian非哺乳动物的犬齿犬齿中，这种特征的组合是未知的。

http://zoobank.org/urn:lsid:zoobank.org:pub:FDC21881-532B-490A-96A1-A65EA5F62737