摘要
The Triassic Period saw the first appearance of numerous amniote lineages (e.g. Lepidosauria, Archosauria, Mammalia) that defined Mesozoic ecosystems following the end Permian Mass Extinction, as well as the first major morphological diversification of crown-group reptiles. Unfortunately, much of our understanding of this event comes from the record of large-bodied reptiles (total body length > 1 m). Here we present a new species of drepanosaurid (small-bodied, chameleon-like diapsids) from the Upper Triassic Chinle Formation of New Mexico. Using reconstructions of micro-computed tomography data, we reveal the three-dimensional skull osteology of this clade for the first time. The skull presents many archaic anatomical traits unknown in Triassic crown-group reptiles (e.g. absence of bony support for the external ear), whereas other traits (e.g. toothless rostrum, anteriorly directed orbits, inflated endocranium) resemble derived avian theropods. A phylogenetic analysis of Permo-Triassic diapsids supports the hypothesis that drepanosaurs are an archaic lineage that originated in the Permian, far removed from crown-group Reptilia. The phylogenetic position of drepanosaurids indicates the presence of archaic Permian clades among Triassic small reptile assemblages and that morphological convergence produced a remarkably bird-like skull nearly 100 Myr before one is known to have emerged in Theropoda.
摘要译文
三叠纪时期首次出现了大量的羊膜系（例如Lepidosauria，Archosauria，Mammalia），它们定义了二叠纪末灭绝后的中生代生态系统，以及冠组爬行动物的第一次主要形态多样化。不幸，我们对这一事件的了解大部分来自大型爬行动物的记录（总体长 1米）。在这里，我们提出了一种新的drepanosaurid（小体型，变色龙般的diapsids）来自新墨西哥州的上三叠统Chinle组。使用微型计算机断层扫描数据的重建，我们首次揭示了这个分支的三维颅骨骨科。头骨呈现三叠纪冠组爬行动物中未知的许多古老的解剖学特征（例如没有骨支撑外耳），而其他特征（例如无牙讲台，前向轨道，膨胀的内颅）类似于衍生的禽类兽脚类恐龙。Permo-Triassic diapsids的系统发育分析支持这样的假设：drepanosaurs是一种古老的谱系，起源于二叠纪，远离冠冠组织Reptilia。三叠纪小爬行动物组合中古老的二叠纪分支和形态的汇合产生了一个非常类似鸟类的头骨近100 Myr，之前已知出现在Theropoda中。
Adam C. Pritchard[1];Sterling J. Nesbitt[2]. A bird-like skull in a Triassic diapsid reptile increases heterogeneity of the morphological and phylogenetic radiation of Diapsida[J]. Royal Society Open Science, 2017,4(10)