ABSTRACT

Fossils of drepanosauromorphs, a clade of non-saurian diapsids, were once considered relatively rare in the Chinle Formation of the southwestern United States as well as in Upper Triassic rocks globally. Recent discoveries have shown that there are at least four drepanosauromorph taxa present in the Chinle Formation including Dolabrosaurus aquatilis, Drepanosaurus sp., Ancistronychus paradoxus, and a new genus and species described here, Skybalonyx skapter. This new taxon is represented by disarticulated manual unguals and is preserved in a microvertebrate bearing bone-bed in the Blue Mesa Member (∼223–220 Ma) of the Chinle Formation at Petrified Forest National Park, which was deposited in a fluvio-lacustrine setting in equatorial Pangaea during the mid-Norian. Different types of substrate use have been hypothesized for the Drepanosauromorpha. By performing discriminant function analyses using the manual unguals of 173 mammal and 13 reptile species with known substrate use, we hope to infer the ecomorphology of drepanosauromorphs. We found that the enlarged second manual unguals of Drepanosaurus sp. are similar to hook-and-pull digging taxa (e.g., Tamandua mexicana and Cyclopes didactylus) although the smaller manual unguals referred to this taxon (likely pertaining to digits other than digit II) are similar to modern arboreal taxa. Our results support the inference of arboreality in some drepanosauromorph species. However, we found that the manual unguals of Ancistronychus paradoxus and Skybalonyx skapter fit within the range of variation of modern fossorial and subterranean taxa, which expands the functional diversity of the Drepanosauromorpha within the Chinle Formation.

摘要

drepanosauromorphs的化石，一种非索非尔的双足类化石，曾经被认为在美国西南部的Chinle组以及全球上三叠统的岩石中相对罕见。最近的发现表明，在Chinle组中至少存在四种drepanosauromorph类群，包括水生Dolabrosaurus，Drepanosaurus sp。，Ancistronychus paradoxus，以及此处描述的一种新属和种，Skybalonyx skapter。。这种新的分类单元由分离的人工蹄类动物代表，并保存在石化森林国家公园Chinle组的Blue Mesa成员（约223–220 Ma）的带有微脊椎骨的床中，该床沉积在河湖相中。在诺里安中期的赤道Pangea中。对于Drepanosauromorpha，已经假设使用不同类型的底物。通过使用已知底物用途的173种哺乳动物和13种爬行动物物种的人工操作进行判别功能分析，我们希望推断drepanosauromorphs的生态形态。我们发现，Drepanosaurus sp。的扩大了的第二只手的幼虫。类似于钩拉挖掘类群（例如Tamandua mexicana和Cyclopes didactylus），尽管与此分类单元相关的较小的手动操作者（可能与数字II以外的数字有关）类似于现代的树木类目。我们的结果支持对某些drepanosauromorph物种的树木的推断。然而，我们发现，Ancistronychus paradoxus和Skybalonyx skapter的人工幼虫正好适应了现代窝和地下类群的变化范围，从而扩大了Chinle组中Drepanosauromorpha的功能多样性。