Baron Matthew G, Barrett Paul M
Department of Earth Sciences, University of Cambridge, Downing Street, Cambridge CB2 3EQ, UK
Department of Earth Sciences, Natural History Museum, London, Cromwell Road, London SW7 5BD, UK.
Biol Lett. 2017 Aug;13(8). doi: 10.1098/rsbl.2017.0220.
The enigmatic dinosaur taxon was originally described as a tetanuran theropod, but this species possesses a highly unusual combination of features that could provide evidence of alternative phylogenetic positions within the clade. In order to test the relationships of , we added it to a new dataset of early dinosaurs and other dinosauromorphs. Our analyses recover in a novel position, as the earliest diverging member of Ornithischia, rather than a tetanuran theropod. The basal position of within the clade and its suite of anatomical characters suggest that it might represent a 'transitional' taxon, bridging the morphological gap between Theropoda and Ornithischia, thereby offering potential insights into the earliest stages of ornithischian evolution, which were previously obscure. For example, our results suggest that pubic retroversion occurred prior to some of the craniodental and postcranial modifications that previously diagnosed the clade (e.g. the presence of a predentary bone and ossified tendons).
这个神秘的恐龙分类单元最初被描述为坚尾龙类兽脚亚目恐龙，但该物种具有一系列极为独特的特征组合，这些特征可能为其在演化支内的其他系统发育位置提供证据。为了检验它的系统关系，我们将其添加到一个包含早期恐龙和其他恐龙形类的新数据集中。我们的分析结果显示，它处于一个新的位置，即鸟臀目最早分化出来的成员，而非坚尾龙类兽脚亚目恐龙。它在演化支内的基部位置及其一系列解剖学特征表明，它可能代表一个“过渡”分类单元，填补了兽脚亚目和鸟臀目之间的形态学空白，从而为此前尚不明确的鸟臀目演化早期阶段提供了潜在的见解。例如，我们的结果表明，耻骨后倾发生在一些先前用于界定该演化支的颅齿和颅后特征（如前齿骨和骨化肌腱的存在）之前。
