Bennett S Christopher
Department of Biological Sciences, Fort Hays State University, Hays, KS, USA.
PeerJ. 2020 Feb 19;8:e8418. doi: 10.7717/peerj.8418. eCollection 2020.
The six known specimens of and casts made from their negative impressions were examined to reassess the osteological evidence that has been used to interpret s locomotion and phylogenetic relationships. It was found that the trunk was dorsoventrally compressed. The upper temporal fenestra was on the lateral surface of skull and two-thirds the size of the lower, the jaw joint posteriorly placed with short retroarticular process, and teeth short and subconical, but no evidence of external nares or antorbital fossae was found. The posterior trunk was covered with ~20 rows of closely spaced transversely elongate dorsal osteoderms. The coracoid was robust and elongate. The acetabulum was imperforate and the femoral head hemispherical and only weakly inturned such that the hip joint was unsuited to swinging in a parasagittal plane. The presence of four distal tarsals is confirmed. The marked disparity of tibial and fibular shaft diameters and of proximal tarsal dimensions indicates that the larger proximal tarsal is the astragalus and the significantly smaller tarsal is the calcaneum. The astragalus and calcaneum bear little resemblance to those of , and the prominent calcaneal tuber confirms that the ankle was crurotarsal. There is no evidence that preserved body and limb postures are unnatural, and most specimens are preserved in what is interpreted as a typical sprawling resting pose. A principal component analysis of skeletal measurements of and other vertebrates of known locomotor type found to plot with frogs, and that finding combined with skeletal morphology suggests was a sprawling quadrupedal hopper. Phylogenetic analyses found that was not an ornithodiran, but was either within the Doswelliidae or outside the clade consisting of the most recent common ancestor of the Erythrosuchidae and Archosauria and all its descendants.
对六个已知标本及其负模制作的铸型进行了检查，以重新评估用于解释其运动方式和系统发育关系的骨学证据。研究发现，其躯干在背腹方向上受到压缩。上颞孔位于头骨侧面，大小为下颞孔的三分之二，下颌关节位于后方，关节后突较短，牙齿短且呈亚圆锥形，但未发现外鼻孔或眶前窝的证据。躯干后部覆盖着约20排紧密排列的横向拉长的背侧骨板。喙骨粗壮且细长。髋臼无孔，股骨头呈半球形且仅轻微内翻，使得髋关节不适合在矢状旁平面内摆动。确认存在四块远端跗骨。胫骨和腓骨骨干直径以及近端跗骨尺寸的显著差异表明，较大的近端跗骨是距骨，明显较小的跗骨是跟骨。距骨和跟骨与[某种动物]的距骨和跟骨几乎没有相似之处，突出的跟骨结节证实踝关节是屈跗型。没有证据表明保存的身体和肢体姿势不自然，大多数标本保存的姿势被解释为典型的伸展休息姿势。对[该动物]和其他已知运动类型的脊椎动物的骨骼测量进行主成分分析发现，[该动物]与青蛙聚在一起，这一发现与骨骼形态相结合表明[该动物]是一种伸展式四足跳跃动物。系统发育分析发现，[该动物]不是鸟颈类主龙，但要么属于道氏鳄科，要么在由艾雷拉龙科和主龙形类的最近共同祖先及其所有后代组成的分支之外。
