CONICET, Buenos Aires, Argentina.
División Paleontología Vertebrados, Museo de La Plata, Paseo del Bosque s/n, 1900, La Plata, Argentina.
Sci Rep. 2020 Mar 20;10(1):5150. doi: 10.1038/s41598-020-62033-8.
The homology and evolution of the archosaur ankle is a controversial topic that has been deeply studied using evidence from both extinct and extant taxa. In early stem archosaurs, the astragalus and calcaneum form the ancestral proximal tarsus and a single ossification composes the centrale series. In more recent stem archosaurs, the centrale is incorporated to the proximal row of tarsals laterally contacting the astragalus. This bone is subsequently lost as an independent ossification before the last common ancestor of birds and crocodilians, but the evolutionary fate of this element remains mostly unexplored. Here, we integrate embryological and palaeontological data with morphogeometric analyses to test the hypothesis of loss of the centrale or, alternatively, its incorporation into the archosaurian astragalus. Our results support the latter hypothesis, indicating that the astragalus developed ancestrally from two ossification centres in stem archosaurs and that the supposed tibiale of bird embryos represents a centrale. This conclusion agrees with previous embryological studies that concluded that the tibiale never develops in diapsids.
主龙类踝部的同源性和演化是一个备受争议的话题，已经使用来自已灭绝和现生物种的证据进行了深入研究。在早期的主龙类中，距骨和跟骨形成了祖先的近端跗骨，并且单个骨化组成了中央系列。在更近的主龙类中，中央系列被纳入近端跗骨列，侧向接触距骨。在鸟类和鳄鱼的最后共同祖先之前，这块骨头作为一个独立的骨化被丢失，但这个元素的进化命运在很大程度上仍未被探索。在这里，我们将胚胎学和古生物学数据与形态几何分析相结合，以检验中央系列丢失或被纳入主龙类距骨的假说。我们的结果支持后一种假说，表明距骨在主龙类中最初是由两个骨化中心发育而来，而鸟类胚胎的所谓胫腓骨代表了中央系列。这个结论与之前的胚胎学研究一致，即胫腓骨在合弓类动物中从未发育。
