Department of Geosciences, University of Tübingen, Hölderlinstr, 12, 72074 Tübingen, Germany.
BMC Evol Biol. 2013 Dec 6;13:266. doi: 10.1186/1471-2148-13-266.
Proterochersis robusta from the Late Triassic (Middle Norian) of Germany is the oldest known fossil turtle (i.e. amniote with a fully formed turtle shell), but little is known about its anatomy. A newly prepared, historic specimen provides novel insights into the morphology of the girdles and vertebral column of this taxon and the opportunity to reassess its phylogenetic position.
The anatomy of the pectoral girdle of P. robusta is similar to that of other primitive turtles, including the Late Triassic (Carnian) Proganochelys quenstedti, in having a vertically oriented scapula, a large coracoid foramen, a short acromion process, and bony ridges that connect the acromion process with the dorsal process, glenoid, and coracoid, and by being able to rotate along a vertical axis. The pelvic elements are expanded distally and suturally attached to the shell, but in contrast to modern pleurodiran turtles the pelvis is associated with the sacral ribs.
The primary homology of the character "sutured pelvis" is unproblematic between P. robusta and extant pleurodires. However, integration of all new observations into the most complete phylogenetic analysis that support the pleurodiran nature of P. robusta reveals that this taxon is more parsimoniously placed along the phylogenetic stem of crown Testudines. All current phylogenetic hypotheses therefore support the basal placement of this taxon, imply that the sutured pelvis of this taxon developed independently from that of pleurodires, and conclude that the age of the turtle crown is Middle Jurassic.
来自德国晚三叠世（诺利阶中期）的 Proterochersis robusta 是已知最古老的化石龟（即具有完全形成的龟壳的羊膜动物），但对其解剖结构知之甚少。一个新准备的历史标本为这个分类单元的肩带和脊柱的形态提供了新的见解，并为重新评估其系统发育位置提供了机会。
P. robusta 的肩带解剖结构与其他原始龟类相似，包括晚三叠世（卡尼阶）的 Proganochelys quenstedti，具有垂直定向的肩胛骨、大的喙骨孔、短的肩峰突和连接肩峰突与背侧突、关节窝和喙骨的骨嵴，并且能够沿着垂直轴旋转。骨盆元素在远端扩张并与壳缝合，但与现代侧颈龟类不同的是，骨盆与荐肋骨相关联。
“缝合骨盆”特征在 P. robusta 和现存的侧颈龟类之间的主要同源性没有问题。然而，将所有新的观察结果整合到最完整的系统发育分析中，支持 P. robusta 的侧颈龟类性质，表明该分类单元更简洁地位于冠龟类的系统发育主干上。因此，所有当前的系统发育假说都支持该分类单元的基础位置，暗示该分类单元的缝合骨盆是独立于侧颈龟类发展而来的，并得出龟类冠的年龄是中侏罗世的结论。
