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Background   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.    Results  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.    Conclusions  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.

The girdles of the oldest fossil turtle, Proterochersis robusta, and the age of the turtle crown