What Is the True “Papa” Turtle? A Discussion About the Origin of The Clade Testudines from Both Morphological and Molecular Perspectives

Abstract

Turtles, from the order Testudines has a debatable origin. The oldest defined species of the order was Proganochelys quenstedti from the late Triassic. However, the origin or the ancestor of this species has been a hot topic among scientists. This paper discussed the potential origin of the turtles using both the morphological and molecular perspectives. Based on the morphological evidence for the evolution of the defining features, one theory suggested that this order originated from the Eunotosaurus africanus which the dorsal ribs fused together first; other theories suggested that it originated from Odontocheyls semi Testacea which the ventral ribs fused first. The skull structure is another debatable topic as evolutionary evidence which the current turtles are classified as anapsid due to its lack of temporal fenestration. However, many of the potential ancestors showed defining two fenestrations of diapsids or at least some features indicating it was evolving into anapsid. The molecular evidence of mitochondrion cDNA showed that the Testudines clade diverged from the other Archosauri in Jurassic which completely overthrow all the hypothesis. Although morphological based theory has its flaw, it was a more convincing theory than the molecular based theory. As some studies suggested that the Odontotomy’s semi Testacea could lost its dorsal shell inherited from its ancestor, the hypothesized evolutionary route is E. africanus àPappocheyl. rosinae àO. semitestaceaàP. quenstedti.