New insight into the paleobiology and systematics of the Mesozoic turtles of central europe (Chelonipus triunguis Karl & Tichy, 2000; Priscochelys hegnabrunnensis Karl, 2005) and their morphological relationship with the toothed turtle (Odontoche

The origin of the turtle body plan remains one of the great mysteries of reptile evolution. To establish the relationships between turtles of different clades in palaeobiological aspects is highly difficult. Here we describe a review of the oldest Mesozoic turtles of Central Europe (Chelyopsis triunguis; Priscochelys hegnabrunnensis) and their morphological relationship with the toothed turtle (Odontochelys semitestacea) of China. P. hegnabrunnensis is a fossil turtle from the Middle Triassic (lower Ladinian) of Hegnabrunn, Germany. It is known from a single, fragmentary shell plate and is considered a very early turtle, potentially the oldest known stem turtle. The fossil provides insights into the early evolution of turtle shells and their transition from a more primitive state. The habitat preferences of Priscochelys hegnabrunnensis remain uncertain. However, given the informative nature of the material available and, since that it was found mixed with marine and terrestrial faunas, it was probably allochthonous. The other older known turtle record is a trackway from the Bunter Sandstone of Thuringia (Germany) and represents the autochthonous ichno-taxon Chelonipus triunguis. Odontochelys semitestacea was a 220-million-year-old specimen excavated in Triassic deposits in Guizhou, China. Odontochelys only possessed the bottom portion of a turtle‘s armour, the plastron. It did not yet have a solid carapace as most other turtles do. Instead of a solid carapace, Odontochelys possessed broadened ribs like those of modern turtle embryos that still have not started developing the ossified plates of a carapace.