Your Daily Fossil

Proganochelys

When: Early Triassic (~210 million years ago)

Where: Germany and Thailand

What: Proganochelys is the oldest known terrestrial turtle. It shows that even in the early Mesozoic turtles already had a very modern body plan, with a fully formed shell. In fact, Proganochelys had a bit more armor than modern turtles. This is because it could not retract it limbs or head into its shell for protection. The way that this ancient turtle protected its head was a series of spikes on the top of its neck. It also had a heavily spiked tail, which ended in a club. Beyond these features, and a slightly larger shell in general, Proganochelys is remarkably simular to a modern turtle. 

Proganochelys and other early Mesozoic turtles are so simular to living forms that for many years they were thought to be closely related to these extant species. Modern turtles are divided into two groups, the Cryptodira and Pleurodira. The major difference between these two forms is how the neck is retracted into the shell, with the former pulling the head straight back and the latter curving the neck into an S-shape. Recent cladistic studies now place Proganochelys and many other early Mesozoic turtles outside either of these two groupings, as stem turtles.