PermeateFree said:
>>According to a new international study, the fact that it had a beak before other ancient turtles, but it didn’t have the partial shell that they did, is an example of mosaic evolution. Essentially, this means that different ancestral species of a modern animal evolved different traits at different times, with those traits eventually all occurring in one animal.<<
https://newatlas.com/prehistoric-beaked-shell-less-turtle/56037
Very interesting. The following is a summary of what was known just two years ago.
https://allyouneedisbiology.wordpress.com/2016/10/19/turtle-shell-evolution/
The origin of turtles is still debated among the scientific community. Turtles show some anatomic characteristics not found among any current vertebrate, which makes their phylogenetic origin confusing. One of the characteristics that has puzzled palaeontologist more is their skull. While the rest of reptiles are diapsid (they present a pair of temporal openings at each side of the skull), turtles present a typically anapsid cranium (without any temporal openings). Yet, recent genomic studies have proved that it’s more likely that testudines (order Testudines, current turtles) descend from a diapsid ancestor and that through their evolution they reverted back to the primitive anapsid form. What is not so clear is if turtles are more closely related to lepidosaurs (lizards, snakes and tuataras) or to archosaurs (crocodiles and birds). The most accepted hypothesis is the second one.
Eunotosaurus africanus is the most ancient candidate to being a turtle’s relative. Eunotosaurus was a fossorial animal that lived 260 million years ago in South Africa. The oldest indisputable relative of turtles is Pappochelys rosiane from Germany (240 million years ago).
The next step in the evolution of turtles is found 220 million years ago, during the late Triassic in China. Its name is Odontochely semitestacea, which means “toothed turtle with half a shell”. This name is due to the fact that, unlike true turtles, Odontochelys still had a mouth full of teeth and it only presented the lower half of the shell, the plastron.
The first testudine known to possess a complete shell is Proganochelys quenstedti from the Triassic period, 210 million years ago. It already presented many characteristics found in current turtles: the shell was completely formed, with carapace and plastron, its skull was anapsid looking and it had no teeth. However, Proganochelys wasn’t able to retract its head and legs inside its shell (even if this may be because of the horns it had). It also presented two extra shell pieces at both sides, which probably served to protect its legs.
———-
Now compare that to the new one from PermeateFree’s link.
Known as Eorhynchochelys sinensis, the turtle was over six feet long (2 m) and lived approximately 228 million years ago. In the past decade, scientists have discovered the fossilized remains of two prehistoric turtles that had a partial shell, but that lacked the toothless beak of modern turtles. Recently, however, a fossil turtle was found that had no shell at all, but that did have a beak.
So, there’s a physiological incompatibility between Eorhynchochelys sinensis and Odontochely semitestacea. How do we interpret this? It seems most likely that modern turtles descended from one or the other but not both. That E sinensis is descended from O semitestacea seems unlikely because E sinensis is the older fossil. On the other hand, that O semitestacea is descended from E sinensis seems unlikely because teeth once lost are unlikely to regrow back exactly as before. So the two seem to be on separate evolutionary paths.
“we know that turtles are not related to the early anapsid reptiles, but are instead related to evolutionarily more advanced diapsid reptiles. This is cemented, the debate is over.”
OK. I agree. DNA says the same thing.
