A small thing made me happy today, which made my inner zoology and paleontology nerd really happy.
So for many animals, their ancestry can be fuzzy and incomplete, and for many others, their origins and ancestors are quite well known. For birds and dinosaurs, we have loads of fossils, for us humans, loads of fossil ancestors, for whales, loads of fossil ancestors, and so on.
And for lizards and snakes, loads of fossil ancestors, and I've always had a love and fondness for reptiles, with my favorite extant reptiles being turtles.
For a long time, turtles were kind of a mystery, as we only had a few fossils of their ancestors, hypotheses about their evolution were hazy and fuzzy, specifically referring to their skull and shell, as turtles were long thought to be anapsids, which is, amniotes that have no temporal openings in the skull, as sights for muscle attachment in turtles is in the rear of the skull.
Which presented a unique anomaly in reptile evolution and ancestry. Birds, crocodiles, lizards, dinosaurs, pterosaurs, tuataras, and snakes all had clear ancestry, and turtles it seemed, were an evolutionary dead-end.
Turns out, actually, that turtles are diapsids, meaning they are descended from amniotes that have two temporal openings in the skull, they just closed over, as that's what early ancestors of turtles showed. So really, turtles are more closely related to the classic diapsids that I just listed.
Then the debate shifted to whether turtles are more closely related to birds and crocodiles, or to lizards, tuataras, and snakes.
Turns out, turtles shared their most recent common ancestor in the clade where birds and crocodiles belong, called Archosauria, meaning turtles are more closely related to birds, crocodiles, pterosaurs, and dinosaurs. They aren't true archosaurs, they are their own group, known as Testudinata, which are reptiles with a bony carapace and plastron forming a shell.
What's more, more fossil evidence came out showing another unique aspect about turtles: how their shells formed.
Turns out, ancestors of turtles go clear back to the Middle Permian, some 300 million years ago, showing that turtles are not just long lived in general, but are
quite an old family of reptiles.
Anyhow, fossils of early turtle ancestors showed that they lacked the carapace, (the back part of the shell), and a plastron (the front part of the shell), but they had shortened torsos, expanded ribs, and lengthened dorsal vertebrae.
In the Late Triassic, that trait continued. Initially, scientists were unsure which part of the shell developed first. Was it the plastron that came first and then the carapace? Was it the carapace first and then the plastron? Or was it both?
Turns out, turtle ancestors in the Late Triassic showed that the plastron formed from expanded gastralia, and the carapace was slowly forming from rib osteoderms.
The first true turtle is
Proganochelys, a turtle from the Late Triassic that had a fully formed plastron and carapace, and one of the stem groups in the clade, Testudinata, a group of reptiles with a bony, protective shell.
In this research, I also found out what species of turtle the Teenage Mutant Ninja Turtles are according to the original comics.
They're Red-eared sliders, a species of pond slider turtles that are semi-aquatic.