A fossil discovered in China has brought science a step closer to connecting the points of turtle evolution, reveals a report published in Nature.
Scientists know that the forerunners of modern turtles and turtles with a generally recognizable body plan appeared for the first time in the late Triassic, about 200 million years ago. But precisely from which group of reptiles they descend, remains one of the most persistent puzzles of evolution.
The oldest known turtle had been around for more than a century proganochelys. It had a fully formed scale, but its origins remained unknown. However, its dating has been offset by a series of recent findings.
A fossil form first identified in the nineteenth century, called Eunotosaurus, has recently been proposed as the last common ancestor of turtles. Eunotosaurus was a landlike lizard-like reptile with a bone structure similar to that of turtles, 260 million years ago from Africa.
Then transition fossils between Eunotosaurus and proganochelys have been discovered and help scientists understand how modern turtles connect with the reptiles of the Mesozoic, of which the Trias was the first part.
In 2015, two German researchers unveiled Pappochelys, a semi-aquatic turtle species that goes back to 240 million years. This continued on the earlier discovery in 2008 of the possible sea house odontochelys, another transition fossil dating back 220 million years.
The study of the evolution of turtles is questioned by a constant conflict between sources of evidence: morphological or anatomical studies suggest a connection with an early sister clade with reptiles known as Parareptilia, while molecular evidence points to a place between the true reptiles.
odontochelys led many to place turtles in the enormous and varied clade known as the diapsides, including birds and crocodiles. This was an unusual case of morphological evidence supporting a reptile classification.
Now, three of the four discoverers of odontochelys have revealed another transition type. Chun Li of the Chinese Academy of Sciences, Beijing, Olivier Rieppel of the Field Museum of Natural History, Chicago, in the US, Xiao-Chun Wu of the Canadian Museum of Nature, Ottawa, have merged with Nicholas Fraser of the National Museums of Scotland in the UK and have published their findings Eorhynchochelys sinensis.
E. sinensis, discovered in southwestern China, is a two and a half meter complete fossil of a turtle ancestor without a fully developed scale. Dating back 228 million years, it fits in between Pappochelys and odontochelysbut strangely shows far more pronounced turtle-like characteristics than the younger ones odontochelys, with a head that looks very much like modern tortoises and the true tortoiseshell beak.
However, E. sinensis also has anatomical features that go back to the early species Eunotosaurus, in what the authors & # 39; an evolutionary reversal & # 39; to mention.
Although evidence is always welcome, the most recent find does little to clarify the evolution of turtles. In any case, it refers to an increasingly complex story that requires much more work to give meaning.