The oldest turtle only has a belly in the abdomen

A new fossil study reveals that hard-shell turtles that live in China's coastal waters 220 million years ago are the oldest 'turtles' ever.

They have apricot belly but the back is not shielded .

Last week, a group of scientists announced the discovery of the oldest underwater turtle, dating back 164 million years . But that is just a title that exists for a short time. The tortoise-shell turtle that Chun Li (Chinese Academy of Science in Beijing) and his colleagues studied and named Odontochelys semistestacea existed a long time ago.

Ancient underwater turtles Odontochelys semitestacea have apricot shells to protect from the bottom as they swim in China's coastal waters. (Photo: Marlene Donnelly)

Li and his research team left the remnant including two skulls and bones unearthed in Guizhou Province - China in 2007. Their analysis was published in the November 27 issue of the journal Nature. Analysis shows that modern turtles have originated from ancestors living in the water. The results also provide evidence for the hypothesis about the evolutionary path of tortoise shells.

Mai formed from the belly

The sample has many signs of primitive turtles. For example, the researchers found Odontochelys turtles with pointed, elongated snout. Most modern turtles have short snout. In addition, the base of the mouth with the lower jaw has teeth. According to the researchers, this is a primitive feature when the present turtle has a muzzle with a beak but no teeth.

In fact, turtles once had a shell (only covering the abdomen). This sheds light on the intermediate development in the evolution of tortoise shells that researchers have never discovered. Before the discovery of Odontochelys, the oldest known turtle was the Proganochelys tortoise, which lived about 210 million years ago . But the turtle now has a fully developed shell, which provides little evidence of the evolutionary path of tortoise shells.

The bone part of the ancient turtle shows its abdomen covered by a shell called a bib. ( Photo: Ancient Institute of Anthropology and Invertebrate Paleontology, Beijing)

It has been suggested that turtle shells evolved from bone plates on the skin, then expanded and joined together to form armor for turtles. The overall structure will then combine with the lower spine and ribs. (Modern reptiles, for example, alligators have bone plates, just like some other dinosaurs.)

However, the recent sample of Odontochelys has no trace of bone disc on the skin. Instead they have large ribs, belly apricot extending from the spine bone. These characteristics point to another way of evolving tortoises, in which the abdomen in the abdomen develops first. Then the ribs and spine will expand to form the apricot above.

Ancient turtles live under water

The evolutionary step, according to research findings, matches the apricot formation in modern tortoise embryos in which the spine extends outward, extending ribs to join together to form apricot.

The complete Mai on the underside of the newly discovered fossil also shows that turtles used to live under water, where their abdomen is easily attacked by opponents. Olivier Rieppel, a geographer at the Field Museum in Chicago, said: 'Reptiles living on the edge have a belly near the ground, so there is little danger.'

The bone part of the ancient turtle shows Odontochelys tortoises without hard shells covering their backs. (Photo: Ancient Institute of Anthropology and Invertebrate Paleontology, Beijing)

Along with the Nature paper, the researchers point out another theory about this partially protected turtle. They argue that more ancient turtles even have perfect upper and lower shells. For newly discovered turtles, they have reduced their consumption in the future, but they are not as hard as bones.And this is a form of adaptation to underwater life.

But Rieppel opposed the point. He said that if the turtle actually carried a complete apricot, the researchers would recognize changes in its ribs and spine. But in fact they did not detect any changes.

The study was funded by the Ministry of Science and Technology of China, the National Natural Science Foundation of China, the Chinese Academy of Sciences and the Canadian Natural Museum.