Based on common knowledge, we know that the oldest turtle in the world is the Odontosaurus, which appeared in the Cretaceous period and is the ancestor of all known turtles. Scientists investigated the fossils of the turtle and found that it lived in the Cretaceous period 220 million years ago, making it the most modern turtle in the world and playing a key role in studying the history of turtles.

1. How big is the oldest sea turtle in the world?

The ancestor turtle that people often call is actually the semi-armored turtle. Since it was discovered to be the oldest and oldest sea turtle in the world, Turtles, so they are called ancestral turtles. Like the Dragon Shark, the Hemlock's toothed turtle lived during the Cretaceous period. Archaeologists discovered through investigation and study of its fossils that the Hemlock's tooth turtle was 3.4 meters long and 3.7 meters wide. It was also the largest in size.

Although it appeared 220 million years ago, the body structure and carapace skin of the semi-armored turtle are very similar to those of the leatherback turtles that still exist today, including the structure of the plastron and ribs in the abdomen. Modern turtles are very similar. However, the body size is much larger, and the age is also unparalleled. It was also through the semi-armored turtle that people learned that turtles originally originated in fresh water.

2. Characteristics of the oldest turtle in the world

Originally, human beings believed that turtles were born with shells and plastrons, which were used to When it senses that danger is approaching, it can withdraw to protect itself, but in fact, the role of the turtle's shell is to dig holes and dig soil. However, the world's oldest sea turtle, Semicodon, does not have this characteristic because it has no shell on its back.

The plastron only has a plastron on the abdomen, which looks more like an extension of the ribs on the abdomen. After investigating the fossils of the turtle, archaeologists discovered that in practice The world's oldest turtle is a transitional body, a product of the turtle's degeneration stage. As the turtle degenerates and changes in the environment, it gradually grows a carapace.

In addition, there are many features of the semi-armored turtle that are different from modern turtles, such as the contact surface of the spine and the proportions of the skull, which are all different from today's turtles. The eyes of the turtle are relatively long in the front half, there is no acromial process on the body, and there are pointed and very fine teeth on the upper and lower jaws. The whole body is more like a transitional embryo of modern turtles.

How did the tortoise’s carapace evolve?

At present, it seems that the formation of tortoise carapace does not come from the small bone plates on the back, but should be formed by the bones of the ribs and abdomen. The board evolved.

Turtles and turtles, including tortoises and soft-shell turtles, are the most primitive group of living reptiles and are also witnesses of the age of dinosaurs.

They survived the mass extinction at the end of the Cretaceous, starting from the Mesozoic Era and continuing to the present.

Concerning the origin of turtles and turtles, there has been a long-standing debate in the field of paleontology.

The reason why this problem has been unsolved for many years is mainly because the body structure of turtles is too strange, and there is a lack of reliable fossil records to study the origin of this strange structure.

Fossils of turtles and turtles are not uncommon, but the body structure of all these fossil groups is almost the same as that of living turtles.

Even the Protognathus from the German Triassic (210 million years ago), which was once considered the oldest turtle fossil, looks like an ordinary turtle.

Not only do they have a carapace structure that is very similar to that of living turtles, but like the latter, there are no teeth in the upper and lower jaws, only beaks wrapped in horny shells like birds.

In 2008, Chinese paleontologists found even older primitive turtle fossils in the 220 million-year-old strata of Guanling, Guizhou.

The body structure of this turtle is very different from all known living or fossil turtles.

Its upper and lower jaws also have fine teeth.

What’s even more strange is that the carapace of this turtle is very special. Its plastron is very similar to that of living turtles, but the carapace is almost invisible, only a few pairs on both sides of the spine. Broad ribs shaped like willow leaves.

Paleontologists believe that this represents the prototype state of the early stages of carapace formation.

For turtles, having teeth and an unformed carapace are very primitive and rare features.

The oldest fossil turtle to date is called a hemipelous turtle, which means a turtle with teeth and only half of its carapace (plastron).

For a long time before the semi-shelled turtle was discovered, paleontologists could not find direct clues to the origin of turtles, especially how turtle shells were formed, so they Two hypotheses were put forward, imagining two possible appearances of turtle ancestors.

The first one is that the skin of the back of turtle ancestors had a large number of small bone plates. These small bone plates slowly merged with each other during the later evolution process, and at the same time sank under the skin, and finally connected with the spine and spine. The ribs heal, forming the turtle's carapace.

The second is that the hypothetical small bone plates do not exist in the back skin of turtle ancestors. The carapace is made up of their ribs that gradually widened during the long evolution, and then connected, healed, and finally closed. Forming.

The half-armored turtle is the perfect embodiment of the second hypothesis. Does it mean that it represents the form of the ancestor of turtles? More than a century ago, European paleontologists discovered another strange reptile fossil in the Triassic strata.

Because the specimens are so fragmented, it is difficult to describe the full picture of this animal, but what is certain is that this type of animal has widened ribs and a carapace-like shell made of many small armor plates. Body structure.

This kind of carapace is different from the carapace of ordinary turtles, but is similar to the carapace of a living sea turtle called the leatherback turtle.

In view of this, paleontologists named this fossil Saurophagis, sauro means reptile, and phagis means young leatherback turtle.

Chinese scientists translated it as dragon turtle.

For a long time, the fossils of dragon turtles have been extremely rare. A small number of specimens have been found in Europe, but some important materials were lost during World War II.

It wasn’t until 2011 that Chinese scholars found the relatively complete skeleton of this animal in Yunnan and Guizhou, and they were able to see its true face.

The Chinese fossil specimen is named Yungui Chinese Dragon Turtle.

The situation of the Yunnan-Guizhou Chinese dragon turtle is very consistent with the first hypothesis mentioned above, that is, the situation described by the hypothesis of the origin of the dorsal bone plate of the turtle carapace.

Stratigraphic data show that the Chinese dragon turtle lived about 20 million years earlier than the semi-armored turtle.

Among the Chinese dragon turtles and the semi-armored turtles, which one is the ancestor of today’s turtles? According to the available materials and through complex paleontological research, scientists believe that the Chinese dragon turtle has nothing to do with the ancestors of turtles, while the semi-armored turtle represents the most reliable primitive turtle at present.

So, it seems that the formation of turtle carapace does not evolve from the small bone plates on the back, but should evolve from the bone plates on the ribs and abdomen.

It is worth mentioning that the Aurodontosaurus among the Triassic toothless dinosaurs had a very wide body and its back and abdomen were covered with bony plates. It looked very much like today's sea turtles.

They live in shallow water, and like turtles, they have beaks instead of teeth, which they use to eat shells.

But they have long since become extinct and have no relationship with living turtles.

What is the earliest turtle?

As for the origin of turtles, paleontological scientists from various countries still have different opinions. Most of the opinions are just speculations based on fossils. However, it is not clear in one or two sentences who is the ancestor of turtles.

According to records, the earliest reptiles that appeared on the earth were called "cuposaurs".

Paleontologists compared the skulls of modern turtles with those of cuposaurs and found that their shapes were very similar, so they believed that the ancestors of turtles were cuposaurs.

The turtle gradually evolved from a branch of Cuposaurus.

Cilisaurus is now called Macrosaurus, which is a double paraphyletic group of early reptiles. It is the earliest and most primitive reptile.

In fact, we can understand it this way. Cuposaurs are a prototype of all reptiles. Turtles naturally evolved from Cuposaurs, and then the prototype of turtles appeared. This was created by a man who worked in Germany and As evidenced by fossils unearthed in Thailand, turtles in this period could reach more than two or three meters in length. Their heads and limbs could not be retracted into the body, and they had no teeth in their mouths, but they had a pair of large ear holes, so in order to protect themselves , their whole body is covered with thorns and sharp thorns, and their appearance looks a bit like a giant snapping turtle. It seems that the snapping turtle still retains some original flavor, but the difference is that the "original snapping turtle" is mainly terrestrial and is mainly found in places. In rivers, lakes and swamp areas.

It was not until the middle Jurassic period 160 million years ago that the first turtle evolved. At the same time, turtles also evolved into two different types. One is that the head can be retracted directly. Cryptoneck turtles in the shell, and the other is side-necked turtles that cannot retract their heads into the shell and can only bend their neck sideways against the side of the body.

These two types of turtles have very obvious characteristics among modern turtles, I think everyone should be very clear about them.

Although there is no direct evidence, this is the strongest theory that humans have for the origin of turtles for a long time. However, in November 2008, that is, just recently, the Chinese Academy of Sciences based on the recent discovery in Guizhou The most primitive tortoise fossils have new insights: it is believed that tortoises did not originate from land but from the water, because the ancient tortoises in this fossil only had a plastron and no back carapace, which shows that they were attacked from below in the water. More, when they arrived on land, due to the increased attacks from the sky, they evolved carapace. This sounds quite reasonable, but this has not yet reached the consensus of the world's paleontological scientists and needs further research.

Whether the ancestors of turtles came from water or from land, they can indeed be called "living fossils". They appeared at the same time as dinosaurs but continue to survive today, even on earth. They also survived in the chalk where most creatures became extinct, and they evolved at an extremely slow speed. Perhaps this is why turtles have such a long lifespan and such strong adaptability.