Although there are still many who remain skeptical of evolution, it is undeniable that it does explain the evolution of many lives from a scientific perspective - from ocean to land, from single cell to multicellular, billions of years of evolution have created the biodiversity we have today.
Almost all species have been able to study the evolutionary process based on existing characteristics, but there is one particular creature that has left scientists at a loss - the tortoise.
The turtle has become a "nightmare" for scientists, which does not mean that it is a horrible creature, but the study of its evolutionary history, so that scientists have embarked on the road of constant face.
As the ultimate evolutionary bug, what is so special about turtles? What makes it a "nightmare" for scientists? How confusing is its evolutionary history? What was its ancestor?
Special turtle shell - bones grow outside the body
The tortoise belongs to the order Tortoises and Turtles in the phylum Chordata. Its most characteristic feature is its hard shell, and it moves extremely slowly, retracting its limbs and head into its shell when in danger.
In the study of turtles, the most headache for scientists is the shell.
The turtle shell is very special, from the body structure, it is not an acquired growth, but consists of ribs and thorax closed, remove the shell to see the internal organs thorax, it is like a part of the turtle body itself.
Most of the world's crustaceans are arthropods, and a few chordates such as pangolins and armadillos have evolved crusts, but their composition is mostly cuticle, or dead keratinocytes.
However, the turtle's shell is made of skeleton, which grows outside the body.
Generally speaking, chordates will hide the vertebral nerves in the bones in order to protect the spine and protect them with layers of muscles and skin, etc. Therefore, most chordates have important nerves inside the body, and fish are the best example.
Survival is the instinct of every species, so this evolutionary course of chordates basically does not change, but the turtle is a maverick, the opposite, the skeleton grows outside the body, equivalent to the human spine grows on the outside of the skin, which also makes scientists wonder.
How did the turtle become a "nightmare" for scientists?
In order to study the turtle's shell, scientists have tried to find the ancestor of the turtle by digging up fossils to find out the reason why the turtle's skeleton grows outside of its body.
From the perspective of evolution, organisms evolved to adapt to their environment in order to survive. Scientists speculate from the phenomenon that turtles shrink when in danger that the emergence of the shell is driven by the turtle's instinct to protect itself, that is, the species' own defense mechanism.
- Proto-snapping turtle.
In 1887, German scientists unearthed fossils of a 210 million-year-old Triassic turtle, known as the proto-jawed turtle, also known as the Triassic turtle.
Interestingly, 210 million years ago, turtles already had the same complete shell as today, and are therefore considered to be the ancestors of modern turtles.
This shows that the turtle at least 210 million years ago has a shell, then its evolutionary path has to continue to trace back, perhaps even earlier than the dinosaurs; on the other hand, the turtle skeleton outside the body after 200 million years of the phenomenon has not changed, which runs counter to most chordates, it is worth investigating.
Moreover, the heavy shell increases the difficulty of the turtle crawling, limbs can not stretch freely, but in danger when the action is restricted, die faster, which does not meet the purpose of evolution, and therefore contrary to the scientists' initial speculation.
Scientists believe that the turtle can not start to grow out of the shell, has remained the same to this day, there must be an opportunity to prompt the turtle to grow the skeleton outside the body, but this point in time, the reasons and purposes need to continue to study.
Scientists have once again deduced that the proto-jawed turtle evolved from a more ancient reptilian creature, starting with the Permian period, which has also started a long "nightmare" of constant research only to be smacked in the face.
- Sawtooth Dragon.
Scientists speculate that the proto-snapping turtle evolved from the sawtooth dinosaur based on the way it walked 290 million years ago and the way it stacked its armor.
Sawtooth dragon body length and 2.5 meters, legs as thick as an elephant, in order to avoid the sharp tusks of natural enemies and evolved a superimposed armor, scientists believe that this is the origin of the original snapping turtle superimposed armor.
However, this speculation was quickly disproved.
- Half-armored toothed turtles.
In 2008, scientists discovered a new turtle fossil in Guizhou that predates the appearance of the original snapping turtle by about 1,000 years, with tiny, sharp teeth and a carapace that grows on its abdomen, and was named the semi-armored toothed turtle.
The half-armored toothed turtle looks like a half-evolved turtle, and the biggest difference with the current turtle is the location of the shell, and its appearance disproves the claim that the sawtooth dragon was the ancestor of the original snapping turtle.
- Ancestral turtles.
(a) As research continued, scientists discovered a 280-million-year-old proper southern turtle, but it did not evolve a dorsal and ventral armor, only a widening rib cage.
Subsequently, scientists discovered a fossil with a clavicle on the front thorax that had become a closed carapace and ribs that were wider than those of the Jeongnam turtle, which is known as the ancestral turtle.
Thus, scientists have determined the evolutionary path of the "Southern Tortoise - Ancestral Tortoise - Proto Snapping Turtle - Tortoise", however, when the genetic map appeared, scientists once again fell into a "nightmare".
Genetic mapping controls of reptiles indicate that the turtle may have shared a common ancestor with birds and crocodiles, and that it had common characteristics of turtles and crocodiles in the Permian.
Together with the temporal side holes, the ancestor of the tortoise should be a lepidosaurian supermassive creature, but this claim remains controversial because the tortoise has no holes.
The discovery of the fossil of the first beaked turtle in 2018 has further complicated the evolutionary path of the turtle, which has evolved a partial beak but still has no turtle armor and is in between the semi-armored toothed turtle and the ancestral turtle, so where did the turtle's later beak go?
Scientists have repeatedly been hit in the face, the turtle also ancestors have not studied a result so far, but also known as the ultimate bug of evolution, many people are also therefore skeptical of evolution.
Regardless of which speculation, with the progress of technology, more and more paleontological excavations will give a perfect answer.
What species do you think the originator of the tortoise actually was?