Monday , January 18 2021

We scanned one of our closest relatives, a collaborator, to find out how the brain grows



There's a lot that's fascinating for the collagen Latimeria. Now under threat, this deep sea fish is closely related to humans and other animals living in the country (tetrapods).

Colakant Latimeria is a relatively large fish (reaching about 2 meters in length), but there is a very tiny brain lying in the hinges of waves – a very primitive feature found in many fossil fish.

How the cranny's skull grows and why the brain remains so small scientists have been confused for years. Our new study published today in Nature for the first time illuminates the development of the brain and skull of this curious animal.

This is another proof that it can help us to see where people come from.



Read more:
It is less than 2 centimeters long, but this fossil fish of 400 million years changes our view on the evolution of 'vertebrates


Discovering a Living Collaborator

Detection of life Latimeria a collagen rocked the world in 1939, as scientists thought they had died out with dinosaurs about 66 million years ago.

The first one Latimeria once found was accidentally caught in the tram from the South African coast. Incredibly, her overall body shape was remarkably similar to some of her fossilized relatives, whom paleontologists have known since the 19th century.

The fossil collagen trachymetopone from the Jurassic of Germany. This sample is located in the collections of the Museum of the University of Tübingen.
Hugo Dutel (no commercial use)

Scientific fury around Latimeria was really caused by the fact that the animal can discover the origin of humans and other animals with four limbs.

At the time of its discovery, Latimeria held a key position in the family tree of 'vertebrates' (bone animals). It was considered a direct descendant of hunting fish, a group of fish that developed tetrapods.

So, the discovery of life Latimeria a cocktail was expected to shed light on the biology of our very early ancestors.



Read more:
Ancient fish evolved into shallow seas – the places where people today threaten


Our fish family tree

Today, expectations have been alleviated. The development of new methods for the reconstruction of the evolution of organisms, the discovery of new fossils, and more recently the information obtained from DNA and other molecules, have slightly changed this picture.

Among living 'vertebrates', collagens are no longer considered to be closest relatives of tetrapods – they have been replaced by another old group of fish, deep hazelnuts.

Simplified phylogenia of bony fish (osteitis). Colaccents and brass fish are the only fish that are ribbed with a living lobe and are closely related to tetrapods, vertebrates of terrestrial habitats. The intracranial joint is a primitive feature of sarcopteriasis, a group that includes fish and tetrapods. It is found in many fossil lobes from Devon, but is independently lost in tetrapods and live palms. Collagen is the only living 'vertebrate possessing an intracranial wrist.
Hugo Dutel (no commercial reuse)

However, the Latimeria the collagen possesses some unusual characteristics that are still of interest in understanding the evolution of our fossil relatives.

Skull of Latimeria is fully divided into half the joint called the "intracranial wrist". This joint is a very primitive characteristic that is otherwise found only in many extinct fish.

Unlike other 'vertebrates, the brain of Latimeria is ridiculously small compared with the cavity in which it is placed (1% of the total volume of bronyrosis).

The back of the skull of the Latimeria and missing fish-fishes fish also straddles a surprisingly large structure called the notochord.

3D virtual reconstruction of the skull of the collagen in the right side view. Left: Full view of the skull. Right: Brainage is isolated and virtually opens along the midline to show the brain (yellow) and nohorn (green). The brain represents about 1% of the volume of the cavity in which it is placed.
Hugo Datel

The question of how the skull and brain develop, and what it means to develop 'vertebrates,' provoked our work published today.



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Finding unborn collagens

Latimeria is ovoviviparous, which means that the eggs develop in the female abdomen, and then it gives birth to a youngster.

But studying the development of this fish is not an easy thing to do. Latimeria can not be grown in an aquarium, so embryos and fetuses can not be easily obtained. Moreover, we can not engage any colonels in the wild, because they are protected.

Many adult colonies are held in collections of natural history. However, previous stages of life are extremely rare, since they come from rare pregnancies. For a long time, scientists could not desecrate these precious samples to study their anatomy.

Latimeria's series of growth collected for our study.
Hugo Datel

Thus, we used the most sophisticated X-ray scanning facilities in the European synchrotron and powerful MRI to visualize the internal anatomy of these precious museum specimens.

Thanks to these data, we have created digital 3D models of the skull at every stage of its growth. Detailed 3D models have enabled us to describe how the shape of the skull, brain and nohorse are changing from the very early fetus of an adult.

As the brain grows, it remains small

We found that the relative size of the brain is dramatically decreasing during development. The brain grows, but not as much as the surrounding structures in the head.

This is very unusual, and is not seen in other 'vertebrates' (and especially primates in which the brain increases dramatically during growth).

On the other hand, the nohorn extends significantly and becomes much larger than the adult brain. This is very unique because the nohorn usually degenerates into the early development of most 'vertebrates.

Brain (yellow) within brachinase (blue) in various developmental stages of Latimeria.
Hugo Datel

Why is the brain of Latimeria so small?

As often happens, there is probably not just one explanation. It may be due to the way the newhorn develops, as well as the position and function of the intracranial joint (which probably plays a role in biting). It is also possible that the energy required by a huge electrosensor organ in LatimeriaThe muzzle, the rostrum organ, may come at the expense of a larger brain.

Together with a recent study of its lungs (which has bony plates on it), these findings represent the best of our knowledge about the development of Latimeria. She remains one of our most mysterious cousins, since many aspects of his biology and ecology remain unknown.

Certainly, Latimeria however, there are many promising clues to our understanding of the evolution of 'vertebrates' and our distant descent.

But this only surviving 400 million-year-old group and its marine ecosystem are at risk and should be protected more than ever.


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