Coelacanth is called a living fossil. It is a valuable fish that has almost the same shape as a fossil species. Coelacanth is believed to be deeply related to humans and other terrestrial creatures, and it is expected that the study of such coelacanth will allow us to deepen our understanding of the roots of mankind. This coelacanth is a relatively large fish, reaching 2m in length, but has a small brain compared to its size. A study on how the coelacanth brain develops has been published.
The coelacanth was thought to have gone extinct at the end of the Cretaceous Period, but its survival in South Africa in 1938 surprised the world. What surprised the scientist even more was that the coelacanth had almost the same shape as the species found as fossils.
At the time, the coelacanth was regarded as a direct descendant of fish that advanced to land and evolved into humans and other limb animals. Therefore, a detailed study of coelacanth is expected to be able to unravel the mystery of how humans and other animals evolved.
Of course, the expectation on the coelacanth has slightly decreased now. Advances in research on the origin of evolution, discovery of new fossils, DNA analysis techniques and results of molecular biology studies have made the coelacanth the closest relative to humans or limbs. It is now said that the lungfish are closer to humans or limb animals than coelacanth.
Nevertheless, the coelacanth has features that seem to be the key to clarifying the origin of evolution. The skull of the coelacanth is divided in half by a joint called an intra-two joint, and this joint is said to be seen only in very primitive fish like the ancestors of humans that have already gone extinct.
Compared to other animals, the coelacanth brain is much smaller than the skull and is only about 1% of the skull volume. There is a surprisingly large chord color on the back of the skull, and this function has something in common with fish that are the ancestors of already extinct humans. Researchers at the University of Bristol investigated how the coelacanth brain developed.
Adult coelacanth should be identified in the coelacanth born to study brain development. However, the original coelacanth is a rare fish that cannot be reared in a tank, and it is an ovum born after a female hatches an egg in the womb and raises it until it grows to some extent. Because it is protected worldwide, there is no reason to hold onto the coelacanth with the baby in the stomach.
The research team used specimens from pregnant catch fish. For a long time, the research team was unable to dissect valuable specimens and examine the interior, but they succeeded in analyzing the internal structure of the specimen using X-ray scanning equipment and MRI.
Based on the obtained analytical data, a 3D model of the skull was created in the growth phase. The results revealed that the relative size of the coelacanth’s developing brain is getting smaller. The brain is also growing slowly, but the growth of the skull and other parts is far exceeding that. In addition, in normal animals, the color of the chord degrades in the early stages of development, but coelacanth grows much larger than the brain. From the fetal stage to adulthood, the color of the chord gradually increases, while the brain hardly grows.
Why is the coelacanth brain so small? In this regard, the research team is speculating that various factors such as chordal color development and intracranial joints may overlap. It is also said that there is a possibility that the organs that sense electricity near the nose consume a lot of energy and sacrifice brain growth.
Coelacanth’s ecology is still enigmatic, but it certainly has clues to understanding the evolution and origin of vertebrates. Related information can be found here .