The ancient coelacanth fish is one of the world's oldest and rarest living aquatic species, outliving even the fierce dinosaurs and other animals that have since become extinct.
Now, a new study has uncovered marvelous insights regarding the skull of the coelacanth fish, which may help scientists understand the skull evolution of vertebrates, lobe-finned fishes, and land animals.
Coelacanth Fish Skull Is 100 Times Bigger Than Its Brain
Researchers from Flinders University in Adelaide, South Australia, and the University of Bristol in the United Kingdom have collaborated to examine the skull of a fossilized coelacanth fish (Latimeria chalumnae).
The skull of the coelacanth fish has been found to be completely split in half by an "intracranial joint," and its brain is so small that the coelacanth fish skull is somehow 100 times bigger than the brain, researchers said.
It also makes the brain only 1 percent of the cavity that houses it, which may be why the species' survival is so unique among living vertebrates.
Despite this finding, questions as to how the coelacanth skull grows and why its brain remains so small has puzzled scientists for years. The new study, which has been published in the journal Nature, attempts to answer these questions.
Revealing More Insights On Skull Evolution
Using state-of-the art imaging techniques, scientists Professor John Long, Dr. Hugo Dutel, and their colleagues visualized the internal anatomy of the coelacanth fish without damaging it. They examined specimens of fossilized coelacanth fish from several public natural history collections.
In particular, the team studied the brain cavity of the coelacanth fish at different stages of development to analyze when the skull divides to form a split brain case.
Professor Long said the discovery provides better understanding of why the fossils of most ancient fish had hinged heads and why four-limbed animals later lost the intracranial joint between two parts of the skull.
Long said the formation of the intracranial joint might be caused by the unique development of the notochord, which is a tube that extends below the brain and the spinal cord in the early stages of development.
Among fish, the notochord usually degenerates into a small rod below the brain. However, Long explained that the coelacanth fish showed that the notochord expands dramatically to become 50 times bigger than the brain in most adult fish.
"This process of brain growth is very unusual, especially compared to primates like us in which the brain expands dramatically," said Long.
Coelacanth Fish Is A 'Living Fossil'
The coelacanth fish has indeed been called a "living fossil," as two species of the coelacanth are still swimming in waters today. They remain physically unchanged despite the passage of time. Scientists thought that these animals were extinct for more than 65 million years until an accidental discovery proved otherwise.
This rare aquatic species was first discovered to be lurking around the waters of South Africa in 1938, and it prompted significant debate on whether or not the existence of the coelacanth fits into scientists' understanding of the evolution of land and aquatic animals, especially that of the lobe-finned fishes.
The findings of the study hold clues regarding vertebrate evolution and how important it is to protect the threatened coelacanth fish species and its environment. Dr. Dutel believes the study is a step forward compared to the body of knowledge regarding this species. He also believes there are more to uncover.
"There are still more questions than answers!" added Dr. Dutel.