New Study on Coelacanth Reshapes Understanding of Vertebrate Cranial Evolution

A recent discovery involving the African coelacanth — a rare fish considered a “living fossil” — is changing how scientists understand the evolution of cranial musculature in vertebrates. The study was carried out by researchers from the University of São Paulo (USP) in collaboration with the Smithsonian Institution and was published in the prestigious journal Science Advances.

The coelacanth belongs to an ancient group of lobe-finned fishes, the sarcopterygians, and has retained many of its physical features for tens of millions of years. Despite its primitive appearance, this species revealed anatomical complexities that had been misinterpreted for decades.

According to the new analysis, only a small portion of the previously assumed muscular innovations in major vertebrate lineages were accurate. Additionally, nine previously unrecognized evolutionary changes were identified. One of the most important findings was the realization that some structures previously thought to be muscles were actually ligaments — and therefore incapable of contracting, contradicting earlier studies.

This thorough revision has direct implications for how scientists understand feeding strategies in vertebrates. Ray-finned fishes, like carps, evolved an extremely efficient suction system for catching prey. In contrast, coelacanths and sharks rely on biting, and the study shows that coelacanths lack the muscular system necessary for suction. This suggests that such a mechanism evolved later, exclusively among actinopterygians.

The research also sheds new light on the evolutionary split that occurred around 420 million years ago between lobe-finned and ray-finned fishes. This divergence is particularly significant because sarcopterygians gave rise to tetrapods — the group that includes all land vertebrates, such as amphibians, reptiles, birds, and mammals.

Obtaining specimens for the study was a challenge in itself, as coelacanths live at depths of around 300 meters and are extremely rare. Two U.S. museums provided preserved specimens, which were meticulously dissected by Professor Aléssio Datovo of USP. The process, which took about six months, allowed for the anatomical structures to be carefully preserved and thoroughly analyzed.

Datovo led the study alongside renowned anatomist G. David Johnson, who sadly passed away during the final stages of the research. Their work resulted in a valuable collection that can now serve as a reference for scientists worldwide and as a foundation for future studies.

In addition to traditional dissection, the researchers used advanced 3D micro-CT scanning to compare the coelacanth’s anatomy with that of other fish species, including extinct groups. These images helped trace the evolution of cranial muscles from the earliest jawed vertebrates to modern tetrapods.

With this detailed reinterpretation of the coelacanth’s anatomy, the study corrects errors that persisted for over seventy years and reinforces the crucial role this enigmatic fish plays in reconstructing vertebrate evolutionary history.

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