A recent study published in the journal Science Advances has significantly revised our understanding of vertebrate skull evolution, thanks to new discoveries on the anatomy of coelacanths. The researchers from the University of São Paulo and the Smithsonian Institution found that only 13% of previously identified evolutionary muscle novelties for the largest vertebrate lineages were accurate. This discovery highlights how much more similar coelacanths are to cartilaginous fish and tetrapods than thought, and even more distinct from ray-finned fish.
The study revealed nine new evolutionary transformations related to innovations in feeding and respiration in groups such as sharks, rays, and chimaeras, as well as birds, mammals, amphibians, and reptiles. One significant finding is that muscles responsible for actively expanding the buccopharyngeal cavity were not present in coelacanths at all, but rather ligaments that are incapable of contraction.
The research was made possible by studying coelacanth specimens obtained from museums, which allowed researchers to re-examine and correct errors that had been repeated in the scientific literature for over 70 years. The discovery impacts our understanding of cranial evolution in all other large vertebrate groups and provides new insights into the evolution of muscles in jawed vertebrates.
Coelacanths are rare fish that live deep underwater, with few predators and a relatively protected environment, which has resulted in slow changes to their genome over time. The researchers used three-dimensional microtomography images of coelacanth skulls to infer where muscles would fit and elucidate the evolution of these muscles in the first jawed vertebrates.
The study’s findings provide new opportunities for future research on similarities between coelacanths and tetrapods, such as amphibians and reptiles. The researchers hope that this discovery will shed more light on the evolution of cranial musculature in jawed vertebrates.
Source: https://phys.org/news/2025-07-fossil-fish-anatomy-reshaping-view.html