Ancient Fish Unearths Surprising Truths About Evolution: Insights from 400 Million Years Ago

The coelacanth is often called a “living fossil.” This remarkable fish hasn’t changed much in about 65 million years. Despite being well-studied, it still surprises researchers and reshapes our ideas about vertebrate evolution. A recent study in Science Advances highlights these new insights, led by scientists from the University of São Paulo (USP) in Brazil and the Smithsonian Institution in the U.S.

When studying the coelacanth’s cranial muscles, researchers found that only a small fraction—13%—of previous evolutionary muscle features were correct. They also identified nine new transformations related to feeding and breathing. Aléssio Datovo, a professor at USP and the study’s lead, stated that the coelacanth is “even more similar to sharks and tetrapods than we thought.”

One notable discovery is the misidentification of certain muscles. Previously thought to help with food capture, these were shown to be ligaments that don’t contract. This is a significant shift in understanding, as it clarifies how coelacanths and their relatives feed compared to other fish like ray-finned species, which possess more advanced suction abilities.

Ray-finned fish and lobe-finned fish diverged around 420 million years ago. Lobe-finned fish include coelacanths and lungfish, which are direct ancestors of all tetrapods—mammals, birds, reptiles, and amphibians. The evolution of jaw structure and muscle function in these species is fundamental to our understanding of fish biology.

Most fish, like carp, demonstrate active mouth movement to suck in food. This trait offers a significant survival advantage. In contrast, coelacanths primarily bite their prey, missing out on this efficiency.

Datovo pointed out that past research mistakenly suggested coelacanths had the muscle adaptations that gave rise to suction feeding. In reality, these adaptations appeared much later in evolution.

Coelacanths live about 300 meters deep in the ocean, hidden away in underwater caves. They thrive in this safe environment, contributing to their minimal evolutionary change and slow genetic shifts, as discussed in a 2013 study in Nature. They were long thought to be extinct until a living specimen was found in 1938, surprising many scientists. Another species was discovered in 1999.

Gathering specimens for study is challenging due to their rarity. A team from USP and the Smithsonian had to search for institutions willing to lend specimens for dissection. They eventually secured samples from the Field Museum in Chicago and the Virginia Institute of Marine Science.

Datovo noted the importance of careful dissection, which allows for preserving the specimen for future studies. He spent six months carefully examining the coelacanth’s internal structure, leading to the identification of numerous previously unrecognized features.

Through 3D imaging of skulls from both extinct and living fish, researchers are piecing together the evolutionary history of muscle function in jawed vertebrates. Datovo’s future work will involve comparing coelacanth muscles to those in tetrapods, further unraveling the puzzle of vertebrate evolution.

In conclusion, the study of the coelacanth not only helps clarify its unique adaptations but also sheds light on the broader story of evolution among fish and their terrestrial descendants. Understanding these secrets from “living fossils” continues to inform and challenge our views of life’s history.

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New Species; Fish; Extinction; Animals; Evolution; Fossils; Dinosaurs; Ancient DNA