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A groundbreaking study of the 400-million-year-old coelacanth reveals scientists misidentified key jaw structures for decades, prompting a major rethink of how early vertebrates—including humans—developed the ability to eat and breathe.
A living fossil fish just proved we’ve misunderstood a major chapter in the story of evolution. For decades, the coelacanth — an ancient fish species that first appeared 400 million years ago — was thought to be a window into our evolutionary past. But now, scientists say they may have gotten some big things wrong about how early animals, including humans, developed the ability to eat and breathe.
What’s So Special About the Coelacanth?
The coelacanth (pronounced SEE-la-kanth) is often called a living fossil because its body has barely changed for millions of years. It lives deep in the ocean, hidden in underwater caves, and was once thought to be extinct — until a live one was shockingly found in 1938.
Because of its ancient lineage and unchanged appearance, scientists believed the coelacanth could teach us about the early steps in vertebrate evolution — especially how our ancestors learned to eat and breathe with jaws.
The Big Mistake: Muscles vs Ligaments
This revelation comes from a detailed study conducted by researchers from the University of São Paulo (USP) in Brazil and the Smithsonian Institution in the United States, who recently reexamined the head of the coelacanth using extremely precise dissection techniques. The findings were published in the journal Science Advances on July 29, 2025.
What they discovered was surprising: many of the muscles scientists had believed were present in the fish’s head for decades were not muscles at all — they were ligaments.
Why is this a big deal? Because muscles create movement, while ligaments simply connect bones and transmit force. This correction means the coelacanth’s ability to move its mouth and breathe is far more limited than previously believed.
Why It Matters to Us
So what does a deep-sea fish have to do with us?
The coelacanth belongs to the same group of ancient fish that eventually gave rise to all four-limbed creatures — including mammals, birds, reptiles, and amphibians. That makes it an important puzzle piece in the story of how we got here. Previously, scientists believed that certain jaw muscles used for suction feeding — pulling in food by opening the mouth quickly — were present in coelacanths. That would mean these muscles evolved very early and were passed on to later animals.
But now we know that those muscles were never there, and they likely appeared millions of years later, only in a different group of fish. This shifts the timeline of evolutionary development significantly.
Correcting 70 Years of Mistakes
The study, published in Science Advances, involved dissecting rare coelacanth specimens from museum collections in the U.S. The researchers spent months carefully separating each part of the skull and muscle system. They confirmed that 11 supposed muscles were actually other types of tissue — meaning many anatomy books and scientific papers from the last 70 years need to be re-evaluated.
The team also discovered new features in the skull that were never described before, helping to fill gaps in our understanding of how early vertebrates (animals with backbones) developed.
Looking Ahead: Rewriting the Evolution Textbook
This study doesn’t just correct old mistakes — it gives scientists new tools to trace how skulls, jaws, and breathing systems evolved in the first vertebrates. It also offers insights into how tetrapods — the group that includes humans — began to diverge from their aquatic ancestors. By comparing 3D scans of other ancient fish skulls, the researchers hope to build a more accurate picture of our distant past. Future studies may even explore how amphibians, reptiles, and mammals inherited — or evolved away from — these early features.
This groundbreaking work was led by Brazilian researcher Aléssio Datovo, with contributions from the late G. David Johnson, a world-renowned fish anatomist who sadly passed away before the paper was published. Their efforts remind us that even after hundreds of years of scientific discovery, nature still holds secrets — and sometimes, the best way to move forward is to take a closer look at the past.
Source:
Based on research funded by Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) and published in Science Advances (July 29, 2025).
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