Prehistoric fish fills 100 million year gap in evolution of the skull

2023-09-20

X-rays of an ancient jawless fish shows earliest-known example of internal cartilage skull, unlike that of any other known vertebrate. A 455-million-year-old fossil fish provides a new perspective on how vertebrates evolved to protect their brains, a study has found. In a paper published in Nature today (Wednesday 20th September), researchers from the University of Birmingham, Naturalis Biodiversity Centre in Leiden, Netherlands; and the Natural History Museum have pieced together the skull of Eriptychius americanus. The research, funded by the Leverhulme Trust, suggests that the ancient jawless fish found in ancient deposits in Colorado, USA has a skull unlike that of any previously seen, and fills a gap currently spanning 100 million years in the evolutionary history of the vertebrate skull. Using computed tomography, a form of x-ray technique, scientists recreated a detailed 3D representation of the skull of Eriptychius and is the first time that such a comprehensive recreation has been done on the specimen which was collected in the 1940s, originally described in the 1960s and is housed in the Field Museum of Natural History, Chicago. This ancient fish had separated, independent cartilages encasing the brain, rather than the solid bone or cartilage structure of jawless and jawed fish that followed it. While later specieshave a fully bound cage of cartilage that holds the brain, these results suggest that the early evolution of structures to separate the brain from other parts of the head may have begun with Eriptychius. Dr Ivan Sansom, Senior Lecturer in Palaeobiology at the University of Birmingham and senior author of the paper said: "These are tremendously exciting results that may reveal the early evolutionary history of how primitive vertebrates protected their brains. Eriptychius americanus appears to be the first evidence for a series of cartilages separating the brain from the rest of the head. This study emphasises the importance of museum collections and the application of new techniques in studying them." Dr Richard Dearden, Postdoctoral Research Fellow in Palaeobiology at Naturalis Biodiversity Center and lead author of the paper said: "On the face of it Eriptychius is not the most beautiful of fossils. However, by using modern imaging techniques we were able to show that it preserves something unique: the oldest three-dimensionally preserved vertebrate head in the fossil record. This fills a major gap in our understanding of the evolution of the skull of all vertebrates, ultimately including humans."

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