The most central part of the vertebrate endoskeleton, the cranium, keeps the rest of the body alive. But where did it come from?
Four hundred fifty-five million years ago, Earth was a hot place with high sea levels that had flooded many of the landmasses, including what would later become North America. This spreading ocean was exploding with new life, such as the bony-plated fish that still stand as some of the oldest-known vertebrates.
When they died, some became buried in the sediment that covered the ocean floor and fossilized, to be discovered later by paleontologists living in a drier time. One such find, from ancient deposits in Colorado, contains parts of a jawless fish that a new study has scanned with modern X-ray tomography.contains the earliest ever seen neurocranium — the cartilage protecting the fish’s brain — and one of the strangest.
This novel neurocranium falls somewhere between the loose, open cartilage style seen with lampreys and the more closed-off designs present in gnathosomes, a group that includes humans. Vertebrates exist with both structures, and scientists have tried to determine how they evolved.
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