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The specimen also preserves the first keratinous sheath of a therizinosaur, an element that covers the claw much like human fingernails, aiding defence, movement, or prey catching.

He thinks they are a different kind of keratinous covering, though he agrees they were probably spectacularly colored.

Baleen is a unique keratinous oral tissue, made up of the same protein in human fingernails, that can be found on the jaws of large whales.

The team’s scans revealed roughened patches of bone particularly rich in blood vessels—the same sort of features that underlie the keratinous sheath that makes up the beaks of modern-day birds—near the tips of Ichthyornis’s upper and lower jaws, Bhullar says.

For instance, it seems likely that if the birds’ beaks are elongating, then they would also be experiencing changes to their skulls, as well as the keratinous sheath that covers the beak.