Modern birds are the descendants of dinosaurs. Specifically, paleontologists have shown that birds evolved from a group of two legged dinosaurs called theropods. The theropods include some well known dinosaur favorites, like Tyrannosaurus rex and velociraptor. The first evidence of an evolutionary link from dinosaurs to birds came from one hundred and fifty million year old fossils of Archaeopteryx. Like a bird, Archaeopteryx had broad feathered wings, and like a dinosaur it had sharp teeth and a long bony tail.
In the nineteen nineties, paleontologists working in China found fossils of dinosaurs with clearly preserved feathers. It turns out that theropod dinosaurs themselves, including the famed Tyrannosaurus, had feathers. In 2019 a team of Chinese scientists reported finding traces of feather proteins in dinosaur feather fossils. The feathers were rich in the protein alpha keratin, which made them different from the feathers of modern birds which are rich in beta keratin. It’s beta keratin that makes bird feathers stiff enough for flight. The researchers concluded that an evolutionary change must have happened to produce the stiff feathers of modern birds.
Their findings were questioned in a study published in 2023 by an international research team. The paleontologists studied a one hundred and twenty five million year old dinosaur feather from China, and unlike the first team, found lots of beta keratins, just like modern birds. These researchers also subjected modern bird feathers to conditions that simulated fossilization and found that sometimes beta keratins degraded. They argue that this is what happened to the feathers in the earlier study, and that dinosaur feathers are really just like modern bird feathers in composition.