But for Clarke, the discovery reveals something else by its presence – that these sound-producing organs can fossilise, and their absence from most dinosaur fossils is telling. Birds, or avian dinosaurs to be more precise, evolved from theropod dinosaurs around 165-150 million years ago during the Jurassic period. If the syrinx from a bird living 66-68 million years ago could be preserved as a fossil, why have none been found among the remains of their extinct non-avian cousins, such as Tyrannosaurus rex?