Birds are living dinosaurs, the only evolutionary branch of the great reptiles to have survived the asteroid-driven mass extinction of 66 million years ago.

(But that doesn’t mean all avians survived unscathed through the fires and impact winter of the ancient catastrophe.)

For over 86 million years prior to that moment, birds with teeth thrived among the forests, floodplains and oceans of the Mesozoic world.

Early birds such as Archaeopteryx don’t look all that different from the small, carnivorous dinosaurs they evolved from, with long, bony tails; claws; and, of course, teeth. Other features we associate with living birds—egg-laying, feathers, complex systems of air sacs—all evolved among non-avian dinosaurs first, too. And while Mesozoic bird fossils are rarely uncovered, owing to their small size and fragile bones, experts have discovered enough complete skeletons from deposits formed in the ash or fine-grained sediment at the bottoms of ancient lakes to get a feeling for how much the birds varied.