Dinosaur killing asteroid also killed most bird species due to global deforestation

As they marked up the avian family tree, they noticed that tree-dwelling species—which today vastly outnumber ground-dwelling species—had ground-based ancestors. And the skeletons of the preimpact and postimpact fossils were different as well. Before the impact, there seemed to be many tree-loving species. But those species were missing in the postimpact fossils

Among modern birds, it appears that only five groups predate the impact, including species like today’s ostriches, ducks, and chickens. Their impact-surviving ancestors were probably small ground-dwellers, like quail, Field says. They likely survived on seeds banked in the soil, what Ksepka calls “a food source that’s prepackaged for preservation.”