Zoology 9th Edition by Stephen Miller

Exercise 1

Birds are characterized by adaptations for flight, including the presence of wings, feathers, endothermy, vertebral column modifications, and bones lightened by air spaces. They share many characteristics with other reptiles. Birds evolved in the archosaur lineage from theropod dinosaurs. Flight may have evolved as some theropods used wings to glide from tree branches or as stabilizers as animals ran and jumped during the pursuit of insect prey. Adaptive radiation of modern bird orders began about 70 mya.
Why do we think that the fossil record indicates that theropod dinosaurs used their wings for fl ight or for gliding?