Ostrom presented an impressive array of skeletal similarities between Archaeopteryx and dromaeosaurs, such as a long coracoid, long arms equipped with three fingers, a swivel wrist joint, long slender hind legs, a three-toed foot, and a stiff tail. Except for feathers, Archaeopteryx would look like a small dromaeosaur, Ostrom argued. The striking resemblance between Archaeopteryx and dromaeosaurs must reflect a common descent, not evolutionary convergence. He emphasized the recent discovery of clavicles in some coelurosaurs, which countered Heilmann's principal objection to a theropod ancestry of birds. Like Huxley, Bakker argued that birds should not have their own separate class because they fly.
Bats fly, too, but they are still considered mammals.
Birds are as much dinosaurs as bats are mammals. To understand the bird's place in the dinosaur family tree, we must know the interrelationships of dinosaurs. Dinosaurs began their evolutionary history as small carnivores during the Late Triassic. They became diversified within a relatively short period and then ruled the earth for approximately 160 million years. During that time they adapted to a wide range of conditions and environments and became very successful.