A micrograph image of the tibia, or shin bone, of Protoceratops, a small herbivorous relative of Triceratops. Researchers have estimated the genome size of 31 species of extinct dinosaurs, the ancestors of birds, and find that they seem to have had small genomes similar in size to those of birds. The trait appears to have evolved in the saurischians, the dinosaur group of which birds are the only surviving members.