Pterosaurs were probably egg-layers, and some eggs have been found at pterosaur sites. There is evidence that some species, such as "Pteranodon", had sexual dimorphism (sexes looked different). The skeletons with large cranial (head) crests and small pelvic canals were presumably males. Where several specimens occur at the same location, adults can be distinguished from juveniles. Evidence of tooth wear in "Eudimorphodon" suggests the young were insectivorous, while the adults ate fish. Development took place rapidly in these warm-blooded reptiles, and much of their life-style parallels that of birds. The high energy-level needed for flight explains why both reptilian forms (pterosaurs and birds) developed similar metabolism. In many respects, birds and pterosaurs are good examples of convergent evolution.