‘Dinosaurs Among Us’ at American Museum of Natural History, Selected by Mark Dion

Confuciusornis sanctus is considered a bird, not just a birdlike dinosaur. Instead of dinosaur teeth, it has a beak. And instead of a long, bony tail, it has a short, feathered tail. Yet it probably couldn’t fly as well as modern birds, because its breastbone could not support strong wing muscles. Skeletal features like these continued to evolve after birds first appeared.

ZHAO CHUANG/COURTESY PEKING NATURAL SCIENCE ORGANIZATION