Mount of a Triceratops horridus adult and a juvenile of the same species, at the Museum of the Rockies in Bozeman, Montana. Triceratops was as large as an African elephant, although babies were just the size of a St. Bernard dog. In this mount, white shows actual fossil while brown shows reconstructed areas (where fossil was not recovered).

Dinosaur growth is classified into four categories: baby, juvenile, subadult, and adult. Most collections ignore smaller-sized fossils in favor of the big, eye-catching type. But this has meant that the otogeny (changes in an animal as it grows up) of dinosaurs has often been ignored. It also means that many babies, juveniles, and subadults have been mistaken for unique species rather than just junior versions.