PADIAN, K.*; HORNER, J.R.; de RICQLES, A.: Dinosaurian life history strategies: Evidence of differential growth rates from bone histology

Dinosaurs, like other tetrapods, grew more quickly shortly after hatching than later in life. However, they did not grow like other non-avian reptiles, slowing their trajectory gradually in a convex arc through ontogeny. Rather, dinosaurs (especially large ones) grew to their adult size relatively quickly, much like large birds and mammals do today. Some large duckbills took only seven years to reach seven meters in length; some large sauropods may have taken only a decade to reach full size. Gigantic crocodiles of the past, in contrast, grew along the growth trajectory of living crocodiles, but simply extended and attenuated the growth curve. They may have taken several decades to reach tens of meters in length. Large pterosaurs apparently grew much like large birds and other large dinosaurs. But small pterosaurs and some small dinosaurs apparently grew at slower rates after hatching, comparable to fast-growing rates in crocodiles, judging from bone tissue structure and vascularization. Theropod (carnivorous) dinosaurs seem to have grown very quickly from their early evolution, regardless of size. The first birds apparently slowed growth rates but maintained shape trajectory to produce a smaller adult size; only later in avian history was small size attained quickly.