Paper No. 12
Presentation Time: 11:15 AM
HOW DINOSAURS GREW: GROWTH RATES AND STRATEGIES
Dinosaurs, like other tetrapods, grew more quickly during early post-hatching stages than later in life. However, they did not grow like most other non-avian reptiles, which slow 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 about a decade to reach most of their 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 apparently took several decades to reach eight or nine meters in length. Large pterosaurs evidently grew much like large birds and other large dinosaurs. But small pterosaurs and some small dinosaurs apparently grew at slower rates after hatching, though faster than 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 (and perhaps the small theropods from which they evolved) reduced adult body size by shortening the phase of rapid body growth common to their larger theropod relatives. These changes in timing were primarily related not to physiological differences but to changes in growth strategy. Basal birds maintained (or even extended) most elements of shape trajectory to produce peramorphic changes at smaller adult size. Only later in avian history was growth to small adult size attained very quickly, by secondarily increasing the relative duration of the rapid growth phase.