Dinosaur Life Spans - Reasoning by Bone Growth
You might think that an analysis of actual dinosaur bones would help clear up the issue of how fast dinosaurs grew and how long they lived, but frustratingly, this isn't the case. As the biologist R.E.H. Reid writes in The Complete Dinosaur, "[bone] growth was often continuous, as in mammals and birds, but sometimes periodic, as in reptiles, with some dinosaurs following both styles in different parts of their skeletons." Did you follow that?
What it all boils down to is this: some dinosaurs, such as the duck-billed Hypacrosaurus, grew at phenomenal rates, reaching adult sizes of a few tons in a mere dozen years (presumably, this accelerated growth reduced the window of vulnerability to predators). The trouble is, everything we know about cold-blooded metabolism is inconsistent with this pace of growth, which may well mean that Hypacrosaurus in particular (and large, herbivorous dinosaurs in general) had warm-blooded metabolisms, and thus maximum life spans well below the 300 years quoted on the previous page.
By the same token, other dinosaurs seem to have grown more like crocodiles and less like mammals--at a slow and steady pace, without the accelerated curve seen during infancy and adolescence. Sarcosuchus, the ancient crocodilian better known as "SuperCroc," probably took about 35 or 40 years to reach adult size, and then continued growing slowly for as long as it lived. If sauropods followed this pattern, that would be indicative of a cold-blooded metabolism (such as that of modern crocodiles), and their life spans would once again edge up toward the 300-year mark.
So what can we conclude? Clearly, until we learn more details about dinosaur metabolisms and growth rates, any estimates of dinosaur life spans will have to be taken with a gigantic grain of prehistoric salt!
