Did Dinosaurs Die Young?

18 May 2008

Question

I am curious about how long the large dinos lived. I have a vague and possibly incorrect memory of hearing on a TV special that the large herbivores could live very long lifespans, up to 1,000 years. Then recently I heard on a science podcast that the T Rex only lived about 20 years. So I would like to know what a dino lifespan was. And I am even more curious as to how scientists can estimate the life span of a dino, given that they are working basically with rock.

Answer

Dr John Nudds, University of Manchester, Palaeontologist:The first thing that we can say for certain is that no dinosaur ever lived for a thousand years nor indeed for anything approaching that sort of time.

If you compare dinosaurs to present day animals we might expect that the very large herbivores, things like brachiosaurs and diplodocus which were comparable in size to an elephant would have lived, therefore, for 70-80 years. Maybe a bit more. Whereas the smaller, more meat eating dinosaurs would have been more comparable to some of today's larger birds, to which they are closely related. If you think of something like an eagle or raven they live for 20-30 years and that would probably have been the lifespan of a tyrannosaurus rex. How do we know this? Dinosaur bone is sometimes preserved in exquisite detail and we can take thin sections of the dinosaur bone and look at the bone histology as we call it - that's the microarchitecture of the bone, just as we do with modern day bone. This has shown that some dinosaur bones, especially the long limb bones and also dinosaur teeth grew in distinct layers. The teeth added new layers on a daily basis and limb bones, on the other hand, often added yearly layers. Just like counting tree rings to work out the age of a tree we can count the annual layers in a dinosaur bone to work out the age of a dinosaur.

Interestingly, some of this work has been carried out on tyrannosaurus and it's been shown that the largest known specimen: that's the one known as Sue, which is in the field museum in Chicago, would have weighed more than 5000kg when living and lived to an age of 28 years.

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