Being huge

Dinosaurs are noted for their huge size, but how did they do it? The largest dinosaurs, such as the sauropods Brachiosaurus and Argentinosaurus, might have weighed 50 tonnes or more. That’s ten times the size of the largest elephant!

Do we explain this by suggesting, for example, that gravity was less in the Jurassic than today, or that they lived underwater? No, of course not. The rules of physics were the same then as now, and the Earth system functioned in the same way as today. There is no evidence these giants lived floating in water – their bones show adaptation to supporting their huge weight, and there are hundreds of sites with their footprints preserved on dry land.

Martin Sander at the University of Bonn, and his team, worked it out. Dinosaurs enjoyed many of the advantages of being warm-blooded (e.g. efficient physiological processes, active at all times of day and night) but without the disadvantages. The key is that mammals, such as elephants and ourselves, use 90% of our food simply to keep our body temperature constant. Reptiles don’t do that, and so they eat one-tenth of what mammals do. So, a giant sauropod could reach 50 tonnes while eating as much in a day as a 5-tonne elephant!

The giant dinosaurs did other smart things, such as laying quite small eggs (less effort for the mother than producing large young) and offering minimal parental care. It was all about saving energy and getting huge, whereas mammals invest enormously in temperature control and caring for their young. There’s more too, which you can read about in The Dinosaurs Rediscovered.