Is this the way to the Met? (Image: Christian Darkin/SPL)

How common were the giant dinosaurs? Were house-sized plant-eating sauropods and stegosaurs rare beasts, or did they swarm over the Jurassic landscape?

The fossil record is far too patchy to answer this question merely by counting bones. Instead, palaeontologist James Farlow of Indiana University-Purdue University Fort Wayne and colleagues have worked out the food needs and resources of a dino population preserved in a deposit called the Morrison formation, which stretches across Colorado, Utah and Wyoming. Dating from around 150 million years ago, near the end of the Jurassic period, the Morrison formation holds many of the long-necked giants called sauropods.

The formation also holds fossil ferns and cycads, which allowed Farlow and colleagues to estimate how much food was available for Jurassic herbivores to eat. And to see what was eating it, the team surveyed the species present. In one layer, they counted 135 sauropod specimens – including 31 Apatosaurus, the behemoth formerly known as Brontosaurus. These huge herbivores account for much more biomass than smaller creatures in this region, including their own young, and would have gulped down most of the available food.


Calculating dinosaur appetites was a slightly more complicated task because their metabolism is unknown. If they were warm-blooded like mammals, their needs would be similar to those of modern hippos and elephants – although their larger sizes should have made them somewhat more energy-efficient. Farlow calculates that a square kilometre could host only a few full-sized sauropods with mammalian metabolisms.

But if they had slow, cold-blooded metabolisms like lizards, they could have survived on a much more meagre diet, and the same area could hold tens of the giants.

Dinos in the park

To put that into more concrete terms, consider New York’s Central Park, which sits across the street from the American Museum of Natural History’s famed dinosaur collection, and which has been populated with dinosaurs in films from The Beast From 20,000 Fathoms to Night at the Museum.

At 3.4 square kilometres, a slice of Morrison landscape the size of Central Park might have fed several warm-blooded adult sauropods, including one or two full-sized apatosaurs. Alternatively, perhaps 100 cold-blooded sauropods could have crowded into this Jurassic city park.

Farlow did not try to estimate the population density of the fearsome Jurassic predator Allosaurus, which is also present in the Morrison formation. That, he says, would have been even more complicated.

Journal reference: Historical Biology, DOI: 10.1080/08912961003787598