So Big!

Q. What was going on in the Jurassic and Cretaceous periods that allowed the largest known land animals, like the Brontosaurus, to thrive and survive?

A. The Brontosaurus, now properly named the Apatosaurus, and the other great sauropod species benefited from a complex interaction of resource availability and evolved physical traits, according to a multi-author review article that appeared online in April in Biological Reviews, published on behalf of the Cambridge Philosophical Society.

The dinosaurs’ genetic heritage and evolutionary innovations “triggered a remarkable evolutionary cascade,” the article said. The most important innovation, the study suggested, was probably the very long neck, which made “food accessible that was out of the reach of other herbivores.” The long neck could only evolve because of the creatures’ small head, lightening the load on the neck, and the small head was possible because food was ingested without being chewed but retained for long periods of digestion.

The large dinosaurs also seem to have retained an avian-style, highly dispersed respiratory system, which required less energy for breathing and in addition may have helped with cooling such large creatures. Size itself was an advantage in survival, protecting against predators, for example. Another advantage was an oviparous reproduction system, with many small offspring being born, but only a few surviving to reach giant adulthood.