Dinosaurs evolved gigantism over and over again

Dinosaur gigantism evolved independently much more often than previously thought. Such gigantic animals arose in 36 genera with different characteristics and ecological niches over a period of 100 million years, according to a new study.

Michael D’Emic of Adelphi University in Garden City, New York, used measurement data from fossil leg bones for his research, from which he calculated the evolution of the body mass of nearly 200 dinosaurs. He presents the results in the journal “Current Biology”.

All the dinosaurs studied belong to the group of sauropods, which gave rise to such well-known genera as Brontosaurus, Brachiosaurus and Diplodocus. Characteristic of sauropods are a massive body on thick legs, a very long tail and neck with a relatively small head. “It was previously thought that sauropods of their extraordinary size evolved independently a number of times in their evolutionary history, but with the new analysis we now know that this number is much higher.”D’Emic is quoted in a statement from his university.

As a limit for gigantism, the researcher chose the body mass of the largest mammal that ever lived on land: the mammoth. “These largest of the largest sauropods were ecologically diverse, had differently shaped teeth and heads and differently proportioned bodies, indicating that they occupied the ‘big body’ niche somewhat differently,” D’Emic said.

There are also no traits that characterize only those sauropods larger than land mammals, the study author writes. Climate probably plays a minor role in evolution, as there is no relationship between global mean temperature and body mass in sauropods. Hence the new research question why some genera developed gigantism and others did not.

(yam/sda/dpa)