Therapods, the meat eating dinosaurs, ranged in size from the impressively powerful T.Rex to velociraptors and eventually to the birds we have today.

How did this variety of size evolve?

A team of researchers at Adelphi University, New York, have been studying this evolutionary question.

Palaeontologist Michael D. D’Emic, explained:

“Most animals are thought to evolve to be larger or smaller by growing faster or slower than their ancestors, but this study shows that it’s just as likely that bigger or smaller animals grew for longer or shorter periods of time during growth spurt.”

The bones of many animals, including dinosaurs, slow or pause growth every year, leaving marks like tree rings that indicate the animal’s age and growth rate. 

“Widely spaced rings indicate faster growth and narrowly spaced rings tell us that an animal was growing more slowly,” said D’Emic.

D’Emic and a team of international researchers measured about 500 such growth rings in about 80 different theropod bones.

“We found that there was no relationship between growth rate and size,” said D’Emic. “Some gigantic dinosaurs grew very slowly, slower than alligators do today. And some smaller dinosaurs grew very fast, as fast as mammals that are alive today.”

 The team found that it was just as common for meat-eating dinosaurs to evolve changes to how fast they grew as it was to evolve changes to how long they grew.

“This has really important implications because changes in rate versus timing can correlate to many other things, like how many or how large your offspring are, how long you live, or how susceptible to predators you are,” D’Emic said.

“Hopefully this research spurs investigations into other groups, both alive and extinct, to see what developmental mechanisms are most important in other types of animals.” 

Click on this link to access the paper, Developmental strategies underlying gigantism and miniaturization in non-avialan theropod dinosaurs, published in the Journal Science