Why Some of T. Rex’s Cousins ​​Were Small

About the episode

In a major study of dinosaur shin bones, scientists show that even within the same family there can be vastly different growth strategies, some of which evolved into huge beasts like T. rex and others into small bird-like creatures.

The idea has long been, and in many cases still is, that large-bodied animals are taller than smaller-bodied related species because they grew faster during the period when growth occurs. most. This is true for most mammals and birds. An elephant grows faster than a chihuahua and an ostrich faster than a starling.

However, there are also exceptions. Crocodiles for example. They don’t grow fast, but because they can age and grow for a long time, they eventually get big.

T. rex and its relatives have always been assumed to be the growth spurt version. But that’s not what a researcher saw when he sawed through the bones of a 7-meter-long relative of the T. rex that lived 66 million years ago in what is now Madagascar.

Just like with trees, growth rings indicate how much the bone has grown in a year. And there was no pubertal growth spurt to be seen. The animal therefore had to grow by lying down, just like a crocodile.

They eventually examined the growth rings in the bones of 42 species in the family and found that 31% had grown larger than their ancestors due to a growth spurt and 28% had grown taller. Some species had also become smaller than their ancestors. 21% of this due to a shorter growth spurt and 19% due to slower growth.

Thus, even within the same family, there is not just one way up or down the ladder. Now, it would be interesting to know what circumstances led to these different strategies. And it would be nice to look into that for other animal species as well.

Read more about research here: Big dino, little dino: how t rexRelatives of have changed in size.