Why some of T. rex’s cousins ​​were so short

about the episode

In a major study of tibia bones in dinosaurs, scientists have shown that even within a single family there can be very different growth strategies, some evolving into massive beasts like T. rex and others into tiny, bird-like creatures.

The idea has long been, and in many cases remains true, that large animals are larger than smaller related species because they grew faster during the period when most growth occurs. This is true of 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 do not grow quickly, but because they can age and grow for a long time, they eventually grow quite large.

It has always been assumed that T. rex and its relatives are the growth spurt version. But that’s not what one researcher saw when he saw the bones of a 23-foot-long relative of T. rex that lived 66 million years ago in what is now Madagascar.

Just as with trees, growth rings show how much bone has grown in a year. There was no pubertal growth spurt. So the animal must have grown up by growing up for a long time, just like a crocodile.

They finally examined the growth rings in the bones of 42 species in the family and found that 31 percent grew larger than the ancestors due to the growth spurt and 28 percent grew taller. Some species have also become smaller than their ancestors. 21 percent of this is due to a shorter growth spurt and 19 percent due to slower growth.

Therefore, even within the same family, there is no single way to get to the top or bottom of the scale. It would now be interesting to see what conditions led to these different strategies. And it would be nice to consider this for other animal species as well.

Read more about research here: Big Dino, Little Dino: How t-rexRelatives changed their size.