Researchers think they understand how some ancient dinosaurs grew to such a size. NPR’s Eyder Peralta talks with Michael D’Emic, a paleontologist at Adelphi University.
EYDER PERALTA, HOST:
If you’ve ever seen a tree cut down, you’ve seen the rings that mark each year’s growth. But those rings do not only show the age of the tree. How quickly the tree grew. A new study took this idea and applied it to dinosaur bones to learn just how some dinos got so big. Michael D’Emic is a paleontologist at Adelphi University. He joins us now. Hello, Michael.
MICHAEL D’EMIC: Hi. Thanks for having me.
PERALTA: Yes. So your research focuses on a particular group of dinosaurs, right? How do you shake their bones?
D’EMIC: So we looked at a group of dinosaurs called theropods, which includes some of the most famous examples, like T. rex and Velociraptor, Archeopteryx. And, above all, this is the group that includes birds alive today. So we had to take samples or segments from each of the bones of the leg and stick them to the glass – the big microscope – and the sand, which was about the thickness of a human hair, so thin that it could be transparent. And then we could count and measure the growth of the rings.
PERALTA: So you studied theropods, these great ancient dinosaurs. And what interest do they grow on the road?
D’EMIC: Our study found that there was no way for dinosaurs to grow, that the largest dinosaurs sometimes took more or less ten years or so to reach their truly immense sizes, and some others took decades. So in the greatest dinosaurs the resources and durations were very different. And we found that to be true even of the medium- and small-sized early theropod dinosaurs.
PERALTA: And that challenges conventional wisdom, what have we thought about how dinosaurs evolved to get so big?
D’EMIC: It does. It was thought that in the group Dinosauria, which includes the group we studied, the predominant mechanism for developing a larger body mass was thought to be through the acceleration of evolution, in order to have faster growth. But what our paper shows is that they are just as likely to slow down growth, but to grow in the long run.
PERALTA: Are these two types of growth advantageous for development?
D’EMIC: Yeah, there are advantages and disadvantages. There are tradeoffs. So evolving to grow faster than your ancestors means you can outcompete other species in the environment for your resources. So maybe you can reach taller trees or crops that smaller species can’t reach. And then you can also avoid the growth of predators in your environment. You are not so young as long, and perhaps you are not a potential dinner for so long in your life. The disadvantage is that it takes a lot of energy. So if lean times come, such as a drought where there is not much food around, then you would be more prone to extinction.
PERALTA: Can we talk about live animals? Shall we see that variety, how quickly or slowly great species grow in the animals now living?
D’EMIC: Absolutely. Yeah, we see a whole range of growth and patterns in animals today. The funny thing is that the ideal animals that we have today are the animals that happen to us, right? I call the animals that have not become extinct. So it is not a true example of evolution. To get a sense of how evolution proceeds, you need a fossil example of the past. It is a famous passage – nothing in biology makes sense except in the light of evolution. We can make mistakes as we look at animals today.
PERALTA: This is Michael D’Emic, a paleontologist at Adelphi University. Michael, thank you so much.
D’EMIC: Thank God for having me.
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