Broken tibia of a carnivorous dinosaur with treelike rings. These closely spaced rings form annually and indicate a slow-growing, long-lived animal. MICHAEL D. D’EMIC
As with trees, it is possible to deduce a dinosaur’s age and the differences in its growth by examining the rings that concentrically mark its bones year after year. An international team has just analyzed what happened to 42 species of theropods, carnivorous dinosaurs, ranging in size from 50 centimeters to more than 12 meters long, ranging from 230 million years ago to the disappearance of the dinosaurs non-bird dinosaurs lived 66 million years ago. Among the theropods we encounter the slender Velociraptor as well as the inevitable T. rex.
“Rings that are far apart indicate faster growth, and narrow rings tell us that an animal grew more slowly,” says Michael D’Emic (Stony Brook University, New York), first author of this analysis, published FEBRUARY 24 in Science was published. The results offer a contrasting picture of the different growth strategies underlying both gigantism and miniaturization observed in the evolution of this large sample. Michael D’Emic and his colleagues show that some individuals were able to grow to a respectable size while maintaining sustained growth over time, while others showed a significant “rise” in their younger years. On the other hand, the youngest ones might see their growth rate slow down or even represent a standstill in their development after a few years.
“This article shows that in dinosaurs, adult size, large or small depending on the species, is related to either the rate of growth or the duration of that growth, with the two factors possibly playing equal roles,” comments paleontologist Eric Buffetaut , Research Director Emeritus at the CNRS. This contradicts a commonly held notion that growth rate was the main determinant, a high growth rate that allows large dinosaurs to quickly attain their large dimensions – unlike, say, crocodiles, which attain large size because they grow tall. »
Evolution of the different lines
Take, for example, two species of the same size, Ceratosaurus, which lived about 150 million years ago, was 6 meters long and weighed about 800 kilos, and Majungasaurus, which appeared in Madagascar just before the dinosaurs went extinct. The first grew rapidly, while the second grew more slowly than is observed in alligators today.
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