As with trees, it is possible to deduce the age of a dinosaur and the variations in its growth by studying the rings that mark its bones concentrically year after year. An international team has just analyzed what happened to 42 species of theropods, carnivorous dinosaurs, presenting very disparate sizes – ranging from 50 centimeters to more than 12 meters long – and having lived during the period extending from 230 million years ago to the disappearance of the non-avian dinosaurs, 66 million years ago. Among theropods, we come across both the slender velociraptor and the inevitable T. Rex.
“Widely spaced rings indicate faster growth and narrow rings tell us that an animal was growing more slowly”explains Michael D’Emic (Stony Brook University, New York), first author of this analysis, published in Science of February 24. The results offer a contrasting picture of the different growth strategies, underlying both the gigantism and the miniaturization observed in the evolution of this large sample. Michael D’Emic and his colleagues show that some individuals could grow to a respectable height while maintaining sustained growth over time, while others exhibited a marked “surge” in their younger years. On the other hand, the smallest could see their growth rate decelerate, or even present a stop in their development after a few years.
“This article shows that in dinosaurs, the adult size, large or small depending on the species, was linked either to the speed of growth or to the duration of this growth, the two factors possibly being involved in equal parts.comments paleontologist Eric Buffetaut, emeritus research director at the CNRS. This goes against a frequently expressed idea that growth rate was the main determinant, a high growth rate allowing large dinosaurs to reach their large dimensions quickly – unlike, for example, crocodiles, which reach a large size. size because they grow long. »
Evolution of the different lineages
Take, for example, two species of the same size, Ceratosauruswhich lived about 150 million years ago, and was 6 meters long and about 800 kilos, and Majungasaurus, appeared in Madagascar shortly before the extinction of the dinosaurs. The first grew rapidly, while the second had a slower growth than that observed today in alligators.
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