(ORDO NEWS) — Among the predatory dinosaurs, the ancestors of modern birds, there were crumbs no larger than a chicken, and giants the size of a bus. Now scientists have managed to find out how tyrannosaurs were able to grow so huge.
The weight of modern land predators varies from a few grams to more than a ton, while in the Mesozoic era these limits were much wider.
The smallest known carnivorous dinosaur weighed no more than 200 grams, while the weight of the largest is estimated to be between seven and 20 tons. For example, an adult Tyrannosaurus rex weighed about eight tons – four times the mass of an average hippo.
Previously, scientists believed that such a monstrous difference in size was due to the growth rate: small dinosaurs grew slowly, and giant dinosaurs grew abnormally fast.
However, after studying bone cuts from about 80 species of carnivorous dinosaurs, an international team of paleontologists from the United States and Argentina concluded that there was only a very weak relationship between growth rate and final body size. The study is published in the journal Science.
The fact is that the growth rate of the body and, accordingly, the skeleton is “recorded” on the saw cuts of large tubular bones in the same way as on the saw cut of a tree trunk, in the form of growth rings.
Since life conditions change during each year (for example, the rainy season is replaced by droughts when food is scarce), the growth rate of the organism also changes, which is why on the cut of the bone you can see wide stripes that formed during the feeding seasons, and narrow (which means that at this time the owner of the skeleton was malnourished).
Comparing the number of years it took the animal to grow and the width of the rings on the cut of the bone, one can determine the rate and duration of growth.
It turned out that some giant carnivorous dinosaurs grew as slowly as the current alligators, but among the smaller species there were those whose growth rate was comparable to the development rates of modern mammals and birds.
Another thing is that the life span of small species was approximately 10–20 years, while tyrannosaurs reached maturity only by the age of 20, and lived for about 30–40 years.
In other words, it was not so much the rate of growth as the duration of the period of active mass gain that played a key role in the fact that representatives of some species of dinosaurs became so huge.
At the same time, tyrannosaurs did not grow excessively fast: the smallest skeleton found belonged to an animal weighing some 30 kilograms, which died at the age of two.
But these dinosaurs had plenty of time for gradual development and growth: by the age of 14-16, tyrannosaurs gained about two tons, after which, over four to six years, they more than doubled their weight, finally reaching the dimensions of such a dinosaur, to which we used to movies.
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