When dinosaurs became extinct 65 million ago, mammals began to grow, multiplying their size by a thousand in some cases. This is the case of Deinotherium, a distant relative of elephants that disappeared 2.7 million years ago and weighed 17.00 kilograms.
“The dinosaurs disappear and, suddenly, nobody else eats the vegetation. That means a great availability of food , and the mammals begin to eat, and if you are a herbivore it is more efficient to be large”, explains Jessica Theodor, biologist of the University of Calgary (Canada) and co-author with 19 other researchers of the article published today in the journal Science. Mammals, whose weight until then oscillated between 3 grams and 15 kilograms, began to consume this food and in some cases reached up to 17 tons in weight .
For the study, Theodor and his colleagues first analyzed preserved mammalian fossils from all successive periods. In order to demonstrate how much mammals grew after the extinction of the dinosaurs, the researchers collected data on the maximum size of each major group of land mammals from each continent, including perissodactyls (odd-toed ungulates such as horses and rhinos), proboscis (including elephants, mammoths, and mastodons) , xenarthros (anteaters, tree-dwelling sloths, and armadillos), as well as a large number of other groups of now extinct animals.
The results give clues about what factors define the size limits of land mammals: the amount of space available for each animal and the climate in which they live. According to scientists, the colder the climate, the larger the animals , because larger animals conserve heat better.In addition to confirming the extraordinary growth that mammals experienced when the dinosaurs disappeared , the study shows that this evolution took place relatively quickly. “The dinosaurs became extinct 65 million years ago and in 25 million years the ecosystem was reprogrammed to respond to the growing demand for these ever-larger animals, which is, in geological terms, a short period, a truly evolution fast, “emphasizes Theodor.
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