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An international group of scientists has revealed why some animals became giants after the extinction of the dinosaurs, which occurred 66 million years ago, in an article published this week in the journal Science.
The study indicates that the largest land animals that survived that event that occurred at the end of the Cretaceous barely weighed 10 kilos, while some 15 million years later mammals weighing several tons already existed.
Paleontologists have spent more than two centuries trying to explain the evolution of the body size of certain species, so a few years ago, the group of researchers set to work to try to find an answer.
To do this, they analyzed the case of brontotheres ('thunder beasts', in Greek), distant cousins ??of tapirs and rhinos, which inhabited our planet during the Eocene, between 56 and 34 million years ago. These went from weighing about 20 kilos to five tons, that is, the equivalent of a current elephant.
Unrepeatable evolution
Using mathematical models that simulate evolutionary processes and the most accurate data available, the experts concluded that the new species of brontotheres were not systematically larger than their ancestors.
However, once they settled, the smaller ones had a higher risk of extinction, because the ecological communities of herbivores in that era were full of small and medium-sized species, so "the typical ecological niches of moderate sizes were more saturated and smaller brontotheres species had more competitors.
In other words, when larger species appeared, they escaped from said competition, survived longer and, in this way, could produce other species, thus becoming more abundant than the small ones and producing the pattern observed in the fossil record.
"What this type of finding teaches us is that the brontotheres were not predestined to increase in size. It was contingency and chance that projected their evolution towards gigantic sizes," explained Oscar Sanisidro Morant and Juan López Cantalapiedra, paleontologists from the University de Alcalá (Spain) and co-authors of the study. "Our discovery shows us a less predictable and, therefore, unrepeatable evolution," they concluded. (RT) (Photo: Gettyimages)
