Researchers from the New York Institute of Technology and the Universidad de Alcalá find that the evolutionarily increased size of brontotheres was probably due to unequal species proliferation.
Oscar Sanisidro, Juan Cantalapiedra, and Matthew Mihlbachler examined the dinosaurs’ fossil record and used computer models to explain how they most likely evolved in their study, which was published in the journal Science.
Zoologist Edward Drinker Cope created a rule in the late 1800s to explain how animals adapt to get bigger since larger species typically have more advantages.
This concept, now known as Cope’s rule, seems to hold true for a vast number of species, but occasionally, other elements may be present that circumvent the rule and encourage development for different purposes.
In this new study, the researchers discovered that there was probably another component involved in the evolution of the family of extinct animals known as brontotheres, some of which were notable for their enormous size. And that difference convinced the researchers that Cope’s rule did not apply.
Prior to the Chicxulub impact, dinosaurs were the only large land-dwelling animals. After their demise, mammals began filling their niche, with brontotheres leading the way. Some evolved from canine-sized critters to rhinoceros-looking behemoths weighing more than a metric ton in just 16 million years.
In this new effort, Sanisidro, Cantalapiedra and Mihlbachler sought to learn more about the factors that allowed them to grow so quickly.
The study of 276 brontothere fossils by the researchers led to the development of models. They presummated that one of three scenarios best explained the rise of brontotheres: Cope’s rule; adaptations to shifting adaptive zones; or, thirdly, some form of preferentially neutral speciational evolution.
The researchers concluded that the third option was the most likely one after looking at their models and data. According to the evidence they offer, some brontotheres species grew smaller over time, while others increased in size.
The larger species continued to thrive and grow as more time went by, right up to the end of the Eocene era, when they went extinct, perhaps as a result of a changing climate.
