Brontotheres Evolved Their Enormous Sizes as Way to Survive in Competitive Ecological Niches: Study
However, only 20 million years later, megaherbivores with bodies weighing more than a ton were abundant and profoundly influenced terrestrial landscapes.
This rapid diversification of body size is often considered one of the most extraordinary feats in mammalian evolution.
Although several hypotheses explaining this expansion have been proposed, the evolutionary processes underpinning the increase in mammal size diversity remain poorly understood.
While the first known brontotheres were only about 18 kg in size, most brontothere species during their time on Earth were estimated to have grown to be well over 1,000 kg.
Using phylogeny-based trait evolution modeling and diversification analysis, the study authors discovered that brontothere body-mass evolution mainly occurred during speciation.
The findings suggest that smaller brotothere species who lived in highly competitive ecological settings experienced higher extinction risk, which drove biased diversification towards larger animal sizes, revealing a complex, long-term macroevolutionary pattern of increased survival of larger species due to reduced competition with other herbivores in crowded ecological niches.
“Body-mass evolution in brontotheres mainly occurred during speciation and had no preferential direction,” the researchers said.
“Long-term directional change stemmed from the higher survival of larger lineages in less-saturated herbivore guilds.”
“Our study emphasizes the role of differential species proliferation in explaining the long-term phenotypic trends observed in the fossil record, which are more than an accumulation of steady microevolutionary changes.”
Source: Sci News