Animals grew in size

 

Image courtesy of Corey Ford/Stocktrek Images/Science Source, 

Joel Kontinen

According to evolution, when the Cretaceous did away with the dinosaurs, many mammals underwent a rapid increase in size. Several hypothesis have been put forward for this increase in size.

For instance, the in brontotheres, was a large mammal from the from the Eocene that grew in size. 

The researchers think that the increase in body size was caused by a macroevolutionary process of species being sorted. 

Source:

Vignieri,  Sacha,  Growing bigger, Science 12 May.