‘Thunder beast’ fossils show how some mammals might have gotten big
Rather than a straightforward march, evolving to be big sometimes involved getting smaller
![illustration of Megacerops kuwagatarhinus with small, striped mammals in the foreground and background](https://i0.wp.com/www.sciencenews.org/wp-content/uploads/2023/05/051023_ec_brontotheres_feat.jpg?fit=1030%2C580&ssl=1)
Extinct brontotheres like Megacerops kuwagatarhinus (illustrated) were once titans weighing a metric ton or more. But the mammals’ evolutionary history wasn’t a straight path to gigantism.
Oscar Sanisidro © 2018, KU Biodiversity Institute/The University of Kansas