That was the fate of the earliest-known horse, Sifrhippus sandrae (or its jaw bone, at least). It started out at around 5.4 kilograms (12 pounds) but during the Paleocene-Eocene Thermal Maximum ...

Get Instant Summarized Text (Gist) Fossils from the Eocene mudflats of Utah reveal four new ichnospecies, indicating diverse foraging behaviors of ancient waterbirds. These trace fossils ...