Scientists from the University of Chile have discovered a 74-million-year-old fossil of a tiny, mouse-sized mammal named Yeutherium pressor in Chilean Patagonia. This mammal lived during the Upper Cretaceous period alongside dinosaurs. The finding provides new insights into evolutionary transitions and represents the third species from this era found in Chile. The fossil, which includes a jawbone, highlights the presence of small mammals coexisting with dinosaurs in the region during that time.