Question: What creature was the first mammal on Earth?

Ceri-Wyn Thomas answered on 17 Jun 2010:

Mammals evolved during the Triassic Period (when the dinosaurs were still roaming about) and they looked like tiny shrew-like creatures (as far as we can tell from fossils!). The remains of one of the earliest mammals were found near Bridgend in Wales! That creature was called Morganoducidon and again, looked a bit like a tiny shrew. Awwww.

Before that there were mammal-like reptiles! In fact many of the mammalian traits are thought to have evolved from reptilian ones- so our hair follicles evolved from reptilian scales, our inner ear developed from the reptilian jaw etc. We’re all related somewhere back in time!