Leptictidium

Lepticitidium was a primitive, early offshoot of the eutherians, meaning that although it was a eutherian, it wasn't a placental mammal. Despite being a basal eutherian, it was quite derived - Leptictidium was the first known fully bipedal mammal. Judging from its hip structure, it likely locomoted like a kangaroo. In life, Leptictidium resembled a bit like modern elephant shrews. It fed on insects and small vertebrates, as deduced from its stomach contents. Its fossils were found in the Messel Pit of Germany in the Eocene epoch, and due to its fossils being dated in the Paleocene-Eocene thermal maximum, its habitat was a humid, balmy rainforest. In Walking With Beasts, a Leptictidium mother teaches her offspring to survive on their own, and it must be done quick, since they're rather defenseless animals. She does this by regularly taking her progeny out on hunting trips where she shows them the many tips and tricks of Leptictid survival, one of which involves the mother using her senses to identify which organisms are safe to consume. Leptictidium is one of those organisms with no foreseeable future; they died out 35 mya in the Late Eocene with no living descendants, possibly because the climate grew cooler and drier as forests were phased out by open prairies.