Abstract: Mammals are prominent living vertebrates not only by their morphological disparity, but also by a spectacular diversity of ecological specializations of their 5400 species. Evolution of mammals and their mammaliaform precursors can be traced back to Mesozoic Era (250 to 65 million years). Because Mesozoic mammaliaforms lived in the Age of Dinosaurs, a historical view was that early mammals were generalized, and had very limited ecomorphological diversity, under the dominance of dinosaurs. Recent and rapid discoveries of spectacular fossils, many of which from China, have now revealed a previously unsuspected ecomorphological diversity: ranging from burrower with possibly subterranean life, to semi-aquatic forms that could swim, to fully arboreal mammals that could glide. Several key mammalian features also evolved more than once in different clades, possibly related morphogenetic homoplases. Taken together, the latest fossil findings clearly indicate that different mammaliaforms developed similar biological adaptations in iterative evolutionary experiments, and that different mammaliaform clades of Mesozoic evolved similar ecomorphotypes repetitively, congruent with the Jurassic-Cretaceous (J-K) and the Cretaceous-Paleogene (K-Pg) turnovers of ecosystems.