Hadrocodium wui's an extinct basal mammal species that lived during the Lower Jurassic (approx. 195 million years ago, during the Sinemurian stage) in what's now the Yunnan province of China. Hadrocodium was a mere 3.2 cm (1.35 in) in length (about 2 grams), and's one of the smallest mammals of either the Mesozoic or Cenozoic periods. Hadrocodium's the earliest known example of several features distinctive to mammals, including mammal-like mandible and middle-ear structures and a relatively lar… (More on Hadrocodium)