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