Hadrocodium wui is an extinct Mammaliaform from the lower Jurrasic of China. At a mere 1.35 inches (3.2 cm), it is one of the smallest “mammals” to have ever existed. Hadrocodium was an important discovery with interesting implications. It had evolved features that were though to define true mammals from their mammal-like ancestors. Relatively speaking, it had a large brain. It also had an advanced jaw structure and middle ear (the three tiny bones of which evolved from reptilian jaw bones). This shows that these features appeared a full 45 million years earlier than previously thought. It was also probably a warm-blooded, nocturnal insectivore.