Hadrocodium wui was a basal mammal species which lived during the Lower Jurassic in what is now China.
Hadrocodium does not completely exhibit all of the typical features of mammals. But it did have a separate jawbone, a large brain cavity (for its size-3.2 cm), and a complex hearing system.
Whether Hadrocodium was endothermic or cold-blooded is still disputed. It was nocturnal, a fact which seems to place it in the endotherm group. But it is thought that its small size would have been a disadvantage for an endothermic animal.
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