Hadrocodium is known only from a skull .
The body is estimated to have been a mere 3.2 cm ( 1.3 in ) in length and about 2 g ( 0.071 oz ) in mass , making Hadrocodium one of the smallest mammals ever .
Hadrocodium is known only from a skull , but the body is estimated to have been a mere 3.2 cm ( 1.3 in ) in length and about 2 g ( 0.071 oz ) in mass , making it one of the smallest mammals ever .