It belongs to group of creatures called gondwanatherians. Until now, we didn't really know where they fitted into the story of mammals as a whole, because the only evidence we had for their existence was teeth and some lower jaw fossils.
The newly discovered skull, which has been analysed by David Krause and colleagues from Stony Brook University, New York, is 12.5cm long. The researchers estimate the mammal weighed around 9kg in total, which would make it the largest mammal of its time on the supercontinent Gondwana.
Based on its large size, and its jaws and teeth, Krause and his colleagues think the mammal had a mixed diet. "It is likely that Vintana had a mixed diet that included large, hard and/or abrasive food items such as roots, seeds or nut-like fruits," they wrote in a paper published today in the journal Nature.
The anatomy of the skull suggests gondwanatherians were related to multituberculates, a successful group of rodent-like mammals that existed for 120 million years and survived the Cretaceous mass extinction.