The surprise discovery of the fossilised skull of a 66 to 70 million-year-old groundhog-like creature in Madagascar has shaken up the scientists' views of the mammalian "family tree", says a research.
The skull of this animal, named Vintana sertichi, was found in 2010.
Vintana belongs to a group of early mammals known as gondwanatherians, until now known only from isolated teeth and a few jaw fragments.
The well preserved skull allowed the first clear insight into the life habits and relationships of gondwanatherians.
Vintana "reshapes some major branches" of that (family) tree, grouping gondwanatherians with others that have been "very difficult to place", said lead author paleontologist David Krause of Stony Brook University.
The researchers compared the skull to those of hundreds of other fossil and extant mammals and concluded that it likely had large eyes, the ability to hear high frequency sounds and a good sense of smell.
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With the addition of this new information on cranial anatomy of gondwanatherians, which was previously completely unknown, the researchers also explored its possible relationship to other early mammals.
Vintana was probably closely related to multituberculates, the most successful mammalian contemporaries of dinosaurs on the northern continents, and early herbivores known as Haramiyida, the study showed.
With a skull that is almost five inches (125 mm) long, it was double the size of other mammals from the southern super continent, Gondwana, during the age of dinosaurs.
The authors estimate a body mass of about nine kg.
The findings appeared in the journal Nature.