But, Luo added, unlike the water-dwelling platypus, Akidolestes was a land mammal that preyed on insects using its sharp teeth.
Such a mix of modern and primitive features hasn't been seen before in a mammal, the authors say.
They add that the fossil challenges conventional wisdom about how placental mammals split from earlier egg-layers.
The split may not have been as clear-cut as previously thought, they say. Some placental mammals have have readopted some of the physical characteristics of monotremes.
"It is quite unusual that this mammal reacquired some primitive hind-limb feature," Luo said.
Evolutionary Throwback
Thomas Martin, head of mammalogy at the Senckenberg Research Institute in Frankfurt, Germany, agrees that Akidolestes may represent some kind of evolutionary throwback.
The animal's curious combination of traits could be caused "by developmental genes that sporadically become active in widely separated mammalian [groups]," he said.
"Akidolestes impressively shows that the evolution of the mammalian skeleton followed a mosaic pattern," Martin added.
The fluffy animal also offers further clues to the origins of the large group of mammals that arose following the demise of the dinosaurs some 65 million years ago.
The researchers say Akidolestes and its immediate fossil relatives all belong to the same extinct family of mammals, whose older species all lived in Asia while the younger species were found in North America.
"Akidolestes strengthens the case for Asia being the place where the main mammal groups first originated," Martin said.
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