Chinese researchers have discovered three new species of squirrel-like creatures belonging to an extinct group of haramiyids that lived during the Jurassic period.

Over the last three years, researchers from the American Museum of Natural History and the Chinese Academy of Sciences uncovered the preserved fossils of the new species in Liaoning province in northeastern China.

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Dr Jin Meng, a curator in the Museum's Division of Paleontology, said scientists have long debated if the Haramiyida group belongs to mammals or not. In previous studies, scientists only had molar teeth as evidence to represent the animals.

But based on the new fossils findings, researchers confirmed that these animals are "indeed mammals".

Dr. Mengsaid they already have a complete skeleton that shows the morphology of the skull, arm, leg, foot and hands of the species.

"All that morphology shows that these animals had mammalian features," he added.

"What we're showing here is very convincing that these animals are mammals, and that we need to turn back the clock for mammal divergence."

The discovery of fossils supports the idea the earliest mammals have been around for more than 200 million years.

This is contrary to previous research that suggested mammals originated in the Middle Jurassic period, which ranged from 174 million to 164 million years ago.

The three new species, which were named Shenshou lui, Xianshou linglong and Xianshou songae, lived about 160 million to 170 million years ago.

These animals represent a new group called Euharamiyida, mysterious rodent-like mammals that looked similar to small squirrels.

The newly discovered animals weighed between 1 and 10 ounces. They had long tails and feet that indicated they were tree dwellers.

Tags squirrel, Euharamiyida, Scientists, Shenshou lui, Xianshou linglong, Xianshou songae