Mammals Originated Much Earlier than Previously Assumed

Mammals originated 208 million years ago in the late Triassic period, much earlier than previous estimates, a new study suggests.

Previous research had suggested that mammals originated in the middle Jurassic (between 176 and 161 million years ago). The current study states that mammals were roaming the earth as early as the late Triassic period (between 235 and 201 million years ago).

The study was conducted by researchers at the American Museum of Natural History and the Chinese Academy of Sciences. The team described three new species of squirrel-like animals - Shenshou lui, Xianshou linglong, and Xianshou songae. These species were described using six fossils found in China.

The research also adds new members to the mammalian family tree.

"For decades, scientists have been debating whether the extinct group, called Haramiyida, belongs within or outside of Mammalia," said co-author Jin Meng, a curator in the Museum's Division of Paleontology, according to a news release.

According to the scientists, their study was based on near-complete, 160-million-year-old fossils from China.

"Previously, everything we knew about these animals was based on fragmented jaws and isolated teeth. But the new specimens we discovered are extremely well preserved. And based on these fossils, we now have a good idea of what these animals really looked like, which confirms that they are, indeed, mammals," Meng said in a news release.

The species described in the study had slim bodies and long fingers and probably looked like small squirrels, Reuters reported. Their limbs show that they were mostly tree-dwellers. These animals had a long tail that could have helped them stay on tree branches.

The researchers have placed the new species in a new group called Euharamiyida. These animals, most likely, ate nuts and small insects. They also had an unusual arrangement of teeth, with many cusps or points on the crown of their teeth.

The species have typical mammalian middle ear. This part of the ear turns vibrations in the air into ripples in fluid in the ear. The newly described species - like all mammals - have three bones in the middle ear.

A major problem presented by the study findings is that mammals might have split from reptiles much earlier than previous estimates. "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," Meng said

The study is published in the journal Nature.