Paleobiologists have identified three new species from the Jurassic period that are unearthed in northeast China, which may push back the origin of mammals by millions of years.
Mammals are generally believed to have originated in the Middle Jurassic period between 174 million and 164 million years ago. The newly discovered fossils date back to 160 million years ago, which implies,according to Chinese Academy of Sciences researcher Wang Yuanqing,that mammals may have appeared in the Late Triassic period, perhaps around 208 million years ago.
The three are collectively known as Haramiyidans, a group that has previously been difficult to classify, for lack of sufficient specimens. The fossils in question show, for the first time, the complete skull,jaw and postcranial bones. The vast majority of previously discovered fossils were merely teeth.
Wang said the three species--shenshou lui, xianshou linglong, xianshou songae--show bones in the middle ear and thoracic diaphragm characteristic of all mammals.
The size of squirrels and rats, they weighed 40 grams to 300 grams. Scientists also believe they had foot stingers similar to those of the platypus today and probably ate insects, fruit and nuts.