Humans may have evolved from a mouse-like animal: Scientists

The small and furry placental mammal, named Juramaia sinensis, lived in what is now north east China during the Jurassic era when dinosaurs ruled the Earth.

Its well-preserved fossil, unearthed in the fossil-rich region of Liaoning Province, is believed to be the oldest ever found of a group of eutherians, or placental animals that give birth to live offspring, the Daily Mail reported.

Juramaia, hairy and about the size of a mouse, provides fossil evidence of the date when eutherian mammals diverged from other mammals -- metatherians whose descendants include marsupials such as kangaroos and monotremes such as the platypus, the researchers said.

Dr Zhe-Xi Luo of the Carnegie Museum of Natural History in Pittsburgh said: "Juramaia, from 160 million years ago, is either a 'great-grand-aunt', or a 'great-grandmother' of all placental mammals that are thriving today.

"Analysis of the fossil skeleton indicates the animal was an agile creature with a powerful ability to climb.

"This may explain how it managed to survive during the age of the dinosaurs - by climbing and hiding in trees."

Detailing the find in the journal Nature, the researchers said the fossil represents a new milestone in mammal evolution that was reached 35 million years earlier than previously thought, filling an important gap in the record.

According to researchers, the fossil has an incomplete skull, part of the skeleton, and impressions of residual soft tissues such as hair.

Most importantly, its complete teeth and fore paw bones enable paleontologists to pinpoint it is closer to living placentals on the mammalian family tree than to the pouched marsupials, such as kangaroos.

"Understanding the beginning point of placentals is a crucial issue in the study of all mammalian evolution," Dr Luo said.

The date of an evolutionary divergence, when an ancestor species splits into two descendant lineages, is among the most important pieces of information scientists can have.

Modern molecular studies, such as DNA-based methods, can calculate the timing of evolution by a "molecular clock." But this needs to be cross-checked and tested by the fossil record.

Before the discovery of Juramaia, the divergence point of eutherians from metatherians posed a quandary for evolutionary historians.

Evidence from DNA suggested eutherians should have shown up earlier in the fossil record, around 160 million years ago.

Yet, the oldest known eutherian was Eomaia, another shrew like animal dated to 125 million years ago.

The discovery of Juramaia gives much earlier fossil evidence to corroborate the DNA findings, filling an important gap in the fossil record of early mammal evolution and helping to establish a new milestone of evolutionary history, the researchers added.