Aug 25, 2011 08:34 GMT  ·  By

A new scientific discovery pushes the time frame when the first placental mammals evolved back an estimated 35 million years. This conclusion is based on the discovery of an excellently-preserved fossils that was discovered in northeastern China.

Placental mammals are animals that have a placenta. This structure helps nurture the fetus while in its mother's womb, facilitating the exchange of chemicals between the two. It is expelled from the body shortly after birth.

In this sense, this group of animals was the precursor of the vast majority of mammals we see on the planet today. Therefore, the discovery of this particular fossil puts yet another marker on the long and intricate evolutionary path mammals took to reach their current configuration.

Details of the new investigation are published in the August 24 issue of the top scientific journal Nature. The paper argues that placental mammals evolved about 35 million years earlier than other fossils indicated.

An important implication this study has is that it provides experts with additional means of refining DNA-based techniques of analyzing evolution in general. Furthermore, it fills a gap in the fossil record that has been bugging evolutionary biologists for many years.

The investigation was conducted by scientist Zhe-Xi Luo, who holds an appointment as a paleontologist at the Carnegie Museum of Natural History. His team focused its analysis on the small, shrew-like mammal called Juramaia sinensis.

This creature lived in what is now China during the Jurassic Epoch, some 160 million years ago. At this point, the creature is the earliest known fossil of eutherians, which is a group of animals that eventually developed to include all placental mammals that ever lived.

Other groups that developed from eutherians include metatherians (marsupials such as kangaroos) and monotremes (a group that also includes the platypus). Juramaia sinensis provide additional insight into how the split occurred between the three distinct groups of mammals.

“Juramaia, from 160 million years ago, is either a great-grand-aunt or a great-grandmother of all placental mammals that are thriving today,” Luo explains. Juramaia sinensis is Latin for “Jurassic mother from China.”

The US National Science Foundation (NSF) Divisions of Environmental Biology and Earth Sciences co-funded the new investigation, which also included experts from the Chinese Academy of Geological Sciences and the Beijing Museum of Natural History.

“These scientists have used the rich fossil mammal record to test evolutionary hypotheses proposed by their colleagues studying living mammals using genetic data,” NSF DEB program director Chuck Lydeard explains.

“The divergence of eutherian mammals from marsupials eventually led to the placental birth and reproduction that are so crucial for the evolutionary success of placentals. But it is their early adaptation to exploit niches on trees that paved their way toward this success,” Luo concludes.