Featured Research

from universities, journals, and other organizations

Discovery of a 160-million-year-old fossil represents a new milestone in early mammal evolution

Date:
August 24, 2011
Source:
Carnegie Museum of Natural History
Summary:
A remarkably well-preserved fossil discovered in northeast China provides new information about the earliest ancestors of most of today's mammal species -- the placental mammals. This fossil represents a new milestone in mammal evolution that was reached 35 million years earlier than previously thought, filling an important gap in the fossil record and helping to calibrate modern, DNA-based methods of dating the evolution.

New Jurassic eutherian mammal Juramaia sinensis: The original fossil (type specimen) is preserved on a shale slab from the Jurassic Tiaojishan Formation. The fossil belongs to the Beijing Museum of Natural History (BMNH PM1143) and is being jointly studied by Chinese and American scientists. Etymology: "Jura" represents the Jurassic Period of the geological time scale; "-maia" means "mother;" sinensis means "from China." The full name means "Jurassic mother from China."
Credit: Zhe-Xi Luo/Carnegie Museum of Natural History

A remarkably well-preserved fossil discovered in northeast China provides new information about the earliest ancestors of most of today's mammal species -- the placental mammals. According to a paper published August 25 in the journal Nature, this fossil represents a new milestone in mammal evolution that was reached 35 million years earlier than previously thought, filling an important gap in the fossil record and helping to calibrate modern, DNA-based methods of dating the evolution.

Related Articles


The paper by a team of scientists led by Carnegie Museum of Natural History paleontologist Zhe-Xi Luo describes Juramaia sinensis, a small shrew-like mammal that lived in China 160 million years ago during the Jurassic period. Juramaia is the earliest known fossil of eutherians -- the group that evolved to include all placental mammals, which provide nourishment to unborn young via a placenta. As the earliest known fossil ancestral to placental mammals, Juramaia 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). As Luo explains, "Juramaia, from 160 million years ago, is either a great-grand-aunt, or a 'great-grandmother' of all placental mammals that are thriving today."

The "Jurassic mother from China"

The fossil of Juramaia sinensis was discovered in the Liaoning Province in northeast China and examined in Beijing by Zhe-Xi Luo and his collaborators: Chong-Xi Yuan and Qiang Ji from the Chinese Academy of Geological Sciences, and Qing-Jin Meng from the Beijing Museum of Natural History, where the fossil is stored. The name Juramaia sinensis means "Jurassic mother from China." The fossil has an incomplete skull, part of the skeleton, and, remarkably, impressions of residual soft tissues such as hair. Most importantly, Juramaia's complete teeth and forepaw bones enable paleontologists to pin-point that it is closer to living placentals on the mammalian family tree than to the pouched marsupials, such as kangaroos.

Resetting the evolutionary clock

"Understanding the beginning point of placentals is a crucial issue in the study of all mammalian evolution," says Luo. The date of an evolutionary divergence -- when an ancestor species splits into two descendant lineages -- is among the most important pieces of information an evolutionary scientist can have. Modern molecular studies, such as DNA-based methods, can calculate the timing of evolution by a "molecular clock." But the molecular clock needs to be cross-checked and tested by the fossil record. Prior to the discovery of Juramaia, the divergence point of eutherians from metatherians posed a quandary for evolutionary historians: DNA evidence suggested that eutherians should have shown up earlier in the fossil record -- around 160 million years ago. Yet, the oldest known eutherian, was Eomaia*, 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.

Juramaia also reveals adaptive features that may have helped the eutherian newcomers to survive in a tough Jurassic environment. Juramaia's forelimbs are adapted for climbing; since the majority of the Jurassic mammals lived exclusively on the ground, the ability to escape to the trees and explore the canopy might have allowed eutherian mammals to exploit an untapped niche.

Luo supports this perspective: "The divergence of eutherian mammals from marsupials eventually led to placental birth and reproduction that are so crucial for the evolutionary success of placentals. But it is their early adaptation to exploit niches on the tree that paved their way toward this success."

*Eomaia was originally described in 2002 by a team of scientists led by Zhe-Xi Luo and Carnegie mammalogist John Wible.


Story Source:

The above story is based on materials provided by Carnegie Museum of Natural History. Note: Materials may be edited for content and length.


Journal Reference:

  1. Zhe-Xi Luo, Chong-Xi Yuan, Qing-Jin Meng, Qiang Ji. A Jurassic eutherian mammal and divergence of marsupials and placentals. Nature, 2011; 476 (7361): 442 DOI: 10.1038/nature10291

Cite This Page:

Carnegie Museum of Natural History. "Discovery of a 160-million-year-old fossil represents a new milestone in early mammal evolution." ScienceDaily. ScienceDaily, 24 August 2011. <www.sciencedaily.com/releases/2011/08/110824131535.htm>.
Carnegie Museum of Natural History. (2011, August 24). Discovery of a 160-million-year-old fossil represents a new milestone in early mammal evolution. ScienceDaily. Retrieved December 27, 2014 from www.sciencedaily.com/releases/2011/08/110824131535.htm
Carnegie Museum of Natural History. "Discovery of a 160-million-year-old fossil represents a new milestone in early mammal evolution." ScienceDaily. www.sciencedaily.com/releases/2011/08/110824131535.htm (accessed December 27, 2014).

Share This


More From ScienceDaily



More Fossils & Ruins News

Saturday, December 27, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

300-Million-Year-Old Fossil Reveals Fish Saw In Color

300-Million-Year-Old Fossil Reveals Fish Saw In Color

Newsy (Dec. 24, 2014) A 300-million-year-old fish fossil discovered in Kansas has evidence of photoreceptor eye tissue. It's the earliest known display of seeing in color. Video provided by Newsy
Powered by NewsLook.com
Hopes Ride High for Classic Car Boom in Havana

Hopes Ride High for Classic Car Boom in Havana

Reuters - Business Video Online (Dec. 23, 2014) Cuba's vintage cars may see new roads ahead as restored diplomatic relations with the U.S. raise hopes of an American tourist boom to see the 1950s 'yank tanks'. Deborah Lutterbeck reports. Video provided by Reuters
Powered by NewsLook.com
Researchers Bring Player Pianos Back to Life

Researchers Bring Player Pianos Back to Life

AP (Dec. 17, 2014) Stanford University wants to unlock the secrets of the player piano. Researchers are restoring and studying self-playing pianos and the music rolls that recorded major composers performing their own work. (Dec. 17) Video provided by AP
Powered by NewsLook.com
Domestication Might've Been Bad For Horses

Domestication Might've Been Bad For Horses

Newsy (Dec. 16, 2014) A group of scientists looked at the genetics behind the domestication of the horse and showed how human manipulation changed horses' DNA. Video provided by Newsy
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:

Breaking News:

Strange & Offbeat Stories


Plants & Animals

Earth & Climate

Fossils & Ruins

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News



Save/Print:
Share:

Free Subscriptions


Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

Get Social & Mobile


Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

Have Feedback?


Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
Mobile: iPhone Android Web
Follow: Facebook Twitter Google+
Subscribe: RSS Feeds Email Newsletters
Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins