Navigation Links
Fossil discovery represents new milestone in early mammal evolution

A 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 today in the journal Nature, the fossil represents a new milestone in mammal evolution that was reached 35 million years earlier than previously thought.

It fills an important gap in the fossil record and helps to calibrate modern, DNA-based methods of dating evolution.

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.

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 ancestor 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 fossil of Juramaia sinensis was discovered in the Liaoning Province in northeast China and examined in Beijing by Luo and 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.

Juramaia's complete teeth and forepaw bones enable paleontologists to pinpoint that 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," says Luo.

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 of eutherians from metatherians posed a quandary for evolutionary biologists: DNA evidence suggested that eutherians should have shown up earlier in the fossil record--around 160 million years ago.

The oldest known eutherian was Eomaia, dated to 125 million years ago. (Eomaia was originally described in 2002 by a team of scientists led by Luo and Carnegie mammalogist John Wible.)

The discovery of Juramaia provides 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.

"These scientists have used the rich fossil mammal record to test evolutionary hypotheses proposed by their colleagues studying living mammals using genetic data," says Chuck Lydeard, program director in the National Science Foundation's NSF) Division of Environmental Biology, which co-funded the research with NSF's Division of Earth Sciences.

Juramaia also reveals adaptive features that may have helped the eutherian newcomers survive in a tough Jurassic environment.

Juramaia's forelimbs are adapted for climbing. Since the majority of 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 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."


Contact: Cheryl Dybas
National Science Foundation

Related biology news :

1. Europe rallies behind nanotechnology to wean world from fossil fuels
2. Researchers uncover worlds oldest fossil impression of a flying insect
3. Caltech geobiologists discover unique magnetic death star fossil
4. Living fossil tree contains genetic imprints of rain forests under climate change
5. Bacterial biofilms as fossil makers
6. Hobbit fossils represent a new species, concludes University of Minnesota anthropologist
7. Dinosaur fossils fit perfectly into the evolutionary tree of life
8. Early whales gave birth on land, fossil find reveals
9. Worlds largest snake discovered in fossilized rainforest
10. Origin of claws seen in 390-million-year-old fossil
11. Famous fossil Lucy scanned at the University of Texas at Austin
Post Your Comments:
Related Image:
Fossil discovery represents new milestone in early mammal evolution
(Date:11/17/2015)... , Nov. 17, 2015  Vigilant Solutions announces ... joined its Board of Directors. --> ... after recently retiring from the partnership at TPG Capital, ... companies with over $140 Billion in revenue.  He founded ... across all the TPG companies, from 1997 to 2013.  ...
(Date:11/12/2015)... Nov. 12, 2015  A golden retriever that stayed ... dystrophy (DMD) has provided a new lead for treating ... the Broad Institute of MIT and Harvard and the ... . Cell, pinpoints a protective ... the disease,s effects. The Boston Children,s lab of ...
(Date:11/11/2015)... --  MedNet Solutions , an innovative SaaS-based eClinical technology company ... to announce that it will be a Sponsor of the ... be held November 17-19 in Hamburg , ... iMedNet , MedNet,s easy-to-use, proven and affordable ... been able to deliver time and cost savings of up ...
Breaking Biology News(10 mins):
(Date:12/1/2015)... ... , ... Matthew “Tex” VerMilyea, PhD, HCLD, has joined Texas Fertility Center as ... lab procedures as well as continue his research efforts into the emerging technologies of ... New Zealand to bring home a High Complexity Clinical Laboratory Director named Tex,” says ...
(Date:11/30/2015)... ... 30, 2015 , ... Global Stem Cells Group ... the Santiago Marriott. The Global Stem Cells Group GMP facility is equipped with ... qualified medical researchers and practitioners, experienced in administering stem cell protocols using highly ...
(Date:11/30/2015)... 2015 Partnership includes an MPP ... for the u niversity , s ... treatment s cale - up through ... Africa , where licensees based anywhere in the world will have ... --> Africa , where licensees based anywhere in the world ...
(Date:11/30/2015)... Spherix Incorporated (Nasdaq: SPEX ) an ... and monetization of intellectual property, today provided an ... to create shareholder value. Anthony ... on published reports, the total addressable market of ... Spherix will seek to secure fair and reasonable ...
Breaking Biology Technology: