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discover the earliest known placental mammal
Pittsburgh … An international team, including scientists from Carnegie Museum of Natural History, has discovered the earliest-known placental mammal with unusually well preserved skeleton and fur impression. The new fossil is the most primitive known relative to all placental mammals, and provides rare evidence for the earliest history of placental mammals.
In an article published today in the prestigious scientific journal, Nature, the team of American and Chinese scientists describe a 125 to 128 million year old fossilized skeleton of Eomaia scansoria, ([Eomaia] - Greek for "ancient mother" and [scansoria] - Latin for "climber"), named because it could be the "mother of all placental mammals."
Eomaia was a shrew-sized (about 5 inches or 14 cms long and weighed 20 to 25 grams) placental mammal that co-existed with large sauropod dinosaurs and the carnivorous therapod dinosaurs of the Cretaceous. It lived in low branches and bushes and ate insects much like modern-day shrews. It may have also been food for several of the carnivorous dinosaurs of that time.
The research team was led by Dr. Qiang Ji of the Chinese Academy of Geological Sciences; Carnegie Museum of Natural History Associate Curator of Vertebrate Paleontology Zhe-Ki Luo, PhD; and Carnegie Museum of Natural History Associate Curator of Mammals John Wible, PhD. Additional team members are Chong-Xi Yuan, Jian-Ping Zhang of the Chinese Academy of Geological Sciences, and Justin Georgi of Carnegie Museum of Natural History.
"This discovery is the closest and earliest known relative of all placental mammals, which include humans and other primates," said Luo. "This mammal could be our great, great-aunt or uncle, or it could be our great-grandparent 125 million years removed.
"Most of the animals humans depend on are placentals. "And because humans and other primates are placentals, the evolutionary beginning of all placental mammals is extremely important for understanding the history of life and especially how primates and humans evolved from primitive placentals."
"The vast majority of living mammals are placentals," said Wible. "To have discovered their earliest known common ancestor, and one that is well preserved, provides scientists with the anatomical basis for understanding the origins of the placental lineage. In the case of Eomaia, we have a small animal adapted to climbing and scurrying."
Prior to this discovery, the earliest record of a placental mammal was represented by isolated teeth about 115 million years old. Wible points out, "Our new study shows that, in the Cretaceous, there was a far greater burst of diversity of extinct relatives of placentals than anyone had previously realized."
The fossil was found in early 2000, in northeastern China in the famed feathered dinosaur quarry in the Liaoning Province. It was turned over to a scientific team at the Chinese Academy of Geological Sciences, led by Professor Ji, and eventually to Drs. Luo and Wible at Carnegie Museum of Natural History.
The site in the western Liaoning Province has not only produced the exquisite feathered dinosaurs and some very primitive birds, it has also produced some of the world's most important early mammals. In the last several years, Luo and several Chinese collaborators described an unusually well preserved skeleton of a mouse-sized, insect-eating triconodont mammal named Jeholodens and the symmetrodont mammal Zhangheotherium that yielded very important insights into the earliest mammal evolution.
This research is supported by National Science Foundation (USA), National Geographic Society (USA), Carnegie Museum of Natural History, National Natural Science Foundation of China and Ministry of Land Resources of China.
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Contact information for authors:
Zhe-Xi Luo, Associate Curator, Vertebrate Paleontology
John R. Wible, Associate Curator, Mammals
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