> Eomaia scansoria in the News
> Scientist Pages:
Zhe-Xi Luo
John R. Wible
Reconstruction
Art:
Mark A. Klingler/CMNH
Eomaia scansoria – Eomaia, Greek for “ancient mother” and scansoria, Latin for “climber” – is the world’s earliest known placental mammal.
This
nearly complete skeleton was discovered by an international team of scientists
– including Carnegie Museum of Natural History’s Zhe-Xi Luo
and John Wible – in the famed feathered dinosaur quarry of China’s
Liaoning Province.
Eomaia lived approximately 125 million years ago during the early Cretaceous period. It spent its days along the shore of a lake, scampering about the bushes and feeding on the abundant insects. Like the other small mammals of its time, it tried to avoid predatory carnivorous dinosaurs and the threat of being trampled by giant sauropods.
The
proportion and curvature of Eomaia’s fingers reveal it was
a climber. It could grasp branches and move very fast in trees and on
the ground. Similar to the modern tree shrews of Asia, it was nearly five
inches long and weighed about 25 grams.
The
discovery of this little creature is of big importance to the understanding
of the evolution of mammals. Since most mammals living today are placental,
all may point to Eomaia scansoria as an ancient ancestor.
Placental Mammals
A whale. A bat. A dog. A human. What do these animals have in common? They’re all placental mammals.
All mammals are divided into three groups based on their reproductive systems – monotremes (egg-laying mammals), marsupials (pouched mammals), and placental mammals.
Non-placental mammals
are born premature and must reside in either an egg (monotremes) or their
mothers’ pouches (marsupials) as they mature. 
Placental
mammals, however, are able to nurture their developing young within their
bodies prior to birth through the use of an organ called a placenta.
The placenta serves as a channel between the fetus and mother, supplying
the unborn young with food, oxygen, and a means of waste disposal. The
fetus is allowed a longer time for development, resulting in a more mature
baby.
The placenta is a major development in animal history. As a result of its success, the majority of mammals are placental.