| Vertebrate Paleontology
Eomaia scansoria
Earliest known placental mammal Eomaia (Greek for “ancient mother”) 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 John Wible and former Carnegie curator Zhe-Xi Luo 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 All mammals are divided into three groups based on their reproductive systems: monotremes (egg-laying mammals such as the platypus), marsupials (pouched mammals such as kangaroos), and placental mammals (such as humans). Non-placental mammals are born premature and must reside in either an egg (monotremes) or in 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.
For more information Eomaia in the News
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