Carnegie Museum of Natural History News

Researchers discover the earliest known placental mammal
Fossil from the famous feathered dinosaur quarry may be last common
ancestor of most modern day mammals, including humans

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Caption 1. The earliest eutherian (placental) mammal Eomaia scansoria, preserved in shale, and consisting of a part and a counter-part. Eomaia scansoria is from the lake sediments of Yixian Formation of Liaoning Province of China, estimated to be at least 125 million years old.
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Caption 2. Skeletal Anatomy of Eomaia scansoria © Nature (4/25/02. Volume 416. Pages 816-822) Art Credit: Mark A. Klingler/CMNH
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Caption 3.The family tree of modern placental mammals and the position of Eomaia scansoria on the mammalian evolutionary tree. Fossil eutherians mammals are defined as those mammals more closely related to living placental mammals (such as humans) than to marsupials (such as kangaroos). Living placentals are descendants of the Mesozoic stem eutherian mammals. Living placental mammals are the most diverse mammalian group in world. They are characterized by an important evolutionary innovation, the placenta - this allows a much longer gestation for a more mature fetus at birth. Placentals are also different from marsupials and monotremes in many derived dental and skeletal features that can be studied in fossils. By its dental and skeletal features, Eomaia scansoria is the oldest-known and most primitive fossil eutherian. The study by the scientists of Carnegie Museum of Natural History and the Chinese Academy of Geological Sciences show that Eomaia is at the root of the placental mammals, and helps to establish the earliest possible divergence time of all eutherians (including the placentals). Art Credit: Mark A. Klingler/CMNH
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Caption 4. Reconstruction of the earliest eutherian, Eomaia scansoria as a small and agile mammal capable of climbing and branch-walking in low bushes. Eomaia scansoria was approximately 14 cm (~5 inches) long with an estimated body mass of 20 to 25 grams. It was an insectivore and lived in a lake-shore and bush environment. Reconstruction Art by: Mark A. Klingler/CMNH
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Caption 5. Skeletal reconstruction of Eomaia scansoria as a climbing mammal on tree branches. The limb and foot structures indicate Eomaia scansoria was an active animal both on the ground and in the low branches of bushes. The specific name scansoria (Latin) reflects the new mammal's skeletal specialization for climbing. Reconstruction Art Credit: Mark A. Klingler/CMNH
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Caption 6 Dr. Zhe-Xi Luo (left) and Dr. John Wible (right) of Carnegie Museum of Natural History with the fossil of the earliest eutherian Eomaia scansoria. Photograph by: Mark A. Klingler/CMNH
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Caption 7. The fossil site of Eomaia scansoria is in Liaoning Province of northeastern China, approximately 300 kilometers northeast of Beijing. Eomaia scansoria is from the Yixian Formation that also yielded the famous feathered dinosaurs, fossil birds, and other early mammals.
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Caption 8. The fossil site of Eomaia scansoria is in Liaoning Province of northeastern China, approximately 300 kilometers northeast of Beijing. Eomaia scansoria is from the Yixian Formation that also yielded the famous feathered dinosaurs, fossil birds, and other early mammals.