An international team of researchers led by Carnegie Museum of Natural History Vertebrate Paleontologist Dr. Zhe-Xi Luo has discovered a 195-million-year-old fossil mammal. This find is the smallest known mammal of the Mesozoic and represents a new branch on the mammalian family tree.

In an article published in Science, the team of American and Chinese scientists described this new mammal as having a precociously large brain and the middle ear of modern mammals. The team suggests that these two features may have evolved together.

The new species is named Hadrocodium wui for its exceptionally large brain (hadro – Greek for "large and full" and codium – Greek for "head"). The discovery has widespread implications as scientists piece together the earliest mammalian evolutionary history.

"Mammals differ from non-mammalian vertebrates by possessing a very large brain and an advanced ear structure," said Dr. Luo. "It has been a challenge for scientists to trace the origins of these important mammalian features in the fossil record. Previously, these important mammalian traits could only be traced to the Late Jurassic (approximately 150 million years ago). The discovery of Hadrocodium pushes back their origins by some 45 million years to the Early Jurassic."

The newest addition to the mammalian family group also happens to be the tiniest mammal known from the Mesozoic Era, and one of the smallest mammals ever. Based on the size of its well-preserved skull, it is estimated that the entire animal weighed only two grams, less than the weight of a paperclip. With such a tiny body, it was most likely limited to eating very small insects and small worms. Its enlarged brain and very small body also tell scientists that the animal had a very high metabolism, forcing it to eat continuously.

Co-existing with the extremely small Hadrocodium in the Early Jurassic were several other primitive mammals with much larger body size. "This tiny creature greatly stretches the range of body size for the earliest known mammals," added Dr. Luo.

Hadrocodium was recovered from the famous Lufeng Basin in Yunnan Province, southwestern China. It is one of the most prolific sites for early Jurassic land vertebrates. The Mesozoic Redbeds of the Lufeng Basin have yielded many vertebrate fossils. Among the fossils that have been unearthed are the carnivorous dinosaur Dilophosaurus and the prosauropod Lufengosaurus, crocodiles, and lizard-like forms, herbivorous mammal-like reptiles and some of the earliest mammals ever discovered.

Dr. Luo's research team includes Alfred W. Crompton of Harvard University and Ai-Lin Sun of the Chinese Academy of Sciences. This research is supported by the National Science Foundation (USA), National Geographic Society, Carnegie Museum of Natural History, and Museum of Comparative Zoology, Harvard University.

See the Press Release page for the release, images, and research team contact information.
Visit Dr. Zhe-Xi Luo's Web page.

Hadrocodium in the News (Note: this event occurred in 2001 and some links may have expired)
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Pittsburgh Post-Gazette

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