Maotherium asiaticus Reconstructions (IMAGE) Carnegie Museum of Natural History Caption The new Cretaceous mammal Maotherium is a chipmunk-sized nocturnal mammal. It lived 123 million years ago. It had terrestrial habits and scampered around on the ground. From its skeleton it is estimated to have weighed about 70-80 grams (2 ounces), and was about 15 cm (5 inches) in length. Maotherium is a generalized ground-living mammal. Because it is related to the common ancestor of marsupials and placentals, its tooth and skeletal structures show the ancestral condition from which marsupials and placentals could have evolved. Credit Mark A. Klingler/Carnegie Museum of Natural History Usage Restrictions Credit must accompany image. Caption is optional. License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.