DELTATHERIDIUM

primitive genus of extinct mammals found as fossils in Late Cretaceous rocks (66.4 to 97.5 million years old) of Mongolia. Deltatheridium, a tiny animal, was an insectivore and represents a stage of development from which the modern insectivores and perhaps the modern placental mammals as a group may have been derived. The skull was only about 5 cm (2 inches) long. Deltatheridium had a blend of primitive and advanced dental features.