Deltatheridium
Deltatheridium (meaning "triangle beast" or "delta beast") is an extinct species of metatherian. It lived in what is now Mongolia during the Upper Cretaceous, "circa" 80 million years ago. It was a basal metatherian, which places it near to the start of the lineage that led to the marsupials, such as kangaroos, wallabies, koalas, and opossums. It had a length of about . Its teeth indicate it was carnivorous. One specimen of "Archaeornithoides" might attest an attack by this mammal, the skull bearing tooth marks that match its teeth.