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.[1] It was a basal metatherian, which places it near start of the lineage that led to the marsupials, such as kangaroos, wallabies, koalas, and opossums.

Temporal range: Santonian-Campanian
~84.9–70.6 Ma
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Deltatheroida
Family: Deltatheridiidae
Genus: Deltatheridium
Gregory & Simpson, 1926
  • D. pretrituberculare (type)
  • D. nessovi

It had a length of about 15 cm (5.9 in). 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.[2]

Other Mesozoic mammals from Mongolia


  2. Elżanowski, A. Wellnhoffer, P. (1993). "Skull of Archaeornithoides From the Upper Cretaceous of Mongolia". . American Journal of Science

Further reading

  • Parker, Steve. Dinosaurus: the complete guide to dinosaurs. Firefly Books Inc, 2003. Pg. 403
  • Rougier, G. W.; Wible, J. R.; Novacek, M. J. (1998). "Implications of Deltatheridium specimens for early marsupial history". Nature. 396 (6710): 459–63. doi:10.1038/24856. PMID 9853752.