| Deltatheroida Temporal range: Aptian–Maastrichtian Early-Late Cretaceous |
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| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Mammalia |
| Subclass: | Theria |
| (unranked): | Metatheria |
| Order: | †Deltatheroida Gregory and Simpson, 1926 |
| Families & Genera | |
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Deltatheroida is an extinct group of basal metatherians that lived in the Cretaceous and were closely related to marsupials. Their fossils are restricted to Central Asia and North America. This order can be defined as all metatherians closer to Deltatheridium than to Marsupialia.
These mammals possessed tritubercular lower molars and these were not tribosphenic and were quite primitive. This is awkward because tribosphenic molars are found commonly in most therian mammals (there exist some exceptions such as anteaters and some whales which have no teeth at all).
When they were first identified in the 1920s, they were believed to be placentals and possible ancestors of the creodonts (extinct carnivorous mammals), but this was later disproven.
Zofia Kielan-Jaworowska, Richard L. Cifelli, and Zhe-Xi Luo, Mammals from the Age of Dinosaurs: Origins, Evolution, and Structure (New York: Columbia University Press, 2004), 444-448.