Alphadon (meaning “first tooth”) was a small, primitive mammal that was a member of the metatherians, a group of mammals that includes modern-day marsupials. The first fossil of Alphadon was discovered and named by George Gaylord Simpson in 1929.
The appearance of this animal is only a guess because only facts about the teeth are known. The appearance is mainly based on the look of today's opossum. Alphadon usually grew to 1 foot (30 cm), making it one of the largest Mesozoic mammals.
Alphadon lived in the late Cretaceous period and may have had a large variety in its diet, eating fruit, insects, and occasionally small vertebrates.
There are twelve different named species in the genus Alphadon. On Gaylord's fossil hunt, he discovered and named the type A. marshi.