Currently, the family includes four genera, Eodelphis, Didelphodon, Fumodelphodon and Hoodootherium, which together include some seven different species. In addition, the Cenomanian species Pariadens kirklandi might be a member of the family. Carneiro and Oliveira (2017) considered the species Eobrasilia coutoi from the early Eocene (Itaboraian) of Brazil to be a stagodontid; if confirmed it would make it the only known Cenozoic and the only known South American member of the family. Stagodontids were some of the largest known Cretaceous mammals, ranging from 0.4 to 2.0 kilograms (0.88–4.41 lb) in mass. One of the most unusual features of stagodontids are their robust, bulbous premolars, which are thought to have been used to crush freshwater mollusks, a diet that apparently evolved independently at least twice within this clade. Postcranial remains suggest that stagodontids may have been semi-aquatic. The most well described forms are found in Laramidia, but they are also present on Appalachian and South American sites, further leading credence to their aquatic habits.
The evolution of Didelphodon and other large stagodontids (as well as large deltatheroideans like Nanocuris) occurs after the local extinction of eutriconodont mammals, suggesting passive or direct ecological replacement. They are considered rare in any given fauna they appear in, probably due to their specialised habits.
Stagodontids were once thought to be closely related to the Sparassodonta, but later studies suggest they belong to a more ancient branch of the metatherian family tree, possibly closely related to pediomyids, being in particular closest to Pariadens, which forms the immediate outgroup to Stagodontidae. With the possible exception of Eobrasilia (see above), stagodontids are last known from the Maastrichtian, and are thought to have gone extinct in the K-T Extinction.
Aegialodon dawsoni is an extinct mammal from the early Cretaceous, known from fossilised teeth discovered in the Wadhurst Clay Formation (dating to about 136 million years ago) near Cliff End, Hastings, East Sussex.Alphadon
Alphadon (meaning "first tooth") was a genus of small, primitive mammal that was a member of the metatherians, a group of mammals that includes modern-day marsupials. Its fossils were first discovered and named by George Gaylord Simpson in 1929.Alphadontidae
Alphadontidae was a family of small, primitive mammal that was a member of the metatherians, a group of mammals that includes modern-day marsupials.Barylambdidae
Barylambdidae is an extinct family of pantodont mammals from North America.Cladotheria
Cladotheria is a group (legion) of mammals that includes the ancestor of Dryolestoidea, Peramuridae and Zatheria (living therians plus all of its ancestors).Comodon
Comodon is an extinct genus of Late Jurassic mammal from the Morrison Formation.
Present in stratigraphic zone 5.Deltatheroides
Deltatheroides is an extinct genus of Deltatheridiidae from Cretaceous of Mongolia.Didelphodon
Didelphodon (from Didelph[is] "opossum" plus ὀδών odōn "tooth") is a genus of stagodont metatherians from the Late Cretaceous of North America.Eodelphis
Eodelphis (ee-o-DEL-fiss), from eo- plus [Di]delphis, thus meaning "very early opossum", is a genus of stagodont metatherians from the Late Cretaceous of North America, with distinctive crushing dentition. Named species include E. browni and the more advanced E. cutleri. Both come from the Late Campanian (Judithian "Land Mammal Age") of Dinosaur Provincial Park, Alberta. Specimens are also known from the Judith River Formation of Montana. E. cutleri is related to the Maastrichtian genus Didelphodon as indicated by its enlarged premolars and more robust jaw. Eodelphis was probably an aquatic predator like its relative Didelphodon, and may have weighed about 0.6 kg (1.3 lb), making it one of the largest mammals of its time.Gurlin Tsav skull
The "Gurlin Tsav" skull is a currently unnamed carnivorous metatherian fossil from the Nemegt Formation of Mongolia. Composed of a single semi-complete skull, this specimen is notable in regards to the evolution and systematics of Metatheria as a whole, and thus nigh-omnipresent in phylogenetic analyses of this group.Henosferidae
Henosferidae (also spelled "Henospheridae") is an extinct family of Australosphenida. Its defined as a clade including the most recent common ancestor of Henosferus and Asfaltomylos and all its descendants.Leptolambda
Leptolambda is an extinct genus of pantodonts in the family Barylambdidae from North America.Palaeosinopa
Palaeosinopa is an extinct genus of semi-aquatic, non-placental eutherian mammals belonging to the family Pantolestidae. Their diet consisted of other semi-aquatic life forms.Paressonodon
Paressonodon is an extinct genus of multituberculate which existed in Colorado during the late Cretaceous period. It contains the species Paressonodon nelsoni.Plethorodon
Plethorodon is an extinct genus of tillodont that lived during Early to Late Paleocene. The type species is P. qianshanensis. which known from partial skull and upper teeth that had been discovered by Huang and Zheng at 1987 at Qianshan, Anhui Province, China.Presbytherium
Presbytherium is an extinct pantodont which existed in what is now Alberta, Canada, during the Paleocene period. It was first named by Craig S. Scott in 2010.Pucadelphys
Pucadelphys is an extinct genus of non-marsupial metatherian species. The genus contains a single species, P. andinus. Fossils of Pucadelphys have been found in the Santa Lucía Formation in Tiupampa in Bolivia.Tathiodon
Tathiodon is an extinct genus of Late Jurassic (Kimmeridgian - Tithonian) mammal from the Morrison Formation.
Present in stratigraphic zone 5.