Deltatheroida is an extinct group of basal metatherians that were distantly related to modern marsupials. The majority of known members of the group lived in the Cretaceous; one species, Gurbanodelta kara, is known from the late Paleocene (Gashatan) of China. 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 (three-cusped) lower molars and these were not tribosphenic and were quite primitive. This is awkward because tribosphenic molars are commonly found 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" (a polyphyletic group of extinct carnivorous mammals from the Paleogene and Miocene), but this was later disproven. Nonetheless, deltatheroideans do converge on hyaenodontids, oxyaenids, carnivorans, dasyuromorphs and sparassodonts in many details of their dental anatomy, suggesting a carnivorous lifestyle.
Gregory and Simpson, 1926
|Families & Genera|
†Deltatheroida Kielan-Jaworowska 1982 [Deltatheralia Marshall & Kielan-Jaworowska 1992; Holarctidelphia Szalay 1993]
Deltatheroideans are thought to be carnivorous mammals, converging on hyaenodontids, oxyaenids, carnivorans, dasyuromorphs and sparassodonts in many details of their dental anatomy, suggesting a carnivorous lifestyle.
Deltatheroideans in this regard appear to have replaced eutriconodont mammals as the dominant carnivorous mammals of the Mesozoic, either directly through competition or occupying vacant ecological niches; in North America, Nanocuris came to succeed the larger gobiconodontids and Jugulator, while in Asia the Early Cretaceous gobiconodontid radiation is replaced in the Late Cretaceous by a deltatheroidean one. Given that all insectivorous and carnivorous mammals groups suffered heavy losses during the mid-Cretaceous, it seems likely these metatherians simply occupied niches left after the extinction of eutriconodonts.
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.
Atokatheridium is an extinct genus of Deltatheridiidae from Cretaceous of United States.Barylambdidae
Barylambdidae is an extinct family of pantodont mammals from North America.Comodon
Comodon is an extinct genus of Late Jurassic mammal from the Morrison Formation.
Present in stratigraphic zone 5.Deltatheridiidae
Deltatheridiidae is an extinct family of basal carnivorous metatherians that lived in the Cretaceous and were closely related to marsupials. Their fossils are restricted to Central Asia (Mongolia and Uzbekistan) and North America (United States - Oklahoma, Texas, Utah, Wyoming). They mostly disappeared in the KT event, but a ghost lineage, currently represented by Gurbanodelta, survived until the late Paleocene by decreasing in size and becoming insectivorous.The family consist in six genera:
Atokatheridium Kielan-Jaworowska & Cifelli, 2001
Deltatheridium Gregory & Simpson, 1926
Deltatheroides Gregory & Simpson, 1926
Gurbanodelta X. Ni et al. 2016
Lotheridium S. Bi et al. 2015
Oklatheridium Davis, Cifelli & Kielan-Jaworowska, 2008
Nanocuris Fox, Scott & Bryant, 2007
Sulestes Nessov, 1985
Tsagandelta G. W. Rougier et al. 2015Deltatheridium
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 start of the lineage that led to the marsupials, such as kangaroos, wallabies, koalas, and opossums.
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.Deltatheroides
Deltatheroides is an extinct genus of Deltatheridiidae from Cretaceous of Mongolia.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.Holotheria
Holotheria are a diverse group of mammals that are descendants of the last common ancestor of Kuehneotherium and Theria (the group that includes marsupials and placental mammals).Khuduklestes
Khukduklestes is a genus of extinct mammal of uncertain affinities from the Late Cretaceous of China. It is rather similar to the also carnivorous and taxonomically uncertain Oxlestes, being slightly smaller.Leptolambda
Leptolambda is an extinct genus of pantodonts in the family Barylambdidae from North America.Nanocuris
Nanocuris is an extinct genus of Deltatheridiidae from Cretaceous of Canada (Saskatchewan) and United States (Wyoming - Lance Formation). Initially was classified in a proper family, Nanocuridae, in clade Eutheria, but a reanalysis of a new specimen reveal a deltharoid affinity of the genus.Oklatheridium
Oklatheridium is an extinct genus of deltatheroidan.Oxlestes
Oxlestes is an extinct mammal from the Late Cretaceous of Asia, more specifically from the Cenomanian of Uzbekistan. A carnivorous species of uncertain affinities, it is notable for its relatively large size, being among the largest of all Mesozoic mammals. Due to the limited amount of material, it has been considered a nomen dubium.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.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.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.Sulestes
Sulestes is an extinct genus of Deltatheridiidae from Cretaceous of Uzbekistan.Tathiodon
Tathiodon is an extinct genus of Late Jurassic (Kimmeridgian - Tithonian) mammal from the Morrison Formation.
Present in stratigraphic zone 5.Tsagandelta
Tsagandelta (from "tsagan", Mongolian for white, and "delta", Greek for "crest") is an extinct mammal genus from the Late Cretaceous of Mongolia. Distantly related to modern marsupials, it is part of Deltatheroida, a lineage of carnivorous metatherians common in the Cretaceous of Asia and among the most successful non-theropod carnivores of the region.