Deltatheroida is an extinct group of basal

metatheria Metatheria is a mammalian clade that includes all mammals more closely related to marsupials than to placentals. First proposed by Thomas Henry Huxley in 1880, it is a more inclusive group than the marsupials; it contains all marsupials as wel ...

ns that were distantly related to modern marsupials. The majority of known members of the group lived in the

Cretaceous The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of ...

; one species, '' Gurbanodelta kara'', is known from the late

Paleocene The Paleocene, ( ) or Palaeocene, is a geological epoch that lasted from about 66 to 56 million years ago (mya). It is the first epoch of the Paleogene Period in the modern Cenozoic Era. The name is a combination of the Ancient Greek ''pal ...

(

Gashatan The Gashatan is an Asian Land Mammal Age, a large biozone which corresponds to ages between 58.7–55.8 Ma for finds of fossil mammals in Asia. This zone lies within the Thanetian stage of the Paleocene series. It precedes the Bumbanian The Bumba ...

) of China. Their fossils are restricted to

Central Asia Central Asia, also known as Middle Asia, is a subregion, region of Asia that stretches from the Caspian Sea in the west to western China and Mongolia in the east, and from Afghanistan and Iran in the south to Russia in the north. It includes t ...

and North America. This order can be defined as all

metatherian Metatheria is a mammalian clade that includes all mammals more closely related to marsupials than to placentals. First proposed by Thomas Henry Huxley in 1880, it is a more inclusive group than the marsupials; it contains all marsupials as well ...

s closer to ''

Deltatheridium ''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. A study in 2022 strongly suggested that De ...

'' than to

Marsupialia Marsupials are any members of the mammalian infraclass Marsupialia. All extant marsupials are endemic to Australasia, Wallacea and the Americas. A distinctive characteristic common to most of these species is that the young are carried in a po ...

. These mammals possessed primitive tritubercular (three-cusped) lower molars that were not tribosphenic. This is awkward because tribosphenic

molars The molars or molar teeth are large, flat teeth at the back of the mouth. They are more developed in mammals. They are used primarily to grind food during chewing. The name ''molar'' derives from Latin, ''molaris dens'', meaning "millstone to ...

are commonly found in most

theria Theria (; Greek: , wild beast) is a subclass of mammals amongst the Theriiformes. Theria includes the eutherians (including the placental mammals) and the metatherians (including the marsupials) but excludes the egg-laying monotremes. ...

n mammals (there exist some exceptions such as anteaters and some

whale Whales are a widely distributed and diverse group of fully aquatic placental marine mammals. As an informal and colloquial grouping, they correspond to large members of the infraorder Cetacea, i.e. all cetaceans apart from dolphins and ...

s, which have no teeth at all). When they were first identified in the 1920s, they were believed to be

placentals Placental mammals (infraclass Placentalia ) are one of the three extant subdivisions of the class Mammalia, the other two being Monotremata and Marsupialia. Placentalia contains the vast majority of extant mammals, which are partly distinguishe ...

and possible ancestors of the "

creodonts Creodonta ("meat teeth") is a former order of extinct carnivorous placental mammals that lived from the early Paleocene to the late Miocene epochs in North America, Europe, Asia and Africa. Originally thought to be a single group of animals ance ...

" (a

polyphyletic A polyphyletic group is an assemblage of organisms or other evolving elements that is of mixed evolutionary origin. The term is often applied to groups that share similar features known as homoplasies, which are explained as a result of conver ...

group of extinct carnivorous mammals from the Paleogene and

Miocene The Miocene ( ) is the first epoch (geology), geological epoch of the Neogene Period and extends from about (Ma). The Miocene was named by Scottish geologist Charles Lyell; the name comes from the Greek words (', "less") and (', "new") and mea ...

), but this was later disproven. Nonetheless, deltatheroideans do converge on hyaenodontids, oxyaenids, carnivorans,

dasyuromorphs Dasyuromorphia (, meaning "hairy tail" in Greek) is an order comprising most of the Australian carnivorous marsupials, including quolls, dunnarts, the numbat, the Tasmanian devil, and the thylacine. In Australia, the exceptions include the ...

and

sparassodonts Sparassodonta (from Greek to tear, rend; and , gen. , ' tooth) is an extinct order of carnivorous metatherian mammals native to South America, related to modern marsupials. They were once considered to be true marsupials, but are now though ...

in many details of their dental anatomy, suggesting a carnivorous lifestyle.CHRISTIAN DE MUIZON and BRIGITTE LANGE-BADRÉ, Carnivorous dental adaptations in tribosphenic mammals and phylogenetic reconstruction, Article first published online: 29 MAR 2007 DOI: 10.1111/j.1502-3931.1997.tb00481

Taxonomy

The following is a species list of Deltatheroida.Mikko's Phylogeny Archiv

†Deltatheroida Kielan-Jaworowska 1982 eltatheralia Marshall & Kielan-Jaworowska 1992; Holarctidelphia Szalay 1993* † Pappotheriidae ** †'' Pappotherium''Guillermo W. Rougier; Brian M. Davis; Michael J. Novacek (2015). "A deltatheroidan mammal from the Upper Cretaceous Baynshiree Formation, eastern Mongolia". Cretaceous Research. 52, Part A: 167–177. doi:10.1016/j.cretres.2014.09.009.S. Bi, X. Jin, S. Li and T. Du. 2015. A new Cretaceous metatherian mammal from Henan, China. PeerJ 3:e896 * † Deltatheridiidae Gregory & Simpson 1926 eltatheridia Van Valen 1965; Nanocuridae Fox, Scott & Bryant 2007; Sulestinae Nessov 1985; Deltatheroididae Kielan-Jaworowska & Nesov 1990** †'' Hyotheridium dobsoni'' Gregory & Simpson 1926 ** †'' Lotheridium mengi'' Bi et al. 2015 ** †'' Nanocuris improvida'' Fox, Scott & Bryant 2007 ** †'' Prodeltitheridium kalandadze'' Trofimov 1984 ** †'' Oklatheridium'' Davis, Cifelli & Kielan-Jaworowska 2008 *** †'' O. szalayi'' Davis, Cifelli & Kielan-Jaworowska 2008 *** †'' O. minax'' Davis & Cifelli 2011 *** †'' O. wiblei'' Cifelli & Davis 2015 ** †'' Atokatheridium boreni'' Kielan-Jaworowska & Cifelli 2001 ** †''

'' Gregory & Simpson 1926 *** †'' D. pretrituberculare'' Gregory & Simpson 1926 *** †'' D. nesovi'' Averianov 1997 ** †'' Sulestes karakshi'' Nesov 1985 'Deltatherus''_Nesov_1997;_''Marsasia.html" ;"title="Deltatherus.html" ;"title="'Deltatherus">'Deltatherus'' Nesov 1997; ''Marsasia">Deltatherus.html" ;"title="'Deltatherus">'Deltatherus'' Nesov 1997; ''Marsasia'' Nesov 1997; ''Deltatheroides kizylkumensis'' Nesov 1993; ''Deltatherus kizylkumensis'' (Nesov 1993) Nesov 1997; ''Marsasia aenigma'' Nesov 1997] ** †''Tsagandelta, Tsagandelta dashzevegi'' Rougier, Davis & Novacek 2015 ** †'' Deltatheroides, Deltatheroides cretacicus'' Gregory & Simpson 1926 ** †'' Gurbanodelta kara'' Ni ''et al.'' 2016

Biology

Deltatheroideans are thought to be carnivorous mammals, converging on hyaenodontids, oxyaenids, carnivorans,

and

in many details of their dental anatomy, suggesting a carnivorous lifestyle. Deltatheroideans in this regard appear to have replaced

eutriconodont Eutriconodonta is an order of early mammals. Eutriconodonts existed in Asia, Africa, Europe, North and South America during the Jurassic and the Cretaceous periods. The order was named by Kermack ''et al.'' in 1973 as a replacement name for the p ...

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 ''Jugulator'' is the thirteenth studio album by English heavy metal band Judas Priest. It was released in Japan on 16 October 1997 and the rest of the world on 28 October 1997. It was their first studio album since ''Painkiller'' in 1990 an ...

'', 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. Evidence of direct predation on dinosaurs may be attested on a skull belonging to '' Archaeornithoides'', which seems to have been punctured by ''

'' teeth and later healed.Elżanowski, A. Wellnhoffer, P. (1993). "Skull of Archaeornithoides From the Upper Cretaceous of Mongolia". earth.geology.yale.edu/~ajs/1993/11.1993.08Elzanowski.pdf . American Journal of Science

Taxonomy

Biology

See also

References

Further reading