''Tsagandelta'' (meaning "white crest") is a

genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

of deltatheroidean

theria Theria ( or ; ) is a scientific classification, subclass of mammals amongst the Theriiformes. Theria includes the eutherians (including the Placentalia, placental mammals) and the metatherians (including the marsupials) but excludes the egg-lay ...

mammal A mammal () is a vertebrate animal of the Class (biology), class Mammalia (). Mammals are characterised by the presence of milk-producing mammary glands for feeding their young, a broad neocortex region of the brain, fur or hair, and three ...

that lived in

Asia Asia ( , ) is the largest continent in the world by both land area and population. It covers an area of more than 44 million square kilometres, about 30% of Earth's total land area and 8% of Earth's total surface area. The continent, which ...

during the

Late Cretaceous The Late Cretaceous (100.5–66 Ma) is the more recent of two epochs into which the Cretaceous Period is divided in the geologic time scale. Rock strata from this epoch form the Upper Cretaceous Series. The Cretaceous is named after ''cre ...

. Distantly related to modern

marsupials Marsupials are a diverse group of mammals belonging to the infraclass Marsupialia. They are natively found in Australasia, Wallacea, and the Americas. One of marsupials' unique features is their reproductive strategy: the young are born in a ...

, it is part of Deltatheroida, a lineage of

carnivorous A carnivore , or meat-eater (Latin, ''caro'', genitive ''carnis'', meaning meat or "flesh" and ''vorare'' meaning "to devour"), is an animal or plant whose nutrition and energy requirements are met by consumption of animal tissues (mainly mu ...

metatherians 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 ...

common in the Cretaceous of Asia and among the most successful non-

theropod Theropoda (; from ancient Greek , (''therion'') "wild beast"; , (''pous, podos'') "foot"">wiktionary:ποδός"> (''pous, podos'') "foot" is one of the three major groups (clades) of dinosaurs, alongside Ornithischia and Sauropodom ...

carnivores of the region. It represents the first known mammal from the

Bayan Shireh Formation The Bayanshiree Formation (also known as Baynshiree/Baynshire, Baynshirenskaya Svita, Baysheen Shireh, or Bayan Shireh) is a geological formation in Mongolia, that dates to the Cretaceous period. It was first described and established by Vasilie ...

Discovery and naming

The

holotype A holotype (Latin: ''holotypus'') is a single physical example (or illustration) of an organism used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of s ...

was first discovered and collected in 2002 during the field expedition conducted by the Mongolian Academy of Sciences and the American Museum of Natural History, the specimen only preserved a partial left

dentary In jawed vertebrates, the mandible (from the Latin ''mandibula'', 'for chewing'), lower jaw, or jawbone is a bone that makes up the lowerand typically more mobilecomponent of the mouth (the upper jaw being known as the maxilla). The jawbone ...

. It was discovered on the outcrops at the Tsagan Tsonj locality in the

, the age is estimated to be around 102 million to 86 million years ago, between the

Cenomanian The Cenomanian is, in the International Commission on Stratigraphy's (ICS) geological timescale, the oldest or earliest age (geology), age of the Late Cretaceous epoch (geology), Epoch or the lowest stage (stratigraphy), stage of the Upper Cretace ...

and

Santonian The Santonian is an age in the geologic timescale or a chronostratigraphic stage. It is a subdivision of the Late Cretaceous Epoch or Upper Cretaceous Series. It spans the time between 86.3 ± 0.7 mya ( million years ago) and 83.6 ± 0.7 m ...

stages Stage, stages, or staging may refer to: Arts and media Acting * Stage (theatre), a space for the performance of theatrical productions * Theatre, a branch of the performing arts, often referred to as "the stage" * ''The Stage'', a weekly Brit ...

of the

epoch. The generic name, ''Tsagandelta'', is derived from the

Mongolian Mongolian may refer to: * Something of, from, or related to Mongolia, a country in Asia * Mongolian people, or Mongols * Bogd Khanate of Mongolia, the government of Mongolia, 1911–1919 and 1921–1924 * Mongolian language * Mongolian alphabet * ...

цагаан (tsagaan, meaning white) and the

Greek Greek may refer to: Anything of, from, or related to Greece, a country in Southern Europe: *Greeks, an ethnic group *Greek language, a branch of the Indo-European language family **Proto-Greek language, the assumed last common ancestor of all kno ...

δέλτᾰ (delta, meaning crest or point-shaped) in reference to the withish sediments at the Tsagan Tsonj locality and the prominent dentition of the

Deltatheroida 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 ( ...

. The specific name, ''dashzevegi'', is in honor to the Mongolian paleontologist Demberlyin Dashzeveg who did notable research on early mammals.

Description

''Tsagandelta'' is currently known from one

specimen Specimen may refer to: Science and technology * Sample (material), a limited quantity of something which is intended to be similar to and represent a larger amount * Biological specimen or biospecimen, an organic specimen held by a biorepository f ...

, the

PSS-MAE 629. This specimen is composed of a left

fragment containing an almost intact second molar, the base of the third molar and the roots of the first premolar; various other tooth sockets are empty, and the dental formula is probably similar to that of ''

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 ...

''. Based on comparisons with the related ''

Lotheridium ''Lotheridium'' is an extinct genus of deltatheroidan mammals that lived in what is now Asia during the Late Cretaceous, about 72–66 million years ago. The genus contains a monotypic taxon, single species, ''Lotheridium mengi'', named in 2015 ...

'', the preserved dentary indicates that ''Tsagandelta'' was slightly smaller than the former; ''Lotheridium'' is about the size of a modern

marten A marten is a weasel-like mammal in the genus ''Martes'' within the subfamily Guloninae, in the family Mustelidae. They have bushy tails and large paws with partially retractile claws. The fur varies from yellowish to dark brown, depending on ...

Classification

''Tsagandelta'' was classified within the

Deltatheridiidae Deltatheridiidae is an extinct family (biology), family of basal carnivore, carnivorous Metatheria, metatherians that lived during the Cretaceous and Paleogene. They were closely related to marsupialia, marsupials. Their fossils are restricted to ...

, being more derived than ''

Sulestes ''Sulestes'' is an extinct genus of Deltatheridiidae from Cretaceous period. It has only been recovered from the Bissekty Formation, Bissekty and Aitym Formation, Aitym Formations in Uzbekistan.A. O. Averianov, J. D. Archibald, and E. G. Ekdale. ...

'' and ''

Oklatheridium ''Oklatheridium'' is an extinct genus of deltatheroidan from the United States The United States of America (USA), also known as the United States (U.S.) or America, is a country primarily located in North America. It is a federal republic ...

'' but less so than the rest of the family. This phylogenetic position has been argued to suggest an Asian origin for Deltatheroida.

Paleobiology

Like most deltatheroideans, ''Tsagandelta'' was a

carnivore A carnivore , or meat-eater (Latin, ''caro'', genitive ''carnis'', meaning meat or "flesh" and ''vorare'' meaning "to devour"), is an animal or plant Plants are the eukaryotes that form the Kingdom (biology), kingdom Plantae; they ar ...

, its molar anatomy similar to the

carnassial Carnassials are paired upper and lower teeth modified in such a way as to allow enlarged and often self-sharpening edges to pass by each other in a shearing manner. This adaptation is found in carnivorans, where the carnassials are the modified f ...

s of other carnivorous therians. ''Tsagandelta'' and its relatives (as well as the unrelated

eutriconodonts Eutriconodonta is an order of early mammals. Eutriconodonts existed in Asia (including pre-contact India), Africa, Europe, North and South America during the Jurassic and the Cretaceous periods. The order was named by Kermack ''et al.'' in 1973 ...

) are among the Mesozoic mammals most clearly specialised to meat-eating.

Paleoecology

''Tsagandelta'' hails from the

, dating from the Cenomanian to the Santonian. It is adjacent to the

Iren Dabasu Formation The Iren Dabasu Formation (also known as Erlian Formation) is a Late Cretaceous geologic Formation (geology), formation in the Erenhot, Iren Nor region of Inner Mongolia. Dinosaur remains diagnostic to the genus level are among the fossils that h ...

, these formations bear a very similar fauna. A great diversity of reptiles are known from the Bayan Shireh Formation, mainly compromising dinosaur and non-dinosaur taxa that likely preyed on ''Tsagandelta'', mammals however, are pooly known from this formation.

References

{{Taxonbar, from=Q28163503 Prehistoric metatherians Cretaceous mammals Fossils of Mongolia Fossil taxa described in 2015 Prehistoric mammal genera