Deltatheroida
Encyclopedia
Deltatheroida is an extinct group of basal metatherians that lived in the Cretaceous
and were closely related to marsupials. 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 lower molars and these were not tribosphenic and were quite primitive. This is awkward because tribosphenic molars
are found commonly in most theria
n mammals (there exist some exceptions such as anteater
s and some whale
s 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
(extinct carnivorous mammals), but this was later disproven.
Cretaceous
The Cretaceous , derived from the Latin "creta" , usually abbreviated K for its German translation Kreide , is a geologic period and system from circa to million years ago. In the geologic timescale, the Cretaceous follows the Jurassic period and is followed by the Paleogene period of the...
and were closely related to marsupials. Their fossils are restricted to Central Asia
Central Asia
Central Asia is a core region of the Asian continent from the Caspian Sea in the west, China in the east, Afghanistan in the south, and Russia in the north...
and North America
North America
North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...
. This order can be defined as all metatherians closer to Deltatheridium
Deltatheridium
Deltatheridium is an extinct species of metatherian. It lived in what is now Mongolia during the Upper Cretaceous. It was a basal metatherian, which places it near start of the linage that led to the marsupials, such the kangaroo, koala, and opossum.It had a length of...
than to Marsupialia.
These mammals possessed tritubercular lower molars and these were not tribosphenic and were quite primitive. This is awkward because tribosphenic molars
Molar (tooth)
Molars are the rearmost and most complicated kind of tooth in most mammals. In many mammals they grind food; hence the Latin name mola, "millstone"....
are found commonly in most theria
Theria
Theria is a subclass of mammals that give birth to live young without using a shelled egg, including both eutherians and metatherians . The only omitted extant mammal group is the egg-laying monotremes....
n mammals (there exist some exceptions such as anteater
Anteater
Anteaters, also known as antbear, are the four mammal species of the suborder Vermilingua commonly known for eating ants and termites. Together with the sloths, they compose the order Pilosa...
s and some whale
Whale
Whale is the common name for various marine mammals of the order Cetacea. The term whale sometimes refers to all cetaceans, but more often it excludes dolphins and porpoises, which belong to suborder Odontoceti . This suborder also includes the sperm whale, killer whale, pilot whale, and beluga...
s which have no teeth at all).
When they were first identified in the 1920s, they were believed to be placentals
Eutheria
Eutheria is a group of mammals consisting of placental mammals plus all extinct mammals that are more closely related to living placentals than to living marsupials . They are distinguished from noneutherians by various features of the feet, ankles, jaws and teeth...
and possible ancestors of the creodonts
Creodonta
The creodonts are an extinct order of mammals that lived from the Paleocene to the Miocene epochs. They shared a common ancestor with the Carnivora....
(extinct carnivorous mammals), but this was later disproven.