Triconodontidae is an extinct

family Family (from la, familia) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its members and of society. Idea ...

of small,

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 food and energy requirements derive from animal tissues (mainly muscle, fat and other ...

mammal Mammals () are a group of vertebrate animals constituting the class Mammalia (), characterized by the presence of mammary glands which in females produce milk for feeding (nursing) their young, a neocortex (a region of the brain), fur ...

s belonging to the order

Eutriconodonta 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 t ...

, endemic to what would become

Asia Asia (, ) is one of the world's most notable geographical regions, which is either considered a continent in its own right or a subcontinent of Eurasia, which shares the continental landmass of Afro-Eurasia with Africa. Asia covers an are ...

Europe Europe is a large peninsula conventionally considered a continent in its own right because of its great physical size and the weight of its history and traditions. Europe is also considered a Continent#Subcontinents, subcontinent of Eurasia ...

North America North America is a continent in the Northern Hemisphere and almost entirely within the Western Hemisphere. It is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South America and th ...

and probably also

Africa Africa is the world's second-largest and second-most populous continent, after Asia in both cases. At about 30.3 million km2 (11.7 million square miles) including adjacent islands, it covers 6% of Earth's total surface area ...

and

South America South America is a continent entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere at the northern tip of the continent. It can also be described as the sou ...

during the

Jurassic The Jurassic ( ) is a geologic period and stratigraphic system that spanned from the end of the Triassic Period million years ago (Mya) to the beginning of the Cretaceous Period, approximately Mya. The Jurassic constitutes the middle period of ...

through

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 ...

periods at least from 190–70.6 mya. Triconodontids can be distinguished from other eutriconodonts by the shape of their

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 ...

, which bore three main cusps of roughly equal size. During occlusion, the upper and lower molars interlocked tightly, producing a self-sharpening cutting edge. Historically, the triconodontids were thought to have a different occlusion pattern than other eutriconodonts, with the middle cusp of the lower molar (cusp a) fitting between the middle cusp (cusp A) and the front cusp (cusp B) of the upper molar, as in the basal mammaliaform ''

Morganucodon ''Morganucodon'' ("Glamorgan tooth") is an early mammaliaform genus that lived from the Late Triassic to the Middle Jurassic. It first appeared about 205 million years ago. Unlike many other early mammaliaforms, ''Morganucodon'' is well represent ...

''. However, a 2020 study on ''

Priacodon ''Priacodon'' is an extinct genus of Late Jurassic eutriconodont mammal from the Alcobaça Formation of Portugal and the Morrison Formation of the midwestern United States. It is present in stratigraphic zones 4–6 of the latter.Foster, J. (2007 ...

'' suggests that triconodontids occluded their molars in the same manner as other eutriconodonts (so-called "embrasure occlusion"), with the middle cusp (cusp A/a) fitting between two opposing molars.

Taxonomy

Triconodontidae was named by Marsh (1887). It was assigned to Polyprotodontia by Cope (1889); to Triconodonta by Rasmussen and Callison (1981), Bonaparte (1986), Carroll (1988) and Engelmann and Callison (1998); and to

Mammalia Mammals () are a group of vertebrate animals constituting the class Mammalia (), characterized by the presence of mammary glands which in females produce milk for feeding (nursing) their young, a neocortex (a region of the brain), fur ...

by Marsh (1887) and Luo ''et al.'' (2001). Sometimes Volaticotheria is recovered as a part of this group. However, other phylogenetic studies group it outside of Triconodontidae.

Phylogeny

Cladogram A cladogram (from Greek ''clados'' "branch" and ''gramma'' "character") is a diagram used in cladistics to show relations among organisms. A cladogram is not, however, an evolutionary tree because it does not show how ancestors are related to ...

after Gaetano & Rougier, 2011:

References

{{Taxonbar, from=Q1501530 Eutriconodonts Prehistoric mammal families Middle Jurassic first appearances Late Cretaceous extinctions Jurassic mammals of Africa Cretaceous mammals of Africa Jurassic mammals of Asia Cretaceous mammals of Asia Jurassic mammals of Europe Cretaceous mammals of Europe Jurassic mammals of North America Cretaceous mammals of North America Jurassic mammals of South America Cretaceous mammals of South America Taxa named by Othniel Charles Marsh