Triconodonta

(paleontology) An extinct mammalian order of small flesh-eating creatures of the Mesozoic era having no angle or a pseudoangle on the lower jaw and triconodont molars.

Extinct mammals that are members of many latest Triassic, Jurassic, and Cretaceous faunas in the Northern Hemisphere. Their records in the Southern Hemisphere include a species of earliest Jurassic age from Africa and questionably referable specimens from the Middle Jurassic of Africa and Late Cretaceous of South America. In all triconodontans the dentary and squamosal bones formed at least part of the articulation of the jaw to the skull (the temporomandibular joint). In some, among the most primitive species referred to the Mammalia, the articular, quadratojugal, and quadrate also participated in this articulation. See also Cretaceous; Jurassic; Triassic.

Many modern classifications limit the contents of Triconodonta to the family Triconodontidae and establish new groupings for other, closely related families. This reflects an emerging, poorly understood picture of complex evolutionary interrelationships among the earliest mammals and advanced ther­apsids, members of the group commonly but inappropriately named the mammallike reptiles. See also Animal evolution.

Triconodontids, the central family of the Triconodonta, were relatively large (lower jaw about the size of that of a mink, Mustella vison) common members of European and North American, Late Jurassic mammalian faunas. Their temporomandibular joint was formed entirely by the dentary and squamosal.

Occurrence of a specialized mode of occlusion of the molariforms of triconodontids and Dinnetherium, from the earliest Jurassic of North America, suggests the latter is a very primitive relative of the triconodontids that had not lost the quadrate and articular from its temporomandibular joint. Another primitive group characterized by a complex temporomandibular joint, the morganucodontids, also might be primitive relatives of the triconodontids. The amphilestids (Middle and Late Jurassic, North American and Europe) and gobiconodontids (Middle Jurassic and Early Cretaceous, North America and Asia) were triconodontanlike mammals. Members of both families had temporomandibular joints formed exclusively by the dentary and squamosal. Sinoconodon (Early Jurassic, Asia), another primitive triconodontanlike mammal about the size of contemporaneous morganucodontids, had a complex temporomandibular joint. See also Docodonta; Mammalia.

Triconodonts Fossil range: Late Triassic–Late Cretaceous PreЄ Є O S D C P T J K Pg N
Gobiconodon
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Mammalia
Subclass:	Allotheria
Order:	Triconodonta
Families
Amphilestidae Eutriconodontidae Jeholodentidae Gobiconodontidae Klameliidae Repenomamidae Triconodontidae

Triconodonta (also known as Eutriconodonta) is the generic name for a group of early mammals which were close relatives of the ancestors of all present-day mammals. Triconodonts lived between the Triassic and the Cretaceous. They are one of the groups that can be classified as mammals by any definition. Several other extinct groups of Mesozoic animals that are traditionally considered to be mammals (such as Morganucodonta and Docodonta) are now placed just outside Mammalia by those who advocate a 'crown-group' definition of the word "mammal".^[1]

Illustration of the lower jaw of Triconodon mordax, 1861

Their name, meaning "Three conical teeth", is based on one of their fundamental characteristics. They had the typical morphology of the proto-mammals: small, furry, tetrapod animals with long tails. They probably had a nocturnal lifestyle to avoid dinosaur predators, coming out from their burrows after dusk to hunt for small reptiles and insects^{[citation needed]}. However, recent evidence from China suggests that some triconodonts such as Repenomamus were indeed able to take on small dinosaurs. [1].

Notes

1. ^ Traditionally, membership in Mammalia is diagnosed by the presence of a single dominant jaw joint, in which the dentary contacts the squamosal. However, taxonomists debate whether established names, such as Mammalia, should correspond to the clade which is closest to the traditional definition or, alternatively, should be restricted to the 'crown-group' (which includes only descendants of the most recent common ancestor shared by all living member species and excludes any fossil forms which diverged at an earlier stage, even if they meet the traditional criteria). Supporters of the crown-group approach refer to the broader grouping as the Mammaliformes or Mammaliaformes, whereas traditionalists describe the entire assemblage as "mammals". For a summary of the argument and issues, see Benton 2005: 289.

References

• Michael J. Benton. 2005. Vertebrate Palaeontology. 3rd ed. Oxford: Blackwell Publishing. ISBN 0-632-05637-1
• Jeff Hecht. Large mammals once dined on dinosaurs. NewScientist.com news service, 12 January 2005.

This prehistoric mammal-related article is a stub. You can help Wikipedia by expanding it. v • d • e

This entry is from Wikipedia, the leading user-contributed encyclopedia. It may not have been reviewed by professional editors (see full disclaimer)