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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].

[edit] Notes

^ 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.

[edit] 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.

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[0] 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.

[1]