Eutriconodonta

Gobiconodon, live reconstruction

• Worldwide

The Eutriconodonta (or Triconodonta ) are a potential taxon ( a systematic group) of extinct mammals from the Mesozoic era. They lived from the Middle Jurassic to the Upper Cretaceous and are characterized by common features in the construction of the molars ( back teeth ). Whether they actually form a natural group or merely represent convergent developments, is controversial.

Features

Like many other groups of mammals of the Mesozoic are the Eutriconodonta widely known only by individual teeth or jaw parts, which makes a systematic assignment. A common feature of all these animals is the construction of the molars. This always had three large consecutively arranged cusps, which allowed a cut shredding food. In some Eutriconodonta (about the Triconodontidae ), the three cusps is approximately equal, in other animals, there has been a significant increase in the average bump. Some representatives additional small hump at the front and rear end of the molars were present, which caused an interlocking of adjacent teeth and thus provided additional stability when biting. The construction of the teeth suggests that many Eutriconodonta of insects and other animals fed, for some representatives also an omnivorous ( omnivorous ) diet is adopted.

Fossil record of the limbs and torso are known only from a few species. These often showed about the construction of the pool still primitive features of the mammalian ancestors, while the shoulder belt was relatively highly developed. The most representative must have been mice - to -cat-big, with the over one meter long Repenomamus but also has the largest known mammal of the Mesozoic belongs to this group.

Almost all the evidence comes from the middle and upper Jurassic and Lower Cretaceous ( 165-100 million years ago) and are almost exclusively on the former North continent Laurasia ( Eurasia and North America) have been made. There is anecdotal scant finds from the former southern continent Gondwana, which may suggest a global distribution of the Eutriconodonta, but not systematically assign unique.

System

The term Triconodonta ("three cusps of teeth " ) was coined in 1888 by Henry Fairfield Osborn and took a variety of Mesozoic mammals with a dreihöckrigen construction of the molars together. This feature, however, is plesiomorphic, ie it is also evident in earlier ancestors. Why are taxa such as the Morganucodonta or Sinoconodon, although they have a similar construction of the molars, but are clearly earlier sidelines due to primitive features about the construction of the temporomandibular joint, no longer included as well today. The after exclusion of these primitive mammals remaining animals are Eutriconodonta ( "right three cusps of teeth " ) - or sometimes continue Triconodonta - called. Whether the Eutriconodonta represent actual a monophyletic group, is contentious, cladistic analyzes support at least partially, the monophyly of this group. For many species, however, are simply too few findings available to allow a secure systematic assignment.

Their position in the scheme of mammals is controversial. Due to some primitive features, they are considered relatively early side branch and are therefore more closely related to any modern mammal group.

Related taxa

The often sparse finds and the systematic uncertainties do not allow a precise statement. The following taxa are usually counted among the Eutriconodonta:

• The Amphilestidae lived in the middle and upper Jurassic.
• The Triconodontidae (Upper Jurassic to Upper Cretaceous ) were characterized by three approximately equal sized cusps.
• The Gobiconodontidae are known from the Lower Cretaceous. Repenomamus is classified either in this family or as closely related Repenomamidae own family.
• Jeholodens from the Lower Cretaceous of China is known by a complete skeleton. The genus described in 2007 Yanoconodon, which is known as a transitional form in the construction of the ossicles could be closely related to Jeholodens and form the family of Jeholodentidae.
• The membership of Klamelia from the Upper Jurassic of China is unclear; possibly it forms with the 2007 discovered genus Ferganodon own family Klameliidae.
• Austrotriconodon is characterized by individual teeth that come from the Upper Cretaceous of Patagonia, and are characterized by an enormously enlarged middle hump. Their systematic position is unclear, it would be one of the youngest and one of the few known from Gondwana Eutriconodonta.
• Liaoconodon from the Lower Cretaceous of China is known by a complete skeleton and shows a transitional stage in the development of the middle ear of the higher mammals.