Eutriconodonta

Eutriconodonta Temporal range: Ma PreꞒ Ꞓ O S D C P T J K Pg N
Examples of several eutriconodonts. Clockwise: Repenomamus, Volaticotherium, Jeholodens and Yanoconodon. These occupy vastly different ecological niches: bulky semi-fossorial carnivore, glider, arboreal insectivore and terrestrial carnivore, respectively.[1]
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Class:	Mammalia
Clade:	Theriimorpha
Order:	†Eutriconodonta Kermack et al., 1973
Subgroups
†Amphidontidae †Amphilestidae ?†Dyskritodon ?†Bocaconodon † Gobiconodonta †Jeholodentidae †Liaoconodon †Sangarotherium †Triconodontidae †Volaticotherini

Eutriconodonta is an

Traditionally seen as the classical Mesozoic small mammalian insectivores, discoveries over the years have shown them to be among the best examples of the diversity of mammals in this time period, including a vast variety of bodyplans, ecological niches and locomotion methods.^{[4][5][6][1][7][8]}

Classification

"Triconodonta" had long been used as the name for an order of early mammals which were close relatives of the ancestors of all present-day mammals, characterized by molar teeth with three main cusps on a crown that were arranged in a row.^[4] The group originally included only the family Triconodontidae and taxa that were later assigned to the separate family Amphilestidae,^[9] but was later expanded to include other taxa such as Morganucodon or Sinoconodon.^[4] The phylogenetic analyses found that all these taxa did not form a natural group, and that some traditional "triconodonts" were more closely related to therian mammals than others. Some traditional "triconodonts" do seem to form a natural group (or "clade"), and this was given the name Eutriconodonta, or "true triconodonts).

Most analyses use only dental and mandibular characters.^[3][10][11] Gao et al. (2010) conducted a second analysis as well, using a modified version of the matrix from the analysis of Luo et al. (2007);^[12] this analysis involved a broader range of Mesozoic mammaliaforms and more characters, including postcranial ones. Both Luo et al. (2007) and the second analysis of Gao et al. (2010) recovered a more inclusive monophyletic Eutriconodonta that also contained gobiconodontids and Amphilestes;^[10][12] in the second analysis of Gao et al. it also contained Juchilestes (recovered as amphidontid in their first analysis, the only amphidontid included in their second analysis).^[10] However, Gao et al. (2010) stressed that jeholodentids and gobiconodontids are the only eutriconodonts with known postcranial skeletons; according to the authors, it remains uncertain whether the results of their second analysis represent true phylogeny or are merely "a by-product of long branch attraction of jeholodentids and gobiconodontids".^[10] Phylogenetic studies conducted by Zheng et al. (2013), Zhou et al. (2013) and Yuan et al. (2013) recovered monophyletic Eutriconodonta containing triconodontids, gobiconodontids, Amphilestes, Jeholodens and Yanoconodon.^[13][14][15]

The exact phylogenetic placement of eutriconodonts within

The most recent cladogram is by Thomas Martin et al. 2015, in their description of Spinolestes. Eutriconodonts are recovered as a largely monophyletic group within Theriimorpha.^[6]

A 2020 study found them paraphyletic in regards to crown group

Most eutriconodont remains occur in laurasian landmasses. The exceptions are Argentoconodon and slightly younger Condorodon from the Early Jurassic of Argentina, the putative Dyskritodon indicus from the Early Jurassic of India (Kota Formation), the Late Jurassic Tendagurodon from Tanzania (Tendaguru Formation), several Early Cretaceous north African taxa like Ichthyoconodon, Dyskritodon amazighi and Gobiconodon palaios, and Indotriconodon magnus from Late Cretaceous India. Due to the rarity of the Jurassic gondwanan fossil record the presence of eutriconodonts in southern landmasses may be of interest, due to their comparatively early age.^[19]

Eutriconodonts are among the few Mesozoic mammals present at Arctic locations;

At least in carnivorous niches, eutriconodonts were probably replaced by deltatheroidean metatherians, which are the dominant carnivorous mammals in Late Cretaceous faunal assemblages.^[28] Competition between both groups is unattested, but in Asia the Early Cretaceous gobiconodontid diversity is replaced entirely by a deltatheroidean one, while in North America Nanocuris appears after the absence of Gobiconodon and other larger eutriconodonts.^[29] Given that all insectivorous and carnivorous mammals groups suffered heavy losses during the mid-Cretaceous, it seems likely these metatherians simply occupied niches left after the extinction of eutriconodonts in the northern continents.^[26]

Some eutriconodonts were instead among the most specialised of Mesozoic mammals. Several taxa like