Eutriconodonta

Reconstruction of Repenomamus giganticus, copyright Nobu Tamura.

Belongs within: Mammalia.

The Eutriconodonta are a group of mammals known from the Jurassic and Cretaceous, characterised by triconodont molars with three laterally compressed cusps in a straight alignment (Luo et al. 2007).

Synapomorphies (from Krause et al. 2014): Dens not fused to axis; lumbar ribs not fused to vertebrae; tarsal spur absent; premaxilla with ventral internarial process present but not connected to nasal; single infraorbital foramen present; ventral opening of minor palatine foramen encircled by palatine and maxilla; postpalatine torus present; internal acoustic meatus cribriform plate absent; ear region with lateral flange narrowly separated from anterior paroccipital process (crista parotica); pterygoparoccipital foramen a laterally open notch; mallear manubrium robust; suture separating basioccipital and exoccipital absent; two lower and upper incisors in each quadrant; I3 with single cusp; seven lower postcanine teeth in each quadrant; four lower premolars in each quadrant; ultimate upper premolar (P5) with metacone present; penultimate lower premolar (p4) with paraconid (cusp b) absent or indistinct; ultimate lower premolar tooth (p5) with hypoconid absent; m1–2 with paracristid longitudinally oriented relative to longitudinal axis of molars; m1–2 with buccal curvature of protoconid (cusp a) at base level equivalent to curvature of paraconid (cusp b) and metaconid (cusp c); m1–2 with metacristid (protocristid), crest between protoconid (cusp a) and metaconid (cusp c) parallel to long axis of lower molars and lower jaw axis; m1 with main cusps of trigonid in single longitudinal row; m1–2 with labiolingual compression of primary functional cusps (at level of cusp base but above cingulid); M1–2 with stylar shelf absent; M1–2 with lingual cingulum discontinuous; dentary movement during power stroke of chewing cycle essentially dorsal (orthal); molar with prevallum/postvallid shearing absent.

<==Eutriconodonta
    |  i. s.: Phascolotherium Owen 1838 CM99
    |         ‘Kotatherium’ yadagirii Prasad & Manhas 1997 A02
    |--+--Amphilestes [Amphilestinae] KH14
    |  `--Gobiconodontidae LK-JC02
    |       |--Gobiconodon Trofimov 1978 KH14, CM99
    |       |    `--G. zofiae HM05
    |       `--Repenomamus Li, Wang et al. 2000 LC07, HM05 [Repenomamidae]
    |            |--R. giganticus Hu, Meng et al. 2005 HM05
    |            `--R. robustus HM05
    `--+--+--Jeholodens jenkinsi KH14, LC07
       |  `--Yanoconodon Luo, Chen et al. 2007 LC07
       |       `--*Y. allini Luo, Chen et al. 2007 LC07
       `--Triconodontidae [Triconodontinae] LK-JC02
            |--Priacodon KH14
            |--Trioracodon LK-JC02
            `--Astroconodon LK-JC02

*Type species of generic name indicated

REFERENCES

[A02] Averianov, A. O. 2002. Early Cretaceous “symmetrodont” mammal Gobiotheriodon from Mongolia and the classification of “Symmetrodonta”. Acta Palaeontologica Polonica 47 (4): 705–716.

[CM99] Cifelli, R. L., & S. K. Madsen. 1999. Spalacotheriid symmetrodonts (Mammalia) from the medial Cretaceous (upper Albian or lower Cenomanian) Mussentuchit local fauna, Cedar Mountain Formation, Utah, USA. Geodiversitas 21 (2): 167–214.

[HM05] Hu, Y., J. Meng, Y. Wang & C. Li. 2005. Large Mesozoic mammals fed on young dinosaurs. Nature 433: 149–152.

[KH14] Krause, D. W., S. Hoffmann, J. R. Wible, E. C. Kirk, J. A. Schultz, W. von Koenigswald, J. R. Groenke, J. B. Rossie, P. M. O'Connor, E. R. Seiffert, E. R. Dumont, W. L. Holloway, R. R. Rogers, L. J. Rahantarisoa, A. D. Kemp & H. Andriamialison. 2014. First cranial remains of a gondwanatherian mammal reveal remarkable mosaicism. Nature 515: 512–517.

[LC07] Luo, Z.-X., P. Chen, G. Li & M. Chen. 2007. A new eutriconodont mammal and evolutionary development in early mammals. Nature 446: 288–293.

[LK-JC02] Luo, Z.-X., Z. Kielan-Jaworowska & R. L. Cifelli. 2002. In quest for a phylogeny of Mesozoic mammals. Acta Palaeontologica Polonica 47: 1–78.