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 1838CM99
    |         ‘Kotatherium’ yadagirii Prasad & Manhas 1997A02
    |--+--SpinolestesSK20
    |  `--GobiconodontidaeLK-JC02
    |       |--Gobiconodon Trofimov 1978KH14, CM99
    |       |    |--G. luoianusMH20
    |       |    `--G. zofiaeHM05
    |       `--Repenomamus Li, Wang et al. 2000LC07, HM05 [Repenomamidae]
    |            |--R. giganticus Hu, Meng et al. 2005HM05
    |            `--R. robustusHM05
    `--+--Amphilestes [Amphilestinae]SK20
       `--+--+--Jeholodens Ji, Luo & Ji 1999SK20, JLJ99
          |  |    `--*J. jenkinsi Ji, Luo & Ji 1999JLJ99
          |  `--Yanoconodon Luo, Chen et al. 2007MWL11, LC07
          |       `--*Y. allini Luo, Chen et al. 2007LC07
          `--+--Liaoconodon Meng, Wang & Li 2011MWL11
             |    `--*L. hui Meng, Wang & Li 2011MWL11
             `--Triconodontidae [Triconodontinae]LK-JC02
                  |--Priacodon Marsh 1887MWL11, SM93
                  `--+--Triconodon Owen 1859MWL11, SM93
                     |--Trioracodon Simpson 1928MWL11, SM93
                     `--+--ArundeloconodonMWL11
                        `--+--AstroconodonMWL11
                           `--+--Alticonodon lindoei Fox 1970MWL11, SM93
                              `--CorviconodonMWL11

*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.

[JLJ99] Ji Q., Luo Z.-X. & Ji S.-A. 1999. A Chinese triconodont mammal and mosaic evolution of the mammalian skeleton. Nature 398: 326–330.

[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.

[MH20] Mao, F., Y. Hu, C. Li, Y. Wang, M. H. Chase, A. K. Smith & J. Meng. 2020. Integrated hearing and chewing modules decoupled in a Cretaceous stem therian mammal. Science 367: 305–308.

[MWL11] Meng, J., Y. Wang & C. Li. 2011. Transitional mammalian middle ear from a new Cretaceous Jehol eutriconodont. Nature 472: 181–185.

[SM93] Stucky, R. K., & M. C. McKenna. 1993. Mammalia. In: Benton, M. J. (ed.) The Fossil Record 2 pp. 739–771. Chapman & Hall: London.

[SK20] Sulej, T., G. Krzesiński, M. Tałanda, A. S. Wolniewicz, B. Błażejowski, N. Bonde, P. Gutowski, M. Sienkiewicz & G. Niedźwiedzki. 2020. The earliest-known mammaliaform fossil from Greenland sheds light on origin of mammals. Proceedings of the National Academy of Sciences of the USA 117 (43): 26861–26867.

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