Triconodontidae Explained

Triconodontidae is an extinct family of small, carnivorous mammals belonging to the order Eutriconodonta, endemic to what would become Asia, Europe, North America and probably also Africa and South America^[1] during the Jurassic through Cretaceous periods at least from 190–66 mya.^[2]

Triconodontids can be distinguished from other eutriconodonts by the shape of their molars, which bore three main cusps of roughly equal size. During occlusion, the upper and lower molars interlocked tightly, producing a self-sharpening cutting edge. Historically, the triconodontids were thought to have a different occlusion pattern than other eutriconodonts, with the middle cusp of the lower molar (cusp a) fitting between the middle cusp (cusp A) and the front cusp (cusp B) of the upper molar, as in the basal mammaliaform Morganucodon. However, a 2020 study on Priacodon suggests that triconodontids occluded their molars in the same manner as other eutriconodonts (so-called "embrasure occlusion"), with the middle cusp (cusp A/a) fitting between two opposing molars.^[3]

Taxonomy

Triconodontidae was named by Marsh (1887). It was assigned to Polyprotodontia by Cope (1889); to Triconodonta by Rasmussen and Callison (1981), Bonaparte (1986), Carroll (1988) and Engelmann and Callison (1998); and to Mammalia by Marsh (1887) and Luo et al. (2001).^[4]

Sometimes Volaticotheria is recovered as a part of this group.^[5] However, other phylogenetic studies group it outside of Triconodontidae.^{[6] [7]}

Phylogeny

Cladogram after Gaetano & Rougier, 2011:

Notes and References

1. Gaetano . L. C. . Rougier . G. W. . 2012 . First Amphilestid from South America: A Molariform from the Jurassic Cañadón Asfalto Formation, Patagonia, Argentina . Journal of Mammalian Evolution . 19 . 4 . 235–248 . 10.1007/s10914-012-9194-1 . 254698557 . 11336/68489 . free .
2. Butler . P. M. . Sigogneau-Russell . D. . Diversity of triconodonts in the Middle Jurassic of Great Britain . Palaeontologia Polonica . 2016 . 67 . 35–65 . 10.4202/pp.2016.67_035 . 31 January 2024 .
3. Jäger . K. R. K. . Cifelli . R. L. . Martin . T. . Molar occlusion and jaw roll in early crown mammals . Scientific Reports . 2020 . 10 . 1 . 22378 . 10.1038/s41598-020-79159-4. 33361774 . 7759581 . 2020NatSR..1022378J . free .
4. 10.1126/science.1058476 . Luo . Z.-X. . Crompton . A. W. . Sun . A.-L. . 2001 . A new mammaliaform from the Early Jurassic and evolution of mammalian characteristics . Science . 292 . 5521. 1535–1540 . 11375489 . 2001Sci...292.1535L . 8738213 .
5. Gaetano . L. C. . Rougier . G. W. . New materials of Argentoconodon fariasorum (Mammaliaformes, Triconodontidae) from the Jurassic of Argentina and its bearing on triconodont phylogeny . Journal of Vertebrate Paleontology . 2011 . 31 . 4 . 829–843 . 10.1080/02724634.2011.589877. 2011JVPal..31..829G . 85069761 . 11336/68497 . free .
6. Martin . T. . Marugán-Lobón . J. . Vullo . R. . Martín-Abad . H. . Luo . Z.-X. . Buscalioni . A. D. . A Cretaceous eutriconodont and integument evolution in early mammals . Nature . 2015 . 526 . 7573 . 380–384 . 10.1038/nature14905. 26469049 . 2015Natur.526..380M . 205245235 . 10486/710730 . free .
7. Averianov . A. O. . Lopatin . A. V. . Phylogeny of triconodonts and symmetrodonts and the origin of extant mammals . Doklady Biological Sciences . 2011 . 436 . 1 . 32–35 . 10.1134/s0012496611010042. 21374009 . 10324906 .