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Stylinodon

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Stylinodon
Temporal range: 53.4–39.7 Ma early to middle Eocene
Life restoration of Stylinodon mirus
Skull of Stylinodon mirus
Scientific classification Edit this classification
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: †Taeniodonta
Family: †Stylinodontidae
Subfamily: †Stylinodontinae
Tribe: †Stylinodontini
Marsh, 1875
Genus: †Stylinodon
Marsh, 1874
Type species
†Stylinodon mirus
Marsh, 1874
Synonyms[1]
synonyms of species:
  • S. mirus:
    • Calamodon cylindrifer (Cope, 1881)[2]
    • Stylinodon cylindrifer (Wortman, 1896)[3]
    • Stylinodon inexplicatus (Schoch & Lucas, 1981)[4]

Stylinodon ("tooth with pilar-like fibers") is an extinct genus of taeniodonts that lived in North America from early to middle Eocene.[5]

Description

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Crania

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Similar to modern day rodents, Stylinodon had continuously growing teeth.[6][7] All 6 molars of Stylinodon are similar in shape, being cylindrical, and they have a thin layer of enamel.[8] The incisor teeth of Stylinodon were large and curved. The rest of the skull is short, with prominent temporal fossae and a generally small brain cavity. The sagittal crest is joined with the occipital plane at the top and the skull lacks a prominent occipital condyle, as well as having no paroccipital processes.[9]The lower jaw of Stylinodon is massive and deep, with fused symphysial sutures and large condyles being especially notable features. The ramus is similarly robust.[6][9] The dental formula of the genus is 2.1.4.31.1.4.3.[6][10]

Forelimb and dorsal view of vertebrae of Stylinodon mirus

Postcrania

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Postcranial remains of Stylinodon suggest a degree of fossoriality due to the robustness of the skeletal elements.[11][6] The morphology of the forelimbs too is adapted for digging, with specific adaptations including a long ulnar olecranon which provides a mechanical advantage for digging motions, an expansion of the terminal phalanges, and the presence of numerous palmar sesamoids.[6] Stylinodon had a narrow, but robust, scapula, as well as a well developed, stout clavicle.[6][9] The limb morphology of the genus has been compared to those of modern day xenarthrans, with the radius being much smaller than the robust ulna.[9] Stylinodon likely lacked a first digit, and it is speculated that the median phalanges bore claws.[12] It is suspected that the sacrum of Stylinodon consisted of 3 vertebrae.[13][6]

History of research

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Originally described by American Paleontologist Othniel Charles Marsh, Stylinodon was assumed to be related to the Xenarthra by Marsh, and was also considered related the notoungulate Toxodon.[8] Marsh also considered the chalicotheres to be relatives of Stylinodon.[9] Stylinodonts in general were a confusing group due to the rarity of postcranial specimens. A few near complete specimens of Stylinodon are known, including one, PM 3895, which was found layered on top of the skeleton of a juvenile Uintatherium.[6]

Classification

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Stylinodon belongs to the extinct tribe Stylinodontini within subfamily Stylinodontinae and family Stylinodontidae.[14][15] It was historically suggested that all stylinodontine genera were an orthogenetic sequence, with Ectoganus being directly ancestral to Stylinodon, but differences in the dental formula of Ectoganus and Stylinodon have caused this idea to fall out of favor.[10] Currently, Stylinodon is grouped closest with Ectoganus and Psittacotherium.[14]

Placentalia

Paleoecology

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Stylinodon is known from many Bridgerian and Wasatchian formations, including the Bridger formation, the Wasatch formation, the Huerfano formation and the Wind River formation.[10][15] These environments were typically fluvial, with some such as the Wasatch formation indicating the presence of swamps.[16] Stylinodon lived alongside a numerous amount of animals, including the dinocerates Uintatherium and Eobasileus, the brontothere Dolichorhinus and crocodilians.[17] In terms of lifestyle, Stylinodon was a fossorially adapted herbivore that likely fed on tubers and other roots.[18][11]

References

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  1. ^ J. Alroy (2002.) "Synonymies and reidentifications of North American fossil mammals."
  2. ^ E. D. Cope (1881). ""On the Vertebrata of the Wind River Eocene beds of Wyoming."". Bulletin of the United States Geological and Geographical Survey. 6 (1): 183–202.
  3. ^ Wortman, J. L. (1896.) "The Ganodonta and their relationship to the Edentata." Bulletin of the AMNH; vol. 9, article 6
  4. ^ Schoch, R. M.; Lucas, S. G. (1981). ""The systematics of Stylinodon, a middle to late Eocene taeniodont (Mammalia) from western North America."". J. Vertebr. Paleontol. 1: 175–83. doi:10.1080/02724634.1981.10011890. JSTOR 4522849.
  5. ^ "Stylinodon (PaleoBioDB)".
  6. ^ a b c d e f g h Turnbull, William D. (2004). "TAENIODONTA OF THE WASHAKIE FORMATION, SOUTHWESTERN WYOMING". Bulletin of Carnegie Museum of Natural History.
  7. ^ Scott, William Berryman (1913). A history of land mammals in the western hemisphere. Smithsonian Libraries. New York, The MacMillan Company. p. 274.
  8. ^ a b Marsh, Othniel Charles (1874-05-01). "Notice of new Tertiary mammals, III". American Journal of Science. s3-7 (41). doi:10.2475/ajs.s3-7.41.531.
  9. ^ a b c d e Marsh, Othniel Charles; Royal College of Surgeons of England (1897). The Stylinodontia, a suborder of Eocene edentates. Royal College of Surgeons of England. [New Haven : Yale University].
  10. ^ a b c Schoch, Robert M.; Lucas, Spencer G. (1981). "The Systematics of Stylinodon, an Eocene Taeniodont (Mammalia) from Western North America". Journal of Vertebrate Paleontology. 1 (2): 175–183. ISSN 0272-4634.
  11. ^ a b Janis, Christine M.; Scott, Kathleen M.; Jacobs, Louis L. (1998-05-28). Evolution of Tertiary Mammals of North America: Volume 1, Terrestrial Carnivores, Ungulates, and Ungulate Like Mammals. Cambridge University Press. ISBN 978-0-521-35519-3.
  12. ^ Wortman, Jacob Lawson (1897). The Ganodonta and Their Relationship to the Edentata. American Museum of Natural History.
  13. ^ Kynigopoulou, Zoi; Shelley, Sarah L.; Williamson, Thomas E.; Brusatte, Stephen L. (2024). "The post-cranial anatomy and functional morphology of Conoryctes comma (Mammalia: Taeniodonta) from the Paleocene of North America". PloS One. 19 (10) e0311053. doi:10.1371/journal.pone.0311053. ISSN 1932-6203. PMC 11508153. PMID 39453951.
  14. ^ a b Rook, Deborah L.; Hunter, John P. "Phylogeny of the Taeniodonta: evidence from dental characters and stratigraphy". www.semanticscholar.org. Retrieved 2026-03-03.
  15. ^ a b "Taxonomy and biostratigraphy of the early Tertiary Taeniodonta (Mammalia: Eutheria): Summary". bionames.org. Retrieved 2026-03-03.
  16. ^ Pocknall, David T. (1987). "Paleoenvironments and Age of the Wasatch Formation (Eocene), Powder River Basin, Wyoming". PALAIOS. 2 (4): 368–376. doi:10.2307/3514762. ISSN 0883-1351.
  17. ^ Riggs, Elmer Samuel (1912). New Or Little Known Titanotheres from the Lower Uintah Formations: With Notes on the Stratigraphy and Distribution of Fossils. Field Museum of Natural History.
  18. ^ Kynigopoulou, Zoi; Shelley, Sarah L.; Williamson, Thomas E.; Brusatte, Stephen L. (2024). "The post-cranial anatomy and functional morphology of Conoryctes comma (Mammalia: Taeniodonta) from the Paleocene of North America". PloS One. 19 (10) e0311053. doi:10.1371/journal.pone.0311053. ISSN 1932-6203. PMC 11508153. PMID 39453951.
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