Crocodilian Tooth
GRI #348-1
Crocodilians replace their teeth continuously throughout their lives (Edmund, 1962). This shedding makes their teeth among the most commonly fossilized crocodilian remains, as seen in the Green River Formation (Grande, 1984).
Crocodilian teeth are generally subconical in shape, but considerable variability in size and form can be observed within the tooth row of a single individual (heterodonty), among individuals of the same species, and across different species (D’Amore et al., 2019).
This isolated tooth is robust, subconical, with slight lateral compression. Part of the hollow root is likely preserved, as suggested by sediment infill visible in basal view. Determining the presence of ridges or enamel ornamentation is difficult due to damage to the outermost layer of the tooth.
At least two crocodilians are well known from skeletal remains in the Green River Formation. One species, Tsoabichi greenriverensis (Brochu, 2010), is classified in the group known as caimans, a part of the alligator family (Walter, et al., 2021). Based on the specimens discovered so far, T. greenriverensis appears to have been less than 1 meter in size (Grande, 2013). The second species, Borealosuchus wilsoni, has been classified as a crocodilian not directly related to any living species (Brochu, 1997). It grew up to 4.5 meters in size and belongs to a genus documented within a broad stratigraphic range of Cretaceous to Eocene rocks in North America (Paleobiology Database, n.d.). Remains attributed to other crocodilians (e.g., Procaimanoidea kayi) have been listed as recovered from the Powder Wash locality of the Unita basin (Gunnel & Bartel, 1999).
References:
Brochu, C.A., 1997. A review of “Leidyosuchus” (Crocodyliformes, Eusuchia) from the Cretaceous through Eocene of North America. Journal of Vertebrate Paleontology, 17(4), pp. 679-697.
Brochu, C.A., 2010. A new alligatorid from the lower Eocene Green River Formation of Wyoming and the origin of caimans. Journal of Vertebrate Paleontology, 30(4), pp. 1109-1126. doi:10.1080/02724634.2010.483569.
D’Amore, D.C., Harmon, M., Drumheller, S.K. and Testin, J.J., 2019. Quantitative heterodonty in Crocodylia: assessing size and shape across modern and extinct taxa. PeerJ, 7, p.e6485. doi:10.7717/peerj.6485.
Edmund, A.G., 1962. Sequence and rate of tooth replacement in the Crocodilia. Royal Ontario Museum, University of Toronto Press. Life Science Division Contributions, 56, p. 42.
Grande, L., 1984. Paleontology of the Green River Formation, with a review of the fish fauna. Geological Survey of Wyoming, Bulletin 63, p. 333. (1st ed. 1980).
Grande, L., 2013. The lost world of Fossil Lake: Snapshots from deep time. University of Chicago Press. p. 425.
Gunnell, G.F. and Bartels, W.S., 1999. Middle Eocene vertebrates from the Uinta Basin, Utah, and their relationship with faunas from the southern Green River Basin, Wyoming. Utah Geological Survey Miscellaneous Publication, 99(1), pp. 429-442.
Paleobiology Database (no date) Borealosuchus, The Paleobiology Database. Available at: https://paleobiodb.org/classic/basicTaxonInfo?taxon_no=txn:110899 (Accessed: March 2025).
Walter, J., Darlim, G., Massonne, T., Aase, A., Frey, E. and Rabi, M., 2021. On the origin of Caimaninae: insights from new fossils of Tsoabichi greenriverensis and a review of the evidence. Historical Biology, 34(4), pp. 580-595. doi:10.1080/08912963.2021.1938563.