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  • Tyrannosaurid premaxillary tooth





    Kingdom: Animalia
    Phylum: Chordata
    Class: Reptilia
    Order: Avetheropoda
    Family: Tyrannosauridae
    Genus: Tyrannosaurus
    Species: Tyrannosaurus rex
    Author Citation Osborn, 1905

    Geological Time Scale

    Eon: Phanerozoic
    Era: Mesozoic
    Period: Cretaceous
    Sub Period: None
    Epoch: Late
    International Age: Maastrichtian


    Hell Creek Formation


    Collector: Black Hills Institute
    Acquired by: Purchase/Trade


    Width: 6 mm
    Height: 13 mm
    Thickness: 4 mm


    Garfield County
    United States


    "That some of these teeth are mammalian incisors there can be but little doubt..." - O. C. Marsh1

    This kind of incisor-like ("incisiform") tooth was originally thought to have belonged to a large, Cretaceous mammal.  Later discoveries revealed that these teeth were actually the front teeth ("premaxillary teeth") of Tyrannosaurs - and are now known as a hallmark of their clade, Tyrannosauroidea (along with fused nasals). Closely-spaced, parallel grooves on bones suggest that Tyrannosaurs used these teeth to selectively scrape meat from bone2.


    Tyrannosaurid premaxillary teeth have a "D"-shaped cross section, with the lingual face flattened, and often have an apicobasal ridge on the midline of the lingual face.

    In more technical language, "...premaxillary teeth bear lingually rotated mesial and distal carinae forming a salinon cross-section at mid-crown height, and a highly convex labial aspect as in tyrannosauroids generally. In mesial/distal views carinae are sinuous, transitioning from lingually convex near the base to lingually concave approaching the occlusal surface. Carinae terminate prior to reaching the root/crown juncture. Mesial and distal aspects of the crown are depressed, yielding a weakly hourglass-shaped cross-section at the crown base... The carinae lack serrations [likely ontogenetically variable]... As in other tyrannosauroids, teeth exhibit a pronounced lingual ridge"3.

    Most of the current literature supports only one Tyrannosaurid species in the Hell Creek formation, Tyrannosaurus rex, a hypothesis subject to change in light of new evidence. 


    This tooth exhibits some antemortem wear at the apex (pictured), on the carinae, and near the base of the lingual apicobasal ridge. Given the size, this is from a juvenile animal (smaller than "Jane", BMRP 2002.4.1).


    1. Marsh, O.C., 1892, "Notes on Mesozoic vertebrate fossils", American Journal of Science, 44: 170-176

    2. David W.E. Hone and Mahito Watabe, "New information on scavenging and selective feeding behaviour of tyrannosaurs", Acta Palaeontologica Polonica 55 (4), 2010: 627-634 doi: http://dx.doi.org/10.4202/app.2009.0133

    3. Zanno, L., Tucker, R.T., Canoville, A. et al. Diminutive fleet-footed tyrannosauroid narrows the 70-million-year gap in the North American fossil record. Commun Biol 2, 64 (2019). https://doi.org/10.1038/s42003-019-0308-7

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