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  • Baby Tyrannosaurus rex Tooth




    Tyrannosaurus rex

    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


    Hell Creek Formation


    Acquired by: Purchase/Trade


    Height: 6 mm
    Thickness: 2 mm


    Carter County
    United States



    Originally listed as a Dromaeosaurid tooth, I suspected it was from a Tryannosaurid. Upon receiving the tooth, I contacted a few paleontologists to get expert opinions. Their conclusion was that the tooth was likely from a baby/juvenile Tyrannosaur. Since the only Tyrannosaurs in the Hell Creek Formation are Tyrannosaurus rex and Nanotyrannus lancensis (or only T. rex if N. lancensis is a young T. rex), and considering the cross-section of the base of the tooth, this must be from a baby Tyrannosaurus rex.

    This tooth shares many qualities with adult teeth, a fact which the experts used to justify their identification. The large denticles (serrations) on both carinae (cutting edges) are similar in shape and size, there's virtually no recurvature, no twisting of the carinae, and it has an oval base. The overall shape of the tooth also suggests that it's from the posterior region of the mouth.  

    Among the attached photos are juxtapositions with a high-quality cast replica of an adult T. rex (Stan) posterior tooth, and a juvenile N. lancensis tooth (also from the Hell Creek Formation).  


    Mesial Serration Density: ~ 5.5 - 6 serrations / mm

    Distal Serration Density: ~ 5 - 5.5 serrations / mm

    Note: Serration density alone is not an identifying feature of Tyrannosaur teeth this small.


    The people that support this identification are: @Troodon (experienced and knowledgable collector on TFF); Dr. Philip J. Currie (noted paleontologist, museum curator, and professor specializing in Tyrannosaurs); Dr. David DeMar Jr. (research associate in the Department of Paleobiology of the National Museum of Natural History, Smithsonian Institution); and Dr. Christophe Hendrickx (postdoctoral researcher specializing in the evolution of theropod dentitions).


    OSBORN, HENRY, 1905. Tyrannosaurus and other Cretaceous carnivorous dinosaurs, Bulletin of the AMNH, Volume 21, Article 14, Pages 259-265, https://digitallibrary.amnh.org/handle/2246/1464

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