Baby Tyrannosaurus rex Tooth

Taxonomy

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

Stratigraphy

Hell Creek Formation

Provenance

Acquired by: Purchase/Trade

Dimensions

Height: 6 mm
Thickness: 2 mm

Location

Carter County
Montana
United States

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• tyrannosaurus rex tooth

Comments

Identification:

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).  

Other:

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.

Identifiers:

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).

Citation:

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