Name Meaning: Dwarf Tyrant
Geologic Era: Late Cretaceous
Location Discovered: Montana (Lance Formation/Hell Creek Formation)
Size: 5.5-6.5 meters (based on studied specimens)
Extinction Date: K-T Extinction (65 million years ago)
This tooth was listed as “Tyrannosaur” tooth. It is far too small to be from an adult Tyrannosaurus rex (less than 6 cm long). There are only two Tyrannosaurs that lived in the area at the time, though one species is presently controversial. That species is Nanotyrannus, which I have chosen for our tooth. The tooth is in reasonably good condition, with the upper crown mostly intact. If, at a later date, Nanotyrannus is officially reclassified as a juvenile Tyrannosaurus rex, I will move this tooth to the appropriate entry (and as a bonus, it would mean we have a real Tyrannosaurus rex specimen in our collection).
Assuming that Nanotyrannus is a distinct species from Tyrannosaurus, it certainly does have characteristics that would make it look dissimilar from a Tyrannosaurus. Size aside, the forearms are proportionately much longer than is seen in Tyrannosaurus, and Nanotyrannus has a higher number of teeth compared to adult Tyrannosaurs. The overall build is different as well, being much more slender, especially in the head and torso region. The overall impression is of an animal that was considerably quicker and lighter than Tyrannosaurus.
However, there is one thing to keep in mind. Animals as juveniles often look very different than their adult form. For an easy example, look at a foal’s body proportions compared to an adult horse. The foal is much more gangly, especially in the legs. This is not unlike how a Nanotyrannus compares to an adult Tyrannosaurus. Only two specimens of Nanotyrannus are in museum hands, one in Cleveland, OH and the other in Rockford, IL. The Cleveland specimen (only known from a skull) shows completely fused bones in the skull, which would generally indicate an adult animal.
The Rockford specimen, nicknamed “Jane,” shows signs that she/he was not completely grown at the time of death. This argues in favor of Jane being a juvenile Tyrannosaurus instead of a distinct species. Below, Jane is pictured in the foreground, with Tyrannosaurus in the background. The differences in skull conformation are very apparent in this photo, as is the difference in overall build. There is the possibility that Jane is indeed a juvenile Tyrannosaurus, while the Cleveland specimen may be a different species (Nanotyrannus). Without the rest of the skeleton, it is difficult to say.
What could neatly solve the controversy of Nanotyrannus is a third, very complete specimen that could be used for comparison purposes. Such a specimen does apparently exist. A very complete Nanotyrannus skeleton was unearthed several years ago, and was found very close to a ceratopsian skeleton. This specimen, called “Dueling Dinosaurs,” would probably help put the Nanotyrannus/Tyrannosaurus controversy to rest. Unfortunately, the specimen is still in a private collectors hands, and cannot be studied at all at this time.
“Jane” Skeleton:”T-rex fossil Jane by Volkan Yuksel DSC08683g” by Volkan Yuksel – Own work. Licensed under CC BY-SA 3.0 via Wikimedia Commons – https://commons.wikimedia.org/wiki/File:T-rex_fossil_Jane_by_Volkan_Yuksel_DSC08683g.JPG#/media/File:T-rex_fossil_Jane_by_Volkan_Yuksel_DSC08683g.JPG
Restoration:”Nanotyrannus lancensis TQWR 400″ by Conty – Own work. Licensed under CC BY 3.0 via Wikimedia Commons – https://commons.wikimedia.org/wiki/File:Nanotyrannus_lancensis_TQWR_400.JPG#/media/File:Nanotyrannus_lancensis_TQWR_400.JPG