Nanotyrannus

***Nanotyrannus*** (Greek for "Dwarf Tyrant") is a highly dubious genus of tyrannosaurid dinosaur. *Nanotyrannus* is the fourth smallest known tyrannosauroid (with only Dilong paradoxus, Guanlong wucaii and Proceratosaurus being smaller) and was one of the last tyrannosaurids to exist before the Cretaceous Teritary Extinction, the K-T mass extinction event. It's also the very last non-avian dinosaur ever to appear on Earth, appearing 66 mya ago and living not even 50,000 years. The genus is represented only by a small skull (catalog number **CMN 7541**), and was discovered by Charles W. Gilmore in 1941 and described in 1946 as a specimen of *Gorgosaurus*. In 1988, the specimen was re-described by Robert T. Bakker, Phil Currie, and Michael Williams, the late curator of paleontology at the Cleveland Museum of Natural History, where the original specimen was housed and is currently on display.

Opinions continue to remain divided on the validity of *N. lancensis*. *Nanotyrannus* can be a possible juvenile of a tyrannosaur that is closely related to *Tyrannosaurus* and the adult of this animal is yet to be identified, or it really is a juvenile *Tyrannosaurus*. In either case, an adult *Nanotyrannus* has to be discovered or a juvenile *Tyrannosaurus* of the same size as *Nanotyrannus* but morphologically distinct from it in order to fully resolve this debate. Many paleontologists consider the skull to belong to a juvenile *Tyrannosaurus rex*. However, there are minor differences between the two species, including the higher number of teeth and the presence of fused bones in the holotype. These features have lead some paleontologists to recommend keeping the two genera separate until further research or discoveries clarify the situation. There is a study shown that the specimens assigned to Nanotyrannus are likely young Tyrannosaurus; as the bone age diagnosis indicates these specimens are indeed subadult animals.

A small but nearly complete skull discovered in Montana in 1942 by the Cleveland Museum of Natural History Curator Dr. David Dunkle measured 60 centimeters (2.0 ft) long and may be an exception. The skull was recovered from the upper Lance Formation (the species bear the name *lancensis*), which is now known as the Hell Creek Formation. This skull, and therefore type species was originally classified as a species of *Gorgosaurus* (*G. lancensis*) by Charles W. Gilmore in 1946. In the early 1970s, American paleontologist Dr. Dale Russell of the North Carolina Museum of Natural Sciences, made convincing arguments that the *Albertosaurus* and *Gorgosaurus* were the same genus. Because the name *Albertosaurus* had been in use longer, it became, for a time, the name for all members of both genera. The holotype skull then was assigned the new name *Albertosaurus lancensis*. However, many paleontologists expressed doubt that the skull was actually *Albertosaurus*. In the late 1980s, paleontologist Dr. Robert Bakker of the University of Colorado, performed a detailed comparative study and then visited the Royal Tyrrell Museum of Paleontology in Drumheller, Alberta, Canada, to consult with Dr. Philip Currie, then Head of Dinosaur Research. Together with late Dr. Michael Williams, former Museum Curator of Vertebrate Paleontology from 1975 to 2003, Bakker and Currie published a paper in 1988 describing the new genus and proposing the name *Nanotyrannus*, which means "pygmy tyrant". The inclusion of the "tyrannus" portion of the name was meant, Williams said, to signal that this was a "downsized tyrannosaur closely related to *Tyrannosaurus rex*."

### Holotype skull

Initial research indicated that the skull bones were fused, and that it therefore represented an adult specimen. In light of this, Bakker and colleagues assigned the skull to a new genus, which they named *Nanotyrannus* for its apparently small size. However, subsequent work has cast doubt on this, and some paleontologists no longer consider it a valid genus—since the fossil was a contemporary of *Tyrannosaurus rex*, many paleontologists now believe it to be a juvenile *T.rex*, especially since the discovery in 2001 of a new *Nanotyrannus* specimen, nicknamed "Jane." The original *Nanotyrannus* specimen is estimated to have been around 17 feet (5.2 meters) long when it died.

### "Jane"

Main article: Jane (dinosaur)

In 2001, a more complete juvenile tyrannosaur ("Jane", catalogue number **BMRP 2002.4.1**), belonging to the same species as the original *Nanotyrannus* specimen, was uncovered. It was named after a generous donor to the museum. In 2005, a conference on tyrannosaurs focused on the issues of *Nanotyrannus* validity brought about by the discovery of the Jane specimen, was held at the Burpee Museum of Natural History. Several paleontologists, such as Phil Currie and Donald M. Henderson, saw the discovery of "Jane" as a confirmation that *Nanotyrannus* was a juvenile *T. rex* or closely related species.Peter Larson, on the other hand, continued to support a separate genus for *Nanotyrannus*. The actual scientific study of "Jane", set to be published by Bakker, Larson, and Currie, may help determine whether *Nanotyrannus* is a valid genus, whether it simply represents a juvenile *T. rex*, or whether it is a new species of a previously identified genus of tyrannosaur.

### "Dueling Dinosaurs"

In late 2011, news reports about a 2006 discovery of a new & virtually complete Nanotyrannus specimen found along with a ceratopsid Dinosaur were made. The specimens were studied by Robert Bakker and Pete Larson on-site, who identified the ceratopsian as Triceratops. The Nanotyrannus specimen, nicknamed "Bloody Mary", allegedly has arms almost 3 feet in length, with the bones of the hand said to be one and a half times longer than those of the T. rex specimen "Sue" but the truth to those claims is impossible to determine along with further analysis of the "Bloody Mary" specimen as it remains in private hands. The fact that the small "Bloody Mary" specimen was found alongside such a physically mismatched opponent as a large ceratopsian has been used to suggest that N. lancensis was a pack hunter. Robert Bakker also found evidence for pack hunting in N.lancensis in the presence of some 30 Nanotyrannus teeth embedded throughout the skeleton of one Triceratops carcass.

## Disputed taxonomy

Some paleontologists have considered *Nanotyrannus* to be a synonym of *Tyrannosaurus*, while others disagree and place it within its own genus.

Until further specimens are discovered, however, the genus of *Nanotyrannus* may remain debateable. However, the discovery of a large adult tyrannosaur which is not *Tyrannosaurus* but instead shows derived features otherwise present only in *Nanotyrannus* or the discovery of a juvenile tyrannosaur of the same skull length may finally validate the genus.