Nanotyrannus

*Nanotyrannus lancensis*

***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.

## Material

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"

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.

### *Nanotyrannus* is its own genus

Several features seem to separate it from the *Tyrannosaurus* genus, including the fact that both Jane and the holotype were found in the same area, near Ekalaka, Montana. Both specimens of *Nanotyrannus* also have 16 teeth, which is two more teeth sockets present in its upper jaw than in *Tyrannosaurus*. However, there is also considerable evidence for ontogenetic and individual variation in tooth count for tyrannosaurs.*Nanotyrannus* teeth are also described as being more primitive (basal) than that of other tyrannosaurs, in that the teeth were laterally compressed. This feature, however, is not known only to *Nanotyrannus*, and has also been observed in *Alioramus* teeth and in the "Jordan theropod", now known as *Aublysodon*.

The holotype and "Jane" also have a pneumatic foramen in a bone at the back of the jaw that is not present in *Tyrannosaurus*. The original specimen of N. lancensis had fused bones, indicating it was an adult, and several paleontologists have suggested that if it was a juvenile *T. rex*, fossilized remains would most likely be found elsewhere and be more common. A lacrymal horn is present in *Nanotyrannus* whereas it is absent in *Tyrannosaurus*. Furthermore, the shape of the lacrymal is "T" shaped in *Nanotyrannus* but an inverted "L" in *Tyrannosaurus*.

In the 1998 paper, Bakker *et al.* described that *Nanotyrannus* had "strong adaptations for stereoscopic description", which included forward facing eyes, a sharply downward bending neck, and an enlarged temporal region that was four times the width of the muzzle.

Those that support *Nanotyrannus* as a juvenile *Tyrannosaurus* mention that "Jane" was only about half grown when she died at around the age of 11. This dispute is not just a simple case of lumping or splitting genera. *Nanotyrannus* is either a juvenile or not. Some paleontologists hold that the *Nanotyrannus* holotype is definitely crushed and distorted, and is probably a juvenile *Tyrannosaurus*. However, that leaves open the advanced state of fusion between the bones of the skull, and whether or not this is just an artifact resulting from the sutures being plastered over by the restorer. Bakker *et al*. did a CT scan of the *Nanotyrannus* skull which was able to distinguish between the fossil bone and plaster. The fusion is definitely not from the sutures being plastered over. *Nanotyrannus* apparently did not have the "eye bones" or "horns" over the eye sockets that *Tyrannosaurus* had. Furthermore, the eye sockets are located in a different place than on *Tyrannosaurus*, suggesting *Nanotyrannus* had binocular vision. However, it should also be noted that horns, being mostly for social interactions of some sort, need not develop until near adulthood, and eye position can easily alter during growth, not contradicting a possible juvenile hypothesis for this genus.

In 2004, Dr. Lawrence Witmer of the College of Osteopathic Medicine at Ohio University, performed a series of Computed Tomography (CT) scans on the holotype skull. The internal shape of the braincase suggests that the tyrannosaur represented by **CMNH 7541** could not have grown up to be a *Tyrannosaurus*. Unfortunately, the braincase for Jane was not recovered so it is impossible to directly compare the only potentially differentiating components of the two animals.

### *Nanotyrannus* is *Tyrannosaurus*

According to Thomas Carr, *Nanotyrannus* has many juvenile features present in immature tyrannosaurs, and shares a number of derived characters with *Tyrannosaurus* (such as a narrow snout and broad temporal region), that he placed *Nanotyrannus* as an early ontogenetic stage of *Tyrannosaurus rex*. Many authors have followed up on his assessment and dropped the taxonomic validity of *Nanotyrannus*. Some paleontologists also argue that because some of the skull bones are not fused, it is an immature, juvenile animal. However, if *Nanotyrannus* had a bimodal growth pattern; a rapid growth from hatchling to subadult, then slower indeterminate growth from subadult to large adult, it could well have had skull-bone fusion already at the subadult stage. This would indicate that that skull-bone fusion may not be as good an indicator of juvenility or sub-adulthood as previously thought. Some have suggested that *Nanotyrannus* may even be a dromaeosaur, with Robert Bakker suggesting that *Nanotyrannus* hunted in packs. Teeth from multiple *Nanotyrannus* have been found in the bones of herbivorous dinosaurs. The type of *Nanotyrannus* also shares numerous derived attributes with *Tyrannosaurus rex* which are not found in other tyrannosaurids, as discussed in the next section.

### Basal and derived features

A wedge-shaped skull, narrow jaw, large orbits, forward-pointing parasphenoid, and infratemporal fenestra without any large rostral process of the quadratojugal and squamosal make it the most basal known tyrannosaur. Not all of these unique features can be attributed to young age, as the skulls of other small tyrannosaurids (*Alioramus remotus*, *Gorgosaurus sternbergi*, *Maleevosaurus novojilovi*) have broad snouts and, in particular, large rostral processes across the infratemporal fenestra.

The type specimen of *Nanotyrannus* also shares numerous derived attributes with *Tyrannosaurus rex* which are not found in other tyrannosaurids. *Nanotyrannus* has a widely expanded occiput relative to snout width (best seen in ventral view in Gilmore's 1946 paper), resulting in orbits having a forward-pointing component. This seems to be a derived feature shared by *Nanotyrannus* in common with *Dinotyrannus* and especially *Tyrannosaurus*. Bakker *et al*. illustrate the squamosal-quadratojugal junction of *Nanotyrannus* as more expanded than seen in the photos in Gilmore's 1946 paper, and some paleontologists suspect that the portion within the infratemporal fenestra might be broken off or buried in matrix in the type specimen. But even if this feature is real, it could be a derived character state. These differences between *Nanotyrannus* and *Tyrannosaurus* are similar to the differences found between juvenile and adult *Gorgosaurus libratus* or *Tarbosaurus bataar* skulls. However, Nanotyrannus appeared earlier than Tyrannosaurus rex.

On January 1, 2020, Woodward's study shows the specimens referred to Nanotyrannus are ontogenetically immature and found it probable that these specimens belonged to Tyrannosaurus rex. All of the differences claimed to support Nanotyrannus have turned out to be individually or ontogenetically variable features or products of distortion of the bones.

## Specimens

* Bloody Mary
* Jane
* CMNH 7541

## JPInstitute.com Description

Nanotyrannus is known from a single skull and jaw. The skull was originally thought to be that of an Albertosaurus, but significant differences were noticed years after it had been prepared and stored on a museum shelf. The skull was re-prepared, studied and re-described by Dr. Robert Bakker. Nanotyrannus had the honor of being the first dinosaur to be CAT scanned.

Nanotyrannus had forward-facing eyes like T. rex, which gave it very good depth perception. It had sharp, serrated teeth and powerful neck muscles. Combined, these tools would have made it an excellent hunter.

Some paleontologists believe that Nanotyrannus is a juvenile Tyrannosaurus rex, partly because some of the skull bones are not fused, indicating an immature animal. A few paleontologists have suggested it may be a type of huge dromaeosaur (raptor).

## Appearance in other media

### *Jurassic Park*

* Nanotyrannus is mentioned in You Bet Jurassic at Jurassic Park Discovery Center at Islands of Adventure.

## Links

http://web.archive.org/web/20040214171207fw\_/http://www.jpinstitute.com/dinopedia/dinocards/dc\_nanot.html

1. ↑ 1.0 1.1 1.2 1.3 1.4 1.5 Bakker, Williams, and Currie (1988). "*Nanotyrannus*, a new genus of pygmy tyrannosaur, from the latest Cretaceous of Montana." *Hunteria*, **1**: 1–30.
2. ↑ 2.0 2.1 Gilmore (1946). "A new carnivorous dinosaur from the Lance Formation of Montana." *Smithsonian Miscellaneous Collections*, **106**: 1–19. Cite error: Invalid `<ref>` tag; name "gilmore1946" defined multiple times with different content
3. ↑ 3.0 3.1 Template:Cite book
4. ↑ 4.0 4.1 Template:Cite journal
5. ↑ 5.0 5.1 5.2 5.3 5.4 5.5 5.6 Template:Cite web
6. ↑ Currie, Henderson, Horner and Williams (2005). "On tyrannosaur teeth, tooth positions and the taxonomic status of *Nanotyrannus lancensis*." In "The origin, systematics, and paleobiology of Tyrannosauridae”, a symposium hosted jointly by Burpee Museum of Natural History and Northern Illinois University.
7. ↑ Henderson (2005). "Nano No More: The death of the pygmy tyrant." In "The origin, systematics, and paleobiology of Tyrannosauridae”, a symposium hosted jointly by Burpee Museum of Natural History and Northern Illinois University.
8. ↑ Larson (2005). "A case for *Nanotyrannus*." In "The origin, systematics, and paleobiology of Tyrannosauridae”, a symposium hosted jointly by Burpee Museum of Natural History and Northern Illinois University.
9. ↑ Mortimer, M (2004). "Tyrannosauroidea". *The Theropod Database*. http://web.archive.org/20081212143124/home.comcast.net/~eoraptor/Tyrannosauroidea.html#Tyrannosaurusrex. Retrieved on 2007-08-21.
10. ↑ 10.0 10.1 Carr, T.D. 1999. Craniofacial ontogeny in Tyrannosauridae (Dinosauria:Coelurosauria). *Journal of Vertebrate Paleontology* **19** (3): 497-520
11. ↑ Carr, T.D., and Williamson, T.E. 2004. Diversity of Late Maastrichtian Tyrannosauridae (Dinosauria:Theropoda) from Western North America. *Zoological Journal of the Linnean Society* **142**: 479-523
12. ↑ Glut, D. F. 1997. *Dinosaurs: The Encyclopedia*. McFarland, Jefferson, NC.
13. ↑ Glut, D. F. 2000. *Dinosaurs: The Encyclopedia, Supplement 1. McFarland, Jefferson, NC.*
14. ↑ Glut, D. F. 2003. *Dinosaurs: The Encyclopedia, Supplement 3. McFarland, Jefferson, NC.*
15. ↑ Glut, D. F. 2006. *Dinosaurs: The Encyclopedia, Supplement 4. McFarland, Jefferson, NC.*
16. ↑ Bakker, R. T. 1986. *The Dinosaur Heresies: New Theories Unlocking the Mystery of the Dinosaurs and Their Extinction*. Zebra Books, New York.
17. ↑ 17.0 17.1 Larson, N. L. 2008. One Hundred Years of *Tyrannosaurus rex*: The Skeletons. In K. Carpenter (ed.). *Tyrannosaurus Rex:The Tyrant King* Indiana University Press, Bloomington.
18. ↑ Rauhut, Oliver W. & Fechner, Regina, 2005. Early development of the facial region in a non-avian theropod dinosaur. *Proc Biol Sci.* **272**(1568): 1179–1183.
19. ↑ Smith, Joshua B. 2005. Heterodonty in *Tyrannosaurus rex*: Implications for the taxonomic and systematic utility of theropod dentitions. *Journal of Vertebrate Paleontology* **25**(4):865-887.
20. ↑ Molnar, R. 1978. A new theropod dinosaur from the Upper Cretaceous of Central Montana. *Journal of Paleontology* **52**: 73-82
21. ↑ Molnar, R. E. & Carpenter, K. 1989. The Jordan theropod (Maastrichtian, Montana, U.S.A.) referred to the genus *Aublysodon*.
22. ↑ http://dml.cmnh.org/2005Sep/msg00357.html
23. ↑ http://www.dinosauria.com/jdp/trex/nano.htm
24. ↑ Nordquist, Karen (2004). Karen's Komments. Earth Science Club of Northern Illinois. Last accessed 2007-03-11.