Nanotyrannus lancensis

In the Museum collections is the holotype (first described specimen, CMNH 7541) of Nanotyrannus lancensis—a skull about three feet long. Originally described as a "pygmy" tyrannosaur (a member of the family Tyrannosauridae that includes the Tyrannosaurus rex, Gorgosaurus and Albertosaurus), debate rages among researchers over whether the skull does, indeed, come from a valid genus (Nanotyrannus), or might it instead simply be a juvenile of T. rex. 

Nanotyrannus lancensis is one of the Museum's most significant fossils. Discovered in Montana in 1942 by Museum Curator Dr. David Dunkle, who is best known for the prehistoric fish that bears his name, Dunkleosteous, the skull came from the upper portion of the Lance formation (hence the species name lancensis), which is now called the Hell Creek formation. It died close to the end of the Cretaceous, at the end of the dinosaurs' reign, approximately 65 million years ago.

What's in a Name

In 1946, Charles Gilmore, Smithsonian Institution, identified the skull as a new species of tyrannosaurid genus Gorgosaurus (G. lancensis).

This changed in the 1970s, when paleontologist Dr. Dale Russell, 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 Cleveland skull was assigned the new name Albertosaurus lancensis.

Many dinosaur paleontologists who visited the Museum over the next decade expressed doubts that the skull was actually Albertosaurus. In the late 1980s, paleontologist Dr. Robert Bakker, University of Colorado, performed a detailed comparative study. After making notes on the Cleveland skull, he visited the Royal Tyrrell Museum of Paleontology in Drumheller, Alberta, Canada, to consult with Dr. Philip Currie, then Head of Dinosaur Research, now at the University of Alberta in Edmonton, Alberta, Canada.

After a careful examination of a number of Albertosaurus and Gorgosaurus skulls, they, together with the late Dr. Michael Williams, former Museum Curator of Vertebrate Paleontology from 1975 to 2003, and Dr. Philip Currie, the Royal Tyrrell Museum, wrote 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." Indeed, standing side-by-side the two probably would have looked like siblings, the Nanotyrannus about one-tenth the weight and about one-third the length of the massive T. rex.

New Evidence

In 2001, a crew of paleontologists and volunteers from the Burpee Museum of Natural History in Rockford, Illinois, discovered remains that shed new light on the Nanotyrannus lancensis debate.

In the same general location where CMNH 7541 was unearthed decades earlier, the Burpee crew found the remains of a partial skull and skeleton they nicknamed "Jane" after a major museum donor. Though initial reports indicated Jane was most likely another specimen of Nanotyrannus, as preparation progressed, paleontologists at the Burpee started to refer to the specimen as a T. rex even though the analysis of the specimen has yet to be completed. A cast of Jane is on display in the lobby of the Museum.

At present, Jane has yet to be completely described and analyzed. Studies of the growth rings in the dinosaur's bones (the bones of some dinosaurs, particularly tyrannosaurs, have growth rings a similar to those found in trees) indicate it was probably about 11 years old when it died—still a juvenile.

There are many similarities between CMNH 7541 and Jane. They both have 16 teeth in their upper jaws, two more than any adult specimen of T. rex. They also have an opening called a pneumatic foramen in a bone at the back of the jaw that is not present in T. rex.

Study continues. In 2004, Dr. Lawrence Witmer, the College of Osteopathic Medicine at Ohio University, performed a series of Computed Tomography (CT) scans on the Museum's Nanotyrannus skull. The internal shape of the braincase suggests that the tyrannosaur represented by CMNH 7541 could not have grown up to be a T. rex. Unfortunately, the braincase for Jane was not recovered so we will never be able to directly compare the only potentially differentiating components of the two animals.

At present, Jane is considered a juvenile tyrannosaur and the debate over the Nanotyrannus lancensis’ true identity continues. Ongoing research may provide new clues. The discovery of new specimens would add fresh data to this ongoing scientific saga. Until then, visitors to The Cleveland Museum of Natural History can see casts of the "pygmy" skull and Jane's mounted skeleton, plus a cast of a full-size T. rex, and compare and contrast for themselves.