The Bisti Beast

Western North America is famous for its dinosaur fossils. Many of these come from the San Juan Basin of northwestern New Mexico. Most of these specimens were collected in the early part of the 20th century and the resulting specimens were shipped to Museums far from New Mexico. However, since the New Mexico Museum of Natural History and Science opened in 1986, newly discovered specimens have been found and kept within the state.

Dr. Thomas Williamson, Curator of Paleontology, has led a productive campaign to collect Late Cretaceous dinosaurs from the badlands of the San Juan Basin since 1994. In 1997, a volunteer researcher, Paul Sealey, found an interesting site during a weekend fossil exploration fieldtrip to the Bisti/De-na-zin Wilderness Area. Paul Sealey has a long history of working with Museum curators to recover fossils. Dr. Williamson had previously named a primitive relative of the alligator after Paul, Brachychampsa sealeyi, based on one of his earlier discoveries.

NMMNH P-27469, holotype skull and jaw of Bistahieversor sealeyi
Photograph by David Baccadutre, New Mexico Museum of Natural History and Science.


Dr. Williamson visited the new site and immediately realized that Paul Sealey had found a very rare and important fossil, the partial skeleton of a tyrannosaur, a member of the group of meat-eating dinosaurs that includes Tyrannosaurus rex. Williamson worked closely with the Bureau of Land Management to secure the necessary collecting permits. This was to be the first paleontological excavation to be allowed in a Federal Wilderness area. The permits were granted in 1998 and the dinosaur was excavated that summer. The site was in a rugged, but scenic area, far from any roads. All supplies were carried to the site by hand. Much of the excavation work was done by Museum Volunteers overseen by Dr. Williamson under harsh conditions. Volunteers had to endure high temperatures, voracious gnats, and hard physical labor. By summer’s end, large blocks of rock containing the dinosaur bones were wrapped safely in plaster covered packages, braced with wooden planks. The New Mexico Army National Guard volunteered to airlift the specimens on a calm and cool September morning as part of a training exercise. The heavy jackets were flown safely to a nearby flatbed trailor parked outside of the wilderness boundary and hauled down to the Museum’s fossil preparation lab in Albuquerque.

Group photo of Dr. Thomas Williamson (front row, standing in black t-shirt) with his crew with a field jacket containing portions of the holotype of Bistahieversor sealeyi in the Bisti/De-na-zin Wilderness Area of New Mexico (September, 1998). Photo by Ray Nelson.

The completeness of the new tyrannosaur specimen was revealed only after careful preparation. Much of the preparation was done by long-time Museum Volunteer Warren Slade. Additional preparation was also provided by Ian Morisson of the Royal Ontario Museum and Alex Downs of Ghost Ranch. Preparation of the skull was completed in about two years. Meanwhile, Dr. Williamson collaborated with a colleague, Dr. Thomas Carr (Carthage College), a renowned expert on tyrannosaur dinosaurs. Williamson and Carr obtained grants that supported travel to museums in the U.S. and Canada that contain many of the important tyrannosaur specimens. Together, they carefully analyzed specimens and compared them to New Mexico specimen and other less complete tyrannosaurs that had been collected from the state. Williamson and Carr soon realized that they had a new genus and species that helps to clarify much of the evolutionary history of tyrannosaurs.

Next Page >>