The Process of Smithsonian Fossil Preparators Re-Excavating a Tyrannosaur From its Previous Display

 

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Effort to Free a Century-Old Fossil Skeleton for Research

This National Fossil Day, let’s take a closer look at the ongoing effort to free a Gorgosaurus skeleton from its century-old mount in museum fossil halls. The skeleton, which was found over a century ago in the badlands of Alberta, Canada, has been on display in various fossil halls since its discovery. However, the plaster relief in which it was mounted has made the skeleton difficult to access, study, and care for.

A Notable Tyrannosaur

The Gorgosaurus libratus, a relative of the famous Tyrannosaurus rex, has been a notable attraction at the National Museum of Natural History 12. While the museum’s T. rex skeleton has dominated the Deep Time Hall of Fossils since 2019, the Gorgosaurus has been on display in the FossiLab area, where visitors can observe preparators working on the skeleton.

A close-up of the Gorgosaurus skeleton’s skull before it was removed from its mount illustrates how the fossils were embedded into the plaster display. Smithsonian Institution

The Red Deer River’s rich assembly of dinosaur bones has attracted paleontologists for more than a century. In the 1910s, famed fossil hunters Barnum Brown, who had previously discovered the first T. rex skeleton in Montana, and Charles Sternberg scoured these badlands for spectacular dinosaur skeletons, some of which sported imprints of fossilized skin.

It was Brown who discovered the nearly complete skeletons of two Gorgosaurus individuals between 1913 and 1914. Brown shipped these specimens back to his employer, the American Museum of Natural History (AMNH) in New York City (a third nearly intact Gorgosaurus was discovered by Sternberg and also ended up at AMNH). To prepare them for exhibition, the Gorgosaurus skeletons were partially entombed in plaster and mounted in relief like sculptures protruding out of a wall.

A Journey from the Badlands to the Museum

The Gorgosaurus skeleton was discovered in the fossil-rich badlands flanking the Red Deer River in Alberta. These fossil beds have yielded numerous dinosaur species, including the Gorgosaurus and its contemporary, Daspletosaurus. In the early 1910s, renowned fossil hunters Barnum Brown and Charles Sternberg excavated the Gorgosaurus skeletons from these badlands.

The skeletons were then partially entombed in plaster and mounted in relief at the American Museum of Natural History (AMNH) in New York City. In 1933, one of the Gorgosaurus skeletons, along with the skeleton of another creature called Moropus, was traded to the Smithsonian in exchange for the neck of a Barosaurus. The Gorgosaurus skeleton was subsequently displayed in the Hall of Extinct Monsters at the Smithsonian.

The Gorgosaurus skeleton in the museum’s Hall of Dinosaurs and Fossil Reptiles exhibition in 1963. Smithsonian Institution

At the Smithsonian, the pretzeled Gorgosaurus skeleton was first displayed in the Hall of Extinct Monsters in the mid-1930s. The tyrannosaur mount remained a staple as the museum’s fossil hall evolved over the decades. Museum visitors last saw the display in its entirety in 2014, when it was perched on the wall next to an Edmontosaurus skeleton above the museum’s fossil hall. When the exhibition closed for renovations that spring, the Gorgosaurus skeleton and the rest of the museum’s fossilized showpieces were temporarily returned to the collection.

Only the Gorgosaurus’s skull has made it into the new fossil hall. It is now displayed alongside other Canadian dinosaurs from the Cretaceous on the other side of the Nation’s T. rex skeleton.

The Skeleton Gets Dug Up (Again)

Perez prepares the display side of the specimen to be jacketed by wrapping the fragile parts of the skeleton in a thick felt that will be removed when the jacket is finished. This leaves a pocket for the fragile bone so it never touches the jacket. Myria Perez, NMNH

For over a year, Perez and the FossiLab team have been painstakingly freeing the fossils from the plaster mount. Because the fossil was mounted in relief, only one side of the skeleton has been exposed for the last century. The rest has been buried inside an amalgamation of plaster and metal rods to keep the 75-million-year-old bones secured in place.

Before they could chip away at the old display, they had to build a new, permanent storage solution — an archival jacket — to support the fragile fossils as they are worked on and to store them safely in collections in the foreseeable future. These archival jackets are custom made to fit each specimen snuggly and distribute the specimen’s weight evenly. For large specimens like the Gorgosaurus, the team incorporates supportive structures into the jacket to keep it from flexing and builds “rockers” to allow the final jacketed specimen to be flipped and observed from each side.

Perez stands alongside a section of the dinosaur’s spinal cord that reveals fossil vertebrae alongside the metal rods that were used to keep the skeleton in place. Jack Tamisiea, NMNH

Once the skeleton was secured, the team has been using air scribes, which act like handheld jackhammers, to remove the original plaster display. “The plaster is pretty easy to remove compared to the rock matrix like it would normally be in,” Perez said.

Re-Excavating the Skeleton

In recent years, paleontologist Matthew Carrano and the FossiLab team at the National Museum of Natural History have been working to re-excavate the Gorgosaurus skeleton from its century-old mount 12. The team has been carefully removing the plaster and metal rods that have kept the bones secured in place. They have also been building a new, permanent storage solution called an archival jacket to support and protect the fragile fossils.

The re-excavation process has revealed surprises, including oversized metal screws, bits of burlap, and even original rock from the Red Deer River. The preparators are currently focusing on freeing the buckled neck and hip of the Gorgosaurus skeleton, with the goal of having most of its bones freed by early 2024.

Unlocking Scientific Value

While the Gorgosaurus skeleton is not a holotype, it still holds significant scientific value. Its articulated nature, along with the presence of parts of the forearm and a well-preserved skull, make it a valuable specimen for research. By removing it from its old display, the skeleton will be fully available to researchers for the first time in over a hundred years, opening up the possibility for new discoveries and insights into these ancient creatures.