Published: July 18, 2018

Rediscovering a Dinosaur Named Elmer

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This "little carnivorous dinosaur" revealed something new, 80 years later. 

Close-up view of brown tail vertebrae that curve around. They're positioned on a white cushion.

For every specimen you can see out on display at the Museum, there are many more behind the scenes. Our scientists and visiting researchers are always studying what’s in our collection—and sometimes, we make unexpected discoveries. 

One such mystery in our collection was a dinosaur fossil discovered by Elmer Riggs, the Field’s first paleontologist. Riggs and his team unearthed the specimen in question on a 1922 expedition to Alberta, Canada. Riggs noted in his records that he suspected it was a “little carnivorous dinosaur,” but it was part of our collection for nearly eight decades before we understood what a fascinating find it really was.

Black-and-white photo of a man in a rocky ditch, leaning over several large bundles covered in white plaster. There are mountains in the background.

Geology preparator John Abbott, on the expedition with Riggs, wraps the dinosaur specimen in a plaster jacket, in preparation to move it out of the field. Alberta, Canada, 1922. 

Field Museum Photo Archives

In 1999, fossil preparators finally had the opportunity to open up field jackets containing Riggs's dinosaur. After painstakingly removing rock from around the fossils, our scientists were able to identify the mystery dino: Gorgosaurus, ​​​​​​a young tyrannosaurid that’s related to the fearsome Tyrannosaurus rex.

Fondly nicknamed “Elmer” after Riggs himself, this cousin of T. rex is an exciting find. Though we don’t have the full skeleton, the parts we do have are remarkably complete. Riggs’ team found the skull, neck bones, hips, both legs—including a 100-percent-complete right foot—and a nearly complete eight-foot-long tail. What makes Elmer even more interesting is that it’s a young dinosaur. It gives us a unique look at the bones of a juvenile, which we can study to better understand dinosaur growth as a whole.

Two side-by-side orange scans showing rings inside dinosaur bones. The scan on the left counts up to 5, and the scan on the right counts up to 19 rings.

Growth lines in one of Elmer's leg bones reveal that this dinosaur lived to be just over five years old (left). SUE, on the other hand, lived longer. In this scan showing a section of the T. rex's growth lines, we can see a period of rapid growth between ages 12 and 16 (the darker brown area). 

In 2004, scientists took a (much) closer look at Elmer, using a powerful microscope to see inside the bones. They compared its growth lines to bones from SUE, the largest, most complete T. rex discovered to date. Like tree rings, these growth lines can be used to determine how old a dinosaur was when it died. Elmer lived to be just over five, while SUE lived to the ripe old age of 28.

We don’t always know how a specimen found many years ago will provide valuable information in new research—and Elmer's a perfect example of this. 

Black-and-white photo of a man wearing a hat and glasses leaning over a large bone in a quarry. The typewritten description reads, "Riggs at Lestodon Prospect. Patcaya, Bolivia."

Elmer Riggs on an expedition in Bolivia, 1927. The photo's description notes that this is a dig site for Lestodon, a group of extinct ground sloths. 

Field Museum Photo Archives

So, why did it take so long to fully uncover Elmer, between discovering it in the field and studying it here at the Field? 

One reason is that scientists might find a lot of specimens on one expedition. These trips are rare opportunities to document the natural world. Because of factors like distance and expense, we don’t always know when we’ll be able to return to a particular place. On their 1922 expedition, Riggs and his team unearthed a wealth of specimens like mammals, seeds, plants, and other dinosaurs.

Two men stand at a table covered in large bones, both seemingly unpacking bones. Two especially large leg bones are propped up in the foreground. There are shelves lining both sides of the room.

Elmer Riggs (right) and another man work to prepare fossils from Colorado, including a Brachiosaurus femur still in plaster, 1899.

Field Museum Photo Archives

Once back at the museum, fossil preparation can be very time consuming—uncovering the bones inside a large field jacket requires meticulous work. Fossil preparation is often driven by research, when a scientist has a specific question and thinks a certain fossil will help provide answers. Back in the geology lab after the 1922 trip, scientists prepared a duck-billed dinosaur from Riggs’s trip that was more complete than Elmer the tyrannosaurid.  

Even today when our scientists go out on expeditions—to Antarctica, the Utah desert, or the Vietnam rainforest—they might return with more specimens than they have time to examine right away. This is why saving specimens is perhaps just as important as finding them in the first place: they’ll be around for future scientists to uncover valuable information that we can’t imagine today.