Paleontologists and volunteers at Maryland’s Dinosaur Park discovered a “bone bed” with rare dinosaur fossils earlier this year, including the largest theropod fossil in eastern North America, officials announced this week. 

It was the first bone bed found in Maryland since 1887, Prince George’s County Parks and Recreation said in a news release. Paleontologists use the term “bone bed” when bones of one or more species are found concentrated in a single geologic layer, the department explained.

Dinosaur fossils “are exceptionally rare” in the eastern United States, said Matthew Carrano, a paleontologist with the Smithsonian, in a statement. 

This discovery was made during a dig experience — where members of the public are able to assist Dinosaur Park staff and “be paleontologists for a day,” as the park’s online description reads — that took place on April 22. 

JP Hodnett, a paleontologist at Dinosaur Park, initially found and helped identify a large theropod fossil during the dig. Hodnett classified the fossil, a 3-foot-long shin bone, as a theropod, which is a branch of dinosaur species that includes carnivores like the Tyrannosaurus rex, parks and recreation officials said. 

He hypothesized that the fossil belonged to an Acrocanthosaurus, the largest theropod in the Early Cretaceous period, that measured an estimated 38 feet long. The Early Cretaceous period stretched from 145 million to 100 million years ago, consistent with fossils typically found at Dinosaur Park. Paleontologists have found Acrocanthosaurus teeth at the park in the past.

“Finding a bonebed like this is a dream for many paleontologists as they can offer a wealth of information on the ancient environments that preserved the fossils and provide more details on the extinct animals that previously may have only been known from a handful of specimens,” said Hodnett in a statement.

In a separate statement, University of Maryland paleontologist Thomas Holtz, who first verified the theropod discovery, added that the dinosaur dig site is “historically significant” because “it gives us insights into the diversity of animals and plants at a critical period in Earth’s history.”

Among the fossils found in the bone bed at Dinosaur Park was a 4-foot limb bone encased in ironstone. Experts say it belonged to a large dinosaur, although its specific identity is still unknown. Other bones found included parts of a large armored dinosaur called a Priconodon; a long-necked plant-eating dinosaur called a Suropod, which measured an estimated 60 to 70 feet long; a small tyrannosaur tooth; and the oldest stingray fossil ever found in North America.

Once the fossils are excavated from the dig site, they will be cleaned, examined and catalogued in the museum system run by Prince George’s County Parks and Recreation.