Fossils from animals including dinosaurs and stingrays more than 100 million years old were uncovered in a Maryland park in what experts said could be the widest-ranging discovery of fossils of different species on the East Coast.

In April, a group of paleontologists and volunteers with the Department of Parks and Recreation in Prince George’s County, Md., found and classified a 3-foot-long shin bone as one from a theropod, a branch of the dinosaur family that includes carnivorous dinosaurs such as Tyrannosaurus rex.

“A meat-eating dinosaur of this size has never been found on the East Coast of the United States,” said JP Hodnett, a paleontologist with the Maryland-National Capital Park and Planning Commission.

“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,” he added.

“Bonebed” is a term paleontologists use to describe the discovery of bones of one or more species concentrated within a geologic layer. This was the first dinosaur bonebed discovered in Maryland since 1887.

Researchers linked the shin bone to Acrocanthosaurus, the largest theropod in the Early Cretaceous period that was estimated to be about 38 feet long, Mr. Hodnett said.

The discovery, which was announced this week, happened at Dinosaur Park, in South Laurel, Md., about 25 miles southwest of Baltimore. The bonebed was uncovered during a dig experience program, in which members of the public look for fossils.

Bonebeds are uncommon on the East Coast, said Advait Jukar, a paleontology expert at the University of Arizona, as fossil discoveries have been mostly isolated finds, such as claws or teeth.

“I would say that in the history of dinosaur paleontology, this might be one of the most important findings on the East Coast,” Dr. Jukar said. “We’ve never seen a site like this before.”

Excavations where many species are found are more typical in the West, as the Rocky Mountains continue to grow, causing erosion to uplift dirt and layers of rock and expose fossils, Dr. Jukar said. Drier conditions there also help to preserve them, he said.

Fossils have been found in Dinosaur Park in Maryland since the mid-1800s, when the site was an iron mine. This latest excavation, however, dates to 2014.

Park staff members discovered a large rock, where some of the rock face was broken off and appeared to have a fossil embedded in it. The rock, 5 feet by 3 feet of iron stone, was a difficult sedimentary rock to work with, so staff members decided to let it erode naturally.

By 2018, they determined that it was ready for excavation, but the coronavirus pandemic delayed the project until 2021.

The neck bones of a dinosaur were the first significant finding from the rock. In the years that followed, other parts were found, including turtle skeletal parts, other isolated dinosaur bones and some teeth of dinosaurs and crocodiles.

Among the discoveries were fossils of a Priconodon, a large, armored dinosaur; an Ornithomimoid, an ostrichlike dinosaur; and a Deinonychus, a predatory birdlike dinosaur. Researchers also found the remains of the oldest stingray in North America, Mr. Hodnett said.

The findings will better inform paleontologists about what the ecosystem of that area in Maryland was like during the Cretaceous period, said Adiel Klompmaker, the curator of paleontology at the Alabama Museum of Natural History. The variety of different species found can help paleontologists understand the climate and food chain from millions of years ago, he said.

“It’s a whole host of animals that gives a new window into what the United States might have looked like 115 million years ago,” Dr. Klompmaker said.


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