The most significant paleological discovery to hit Maryland in 100 years – the uncovering of a historic “bone bed” – was announced earlier this month.

But getting to the bottom of the fossil collection and documenting it all took researchers about 10 years.

Discovering the Fossils

In 2013, an employee at Dinosaur Park – a small fossil preserve in Laurel, Maryland – first spotted something blue-green buried in the ground. The former riverbed and mining site had a long history of fossil finds, which tended to reveal themselves with such an aquamarine glimmer. Park staff looked over the spot and decided to leave the bone encased in ironstone and use it for educational purposes.

In 2014, a chance encounter between the same stone and “a piece of heavy landscaping machinery,” TheBaltimore Sun writes, exposed more of the fossil. The collision came as a shock, but scientists at the park decided to let nature erode the ironstone further.

Bone Bed

The staff later changed their minds and began to excavate the area in 2021 and found many more fossils that dated to about 115 million years ago. The researchers first came across a 4-foot limb bone, which remains unidentified, and slowly uncovered more as they kept digging.

At the small, 3.63-acre site, paleontologist J.P. Hodnett and others uncovered a 3-foot-long shin bone belonging to a large theropod, the same group of dinosaurs as Tyrannosaurus rex. But these bones predate T. rex and likely belonged to an Acrocanthosaurus, the largest theropod in the Early Cretaceous period. That made the bone the largest theropod fossil ever found in eastern North America.

As the team dug, it found more and more bones, something unfitting for the eastern half of the country. Large assemblages or “bone beds” are more common in the western U.S., where paleontologists find more exposed stone.

The Lesser-Known Half

In the eastern U.S., “We’ve got light industrial parks or shopping malls or houses or whatever. So we don’t have those rocks exposed,” paleontologist Thomas Holtz told The Baltimore Sun. “And because of that, our knowledge of the dinosaurs from the eastern part of North America has been lacking compared to what we know about in the west. But this site is helping to change that.”

Other fossils recovered from the Maryland bone bed include the bones of a Priconodon, a large, armored dinosaur, and the anatomy belonging to an Ornithomimid, an ostrich-like creature. The scientists also found teeth belonging to a T. rex predecessor and a crocodile, not to mention a bone that had once belonged to a tiny, chicken sized, meat-eating dinosaur called a Coelurosaur. Along the way, the researchers unearthed the oldest-yet stingray fossil from North American and some fossilized dinosaur feces.

“The dinosaur site at Laurel is by far the most important dinosaur dig site in America east of the Mississippi,” said Holtz, the first to confirm the Acrocanthosaurus find, in a statement. “It is historically significant, as it was one of the first dinosaur fossil sites found in the U.S. More importantly, it gives us insights into the diversity of animals and plants at a critical period in earth’s history.”

Read More: 5 Massive Dinosaur Fossils and Where They Were Found