Deborah Painter (USA)
Dinosaur fossils in the US are primarily related to the Mesozoic period age sedimentary rocks of the western states of Montana, Wyoming, Colorado, Arizona and New Mexico. East of the Mississippi River, their fossils are scarcer, though they undoubtedly exist. There may be Mesozoic age surficial bedrock in many east coast states. However, other than the occasional find in Maryland, North Carolina, Alabama and New Jersey, and trackways in Connecticut and in Virginia, dinosaur and other vertebrate land dwellers are not commonly found.
April of 2023 was the month that Maryland became known as a better source for fossil dinosaurs. The Dinosaur Park’s fossil rich deposits are now classified as a bonebed, according to Prince George’s County Department of Parks and Recreation in a 12 July 2023 press conference at the Park (Fig. 1). The first Acrocanthosaurus fossil to be found in Maryland since 1887, was unearthed by J P Hodnett, the Palaeontologists and Program Coordinator for the Maryland-National Capital Park and Planning Commission’s Department of Parks and Recreation.
Hodnett stated to the press:
Most palaeontologists have to travel across the country or go overseas to find something like this, so having this rare find so close to home is fantastic!”
Hodnett classified the 0.91m long shin bone as a theropod (“beast footed”) carnivorous dinosaur related to Tyrannosaurus rex. His initial hypothesis of this fossil is that it is an Acrocanthosaurus, the largest theropod in the Early (Lower) Cretaceous period of 115 million years BCE. The animal was estimated to measure about 11.5m long.
Acrocanthosaurus teeth have been previously collected from the small (16.5) hectare Dinosaur Park, which is a combination recreational and palaeontological site located in a Laurel business park. The sediments are of the Cretaceous Potomac Group – a sand, clay and silt group consisting of many Formations, including the Arundel, Patuxent, and Raritan in Maryland and Delaware and the Potomac and Patapsco Formation in Virginia and Washington, DC. It is the basal geologic unit underlying younger Cenozoic era formations in the Atlantic Coastal Plain in New Jersey, Delaware, Maryland and Virginia.
In some formations, as at Laurel, the Arundel clays are rich in iron. It was while prospecting for this economically important clay in the Laurel area in 1859 that geologist, Phillip Tyson’s slaves discovered sauropod dinosaur teeth. They were scientifically described by palaeontologist Joseph Leidy in 1865.
In 2009, Prince George’s County acquired this property and named it Dinosaur Park. Matthew Carrano, a palaeontologist with the Smithsonian Institution, said of the new discovery:
Typically, only one or two bones are found at a time, so this new discovery of a bonebed of fossils is extremely important. It is certainly the most significant collection of dinosaur bones discovered along the eastern seaboard in the last hundred years.”
Peter A Shapiro, Chairman of The Maryland-National Capital Park and Planning Commission said:
This discovery marks an extraordinary milestone in the field of palaeontology and opens a window into the ancient world and species that once roamed this land millions of years ago. We are proud of our dedicated team of experts at the Department of Parks and Recreation, Prince George’s County and their ongoing efforts in preserving and studying our natural heritage.” (Fig. 2)
The fossils will be catalogued in the Department of Parks and Recreation’s museum system.
University of Maryland palaeontologist, Thomas Holtz, the first to verify the discovery, commented:
“The dinosaur site at Laurel is by far the most important dinosaur dig site in America, east of the Mississippi. It is historically significant, as it was one of the first dinosaur fossil sites found in the US. More importantly, it gives us insights into the diversity of animals and plants at a critical period in Earth’s history.”
He stated that the site had been a wetland and stream, with diverse gymnosperms like cypresses. Contributing to the clearer understanding of this diversity are the plant and animal fossils found from 2018 to 2023, including:
- the Acrocanthosaurus fossil (Fig. 3);
- the teeth, osteoderms and vertebra of Priconodon, a large, armored dinosaur;
- a vertebra from a sauropod, possibly Astrodon;
- an ankle bone, claw and vertebra of an ornithomimid, an ostrich like dinosaur;
- the tooth of a Deinonychus, a cousin of the velociraptors;
- the tooth of a small tyrannosaur, possibly the oldest member of that group in Eastern North America;
- the thigh bone of a coelurosaur, a meat eater the size of a domestic hen chicken;
- a crocodile tooth;
- the tail barb of the oldest known North American fossil stingray;
- a carbonized seed cone cluster and carbonized conifer log segments;
- a freshwater clam; and
- various coprolites.
Acrocanthosaurus appeared in the fossil record millions of years before the large tyrannosaurs and was somewhat more gracile (Fig. 4).
According to the late vertebrate palaeontologist, John H Ostrom, the high humidity of the present day eastern United States and the resultant high rates of weathering and erosion, destroy many fossil vertebrates in situ.
The National Park Service adds that the location of the rocks of the East Coast in Mesozoic time was also a factor. Eastern dinosaurs inhabited the rift valleys of the Late Triassic and Early Jurassic, and during the entirety of the Cretaceous, they roamed coastal areas of the new South Atlantic Ocean. As it was an opening ocean, the shorelines experienced more erosion and weathering than today. The modern Atlantic shoreline features mainly depositional coasts. Gymnosperm (conifer) fossils are the most common terrestrial fossils to be found in Triassic, Jurassic and Cretaceous age strata of the Eastern United States.
It is likely that the actual populations and the species richness are far greater than the fossil record suggests, and discoveries, such as the new Acrocanthosaurus at Dinosaur Park, only hint at more fossil finds that await.
The park is located at 13100 Mid-Atlantic Boulevard, Laurel, Maryland and has been a popular field trip destination for school groups for many years. Younger children can play on the dinosaur bone themed playground. Twice a month, on every first and third Saturday, the public assists palaeontologists in exploring the clays for fossils. For more information, call 301-627-1286 or email dinosaurpark@pgparks.com.
About the author
Deborah Painter is an ecologist and general environmental scientist. She lives in the United States.
References
Domingo, Ida, and Brad Bell. July 12, 2023. 8:27 AM EDT First-of-its-kind dinosaur bones discovered at Laurel, Maryland park. WJLA 13 News: https://wjla.com/news/local/rare-dinosaur-bone-bed-discovered-laurel-maryland-park-prince-georges-county-m-ncppc-1887-major-milestone-paleontological-research-photos-unveiling-paleontologists-species-geologic-layer?fbclid=IwAR2DI4jM4mp2m-sdP2GQ1KRboYyvM7jxt_jntr3C4t2uWb3_Ta8gvYi5Z_E.
Kramer, Jon, Julie Martinez and Vernon Morris. 2016. Dinosaur Destinations: Finding America’s Best Dinosaur Dig Sites, Museums and Exhibits. Adventure Publications. 200 pages.
Munoz, Jennifer, Latino Media Engagement Specialist, Public Affairs and Community Engagement Division Maryland-National Capital Park and Planning Commission, Department of Parks and Recreation, Prince George’s County. Personal communication.
National Park Service. Where Dinosaurs Roamed. Accessed July 19, 2023: https://www.nps.gov/subjects/fossils/where-dinosaurs-roamed-the-u-s.htm#:~:text=Dinosaurs%20are%20rare%20in%20the%20eastern%20half%20of,of%20the%20much%20higher%20seas%20of%20the%20Cretaceous.
Ostrom, John H. Personal communication.
Prince George’s County Department of Parks and Recreation. July 12, 2023. Rare Dinosaur Fossils Discovered at M-NCPPC, Department of Parks and Recreation, Prince George’s County Dinosaur Park: https://www.pgparks.com/rare-dinosaur-fossils-discovered-at-m-ncppc-department-of-parks-and-recreation-prince-georges-county-dinosaur-park.
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