Discover Washington D.C and Explore the Geodiversity and Fossils of Anacostia Park
- Wayne Munday
- Apr 8
- 4 min read
Sip back and discover Washington D.C and explore the geodiversity and fossils of the National Capital Parks-East established in 1933 including Anacostia Park, Fort Circle Parks, and Kenilworth Aquatic Gardens. Its hard to believe that only a short distance from the busy, energetic, and often lively atmosphere of the United States capitol dinosaurs including the giant Astrodon johnstoni once roamed and are preserved in the highly fossiliferous Arundel Formation dating back to the Cretaceous Period. During the Mesozoic Era this area of the National Capital Parks-East was a tropical lowland adjacent to a shallow warm sea. This is also an area of historical significance where the landscape has been shaped by human activity over the past 10,000 years especially along the Potomac River valley. This was a land inhabited by the Native American tribes of the Algonquin and Piscataway peoples.
From the Late Triassic between 237 - 201 million years ago up until the Late Cretaceous from 100.5 - 66 million years ago at least 12 dinosaur species have been found in the local fossil record. Periodic volcanic activity and heavy sedimentation from the western highlands contributed to rapid burial of animal and plant remains. These conditions protected organic material from scavengers and erosion allowing the process of fossil preservation over time.
Both the District of Columbia and the State of Maryland lack exposed Jurassic Period rocks and fossils primarily because he eastern part of North America was generally eroding rather than being a place of deposition and would later transition to a marine environment during the Cretaceous Period covering the land with deep marine sediments.
Fossils within National Capital Parks–East are primarily found in the Arundel Clay of the Lower Cretaceous Potomac Formation. Beyond the park boundaries, additional fossiliferous rock formations include the Severn and Mt. Laurel Formations from the Upper Cretaceous. To the northwest in the Frederick Valley the Upper Triassic Gettysburg Shale is also rich in fossils.
The Arundel Formation dates to the Lower Cretaceous Epoch spanning roughly from between 121.4 - 113.0 million years ago and is one of the most significant fossiliferous rock layers in the eastern United States. It has yielded an important assemblage of dinosaur and vertebrate fossils.
The dinosaur discoveries from the Arundel Formation include several theropods, sauropods, and ornithopods. Notable theropods include Acrocanthosaurus a large carnivorous dinosaur as well as the Allosaurus medius, Creosaurus potens, Coelurus gracilis and the a smaller Deinonychus. Ornithopod remains include Tenontosaurus a medium-sized herbivore and sauropods include represented by Astrodon johnstoni.
In 1858 Philip Thomas Tyson (1799-1877) an American chemist and geologist discovered the fossilised teeth in the Arundel Clay at an iron mine near Muirkirk in Prince George’s County, Maryland. This was the first discovery of large dinosaur fossils in Maryland and the species was named by Dr. Joseph Leidy as Astrodon johnstoni.
Not only was this the first sauropod dinosaur described in North America it would also later become designated as the Maryland State Dinosaur in 1998. This discovery earned the Arundel Clay region between Washington and Baltimore the nickname “dinosaur alley” where numerous fossils have been recovered and are on display in several museums including the Smithsonian Institution.
The Astrodon was a herbivorous sauropod that weighed up to 20 tons and over 18 meters in length lived in Maryland during the Early Cretaceous period, from 95 - 130 million years ago. The original fossil site at J.D. Latchford’s historic property is today preserved as a dinosaur park that ensures the ongoing protection of this valuable fossil site.
In addition to dinosaur fossils the Arundel Formation preserves a diverse fossil assemblage of fragments from other vertebrates including Crocodyliforms such as Goniopholis and Bernissartia. Turtles including species of Glyptops along with lungfish and freshwater sharks are represented as well as gar and other bony fishes.
Other fossils collected by Suitland Parkway National Capital Parks have included bones from Ostrea sinuosa (above left) a species of oyster scientifically classified as Talochlamys pusio; The teeth of Isurus hastalis (above centre) an extinct species of Mako shark and bones from a Cetotheridae Sp (meaning "whale beast") an extinct genus of baleen whale.
The geology of the National Capital Parks–East region has profoundly influenced historical settlement, transportation routes and military strategy. During the American Civil War between April 1861 – May 26 1865 the area's ridges, hills and river crossings provided natural defensive advantages for the building of the Fort Circle Parks a series of earthen forts including Fort Dupont, Fort Foote, Fort Stanton and Fort Mahan used to defend Washington, D.C. One of the best ways to discover the Fort Circles Parks is to experience the 12.7Km Fort Circle Park National Recreation Trail that connects historic forts built to defend the nation's capital during the Civil War.