Various types of dinosaurs have lived in Virginia since that form of life evolved 230 million years ago, when Virginia was in the center of Pangea. Dinosaurs first appeared in what is now South America, but there were ocean barriers and they migrated by land into Virginia.1
Dinosaur herds walked across the muddy shorelines on the edges of lakes in Triassic Period basins as the Atlantic Ocean opened up. A lake, sometimes as much as 60 miles long and 10 miles wide, existed for 30 million years east of the Blue Ridge in Northern Virginia. Other basins near Richmond and Danville were also home to dinosaurs, based on discover of tracks in the sediments.
At the time, the day was only 23 hours long. Since then, the moon has moved further away and the earth spins more slowly. Several hundred feet of sediments have eroded off the Blue Ridge over the last 215 million years, and were deposited in the Triassic basins. Typically the tracks of dinosaurs disappeared quickly as storms or wind moved sediments around, and 50-70 million years of sediments deposited in the Middle Jurassic-Early Cretaceous have also eroded away with whatever evidence they once contained of dinosaurs, ferns, cycads, and the earliest flowering plants. Geologic formations in the western United States and China show that giant sauropods lived in that time period.2
Occasionally, the ancient dinosaur trackways were preserved and expose later by quarry excavations. In Cretaceous clays formed 110 million years ago, dinosaur fossils have been excavated from iron mining pits in "Dinosaur Alley" between Washington and Baltimore. Species identified from those pits include Pleurocoelus nanus, Pleurocoelus altus, Priconodon crassus, Allosaurus medius, and Coelurus gracilis. In the District of Columbia, the thighbone of a 10-ton Astrodon (which could reach foliage as high as 33 feet) was excavated from the McMillan water treatment plant. Fossil remains of the Rutiodon phytosaur were found near Dulles Airport and at Solite Quarry near Danville.3
The tracks remain deeply buried in most cases, but occasionally are exposed. Dinosaur State Park in Connecticut has an extraordinary display of Eubrontes tracks, exposed when the state highway department was constructing a building and preserved because a bulldozer operator quickly recognized that he was about to destroy a rare resource.
ichnofossils (traces of dinosaurs) were formed 200+ million years ago when dinosaurs stepped on mud
| In 1920, efforts to enhance the landscaping at Oak Hill (President Monroe's
former home in Loudoun County) involved building new walkways. The nearby
quarry to acquire the sandstone slabs revealed dinosaur footprints, which
are highlighted today in the sidewalks, patios, and floors at Oak Hill.
The Grallator and Eubrontes tracks are distinctive three-toed
footprints, but not associated with specific fossils; the exact dinosaur
species that made the tracks is still a mystery.
Dinosaur tracks have been found in the Richmond, Danville, and Culpeper basins. The most impressive set of fossil footprints discovered so far in Virginia come from the Culpeper Stone Company quarry (now owned by Luck Stone) in Stevensville, near Culpeper. The quarry workers who initially discovered the tracks were not paleontologists, but realized the depressions in the bedrock were significant. As one said:4
Over 4,800 footprints of dinosaurs and other species were preserved on two levels. On a low level of the quarry are 2,300 Kayentapus footprints aligned into twenty trackways. These were made by dinosaurs 10-13 feet long that moved at nearly 20 miles per hour. Kayentapus was a theropod carnivore, probably hunting ornithischians (dinosaurs with bird-like hips) while avoiding other predators that would eat a Kayentapus.5
Analysis of 830 separate footprints at a higher level has revealed 32 separate trackways with six distinctive patterns. The different species thought to have made those tracks are Gregaripus bairdi, Agrestipus hottoni, Apatichnus minor, Anchisauripus parallelus, plus trackmakers Eubrontes and the smaller Grallator. Gregaripus bairdi and Agrestipus hottoni are thought to have been herbivores, while the other four were carnivores.
The tracks were all made within a few days of each other, and the Gregaripus was running at nearly seven miles/hour. Random chance may have favored the retention of more footprints from carnivores, or perhaps they had gathered in large numbers in anticipation of the herbivores migrating though the area.6
dinosaur track from near Aldie
Source: Virginia Geological Survey, The Geology of the Virginia Triassic (Plate 31)
At the Solite Quarry on the Virginia-North Carolina border near Danville, Atreipus footprints are associated with a particular 10-million year period in the Late Triassic. Near Manassas, Apatopus, Brachuchirotherium, Chirotherium, and Grallator tracks have been documented.7