Dinosaur Trackway: Some 2,000 Footprints a Bulldozer Found in Connecticut

On August 23, 1966, bulldozer operator Edward McCarthy was digging the foundation for a planned Connecticut State Highway Department laboratory in Rocky Hill when he uncovered dinosaur footprints. Within weeks the site was protected; it became Dinosaur State Park on September 13, 1966, and a National Natural Landmark in April 1968. The area turned out to hold more than 2,000 tracks, left by dinosaurs walking — and probably fishing — around a shallow lake about 200 million years ago.

The plaque marking Dinosaur Trackway's 1968 designation as a National Natural Landmark. Credit: Deborah DiQuinzio, National Park Service.

Dinosaurs in New England

American dinosaurs are famous from the remote West, but some of the first dinosaur fossils reported in the United States were footprints found in New England — discovered before the idea of "dinosaurs" existed, and so interpreted as the tracks of birds. That wasn't far off: the small and medium-sized meat-eaters that made them were early relatives of birds.

Mesozoic rocks are rare in much of the eastern and central U.S., but the Connecticut River Valley is an exception. From the Late Triassic into the Early Jurassic, between 230 and 190 million years ago, as the supercontinent Pangaea broke apart and North America separated from Africa, long, narrow, deep rift valleys opened parallel to the future Atlantic. New England lay farther south, in the tropics. The basins filled at different times with lava, lakes or rivers. Few dinosaur bones survive there, but thousands of footprints do — named as track types, since the animals are mostly known only from their tracks:

Reading the rock

The tracks lie in gray sandstones, siltstones and mudstones of the East Berlin Formation, laid down near the end of a lake cycle. Mud cracks and raindrop impressions show some surfaces were exposed to air; ripple marks and cross-bedding show others were under water. Lava-flow basalts about 140 feet (42 meters) above the track layers date them to about 200 million years ago, just after the Jurassic began. Rifting has since tilted the beds to the south.

• Two layers. Most footprints are on two layers about an inch (2 to 3 cm) apart; most on the lower layer are underprints, pressed down beneath the actual footprint.
• A short moment. The main track level may record only a day or so — or a month or more, if some tracks really are swimming traces, which would require water rising fast.
• Walking, not swimming. Some tracks were first read as swimming traces, but comparison with modern birds suggests the animals were just walking on firmer ground such as drying mud.
• No common direction. Unlike some track sites, these trackways show no preferred direction; Eubrontes strides measured about 3.5 to 4.5 feet (1.1 to 1.4 meters).

Protecting the tracks

The first area uncovered held about 1,500 footprints; a smaller area just west held about 700 more. The larger area stayed exposed until 1976 and has been reburied since to protect it from weathering; a cover building has always been planned, but not funded. The smaller area sat under a temporary inflatable structure for several years and, since 1978, under a distinctive geodesic dome. Inside the exhibit center, visitors can see more than 750 tracks surrounded by artwork of the ancient landscape, along with other fossils from the Connecticut River Valley. Scientists now use photogrammetry to build 3D models of the tracks, which can be printed for study and teaching. Outside, an arboretum grows plants comparable or related to those of the Mesozoic.

Dinosaur State Park and Arboretum is run by the Connecticut Department of Energy and Environmental Protection and draws tens of thousands of visitors a year. The National Natural Landmark Program, administered by the National Park Service, recognizes and supports voluntary conservation of outstanding biological and geological sites; many landmarks were designated for their fossils, spanning from marine life 510 million years ago to mammals 40,000 years ago.

Sources

Based on "Paleontology of Dinosaur Trackway National Natural Landmark," by Justin Tweet, NPS Paleontology Program, Park Paleontology News, Vol. 16, No. 1, Spring 2024, National Park Service; a work of the United States government in the public domain.