Connecticut holds a unique position in North American paleontology, primarily due to an abundance of fossilized footprints from the Mesozoic Era. This ancient record documents the presence of dinosaurs that walked the region during the Late Triassic and Early Jurassic periods, roughly 200 million years ago. While skeletal remains of dinosaurs are infrequent in the state, the fossilized tracks offer a detailed glimpse into the types of creatures that inhabited the landscape. The Connecticut River Valley, in particular, is an internationally recognized site that has provided scientists with a long-running, continuous record of early dinosaur life.
Connecticut’s Unique Geologic History and Trace Fossils
The formation of the Connecticut River Valley Rift Basin provided the geologic conditions necessary for this exceptional fossil record. This valley began to form during the break-up of the supercontinent Pangaea, as North America started to pull away from Africa. As the land stretched, deep rift valleys formed and filled with sediment and water, creating a system of large, shallow lakes and floodplains.
The sediment deposited in these ancient lake beds, specifically the sandstones and siltstones of the Portland Formation, proved ideal for preserving the impressions left by passing animals. When a dinosaur stepped onto the soft, wet mud of the lakeshore, the impression was quickly buried and protected by subsequent layers of fine-grained sediment. This process of rapid burial prevented the tracks from being eroded away, allowing them to harden into rock over millions of years.
The study of these fossilized tracks and trails is a specialized field known as ichnology. Ichnologists distinguish these trace fossils, or ichnofossils, from body fossils (preserved skeletal remains). The fossil evidence in Connecticut is overwhelmingly composed of trace fossils, meaning scientists know the behaviors and general forms of the creatures more than their specific anatomy.
The resulting rock layers contain thousands of trackways that capture moments in time from the Early Jurassic ecosystem. The Connecticut Valley is recognized as a cradle of North American ichnology, offering profound insights into the behavior and movement of its prehistoric inhabitants.
Identifying the Valley’s Prehistoric Inhabitants
Because most evidence comes from footprints, scientists assign specialized names, called ichnogenera, to the track types rather than the skeletal species of the trackmaker. The most common and famous track found in Connecticut is Eubrontes, a large, three-toed print that can measure up to 18 inches long. These tracks were left by a large, bipedal theropod dinosaur, likely similar in size and form to Dilophosaurus, a predator that walked the Earth approximately 200 million years ago.
Another abundant track type is Grallator, which is significantly smaller, typically measuring between two and six inches in length. These bird-like tracks were made by small, slender, bipedal theropods, which may have resembled creatures like Coelophysis. The presence of these two track types, Eubrontes and Grallator, shows that the Connecticut Valley was populated by both large and small carnivorous dinosaurs.
A rare but important exception to the track-only record is the discovery of the body fossil Anchisaurus polyzelus. Found in a quarry in Manchester, Connecticut, this partial skeleton represents a prosauropod, a long-necked, plant-eating dinosaur that was an ancestor to the giant sauropods of the later Jurassic period. Anchisaurus measured around 6 to 10 feet long and is one of the few examples of a skeletal remain found in the region.
The Anchisaurus find, along with less common ichnogenera like Anchisauripus and Otozoum, helps paint a more complete picture of the valley’s diversity. Anchisauripus tracks were left by medium-sized theropods, suggesting a range of predator sizes were present. Otozoum is a rare, large, four-toed track that likely belonged to a massive, slow-moving herbivore.
Notable Discovery Sites and Fossil Preservation
The most concentrated and accessible site for viewing these ancient trackways is Dinosaur State Park in Rocky Hill, Connecticut. The site was discovered unexpectedly in 1966 when a bulldozer operator uncovered a massive slab of sandstone during excavation for a new state building. This revealed one of the largest continuous dinosaur track sites in North America, containing an estimated 1,800 or more tracks.
Today, the park’s geodesic dome structure protects and displays approximately 500 of the original Eubrontes tracks. Preserved in the original rock layer of the East Berlin Formation, they provide visitors with a direct view of the prehistoric lake bed. The remaining trackways were carefully documented and then reburied beneath protective layers of soil and sediment.
The reburial was a deliberate preservation strategy to protect the majority of the tracks from the damaging effects of weather and human activity. This method ensures that a significant portion of the trackway remains intact for future study. Beyond Rocky Hill, the historical importance of the region is linked to 19th-century finds in the Portland brownstone quarries, which yielded many of the first tracks studied in America.
The Manchester quarry that produced the Anchisaurus skeletal remains has since been filled in, but the specimens are preserved in museum collections like the Peabody Museum of Natural History at Yale. These scattered sites, from the major public park to the historical quarry locations, affirm Connecticut’s lasting contribution to the understanding of early dinosaur life.