Massachusetts holds a unique position in paleontology, renowned not for vast bone beds, but for preserving the ancient movements of creatures that roamed North America during the Mesozoic Era. Dinosaurs inhabited this region, leaving behind a remarkable record of their existence, primarily anchored in the central portion of the state where geological conditions captured a moment in time.
The Significance of Trace Fossils
The primary evidence of prehistoric life in Massachusetts comes in the form of trace fossils, also known as ichnofossils. These fossils preserve an impression of activity, such as footprints, burrows, or coprolites, contrasting with body fossils like skeletal remains. The Connecticut River Valley is home to one of the world’s most extensive collections of dinosaur trackways, which are the state’s official fossil.
These thousands of preserved tracks offer unique behavioral insights that cannot be gleaned from bones alone. The trackways reveal details about the animals’ gait, speed, and whether they traveled alone or in groups. The first scientifically described dinosaur tracks in North America were found here in 1802. Early naturalists, including Amherst College professor Edward Hitchcock, initially thought the three-toed prints belonged to giant prehistoric birds.
Identifying Massachusetts’ Ancient Dinosaurs
The creatures that created these impressions are identified by the name given to the track itself, called an ichnotaxon, since skeletal remains of the track-maker are rarely found nearby. The most famous ichnotaxon is Eubrontes, a large, three-toed print that translates to “true thunder.” These tracks were left by a bipedal, predatory theropod that likely reached 20 feet long, similar to the dinosaur Dilophosaurus.
Other common track types include Grallator, created by small theropods resembling Coelophysis, and Anchisauripus, a medium-sized theropod track. Prints from a small ornithopod called Anomoepus are also documented. Only two distinct species of dinosaur are known from actual skeletal remains found within the state’s borders.
One rare skeletal find is Anchisaurus polyzelus, an early sauropodomorph, or “prosauropod,” whose bones were discovered near Springfield. The other is Podokesaurus holyokensis, a slender, swift-footed theropod named for the area near Mount Holyoke. Podokesaurus, which grew three to six feet long, was officially named the state dinosaur in 2022 and is one of the few endemic species identified in the eastern United States.
The Mesozoic Environment of New England
The dinosaurs of Massachusetts lived during the Late Triassic and Early Jurassic periods, approximately 200 million years ago, as the supercontinent Pangea began to fracture. This continental breakup led to the formation of the Hartford Basin, a rift valley system stretching through the Connecticut River Valley.
The climate was semi-arid and subtropical, featuring large freshwater lakes and expansive mudflats. This combination of fine-grained sediments and water-saturated ground was perfect for capturing and preserving footprints. As the mud dried and was covered by subsequent sediment layers, the tracks transformed into the durable sandstone and shale seen today. The geological setting created a unique environment where the movements of these early dinosaurs were permanently recorded in stone.