Dinosaur Footprints in Connecticut
A wide variety of tracks made by dinosaurs, reptiles, insects, arthropods, and other invertebrates have been studied in the Mesozoic rocks of the Connecticut Valley, and in similar valleys to the north and south. The science of tracks and other trace fossils is "Ichnology," from a word for "footprints," and the tracks themselves are sometimes called "ichnites." Because many different dinosaur species could make very similar footprints, and no dinosaur skeletons have been found with the tracks, we cannot assign particular animal species to particular footprints. Instead, footprints have their own system of "ichno-species" names that are defined separately from any animal species. Hundreds of footprint species names have been proposed over past 150 years, but in fact, if we allow for differences from the animal's age and sex, as well as differences in mud surfaces and preservation, only five types of dinosaur tracks are actually common in Connecticut. This figure shows examples of the five types that have been described by Paul Olsen and his colleagues, who propose a "lumper" rather than a "splitter" system of names in contrast with older literature.
Three of these track types have "Grallator type" footprint names, which all look alike except for size. They are three-toed prints with the middle toe much longer, often ending with a claw mark. The smallest are only a few inches long and are called "Grallator Grallator," the middle sizes are about 5 to 10 inches long and are called "Grallator Anchisauripus," while the largest are up to 16 inches or more long and are called "Grallator Eubrontes." Eubrontes is the state fossil, and it is the track species that you see in the Exhibit Center trackway. Eubrontes is common only in Early Jurassic rocks (after about 201 million years ago) such as we have at the park, while the smaller Grallator footprints are also found in Late Triassic rocks in the valleys. Theropod dinosaurs are the carnivores that ran around with 3-toed feet on two powerful legs (later to include Tyrannosaurus Rex), and so would make these Grallator-type footprints. This old drawing shows all three tracks together in slabs of rock. A possible animal that made Grallator or Anchisauripus tracks might be Coelophysis, which is known from Late Triassic bones in Connecticut and the western USA. There is also a fine statue of Dilophosaurus at the park exhibit, which was a larger Early Jurassic theropod that made tracks like Eubrontes. It is likely that several different theropod species walked along the lakeshores to make the Grallator-type tracks, but the various sizes also might reflect individuals of the same species at different ages.
Theropods and Sauropods make up the Saurischian (reptile-hip) sub-order of dinosaurs, and a primitive "prosauropod" made the tracks called "Otozoum," which are large, with four wide toes, and made by its back feet (it walked on two legs). Later sauropods included Apatosaurus (Brontosaurus), and all of them were lumbering plant eaters. A possible animal that made Otozoum is Navahopus, also known from bones out west. Another prosauropod known from fossil bones to have lived in Connecticut was Anchisaurus, a 6-foot herbivore that usually walked on its back legs. Anchisaurus feet are too different from theropod feet to have made the tracks called Anchisauripus, which were named by mistake.
The fifth track type is called "Anomoepus," which were made by a member of the other big sub-order of dinosaurs called Ornithischians (bird-hips). Later ornithischians include Stegosaurus and Triceratops. In Early Jurassic Connecticut, it might have been Lesothosaurus or Fabrosaurus, which walked mainly on its back two legs to make small three-toed prints that are splayed out with the middle toe not much longer than the other two. In some places its five-toed front "hand" prints are also found, perhaps where it bent over to drink or eat. The animals looked a little like big featherless turkeys with arms, but despite the name of this sub-order, birds evolved from Therapods, not Ornithischians.
Other, non-dinosaur tracks are also common in the Connecticut Valley. Many were made by a variety of large and small 4-footed reptiles similar to Stegomus (an armored herbivore), Terrestrisuchus (an early long-legged crocodile), and Rutiodon (which looked like modern crocodiles). Other animals walking about included amphibians like Metoposaurus (which had teeth) and a great variety of crustaceans and insects.