Diplodocus now common scientific opinion that "Seismosaurus hallorum" is a species of "Diplodocus". This genus of dinosaurs lived in what is now mid-western North America at the end of the Jurassic period. "Diplodocus" is one of the more common dinosaur fossils found in the middle to upper Morrison Formation, between about 154 and 152 million years ago, during the late Kimmeridgian age. The Morrison Formation records an environment and time dominated by gigantic sauropod dinosaurs, such as "Apatosaurus", "Barosaurus", "Brachiosaurus", "Brontosaurus", and "Camarasaurus". "Diplodocus" is among the most easily identifiable dinosaurs, with its typical sauropod shape, long neck and tail, and
Dinosaur State Park and Arboretum a new state office building. The site opened as Dinosaur State Park in 1968, the same year its dinosaur trackway was memorialized as a Registered National Landmark. The park's geodesic dome (see picture at right) encloses some 500 tracks while another 1,500 remain buried for preservation. The tracks are from the early Jurassic period and were made over 200 million years ago on what must have been a sandy shore of a lake, by a carnivorous dinosaur similar to "Dilophosaurus". The tracks bear the name "Eubrontes", the term for fossilized footprints invented by geologist Edward Hitchcock. The tracks range from