Apatosaurus "Apatosaurus" may have been more solitary than other Morrison Formation dinosaurs. Fossils of the genus have only been found in the upper levels of the formation. Those of "Apatosaurus ajax" are known exclusively from the upper Brushy Basin Member, about 152–151 mya. "A.louisae" fossils are rare, known only from one site in the upper Brushy Basin Member; they date to the late Kimmeridgian stage, about 151mya. Additional "Apatosaurus" remains are known from similarly aged or slightly younger rocks, but they have not been identified as any particular species, and thus may instead belong to "Brontosaurus". The Morrison Formation records a
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