Astrodon (astro: star, don: tooth) was a genus of large herbivorous sauropoddinosaur, related to Brachiosaurus, that lived in what is now the eastern United States during the Early Cretaceous period. Its fossils have been found in the Arundel Formation, which has been dated through palynomorphs to the Aptian-Albian boundary, about 112 million years ago.Adults are estimated to have been more than 9 m (30 ft) high and 15 to 18 m (50 to 60 ft) long.Two teeth were found in the Arundel Formation near Bladensburg, Maryland and named Astrodonin 1859 by Christopher Johnston. However, Johnston did not attach a specific epithet, soJoseph Leidy is credited with naming Astrodon johnstoni (the type species) in 1865. If Johnston had attached a scientific epithet, it would have been the second dinosaur identified in the United States.
In 1888, O.C. Marsh named some bones from the Arundel found near Muirkirk, MarylandPleurocoelus nanus and P. altus. However, in 1921 Charles W. Gilmore argued that they both represent the same species as Astrodon johnsoniand that the name Astrodon therefore had priority, a position that Carpenter and Tidwell (2005) accepted in the first in-depth description of this dinosaur. Interestingly, the majority of the bones ofAstrodon are of juveniles, and Carpenter and Tidwell considered the two species named by Marsh, P. nanus and P. altus, as different growth stages of Astrodon johnsoni.In 1998, Astrodon johnstoni was named the state dinosaur of Maryland. Astrodon also appears in the novel Raptor Red by Robert T. Bakker, as prey of Utahraptor.