Two dinosaur teeth were received in late November 1858 by chemist Philip Thomas Tyson from John D. Latchford. They had been found in Latchford's open iron ore pit in the Arundel Formation at Swampoodle near Muirkirk in Prince George's County, Maryland. Tyson let them be studied by the dentist Christopher Johnston, professor at the Baltimore Dental College, who cut one tooth in half and thereby discovered a characteristic star-formed cross-section. Johnston named Astrodon in 1859. However, he did not attach a specific epithet, so Joseph Leidy is credited with naming Astrodon johnstoni (the type species) in 1865, with as holotype specimen YPM 798. If Johnston had attached a specific epithet, it would have been the second dinosaur species identified in the United States. Johnston incorrectly