Astrodon johnstoni was a member of the group of long-necked dinosaurs
called sauropods. A plant-eater, Astrodon was related to better-known
giants like Brachiosaurus, which lived about 40 million years earlier.
In May 1998, Astrodon was named the official state dinosaur of Maryland.
Astrodon was the first scientifically described North American sauropod, and the second North American dinosaur to be described by a matter of days (the first was Hadrosaurus, discovered in New Jersey). In 1859, geologist Phillip Tyson brought some fossil teeth he had found in Prince George's County to the Maryland Academy of Sciences.
Academy member (and dentist) Christopher Johnson recognized the teeth as
similar to those of the dinosaurs that had recently been discovered in
Europe. Johnson named the animal Astrodon, meaning star tooth, because
the teeth have a star-like shape in cross section.
19th century, many more sauropod fossils have been found in Maryland,
including a 6-foot long, 220 to pound femur (thigh bone) that was
uncovered in the 1990s. Unfortunately, since the name Astrodon was
defined using only teeth, scientists cannot conclusively say that more
recently discovered bones belonged to the same species, although they
were certainly close relatives.