Astrodon (AS-troh-don; “star tooth”) is a genus of titanosauriform sauropod dinosaur that lived during the Early Cretaceous period, approximately 112 million years ago, in what is now eastern North America. The name comes from the Greek words “astron” (star) and “odon” (tooth), referring to the star-like pattern visible on the tops of its teeth when worn. Astrodon was first described in 1865 by American paleontologist Joseph Leidy based on two teeth discovered in the Arundel Clay Formation of Maryland in 1859. It holds the distinction of being one of the first sauropod dinosaurs discovered and named in North America.

Description and Classification

Astrodon was a large, four-legged herbivore with a classic sauropod body plan: a massive body, a long neck and tail, and strong, pillar-like legs. While complete skeletons are unknown, estimates based on fragmentary remains suggest Astrodon could reach lengths of 15 to 18 meters (50 to 60 feet) and weigh upwards of 10 to 20 metric tons (11 to 22 short tons), making it one of the largest animals in its ecosystem.

Astrodon belongs to the infraorder Sauropoda, the group containing the largest land animals ever to have lived. More specifically, it is classified as a member of the Titanosauriformes, a diverse group of sauropods that includes dinosaurs like Brachiosaurus and the later titanosaurs. Its exact placement within Titanosauriformes has been subject to debate, with some researchers considering it a brachiosaurid or a close relative. The genus Pleurocoelus, also named from remains found in the Arundel Formation, is often considered by paleontologists to be the same animal as Astrodon, or at least a very closely related sauropod.

Distinguishing Features

Astrodon, and the material often referred to it, can be identified by several features common to titanosauriform sauropods, as well as its unique dental characteristics:

• The teeth, for which it was named, displayed a distinctive star-shaped (or spoon-shaped with a central ridge) cross-section when worn down.
• Like other sauropods, it possessed an extremely long neck, which would have allowed it to reach high into the treetops to browse on vegetation.
• Its body was robust and supported by four strong, columnar legs designed to bear its immense weight.
• It likely had a relatively small head in proportion to its body size and a long, muscular tail used for balance.
• As a titanosauriform, it would have shared characteristics with this group, such as wide-gauge trackways (meaning its feet were set far apart).

Paleoenvironment and Diet

Astrodon lived during the Early Cretaceous period. Its fossils are primarily found in the Arundel Formation of Maryland, which represents a coastal plain environment. This region was characterized by rivers, swamps, and estuaries, with a warm, humid climate. The landscape was covered with lush vegetation, including conifers, cycads, and ferns, providing an abundant food source for large herbivores like Astrodon.

As a herbivore, Astrodon used its long neck to browse on leaves and other plant material from tall trees, likely consuming large quantities of vegetation daily to sustain its massive size. It coexisted with other dinosaurs in this environment, including the large predatory theropod Acrocanthosaurus, smaller theropods, ornithopods like Tenontosaurus (or similar forms), and ankylosaurs such as Priconodon.

Significance and Ongoing Research

Astrodon holds significant historical importance as one of the earliest sauropod dinosaurs to be described from North America, contributing to the initial understanding of these giants on the continent. In 1998, Astrodon johnstoni was designated the official state dinosaur of Maryland, recognizing its paleontological heritage in the region.

Ongoing research and discussion often revolve around the fragmentary nature of Astrodon’s remains. The primary material consists of teeth, with some limb bones and vertebrae from the Arundel Formation also referred to this genus or the closely related (and possibly synonymous) Pleurocoelus. This limited material makes precise reconstruction and classification challenging. Paleontologists continue to study these fossils to better understand Astrodon’s anatomy, its relationship to other sauropods like Brachiosaurus and various titanosaurs, and its role within the Early Cretaceous ecosystems of eastern North America. Future discoveries of more complete specimens would greatly enhance our knowledge of this early North American sauropod.