Description and Classification

Hadrosaurus was a large, plant-eating dinosaur. Scientists estimate it grew to be about 7 to 8 meters (23 to 26 feet) long and may have weighed between 2 to 4 tons. Like other hadrosaurids, it likely walked primarily on its powerful hind legs but could also move on all four limbs. The original fossil find of Hadrosaurus foulkii (specimen ANSP 10005) included limb bones, parts of the pelvis, and vertebrae, but notably, it did not include a skull.

Because it lacks a skull, the exact appearance of its head is based on related hadrosaurids, which are often called “duck-billed dinosaurs” due to their broad, flattened snouts. These dinosaurs also had complex arrangements of hundreds of teeth, known as dental batteries, which were excellent for grinding tough plant material. It is presumed Hadrosaurus shared these characteristics.

Hadrosaurus is classified as an ornithischian (“bird-hipped”) dinosaur, belonging to the Ornithopoda group and the family Hadrosauridae. It is the type genus of this family, meaning it’s the dinosaur that gives the Hadrosauridae family its name. Its precise position within the Hadrosauridae family is sometimes debated by scientists because the original fossils are incomplete. Some consider it a “hadrosaurine” (a hadrosaurid without a hollow head crest), while others view it as a more basal (primitive) member of the hadrosaur group. Due to the limited fossil material, some paleontologists consider Hadrosaurus a nomen dubium, or “doubtful name,” because it can be hard to distinguish from other hadrosaur species based solely on its known bones. However, it remains historically and scientifically important as the first of its kind to be recognized.

Distinguishing Features

Because the original Hadrosaurus foulkii specimen is incomplete and lacks a skull, identifying unique features that distinguish it from all other hadrosaurids is challenging. However, its historical context and some general features inferred from its family make it noteworthy:

• It was the first dinosaur skeleton mounted for public display in the world (in 1868), dramatically influencing public understanding of dinosaurs.
• Based on its classification, it would have possessed a broad, toothless beak at the front of its mouth for cropping vegetation.
• It would have had complex dental batteries in its cheeks, with multiple rows of teeth that were constantly replaced.
• Its limb proportions, with shorter arms and longer, stronger legs, indicate it was primarily bipedal for movement but could also support itself on all fours, likely for grazing.
• As the type genus for Hadrosauridae, it represents the general body plan of this widespread and successful group of Cretaceous herbivores, even if specific details unique to the genus are limited by the fossil record.

Paleoenvironment and Diet

Hadrosaurus lived during the Late Cretaceous period in what is now the eastern coast of North America. The fossils were discovered in the Woodbury Formation in New Jersey, which, at the time, was a coastal plain environment near the Western Interior Seaway, a large inland sea that split North America in two. This area would have been characterized by rivers, estuaries, and lush vegetation suited to a warm, humid climate.

As a hadrosaurid, Hadrosaurus was a herbivore. It would have used its beak-like mouth to snip off leaves, twigs, and possibly fruits from conifers, ferns, and early flowering plants. The food would then be ground up by the powerful dental batteries further back in its jaws. It likely browsed on vegetation at various heights, from low-lying plants to foliage on small trees. Other animals in its environment included other dinosaurs like the theropod Dryptosaurus, as well as crocodiles, turtles, and various marine creatures in the nearby seaway.

Significance and Ongoing Research

Hadrosaurus foulkii holds immense historical significance in the field of paleontology. Its discovery in 1858 and subsequent description by Joseph Leidy provided the first strong evidence that some dinosaurs were bipedal, contrasting with the earlier view of them as slow, quadrupedal, lizard-like beasts. The mounting of its skeleton at the Academy of Natural Sciences in Philadelphia in 1868 was a global event, sparking public fascination with dinosaurs.

Scientifically, while the incompleteness of the holotype poses challenges, Hadrosaurus remains the foundational genus for the entire Hadrosauridae family. This family includes many well-known dinosaurs such as Edmontosaurus, Parasaurolophus, and Corythosaurus, and understanding Hadrosaurus helps provide context for these later discoveries. In 1991, Hadrosaurus foulkii was designated the official state dinosaur of New Jersey, recognizing its local and historical importance.

Ongoing research related to Hadrosaurus often involves comparative anatomy with more complete hadrosaurid specimens to better understand its evolutionary relationships and biology. Paleontologists continue to study the Late Cretaceous ecosystems of eastern North America to learn more about the environment Hadrosaurus inhabited and its role within that ecosystem. While new fossil finds directly attributed to Hadrosaurus foulkii are rare, the study of hadrosaurids as a whole continues to advance, shedding light on the behavior, growth, and diversity of these remarkable “duck-billed” dinosaurs.