Description and Classification

Ornithotarsus was a type of “duck-billed” dinosaur, belonging to the family Hadrosauridae. Like other hadrosaurs, it would have been a large herbivore, capable of walking on both two legs (bipedally) and four legs (quadrupedally). Based on the size of its leg bones and comparisons with more complete hadrosaur skeletons, such as Edmontosaurus or Hadrosaurus, Ornithotarsus was likely a fairly large animal, perhaps reaching lengths of 7 to 10 meters (23 to 33 feet). However, without more complete fossils, specific details about its appearance, such as the presence or shape of a cranial crest (common in some hadrosaurs like Parasaurolophus), remain unknown. Its classification within Hadrosauridae is uncertain, though it is generally considered to be related to non-crested or solid-crested hadrosaurs (Hadrosaurinae or Saurolophinae) if it is indeed a valid genus distinct from Hadrosaurus.

Distinguishing Features

The primary feature noted by Cope for Ornithotarsus was the structure of its ankle (tarsus), which he perceived as being more bird-like than that of other known dinosaurs at the time. However, modern understanding of dinosaur anatomy, particularly hadrosaur anatomy, has shown that these features are not necessarily unique to Ornithotarsus. Given the limited fossil material, definitively identifying unique distinguishing features is challenging.

• Known primarily from partial hindlimb elements (tibia and metatarsals).
• The original description emphasized a perceived bird-like fusion or arrangement in the ankle bones, though this interpretation is viewed differently today.
• As a hadrosaur, it would have possessed a complex dental battery for grinding tough plant material, though this is inferred rather than directly observed from Ornithotarsus fossils.

Paleoenvironment and Diet

The fossils of Ornithotarsus were discovered in marine sediments, suggesting it lived in or near coastal environments along the eastern edge of North America during the Late Cretaceous. This area was part of a landmass known as Appalachia. The paleoenvironment likely consisted of coastal plains, estuaries, and swampy lowlands. Like all hadrosaurs, Ornithotarsus was a herbivore. It would have used its broad, toothless beak to crop vegetation and its specialized dental batteries, containing hundreds of tightly packed teeth, to grind tough plant matter such as conifers, ferns, and early flowering plants.

Significance and Ongoing Research

Ornithotarsus holds historical significance as one of the early dinosaur discoveries in North America, contributing to the initial understanding of dinosaur diversity on the continent. However, its scientific importance is limited by the scant nature of its fossil remains. Much of the ongoing research related to Ornithotarsus centers on its taxonomic validity. Paleontologists continue to debate whether the available fossils possess enough unique characteristics to warrant recognizing Ornithotarsus as a distinct genus, or if it should be considered a nomen dubium (a doubtful name) or a synonym of another hadrosaur, most commonly Hadrosaurus foulkii, which was found in the same region and time period. Further fossil discoveries from the Late Cretaceous of eastern North America could potentially provide more material to clarify the status and characteristics of Ornithotarsus and its relationship to other hadrosaurid dinosaurs.