Lophorhothon is among the family of dinosaurs known as hadrosaurs, or duck-billed dinosaurs. They inhabited North America during the Late Cretaceous period (65 to 99 million years before the present). The Lophorhothon is known with certainty from only a single juvenile specimen collected from the Late Cretaceous Mooreville Formation, a marine chalk deposit in Dallas County in west-central Alabama.

Lophorhothon atopus Family Hadrosaurs were herbivorous dinosaurs that ranged from 24 to 35 feet long. They were largely bipedal, but their front limbs were sturdy enough to allow for some four-legged walking, standing, and feeding. Most hadrosaur skulls feature flattened, duck-like mouths developed from wide, toothless upper and lower front jaw bones. Hadrosaurs had long rows of grinding rear teeth that the animals used to process vegetation. Hadrosaur skulls also usually display a variety of odd crests, formed by their nasal and upper jaw bones. The more primitive hadrosaurine subfamily, of which Lophorhothon is a member, often developed a “Roman-nose” shape formed by a high, narrow nasal ridge.

Lophorhothon is also the only hadrosaur that has been identified to genus in eastern North America. The fossilized skeleton was collected during the 1940s by researchers investigating the Alabama chalks for the Field Museum of Natural History in Chicago. In 1960, paleontologist Wann Langston Jr. first described the Lophorhothon specimen as a new genus and species of hadrosaur and coined the name Lophorhothon atopus by combining the Greek for “crest-nose” and “out of place” because virtually all other hadrosaurs known at that time came from the western side of North America.

Lophorhothon Skull Reconstruction Langston was able to identifiy the specimen as a juvenile and estimated its length at about 15 feet, well below the estimated adult size for average hadrosaurs. Despite being one of the best-preserved dinosaur fossils in the eastern United States, the skull is represented by only several fragments, and less than one-half of the entire skeleton was found. Fortunately, the preserved parts of the skull included the rear portion of the nasal crest and enough bones of the roof of the skull to allow identification of an opening known as a fontanel, which is a gap in the skull roof bones. The presence of the fontanel identifies the specimen as a juvenile because this gap closes as an animal reaches adulthood. The bones display characteristics that are typical of most hadrosaurines, aside from minor differences in the nasal crest, the crown angle of the teeth, and the fontanel. It appears to be closely related to the western genus Kritosaurus and among the older members of the subfamily in North America.

Lophorhothon Ankle Bone with Shark Tooth The Lophorhothon specimen dates to approximately 80 million years ago, based on associated fossils. Other hadrosaur fossils found in the Coastal Plain, from North Carolina to Tennessee, also may be tentatively identified as Lophorhothon and come from deposits ranging from 76 to 84 million years ago. Unfortunately, it is impossible to identify a specimen accurately as a hadrosaur without certain diagnostic skull parts, and the identification becomes especially difficult when comparing adult specimens with the juvenile type specimen from the Mooreville Formation. For example, researchers have found an adult hadrosaur lower leg in Russell County in deposits of the same age as the Dallas County Lophorhothon specimen and hadrosaurine teeth and bones from contemporary sediments in western Georgia that very likely belong to Lophorhothon. But, to date, the Mooreville Formation specimen remains the only one that can be confidently identified as Lophorhothon atopus.

Lophorhothon Carcass It is interesting to note that although Lophorhothon was a terrestrial animal, the type specimen was found in a marine chalk deposit. In fact, all dinosaur remains from the Southeast have been found in marine deposits and represent floating or otherwise water-transported carcasses that reached the ocean from shorelines or inland rivers. Langston addressed this preservation issue in the original Lophorhothon description, and paleontologist David R. Schwimmer refined what is known as the “bloat-and-float” model of marine dinosaur preservation to include the effects of shark scavenging as a key element of the marine occurrences of dinosaur fossils.

External Links

Share this Article