Gryposaurus

Did You Know?

• The name Gryposaurus is sometimes incorrectly translated as 'griffin lizard'.
• A possible additional species from the Javelina Formation in Texas may extend the genus's temporal range to 66 million years ago.
• The subfamily Gryposaurinae was coined by Jack Horner but is not now in use.

History of discovery

The genus Gryposaurus is based on specimen NMC 2278, a skull and partial skeleton collected in 1913 by George F. Sternberg from what is now the Dinosaur Park Formation of Alberta, along the Red Deer River. Lawrence Lambe described and named the specimen shortly thereafter, emphasizing its unusual nasal crest. Earlier, Barnum Brown had described a partial skull from New Mexico as Kritosaurus, but that skull was missing the snout and was restored with a flat head. Lambe's description of Gryposaurus revealed a different skull configuration, and by 1916 both Brown and Charles Gilmore proposed that Gryposaurus and Kritosaurus were the same. This view influenced William Parks's naming of a nearly complete skeleton from the Dinosaur Park Formation as Kritosaurus incurvimanus, though he left Gryposaurus notabilis in its own genus. Direct comparison between the two is hindered because the incurvimanus type specimen lacks the front part of the skull. The 1942 Lull and Wright monograph favored Kritosaurus for nearly fifty years, but reviews beginning in the 1990s questioned the identity of Kritosaurus navajovius, leading to the temporary separation of Gryposaurus from Kritosaurus.

Description

Gryposaurus was a duck-billed dinosaur of average size for its group. One of the finest known specimens, originally called Kritosaurus incurvimanus but now considered the same as Gryposaurus notabilis, came from an animal about 8.2 meters long. This fossil also preserves the best skin impressions for the genus, revealing several scale types: pyramidal, ridged, and limpet-shaped feature scales up to 3.8 centimeters long on the flank and tail; uniform polygonal basement scales on the neck and body sides; and flattened, fluted pyramidal structures in a single row along the top of the back. In 2016, Gregory S. Paul estimated Gryposaurus latidens at 7.5 meters and 2.5 metric tons, while the other two species, G. notabilis and G. monumentensis, reached about 8 meters and 3 metric tons. The three named species differ in skull and lower jaw details. The genus’s prominent nasal arch, formed by the paired nasal bones, rises into a rounded hump in front of the eyes, as tall as the skull’s highest rear point.

Paleobiology

Gryposaurus was a hadrosaurid that could walk on two legs or all fours and ate plants. Its skull had special joints that let it grind food like chewing, and its teeth were constantly replaced, packed into dense batteries with hundreds of teeth, though only a few were active at once. A broad beak cropped plants, and a cheek-like structure held food in the jaws. It could feed from ground level up to about four meters high. Paleontologists who excavated G. monumentensis in the 2000s found it ate tough, fibrous plants, meaning it both grazed and browsed. One specimen from the Kaiparowits Formation had unusually smooth dental microwear, suggesting it fed on conifers, ferns, and cycads rather than abrasive angiosperms, but this single sample may not represent the whole species. Like other bird-hipped dinosaurs from the Dinosaur Park Formation, Gryposaurus lived only during part of the time those rocks formed. It is missing from the upper layers, where Prosaurolophus appears instead. Its distinctive nasal arch might have served social roles like identifying sex, species, or rank, or been used for pushing or butting during contests. Some specimens have a roughened arch top, indicating it was covered by thick, keratinized skin or had a cartilaginous extension.

Paleoecology

Argon-argon radiometric dating indicates the Kaiparowits Formation was deposited between 76.1 and 74.0 million years ago, during the Campanian stage. At that time, the site was near the western shore of the Western Interior Seaway, a large inland sea that split North America into Laramidia and Appalachia. The plateau was an ancient floodplain with large channels, wetland peat swamps, ponds, and lakes, bordered by highlands. The climate was wet and humid, supporting a diverse range of organisms. Gryposaurus monumentensis shared its environment with dromaeosaurid theropods, the troodontid Talos sampsoni, ornithomimids like Ornithomimus velox, tyrannosaurids such as Albertosaurus and Teratophoneus, armored ankylosaurids, the duckbill Parasaurolophus cyrtocristatus, ceratopsians including Utahceratops gettyi, Nasutoceratops titusi, and Kosmoceratops richardsoni, and the oviraptorosaurian Hagryphus giganteus. Other fauna included chondrichthyans, frogs, salamanders, turtles, lizards, crocodilians, and early mammals such as multituberculates, marsupials, and insectivorans.