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Gryposaurus

Gryposaurus, meaning “hooked-nosed lizard,” is a genus of duckbilled dinosaur from the late Santonian to late Campanian stages of the Late Cretaceous Period (83 to 75.5 million years ago). It lived in what is now North America. It is known from the Dinosaur Park Formation in Alberta, Canada; the Lower Two Medicine Formation in Montana; and the Kaiparowits Formation in Utah, USA.

Gryposaurus, once thought to be part of the similar Kritosaurus genus, is known from numerous skulls, skeletal fragments, and some skin impressions that show that the dinosaur had pyramidal scales pointing out along the midline of the back. It can be distinguished from other duckbills by its narrow arching nasal hump, which may have been used for special or sexual identification, or possibly for combat between individuals of the same species.

Gryposaurus was first discovered in 1913 by George F. Sternberg at what is now known as the Dinosaur Park Formation in Alberta, along the Red Deer River. It was described and named by Lawrence Lambe shortly thereafter. Barnum Brown had collected and described a partial skull from New Mexico a few years earlier, which he named Kritosaurus. After Lambe’s description of Gryposaurus, further evidence showed that Brown’s discovery may have been the same genus as Sternberg’s discovery.

Although the idea was not fully supported at the time, it was the subject of debate for many decades to come. William Park named one nearly complete skeleton taken from Dinosaur Park Formation as Kritosaurus incurvimanus, rather than Gryposaurus incurvimanus. In a 1942 publication by Lull and Wright, the Kritosaurus/Gryposaurus debate was finally put in favor of Kritosaurus.

However, a review beginning in the 1990s called into question the identity of Kritosaurus based on limited material for comparison with other duckbills. Thus, Gryposaurus was once again separated from Kritosaurus.

Even more frustrating is a suggestion in the 1970s made by Jack Horner that Hadrosaurus is also the same as either Kritosaurus, Gryposaurus, or both. He later, in 1990, changed his stance on the suggestion. Hadrosaurus can be distinguished from Gryposaurus by differences in the upper arm and ilium.

The type species, G. notabilis, derived from the Dinosaur Park Formation in Alberta. It is now believed to be the same as another species, G. incurvimanus, taken from the same formation, formerly also named as Kritosaurus incurvimanus. A third species, G. latidens, from the Lower Two Medicine Formation of Montana, USA, is known from partial skulls and skeletons from several individuals. A fourth species, G. monumentensis, is known from a skull and partial skeleton taken from Kaiparowits Formation in Utah, USA.

G. monumentensis was listed second on the top 10 list of new species in 2008 by the International Institute for Species Exploration.

Gryposaurus was a large bipedal/quadrupedal herbivore measuring close to 30 feet long. Skin impressions left in one fossilized specimen show that the dinosaur had several different types of pyramidal, ridged, scutes up to 1.5 inches long on the flank and tail; uniform polygonal scales on the neck and sides of the body; and pyramidal structures found along the top of the back in a single midline row.

There existed a prominent nasal arch formed from the paired nasal bones. The arches rose into a rounded hump in front of the eyes, reaching as tall as the height of the back of the skull. Gryposaurus was a hadrosaurine hadrosaurid of the duckbill subfamily without hollow head crests.

The skull of Gryposaurus had special joints permitting grinding motion analogous to chewing, and its teeth were continually replaced. Plant material would have been cropped by its broad beak, and held in its jaws by a cheek-like organ. It would have fed on vegetation from the ground to as high up as 13 feet.

Gryposaurus may have preferred river-related settings.

Specimens of Gryposaurus are on display at the Royal Tyrrell Museum of Paleontology in Alberta, Canada.

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Gryposaurus


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