Gryposaurus - Discovery and History

Discovery and History

Gryposaurus is based on specimen NMC 2278, a skull and partial skeleton collected in 1913 by George F. Sternberg from what is now known as the Dinosaur Park Formation of Alberta, along the Red Deer River. This specimen was described and named by Lawrence Lambe shortly thereafter, Lambe drawing attention to its unusual nasal crest. A few years earlier, Barnum Brown had collected and described a partial skull from New Mexico, which he named Kritosaurus. This skull was missing the snout, which had eroded into fragments; Brown restored it after the duckbill now known as Anatotitan, which was flat-headed, and believed that some unusual pieces were evidence of compression. Lambe's description of Gryposaurus provided evidence of a different type of head, and by 1916 the Kritosaurus skull had been redone with a nasal arch and both Brown and Charles Gilmore had proposed that Gryposaurus and Kritosaurus were one and the same. Although this idea was not fully supported at the time, it was certainly in the air, as shown by William Parks's naming of a nearly complete skeleton from the Dinosaur Park Formation as Kritosaurus incurvimanus, not Gryposaurus incurvimanus (interestingly, he left Gryposaurus notabilis alone in its own genus). Frustratingly, this skeleton is missing the front part of the skull, ending just before the full shape of the nasal arch can be seen. The 1942 publication of the influential Lull and Wright monograph on hadrosaurs sealed the Kritosaurus/Gryposaurus question for nearly fifty years in favor of Kritosaurus. Reviews beginning in the 1990s, however, called into question the identity of Kritosaurus, which has limited material for comparison with other duckbills. Thus, Gryposaurus has once again been separated, at least temporarily, from Kritosaurus.

This situation is made more confusing by old suggestions by some authors, including Jack Horner, that Hadrosaurus is also the same as either Gryposaurus, Kritosaurus, or both. This hypothesis was most common in the late 1970s-early 1980s, and appears in some popular books; one well-known work, The Illustrated Encyclopedia of Dinosaurs, uses Kritosaurus for the Canadian material (Gryposaurus), but confusingly identifies the mounted skeleton of K. incurvimanus as Hadrosaurus in a photo caption. Although Horner in 1979 used the new combination Hadrosaurus notabilis for a partial skull and skeleton and a second less-complete skeleton from the Bearpaw Shale of Montana (which have since fallen out of the literature), by 1990 he had changed his position, and was among the first to again use Gryposaurus in print. Current thought is that Hadrosaurus, although known from fragmentary material, can be distinguished from Gryposaurus by differences in the upper arm and ilium.

Further research has revealed the presence of a third species, G. latidens, from slightly older rocks in Montana than the classic gryposaur localities of Alberta. Based on two parts of a skeleton collected in 1916 for the American Museum of Natural History, G. latidens is also known from bonebed material. Horner, who described the specimens, considered to be a less derived species.

New material from the Kaiparowits Formation of Utah, in Grand Staircase-Escalante National Monument, includes a skull and partial skeleton that represent the species G. monumentensis. Its skull was more robust than that of the other species, and its predentary had enlarged prongs along its upper margin, where the lower jaw's beak was based. This new species greatly expands the geographic range of this genus, and there may be a second, more lightly built species present as well. Multiple gryposaur species are known from the Kaiparowits, from cranial and postcranial remains, and were larger than their northern counterparts.