Gryposaurus

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. and believed that some unusual pieces were evidence of compression. This idea was reflected in William Parks's naming of a nearly complete skeleton from the Dinosaur Park Formation as Kritosaurus incurvimanus, not Gryposaurus incurvimanus (although he left Gryposaurus notabilis in its own genus). Direct comparison between Kritosaurus incurvimanus and Gryposaurus notabilis is hindered by the fact that the incurvimanus type specimen is missing the front part of the skull, so the full shape of the nasal arch cannot 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 navajovius, which has limited material for comparison with other duckbills. 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 identifies the mounted skeleton of K. incurvimanus as Hadrosaurus in a photo caption. Although Horner in 1979 used the new combination Hadrosaurus [Kritosaurus] notabilis for a partial skull and skeleton and a second less-complete skeleton from the Bearpaw Shale of Montana Further research has revealed the presence of a second 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 it to be a less derived species. Multiple gryposaur species are known from the Kaiparowits Formation, represented by cranial and postcranial remains, and were larger than their northern counterparts. In Texas, specifically at the Javelina Formation and the El Picacho Formation, indeterminate hadrosaur remains resembling Kritosaurus and Gryposaurus have been unearthed for decades, but none were considered to be identifiable as a determined genus of hadrosaur, but do resemble some species of Kritosaurini or at least some species of Kritosaurus. However, in 2016, a possibly forth valid species of Gryposaurus named G. alsatei, which was named after Alsate, who was the last leader of the Mescalero Apaches, was unearthed in the Javelina Formation in Texas. Further research is needed to confirm its validity. Species As of 2016, there are currently three named species that are recognized as valid today: G. notabilis, G. latidens, and G. monumentensis. The type species G. notabilis is from the late Campanian-age Upper Cretaceous Dinosaur Park Formation of Alberta, Canada. G. latidens, from the late Santonian-early Campanian Lower Two Medicine Formation of Pondera County, Montana, USA, is known from partial skulls and skeletons from several individuals. Its nasal arch is prominent like that of G. notabilis, but farther forward on the snout, and its teeth are less derived, reflecting iguanodont-like characteristics. is an early, unused name for this species. G. monumentensis is known from a skull and partial skeleton from Utah. Recently, a possible fourth species of Gryposaurus, Gryposaurus alsatei, was unearthed in the Javelina Formation, which dates to the late Maastrichtian, along with an unnamed species of Kritosaurus and an undescribed saurolophine which closely resembles Saurolophus, but with a more solid crest. Fossil remains of Gryposaurus have also been unearthed in the El Picacho Formation in Texas. The dubious hadrosaurid Stephanosaurus marginatus was considered a possible species of Kritosaurus, following the synonymy of Gryposaurus with Kritosaurus. However, this synonymy was rejected in the 2004 edition of the Dinosauria, with Stephanosaurus being tabulated as dubious. ==Description==

Gryposaurus was a hadrosaurid of typical size and shape; one of the best specimens of this genus, the nearly complete type specimen of Kritosaurus incurvimanus (now regarded as a synonym of Gryposaurus notabilis) came from an animal about long. This specimen also has the best example of skin impressions for Gryposaurus, showing this dinosaur to have had several different types of scalation: pyramidal, ridged, limpet-shaped feature scales forming scutes upwards of 3.8 centimeters long (1.5 inches) on the flank and tail; uniform polygonal basement scales on the neck and sides of the body; and pyramidal structures, flattened side-to-side, with fluted sides, longer than tall and found along the top of the back in a single midline row. In 2016, Gregory S. Paul estimated the size of G. latidens at in length and in body mass and the other two species (G. notabilis and G. monumentensis) at in length and in body mass. The three named species of Gryposaurus differ in details of the skull and lower jaw. The skeleton is known in great detail, making it a useful point of reference for other duckbill skeletons. ==Classification==

Gryposaurus was a saurolophine (hadrosaurine of older references) hadrosaurid, a member of the duckbill subfamily without hollow head crests. The general term "gryposaur" is sometimes used for duckbills with arched nasals. Tethyshadros was once thought to fall into this group as well, before it was described (then known under the nickname "Antonio"). A subfamily, Gryposaurinae, was coined by Jack Horner as part of a larger revision that promoted Hadrosaurinae to family status, but is not now in use. A rough equivalent is Kritosaurini, as used by Alberto Prieto-Márquez. Kritosaurus has been proposed to be a synonym of Gryposaurus, but it is slightly younger. Additionally, while the skull of Kritosaurus is incompletely known, lacking most of the bones in front of the eyes, it was very similar to that of Gryposaurus. The following is a cladogram based on the phylogenetic analysis conducted by Prieto-Márquez and Wagner in 2012, showing the relationships of Gryposaurus among the other kritosaurins: ==Paleobiology==

As a hadrosaurid, Gryposaurus would have been a bipedal/quadrupedal herbivore, eating a variety of plants. Its skull had special joints that permitted a grinding motion analogous to chewing, and its teeth were continually replacing and packed into dental batteries that contained hundreds of teeth, only a relative handful of which were in use at any time. Plant material would have been cropped by its broad beak, and held in the jaws by a cheek-like organ. Its feeding range would have extended from the ground to about above. The dental microwear of a specimen of Gryposaurus sp. from the Kaiparowits Formation was unusually smooth; this smoothness can be interpreted as evidence of this individual feeding on conifers, ferns, and cycads rather than angiosperms, feeding on which is typically more likely to result in significant tooth abrasion. However, because only one specimen had dental microwear texture analysis performed on it, this may not reflect the overall feeding patterns of this taxon. Like other bird-hipped dinosaurs of the Dinosaur Park Formation, Gryposaurus appears to have only existed for part of the duration of time that the rocks were being formed. As the formation was being laid down, it recorded a change to more marine-influenced conditions. Gryposaurus is absent from the upper part of the formation, with Prosaurolophus present instead. Other dinosaurs known from only the lower part of the formation include the horned Centrosaurus and the hollow-crested duckbill Corythosaurus. The top of the arch is roughened in some specimens, suggesting that it was covered by thick, keratinized skin, or that there was a cartilaginous extension. ==Paleoecology==

Utah Argon-argon radiometric dating indicates that the Kaiparowits Formation was deposited between 76.1 and 74.0 million years ago, during the Campanian stage of the Late Cretaceous period. During the Late Cretaceous period, the site of the Kaiparowits Formation was located near the western shore of the Western Interior Seaway, a large inland sea that split North America into two landmasses, Laramidia to the west and Appalachia to the east. The plateau where dinosaurs lived was an ancient floodplain dominated by large channels and abundant wetland peat swamps, ponds and lakes, and was bordered by highlands. The climate was wet and humid, and supported an abundant and diverse range of organisms. This formation contains one of the best and most continuous records of Late Cretaceous terrestrial life in the world. Gryposaurus monumentensis shared its paleoenvironment with other dinosaurs, such as dromaeosaurid theropods, the troodontid Talos sampsoni, ornithomimids like Ornithomimus velox, tyrannosaurids like Albertosaurus and Teratophoneus, armored ankylosaurids, the duckbilled hadrosaur Parasaurolophus cyrtocristatus, the ceratopsians Utahceratops gettyi, Nasutoceratops titusi and Kosmoceratops richardsoni and the oviraptorosaurian Hagryphus giganteus. Other paleofauna present in the Kaiparowits Formation included chondrichthyans (sharks and rays), frogs, salamanders, turtles, lizards and crocodilians. A variety of early mammals were present including multituberculates, marsupials, and insectivorans. ==See also==