Gryposaurus
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[Photo] The hadrosaurid dinosaur Gryposaurus notibilis. Date 2002. Author John Conway (http://palaeo.jconway.co.uk/) Copyright (C) 2002 John Conway
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Gryposaurus (meaning "hooked-nosed (Greek grypos) lizard"; sometimes incorrectly translated as "griffin (Latin gryphus) lizard") was a genus of duckbilled dinosaur that lived about 83 to 75 million years ago, in the Late Cretaceous (late Santonian to late Campanian stages) of North America. Named species of Gryposaurus are known from the Dinosaur Park Formation in Alberta, Canada, the Lower Two Medicine Formation in Montana, USA, and potentially the Kaiparowits Formation of Utah.
Gryposaurus is similar to Kritosaurus, and for many years was regarded as the same genus. It is known from numerous skulls, some skeletons, and even some skin impressions that show it to have had pyramidal scales pointing out along the midline of the back. It is most easily distinguished from other duckbills by its narrow arching nasal hump, sometimes described as similar to a "Roman nose," and which may have been used for species or sexual identification, and/or combat with individuals of the same species. A large bipedal/quadrupedal herbivore around 9 meters long (30 ft), it may have preferred river settings.
Description
Gryposaurus was a hadrosaurid of typical size and shape; one of the best specimens, the nearly complete type specimen of G. incurvimanus now on display at the Royal Tyrrell Museum of Palaeontology, came from an animal about 8.2 meters long (27 feet). 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 scutes upwards of 3.8 centimeters long (1.5 inches) on the flank and tail; uniform polygonal 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.
The three named species of Gryposaurus differ in details of the skull and lower jaw. The prominent nasal arch found in this genus is formed from the paired nasal bones. In profile view, they rise into a rounded hump in front of the eyes, reaching a height as tall as the highest point of the back of the skull. The skeleton is known in great detail, making it a useful point of reference for other duckbill skeletons.
Classification
Gryposaurus was a hadrosaurine hadrosaurid, a member of the duckbill subfamily without hollow head crests. The general term "gryposaur" is sometimes used for duckbills with arched nasals, such as "Kritosaurus" australis and "Antonio", an undescribed hadrosaurine from Trieste, Italy. A subfamily, Gryposaurinae, was coined by Jack Horner for it as part of a larger revision that promoted Hadrosaurinae to family status, but is not in use. The issue of its relationships to other hadrosaurs is equivocal anyway due to the lack of resolution on how it compares to Kritosaurus. At this time, the main differences between the two are location (Alberta and Montana for Gryposaurus, New Mexico for Kritosaurus) and age (Kritosaurus comes from slightly younger rocks than Gryposaurus); otherwise, the skull of Kritosaurus is incompletely known, lacking most of the bones in front of the eyes, but very similar to that of Gryposaurus.
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. Although Horner in 1979 named a skeleton with skull from the Bearpaw Shale of Montana as Hadrosaurus notabilis (which has 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 hip.
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.
Species
Three named species are recognized today: G. notabilis, G. incurvimanus, and G. latidens. Two of them, the type species G. notabilis and G. incurvimanus, are from the same formation, the late Campanian-age Upper Cretaceous Dinosaur Park Formation of Alberta, Canada. They differ in the size of the nasal arch (larger and closer to the eyes in G. notabilis) and the form of the upper arm (longer and more robust in G. incurvimanus). 10 complete skulls and 12 fragmentary skulls are known for G. notabilis along with postcrania, and two skeletons with skulls are known for G. incurvimanus; it may just be a variant of G. notabilis. 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. The informal name "Hadrosauravus" (Lambert, 1990) is an early, unused name for this species.
Scrappy remains from Alberta originally named Trachodon (Pteropelyx) marginatus (Lambe, 1902) were sometimes included with Kritosaurus under the "Kritosaurus=Gryposaurus" hypothesis. This taxon may be the same as G. notabilis, but this synonymy was not supported in the latest review.
New material from the Kaiparowits Formation of Utah, in Grand Staircase-Escalante National Monument may represent a new species, greatly expanding the geographic range of this genus. Multiple individuals known from cranial and postcranial remains are known, showing it to be the largest species.
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 ~4 m (13 ft) above.
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. Gryposaurus may have preferred river-related settings.
Nasal arch
The distinctive nasal arch of Gryposaurus, like other cranial modifications in duckbills, may have been used for a variety of social functions, such as identification of sexes or species and social ranking. It could also have functioned as a tool for broadside pushing or butting in social contests, and there may have been inflatable air sacs flanking it for both visual and auditory signaling. 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.
http://en.wikipedia.org/wiki/Gryposaurus
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