| Gryposaurus | |
|---|---|
 | |
| G. monumentensis skeleton in theNatural History Museum of Utah | |
Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Reptilia |
| Clade: | Dinosauria |
| Clade: | †Ornithischia |
| Clade: | †Ornithopoda |
| Family: | †Hadrosauridae |
| Subfamily: | †Saurolophinae |
| Tribe: | †Kritosaurini |
| Genus: | †Gryposaurus |
| Type species | |
| †Gryposaurus notabilis Lambe, 1914 | |
| Species | |
| Synonyms | |
| |
Gryposaurus (meaning "hooked-nosed (Greekgrypos)lizard";[1] sometimes incorrectly translated as "griffin (Latingryphus) lizard"[2]) was agenus ofduckbilleddinosaur that lived about 80 to 75 million years ago, in theLate Cretaceous (lateSantonian to lateCampanianstages) ofNorth America. Named species ofGryposaurus are known from theDinosaur Park Formation inAlberta, Canada, and two formations in the United States: the LowerTwo Medicine Formation inMontana and theKaiparowits Formation ofUtah. A possible additional species from theJavelina Formation in Texas may extend the temporal range of the genus to 66 million years ago.
Gryposaurus is similar toKritosaurus, and for many years the two were thought to be synonyms. It is known from numerous skulls, some skeletons, and even some skin impressions that show it to have had pyramidal scales projecting 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,"[1] and which may have been used for species or sexual identification, and/or combat with individuals of the same species. A largebipedal/quadrupedalherbivore around 8 meters (26 feet) long, it may have preferredriver settings.
Gryposaurus isbased on specimenNMC 2278, a skull and partial skeleton collected in 1913 byGeorge F. Sternberg from what is now known as theDinosaur Park Formation of Alberta, along theRed Deer River.[2] This specimen was described and named byLawrence Lambe shortly thereafter, Lambe drawing attention to its unusual nasal crest.[3] A few years earlier,Barnum Brown had collected and described a partial skull from New Mexico, which he namedKritosaurus. This skull was missing the snout, which had eroded into fragments; Brown restored it after the duckbill now known asEdmontosaurus annectens, which was flat-headed,[4] and believed that some unusual pieces were evidence of compression.[5] Lambe's description ofGryposaurus provided evidence of a different type of skull configuration, and by 1916 theKritosaurus skull had been redone with a nasal arch and both Brown andCharles Gilmore had proposed thatGryposaurus andKritosaurus were one and the same.[6][7] This idea was reflected inWilliam Parks's naming of a nearly complete skeleton from the Dinosaur Park Formation asKritosaurus incurvimanus, notGryposaurus incurvimanus (although he leftGryposaurus notabilis in its own genus).[8] Direct comparison betweenKritosaurus incurvimanus andGryposaurus notabilis is hindered by the fact that theincurvimanus 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 influentialLull and Wrightmonograph on hadrosaurs sealed theKritosaurus/Gryposaurus question for nearly fifty years in favor ofKritosaurus. Reviews beginning in the 1990s, however, called into question the identity ofKritosaurus navajovius, which has limited material for comparison with other duckbills.[9] Thus,Gryposaurus has once again been separated, at least temporarily, fromKritosaurus.
This situation is made more confusing by old suggestions by some authors, including Jack Horner, thatHadrosaurus is also the same as eitherGryposaurus,Kritosaurus, or both.[10] Thishypothesis was most common in the late 1970s–early 1980s, and appears in some popular books;[11][12] one well-known work,The Illustrated Encyclopedia of Dinosaurs, usesKritosaurus for the Canadian material (Gryposaurus), but identifies the mounted skeleton ofK. incurvimanus asHadrosaurus in a photo caption.[13] Although Horner in 1979 used the new combinationHadrosaurus [Kritosaurus] notabilis for a partial skull and skeleton and a second less-complete skeleton from theBearpaw Shale of Montana[10] (which have since fallen out of the literature), by 1990 he had changed his position, and was among the first to again useGryposaurus in print.[9] Current thought is thatHadrosaurus, although known from fragmentary material, can be distinguished fromGryposaurus by differences in theupper arm andilium.[14]
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 theAmerican Museum of Natural History,[15]G. latidens is also known frombonebed material. Horner, who described the specimens, considered it to be a lessderived species.[16]
New material from theKaiparowits Formation of Utah, inGrand Staircase–Escalante National Monument, includes a skull and partial skeleton that represent the speciesG. monumentensis. Its skull was more robust than that of the other species, and itspredentary 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.[17] Multiple gryposaur species are known from the Kaiparowits Formation, represented by cranial and postcranial remains, and were larger than their northern counterparts.[18]
In Texas, specifically at theJavelina Formation and theEl Picacho Formation, indeterminate hadrosaur remains resemblingKritosaurus andGryposaurus have been unearthed for decades, but none were considered to be identifiable as a determined genus of hadrosaur, but do resemble some species ofKritosaurini or at least some species ofKritosaurus.[19] However, in 2016, a possibly forth valid species ofGryposaurus namedG. alsatei, which was named afterAlsate, who was the last leader of theMescaleroApaches, was unearthed in the Javelina Formation in Texas. Further research is needed to confirm its validity.[20][21][22]
As of 2016, there are currently three named species that are recognized as valid today:G. notabilis,G. latidens, andG. monumentensis.[23] Thetype speciesG. notabilis is from thelate Campanian-ageUpper Cretaceous Dinosaur Park Formation of Alberta, Canada.[23] It is now thought that another species from the same formation,Kritosaurus incurvimanus (also known asGryposaurus incurvimanus), is a synonym ofG. notabilis.[23] The two had been differentiated by the size of the nasal arch (larger and closer to the eyes inG. notabilis) and the form of the upper arm (longer and more robust inK. incurvimanus).[16] Ten complete skulls and twelve fragmentary skulls are known forG. notabilis along withpostcrania,[24] as well as with two skeletons with skulls that had been assigned toK. incurvimanus.[25]G. latidens, from thelate Santonian-early CampanianLower Two Medicine Formation ofPondera County, Montana, USA, is known from partial skulls and skeletons from several individuals. Its nasal arch is prominent like that ofG. notabilis, but farther forward on the snout, and its teeth are lessderived, reflectingiguanodont-like characteristics.[16] Theinformal name "Hadrosauravus"[26] is an early, unused name for this species.[27]G. monumentensis is known from a skull and partial skeleton from Utah.[17]G. monumentensis was listed second on the top 10 list of new species in 2008 by theInternational Institute for Species Exploration.[28] Recently, a possible fourth species ofGryposaurus,Gryposaurus alsatei, was unearthed in theJavelina Formation, which dates to the lateMaastrichtian, along with an unnamed species ofKritosaurus and an undescribedsaurolophine which closely resemblesSaurolophus, but with a more solid crest.[29] Fossil remains ofGryposaurus have also been unearthed in theEl Picacho Formation inTexas.[30]
The dubious hadrosauridStephanosaurus marginatus[31] was considered a possible species ofKritosaurus, following the synonymy ofGryposaurus withKritosaurus.[32][33][2] However, this synonymy was rejected in the 2004 edition of theDinosauria, withStephanosaurus being tabulated as dubious.[24]
Gryposaurus was a hadrosaurid of typical size and shape; one of the best specimens of this genus, the nearly completetype specimen ofKritosaurus incurvimanus (now regarded as a synonym ofGryposaurus notabilis) came from an animal about 8.2 meters (27 feet) long.[34] This specimen also has the best example ofskin impressions forGryposaurus, 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.[35] In 2016, Gregory S. Paul estimated the size ofG. latidens at 7.5 metres (25 ft) in length and 2.5 metric tons (2.8 short tons) in body mass and the other two species (G. notabilis andG. monumentensis) at 8 metres (26 ft) in length and 3 metric tons (3.3 short tons) in body mass.[36]
The three named species ofGryposaurus differ in details of the skull and lower jaw.[2] The prominent nasal arch found in this genus is formed from the pairednasal 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.[3] The skeleton is known in great detail,[37] making it a useful point of reference for other duckbill skeletons.
Gryposaurus was a saurolophine (hadrosaurine of older references) hadrosaurid, a member of the duckbillsubfamily without hollow head crests.[24] The general term "gryposaur" is sometimes used for duckbills with arched nasals.[9]Tethyshadros was once thought to fall into this group as well, before it was described (then known under the nickname "Antonio").[38] A subfamily, Gryposaurinae, was coined byJack Horner as part of a larger revision that promoted Hadrosaurinae to family status,[16] but is not now in use. A rough equivalent isKritosaurini, as used by Alberto Prieto-Márquez.[39]Kritosaurus has been proposed to be a synonym ofGryposaurus, but it is slightly younger. Additionally, while the skull ofKritosaurus is incompletely known, lacking most of the bones in front of the eyes, it was very similar to that ofGryposaurus.[5]
The following is acladogram based on the phylogenetic analysis conducted by Prieto-Márquez and Wagner in 2012, showing the relationships ofGryposaurus among the other kritosaurins:[39]
| Kritosaurini |
| ||||||||||||||||||||||||||||||
As ahadrosaurid,Gryposaurus would have been abipedal/quadrupedalherbivore, eating a variety ofplants. Its skull had special joints that permitted a grinding motion analogous tochewing, and itsteeth were continually replacing and packed intodental 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 acheek-like organ. Its feeding range would have extended from the ground to about 4 m (13 ft) above.[24] The paleontologists who unearthedG.monumentensis back in the 2000s brought the fact that this creature dined on tough, fibrous plant material which would imply thatGryposaurs was both agrazer and abrowser.[40][41][42][43][44]
Like otherbird-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 moremarine-influenced conditions.Gryposaurus is absent from the upper part of the formation, withProsaurolophus present instead. Other dinosaurs known from only the lower part of the formation include the hornedCentrosaurus and the hollow-crested duckbillCorythosaurus.[25]Gryposaurus may have preferredriver-related settings.[24]
The distinctive nasal arch ofGryposaurus, 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.[24] 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.[45] The top of the arch is roughened in some specimens, suggesting that it was covered by thick,keratinized skin,[45] or that there was acartilaginous extension.[16]
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 LateCretaceous period.[46][47] During the Late Cretaceous period, the site of the Kaiparowits Formation was located near the western shore of theWestern Interior Seaway, a large inland sea that split North America into two landmasses,Laramidia to the west andAppalachia to the east. The plateau where dinosaurs lived was an ancient floodplain dominated by large channels and abundant wetlandpeat swamps, ponds and lakes, and was bordered by highlands. The climate was wet and humid, and supported an abundant and diverse range of organisms.[48] This formation contains one of the best and most continuous records of Late Cretaceous terrestrial life in the world.[49]
Gryposaurus monumentensis shared itspaleoenvironment with other dinosaurs, such asdromaeosauridtheropods, thetroodontidTalos sampsoni,ornithomimids likeOrnithomimus velox,tyrannosaurids likeAlbertosaurus andTeratophoneus,armored ankylosaurids, theduckbilled hadrosaurParasaurolophus cyrtocristatus, theceratopsiansUtahceratops gettyi,Nasutoceratops titusi andKosmoceratops richardsoni and theoviraptorosaurianHagryphus giganteus.[50] Other paleofauna present in the Kaiparowits Formation includedchondrichthyans (sharks and rays),frogs,salamanders,turtles,lizards andcrocodilians. A variety of earlymammals were present includingmultituberculates,marsupials, andinsectivorans.[51]
