Kritosaurus

Taxobox
name = "Kritosaurus"

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image_width = 225px
image_caption = "Kritosaurus"
fossil_range = Late Cretaceous
regnum = Animalia
phylum = Chordata
classis = Sauropsida
superordo = Dinosauria
ordo = Ornithischia
subordo = Ornithopoda
infraordo = Iguanodontia
superfamilia = Hadrosauroidea
familia = Hadrosauridae
subfamilia = Hadrosaurinae
genus = "Kritosaurus"
genus_authority = Brown, 1910
subdivision_ranks = Species
subdivision =
* "K. navajovius" (type species) Taxobox authority |author=Brown |date=1910
* ?"K." "australis" Bonparte, Franchi, Powell, and Sepulveda, 1984

"Kritosaurus" (meaning "separated lizard"; sometimes misinterpreted as "noble lizard", in reference to the presumed "Roman nose";cite book |last=Creisler |first=Benjamin S. |year=2007 |chapter=Deciphering duckbills |editor=Carpenter, Kenneth (ed.) |title=Horns and Beaks: Ceratopsian and Ornithopod Dinosaurs |publisher=Indiana University Press |location=Bloomington and Indianapolis |pages=185-210 |isbn=0-253-34817-X] the nasal region was fragmented, disarticulated, and originally restored flat) is an incompletely known but historically important genus of hadrosaurid (duckbilled) dinosaur. It lived about 73 million years ago, in the Late Cretaceous of North and possibly South America. Its taxonomic history is convoluted, also incorporating "Gryposaurus", "Anasazisaurus", and "Naashoibitosaurus"; this tangle will remain unresolved until better remains of "Kritosaurus" are described. Despite the dearth of material, this herbivore appeared in dinosaur books until the 1990s, although what was usually represented was the much more completely known "Gryposaurus", then thought to be a synonym.

Description

"Kritosaurus" is only definitely determined from a partial skull and lower jaws, and associated undescribed postcranial remains.cite book |last=Horner |first=John R. |authorlink=Jack Horner (paleontologist) |coauthors=Weishampel, David B.; and Forster, Catherine A |editor=Weishampel, David B.; Dodson, Peter; and Osmólska, Halszka (eds.)|title=The Dinosauria |edition=2nd |year= 2004|publisher=University of California Press |location=Berkeley |isbn=0-520-24209-2 |pages=438-463 |chapter=Hadrosauridae ] The greater portion of the muzzle and upper beak are missing, but additional reconstruction in the early 2000s using fragments from the skull that had not been placed before show part of a crest in front of the eyes;cite book |last=Kirkland |first=James I. |coauthors=Hernández-Rivera, René; Gates, Terry; Paul, Gregory S.; Nesbitt, Sterling; Serrano-Brañas, Claudia Inés; and Garcia-de la Garza, Juan Pablo |year=2006 |chapter=Large hadrosaurine dinosaurs from the latest Campanian of Coahuila, Mexico |editor=Lucas, S.G.; and Sullivan, Robert M. (eds.) |title=Late Cretaceous Vertebrates from the Western Interior |series=New Mexico Museum of Natural History and Science Bulletin, 35 |publisher=New Mexico Museum of Natural History and Science |location=Albuqueque, New Mexico |pages=299-315] the form of the crest is unknown at this point. The length of the skull is estimated at 87 centimeters (34 in) from the tip of the upper beak to the base of the quadrate that articulates with the lower jaw at the back of the skull.cite book |last=Lull |first=Richard Swann |authorlink=Richard Swann Lull |coauthors= and Wright, Nelda E. |title=Hadrosaurian Dinosaurs of North America |year=1942 |publisher=Geological Society of America |series=Geological Society of America Special Paper 40 |pages=226 ] Potential diagnostic characteristics of "Kritosaurus" include a predentary (lower beak) without tooth-like crenulations, a sharp downward bend to the lower jaws near the beak, and a heavy, somewhat rectangular maxilla (upper tooth-bearing bone). If it turns out to be the same as "Anasazisaurus" or "Naashoibitosaurus", then the form of the complete crest is that of a tab or flange beginning in front of the eyes and rising between and above them, but not extended beyond them.

Classification

"Kritosaurus" was a hadrosaurine hadrosaurid, a flat-headed or solid-crested duckbill. Because it is poorly known, its closest relatives are not yet known. "Naashoibitosaurus" and "K." "australis", both of which appear to be very similar, form a clade with "Saurolophus" in the most recent review of duckbill phylogeny. In the same work, "Kritosaurus" is confusingly considered both as distinct at the species level and as a dubious name. Location and time separate "Kritosaurus" and the slightly older, primarily Canadian "Gryposaurus", along with some cranial details.

Discovery and history

In 1904, Barnum Brown discovered the type specimen (AMNH 5799) of "Kritosaurus" near Ojo Alamo, San Juan County, New Mexico, United States, while following up on a previous expedition.cite journal |last=Brown |first=Barnum |authorlink=Barnum Brown |year=1910 |title=The Cretaceous Ojo Alamo beds of New Mexico with description of the new dinosaur genus "Kritosaurus" |journal=Bulletin of the American Museum of Natural History |volume=28 |issue=24 |pages=267–274 |url=http://digitallibrary.amnh.org/dspace/handle/2246/1398 ] He initially could not definitely correlate the stratigraphy, but by 1916 was able to establish it as from what is now known as the late Campanian-age De-na-zin Member of the Kirtland Formation.cite journal |last=Gilmore |first=Charles W. |authorlink=Charles Whitney Gilmore |year=1916 |title=Contributions to the geology and paleontology of San Juan County, New Mexico. 2. Vertebrate faunas of the Ojo Alamo, Kirtland and Fruitland Formations |journal=United States Geological Survey Professional Paper |volume=98-Q |pages=279–302 ] cite book |last=Williamson |first=Thomas E. |year=2000 |chapter=Review of Hadrosauridae (Dinosauria, Ornithischia) from the San Juan Basin, New Mexico |editor=Lucas, S.G.; and Heckert, A.B. (eds.) |title=Dinosaurs of New Mexico |series=New Mexico Museum of Natural History and Science Bulletin, 17 |publisher=New Mexico Museum of Natural History and Science |location=Albuqueque, New Mexico |pages=191-213] When discovered, much of the front of the skull had either eroded or fragmented, and Brown reconstructed this portion after what is now called "Anatotitan", leaving out many fragments. However, he had noticed that something was different about the fragments, but ascribed the differences to crushing.cite journal |last=Sinclair |first=William J. |coauthors=and Granger, Walter |year=1914 |title=Paleocene deposits of the San Juan Basin, New Mexico |journal=Bulletin of the American Museum of Natural History|volume=33 |pages=297–316 ] He initially wanted to name it "Nectosaurus", but found out that this name was already in use; Jan Versluys, who'd visited Brown before the change, inadvertently leaked the previous choice.cite web |url=http://dml.cmnh.org/1999Nov/msg00560.html |title=Re: What are these dinosaurs? 2: Return of What are these dinosaurs? |accessdate=2007-06-15 |author=Olshevsky, George |authorlink=George Olshevsky |date=1999-11-17 |publisher=Dinosaur Mailing List ] He kept the species name, though, leading to the combination "K. navajovius".

The 1914 publication of the arch-snouted Canadian genus "Gryposaurus"cite journal |last=Lambe |first=Lawrence M. |authorlink=Lawrence Lambe |year=1914 |title=On "Gryposaurus notabilis", a new genus and species of trachodont dinosaur from the Belly River Formation of Alberta, with a description of the skull of "Chasmosaurus belli" |journal=The Ottawa Naturalist |volume=27 |issue=11 |pages=145–155 ] changed Brown's mind about the anatomy of his dinosaur's snout. Going back through the fragments, he revised the previous reconstruction and gave it a "Gryposaurus"-like arched nasal crest. He also synonymized "Gryposaurus" with "Kritosaurus",cite journal |last=Brown |first=Barnum |authorlink=Barnum Brown |year=1914 |title=Cretaceous Eocene correlation in New Mexico, Wyoming, Montana, Alberta |journal=Geological Society of America Bulletin |volume=33 |pages=355–380 |url=http://digitallibrary.amnh.org/dspace/handle/2246/704 ] a move supported by Charles Gilmore. This synonymy was used through the 1920s (William Parks's designation of a Canadian species as "Kritosaurus incurvimanus")cite journal |last=Parks |first=William A. |authorlink=William Parks |year=1920 |title=The osteology of the trachodont dinosaur "Kritosaurus incurvimanus" |journal=University of Toronto Studies, Geology Series |volume=11 |pages=1–76] and became standard after the publication of Richard Swann Lull and Nelda Wright's influential 1942 monograph on North American hadrosaurids.cite book |last=Lull |first=Richard Swann |authorlink=Richard Swann Lull |coauthors= and Wright, Nelda E. |title=Hadrosaurian Dinosaurs of North America |year=1942 |publisher=Geological Society of America |series=Geological Society of America Special Paper 40 |pages=164-172] From this time until 1990, "Kritosaurus" would be composed of at least the type species "K. navajovius", "K. incurvimanus", and "K. notabilis", the former type species of "Gryposaurus". The poorly known species "Hadrosaurus breviceps" (Marsh, 1889),cite journal |last=Marsh |first=O.C. |authorlink=Othniel Charles Marsh |year=1889 |title=Notice of new American Dinosauria |journal=American Journal of Science |volume=38 |pages=331–336] known from a dentary from the Campanian-age Judith River Formation of Montana, was also assigned to "Kritosaurus" by Lull and Wright, but this is no longer accepted.cite journal |last=Prieto-Márquez |first=Alberto |coauthors=Weishampel, David B.; and Horner, John R. |year=2006 |title=The dinosaur "Hadrosaurus foulkii", from the Campanian of the East Coast of North America, with a reevaluation of the genus |journal=Acta Palaeontologica Polonica |volume=51 |issue=1 |pages=77–98 |url=http://www.app.pan.pl/archive/published/app51/app51-077.pdf |format=pdf]

By the late 1970s and early 1980s, "Hadrosaurus" had entered the discussion as a possible synonym of either "Kritosaurus", "Gryposaurus", or both, particularly in semi-technical "dinosaur dictionaries".cite book |last=Glut |first=Donald F. |title=The New Dinosaur Dictionary |year=1982 |publisher=Citadel Press |location=Secaucus, NJ |isbn=0-8065-0782-9 |pages=158 ] cite book |last=Lambert |first=David |coauthors=and the Diagram Group |title=A Field Guide to Dinosaurs |year=1983 |publisher=Avon Books |location=New York |isbn=0-380-83519-3 |pages=161 ] One well-known work, David B. Norman's "The Illustrated Encyclopedia of Dinosaurs", uses "Kritosaurus" for the Canadian material ("Gryposaurus"), but confusingly identifies the mounted skeleton of "K. incurvimanus" as "Hadrosaurus".cite book |last=Norman |first=David. B. |authorlink=David B. Norman |title=The Illustrated Encyclopedia of Dinosaurs: An Original and Compelling Insight into Life in the Dinosaur Kingdom |chapter=Hadrosaurids I|year=1985 |publisher=Crescent Books |location=New York |pages=116-121 |isbn=0-517-468905 ] One more species was added to "Kritosaurus" in these years. In 1984, Argentine paleontologist José Bonaparte and colleagues named "K. australis" for hadrosaur bones from the late Campanian-early Maastrichtian Los Alamitos Formation of Rio Negro, Patagonia, Argentina.cite journal |last=Bonaparte |first=José |authorlink=José Bonaparte |coauthors=Franchi, M.R.; Powell, J.E.; and Sepulveda, E. |year=1984 |title=La Formación Los Alamitos (Campaniano-Maastrichtiano) del sudeste de Rio Negro, con descripcion de "Kritosaurus australis" n. sp. (Hadrosauridae). Significado paleogeografico de los vertebrados |journal=Revista de la Asociación Geología Argentina |language=Spanish |volume=39 |issue=3-4 |pages=284–299] This species has been problematic and may not belong in "Kritosaurus", as suggested by the reviews in both editions of "The Dinosauria".cite book |last=Weishampel |first=David B. |authorlink=David B. Weishampel |coauthors=and Horner, Jack R. |editor= Weishampel, David B.; Dodson, Peter; and Osmólska, Halszka (eds.)|title=The Dinosauria |edition=1st |year=1990 |publisher=University of California Press |location=Berkeley |isbn=0-520-06727-4 |pages=534-561 |chapter=Hadrosauridae]

The history of "Kritosaurus" took another turn in 1990, when Jack Horner and David B. Weishampel once again separated "Gryposaurus", citing the uncertainty associated with the latter's partial skull. Horner in 1992 described two more skulls from New Mexico that he claimed belonged to "Kritosaurus" and showed that it was quite different from "Gryposaurus",cite journal |last=Horner |first=John R. |authorlink=Jack Horner (paleontologist) |year=1992 |title=Cranial morphology of "Prosaurolophus" (Ornithischia: Hadrosauridae) with descriptions of two new hadrosaurid species and an evaluation of hadrosaurid phylogenetic relationships |journal=Museum of the Rockies Occasional Paper |volume=2 |pages=1–119 ] but the following year Adrian Hunt and Spencer G. Lucas put each skull in its own genus, creating "Anasazisaurus" and "Naashoibitosaurus".cite book |last=Hunt |first=Adrian P. |coauthors=and Lucas, Spencer G. |year=1993 |chapter=Cretaceous vertebrates of New Mexico |editor=Lucas, S.G.; and Zidek, J. (eds.) |title=Dinosaurs of New Mexico |series=New Mexico Museum of Natural History and Science Bulletin, 2 |publisher=New Mexico Museum of Natural History and Science |location=Albuqueque, New Mexico |pages=77-91] Not all authors have agreed with this, Thomas E. Williamson in particular defending Horner's original interpretation. At least two recent publications have upheld the different genera, for now.cite book |last=Lucas |first=Spencer G. |authorlink=Spencer G. Lucas |coauthors=Spielman, Justin A.; Sullivan, Robert M.; Hunt, Adrian P.; and Gates, Terry |year=2006 |chapter="Anasazisaurus", a hadrosaurian dinosaur from the Upper Cretaceous of New Mexico |editor=Lucas, S.G.; and Sullivan, Robert M. (eds.) |title=Late Cretaceous Vertebrates from the Western Interior |series=New Mexico Museum of Natural History and Science Bulletin, 35 |publisher=New Mexico Museum of Natural History and Science |location=Albuqueque, New Mexico |pages=293-297]

Finally, the geographic range of potential "Kritosaurus" remains in North America has expanded. Bones from the late Campanian-age Aguja Formation of Texas, including a skull, have been found.cite journal |last=Sankey |first=Julia T. |year=2001 |title=Late Campanian southern dinosaurs, Aguja Formation, Big Bend, Texas |journal=Journal of Paleontology |volumes=75 |pages=208–215 |doi=10.1666/0022-3360(2001)075<0208:LCSDAF>2.0.CO;2 |volume=75] cite journal |last=Wagner |first=Jonathan R. |coauthors=and Lehman, Thomas M. |year=2001 |title=A new species of "Kritosaurus" from the Cretaceous of Big Bend National Park, Brewster County, Texas |journal=Journal of Vertebrate Paleontology |volume=21 |issue=3, Suppl. |pages=110A–111A] Additionally, newly-described remains from Coahuila, Mexico may represent a new species, one about 20% larger than "K. navajovius" (around 11 meters [36 ft] long) and with a distinctively curved ischium. This animal would be the largest known well-documented North American hadrosaurine. Unfortunately, the nasal bones are also incomplete in the skull remains from this material.

Paleoecology

"Kritosaurus" was discovered in the De-na-zin Member of the Kirtland Formation. This formation dates from the late Campanian stages of the Late Cretaceous Period (74 to 70 million years ago), and is also the source of several other dinosaurs, like "Alamosaurus", a species of "Parasaurolophus", "Pentaceratops", "Nodocephalosaurus", "Saurornitholestes", and as-yet-unnamed tyrannosaurids.Weishampel, David B.; Barrett, Paul M.; Coria, Rodolfo A.; Le Loeuff, Jean; Xu Xing; Zhao Xijin; Sahni, Ashok; Gomani, Elizabeth, M.P.; and Noto, Christopher R. (2004). "Dinosaur Distribution". "The Dinosauria" (2nd). 517–606.] The Kirtland Formation is interpreted as river floodplains appearing after a retreat of the Western Interior Seaway. Conifers were the dominant plants, and chasmosaurine horned dinosaurs appear to have been more common than hadrosaurids.cite book |last=Russell |first=Dale A. |authorlink=Dale Russell |title=An Odyssey in Time: Dinosaurs of North America |year=1989 |publisher=NorthWord Press, Inc. |location=Minocqua, Wisconsin |isbn=1-55971-038-1 |pages=160-164]

Paleobiology

Diet and feeding

As a hadrosaurid, "Kritosaurus" would have been a large bipedal/quadrupedal herbivore, eating plants with a sophisticated skull that permitted a grinding motion analogous to chewing. 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. Feeding would have been from the ground up to ~4 meters (13 ft) above. If it was a separate genus, how it would have partitioned resources with the similar and contemporaneous "Naashoibitosaurus" is unknown.

Nasal crest

The nasal crest of "Kritosaurus", whatever its true form, may have been used for a variety of social functions, such as identification of sexes or species and social ranking. There may have been inflatable air sacs flanking it for both visual and auditory signaling.cite journal |last=Hopson |first=James A. |year=1975 |title=The evolution of cranial display structures in hadrosaurian dinosaurs |journal=Paleobiology |volume=1 |issue=1 |pages=21–43 ]

In popular culture

The synonymization of "Kritosaurus" and "Gryposaurus" that lasted from the 1910s to 1990 led to a distorted picture of what the original "Kritosaurus" material represented. Because the Canadian material was much more complete, most representations and discussions of "Kritosaurus" from the 1920s to 1990 are actually more applicable to "Gryposaurus". This includes, for example, James Hopson's discussion of hadrosaur cranial ornamentation, and the adaptation of this for the public in "The Illustrated Encyclopedia of Dinosaurs".cite book |last=Norman |first=David B. |authorlink=David B. Norman |title=The Illustrated Encyclopedia of Dinosaurs: An Original and Compelling Insight into Life in the Dinosaur Kingdom|chapter=Hadrosaurids II |year=1985 |publisher=Crescent Books |location=New York|pages=122-127 |isbn=0-517-468905 ]

References

External links

* [http://www.dinoruss.com/de_4/5a7b0d6.htm "Kritosaurus" in The Dinosaur Encyclopaedia] at Dino Russ' Lair