Kritosaurus is an incompletely known genus of hadrosaurid (duck-billed) dinosaur. It lived about 74.5-66 million years ago, in the Late Cretaceous of North America. The name means "separated lizard" (referring to the arrangement of the cheek bones in an incomplete type skull), but is often mistranslated as "noble lizard" in reference to the presumed "Roman nose"  (in the original specimen, the nasal region was fragmented and disarticulated, and was originally restored flat).
|K. navajovius holotype skull, AMNH|
Anasazisaurus? Hunt & Lucas, 1993
In 1904, Barnum Brown discovered the type specimen (AMNH 5799) of Kritosaurus near the Ojo Alamo Formation, San Juan County, New Mexico, United States, while following up on a previous expedition. 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. When discovered, much of the front of the skull had either eroded or fragmented, and Brown reconstructed this portion after what is now called Edmontosaurus, leaving out many fragments. However, he had noticed that something was different about the fragments, but ascribed the differences to crushing. He initially wanted to name it Nectosaurus, but found out that this name was already in use; Jan Versluys, who had visited Brown before the change, inadvertently leaked the previous choice. He kept the specific name, though, leading to the combination K. navajovius.
The 1914 publication of the arch-snouted Canadian genus Gryposaurus 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, a move supported by Charles Gilmore. This synonymy was used through the 1920s (William Parks's designation of a Canadian species as Kritosaurus incurvimanus, now considered a synonym of Gryposaurus notabilis) and became standard after the publication of Richard Swann Lull and Nelda Wright's 1942 monograph on North American hadrosaurids. 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), 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.
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". David B. Norman's The Illustrated Encyclopedia of Dinosaurs, uses Kritosaurus for the Canadian material (Gryposaurus), but identifies the mounted skeleton of K. incurvimanus as Hadrosaurus.
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.
In 1984, Argentine paleontologist José Bonaparte and colleagues named Kritosaurus australis for hadrosaur bones from the late Campanian-early Maastrichtian Los Alamitos Formation of Rio Negro, Patagonia, Argentina. This species is now thought to be a synonym of Secernosaurus koerneri.
In 1990, 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, but the following year Adrian Hunt and Spencer G. Lucas put each skull in its own genus, creating Anasazisaurus and Naashoibitosaurus.
Adrian Hunt and Spencer G. Lucas, American paleontologists, named Anasazisaurus horneri in 1993. The name was derived from the Anasazi, an ancient Native American people, and the Greek word sauros ("lizard"). The Anasazi were famous for their cliff-dwellings, such as those in Chaco Canyon, near the location of fossil Anasazisaurus remains. The term "Anasazi" itself is actually a Navajo language word, anaasází ("enemy ancestors"). The species was named in honor of Jack Horner, the American paleontologist who first described the skull in 1992. The holotype skull (and only known specimen) was collected in the late 1970s by a Brigham Young University field party working in San Juan County, and is housed at BYU as BYU 12950.
Horner originally assigned the Anasazisaurus skull to Kritosaurus navajovius, but Hunt and Lucas could not find any diagnostic features in the limited material of Kritosaurus and judged the genus to be a nomen dubium. Since the Anasazisaurus skull did have diagnostic features of its own, and did not appear to them to share any unique features with Kritosaurus, it was given the new name Anasazisaurus horneri, an opinion which was supported by some later authors. Not all authors have agreed with this, Thomas E. Williamson in particular defending Horner's original interpretation, and several subsequent studies recognized both distinct genera.
A comprehensive study of known Kritosaurus material published by Albert Prieto-Márquez in 2013 upheld the status of Naashoibitosaurus as a distinct genus, but found that the type specimens of Kritosaurus and Anasazisaurus were indistinguishable when comparing overlapping elements (i.e. only those bones preserved in both specimens). Prieto-Márquez therefore regarded Anasazisaurus as a synonym of Kritosaurus, but retained it as the distinct species K. horneri.
A partial skeleton from the Sabinas Basin in Mexico was described as Kritosaurus sp. by Jim Kirkland and colleagues, but considered an indeterminate saurolophine by Prieto-Márquez (2013). This skeleton is about 20% larger than other known specimens, around 11 meters [36 ft] long, and with a distinctively curved ischium, and represents the largest known well-documented North American saurolophine. Unfortunately, the nasal bones are also incomplete in the skull remains from this material.
The type specimen of Kritosaurus navajovius is only represented by a partial skull and lower jaws, and associated postcranial remains. The greater portion of the muzzle and upper beak are missing. 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. 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).
Based on the skull originally referred to Anasazisaurus, the form of the complete crest is that of a tab or flange of bone, from the nasals, that rises between and above the eyes and folds back under itself. This unique crest allows it to be distinguished from similar hadrosaurs, like Gryposaurus. The top of the crest is roughened, and the maximum preserved length of the skull is ~90 centimeters (~35 in).
According to Prieto-Márquez who re-diagnosed this genus in 2013, Kritosaurus can be distinguished based on the following characteristics: the length of the dorsolateral margin of the maxilla is extensive, the jugal features an orbital constriction that is deeper than the infratemporal one, the infratemporal fenestra is greater than the orbit and has a dorsal margin that is greatly elevated above the dorsal orbital margin in adults, the frontal bone is participating in the orbital margin, the presence of paired caudal parasagittal processes of the nasals resting over the frontal bones.
Kritosaurus was a hadrosaurine hadrosaurid, a flat-headed or solid-crested duckbill. Though many species and specimens have been referred to the genus in the past, most of them do not show the shared distinguishing characteristics to allow them to be considered part of the genus, or have been synonymized with other genera of hadrosaurs. The closest relative of Kritosaurus navajovius is Anasazisaurus horneri (or Kritosaurus horneri), which, together with close relatives such as Gryposaurus and Secernosaurus, form a clade called the Kritosaurini within the larger clade Saurolophinae. Location and time separate Kritosaurus and the slightly older, primarily Canadian Gryposaurus, along with some cranial details.
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.
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.
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 Bistahieversor. 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. The presence of Parasaurolophus and Kritosaurus in northern latitude fossil sites may represent faunal exchange between otherwise distinct northern and southern biomes in Late Cretaceous North America. Both taxa are uncommon outside of the southern biome, where, along with Pentaceratops, they are predominate members of the fauna.
The geographic range of Kritosaurus remains in North America was expanded by the discovery of bones from the late Campanian-age Aguja Formation of Texas, including a skull. Additionally, a partial skull from Coahuila, Mexico has been referred to K. navajovius.
Since the 1930s, Barnum Brown described that an unsubscribed species of Kritosaurus, the most likely candidate being Kritosaurus navajovius, had inhabited the late Maastrichtian Ojo Alamo Formation, the Javelina Formation in Texas and the El Picacho Formation, which was a flood plain type environment at the time of the Cretaceous. These fossils might be of an unknown species of hadrosaur or an undescribed specimen of Kritosaurus. This genus lived alongside numerous species of dinosaurs including the sauropod Alamosaurus, the ceratopsians Bravoceratops, Ojoceratops, Torosaurus and a possible species of Eotriceratops, hadrosaurs which included a possible species of Edmontosaurus annectens, Saurolophus and Gryposaurus and the armored nodosaur Glyptodontopelta. Theropods from this environment which included Tyrannosaurus, smaller theropods like a species of Troodon and Richardoestesia, the oviraptorid Ojoraptorsaurus, indeterminate ornithomimids and dromaeosaurs. Non-dinosaur species that had shared the same environment with Kritosaurus included the giant pterosaur Quetzalcoatlus, various species of fishes and rays, amphibians, lizards, turtles like Adocus, and multiple species of mammals like Alphadon and Mesodma.
Paleontology or palaeontology is the study of prehistoric life forms on Earth through the examination of plant and animal fossils. This includes the study of body fossils, tracks (ichnites), burrows, cast-off parts, fossilised feces (coprolites), palynomorphs and chemical residues. Because humans have encountered fossils for millennia, paleontology has a long history both before and after becoming formalized as a science. This article records significant discoveries and events related to paleontology that occurred or were published in the year 1910.Acristavus
Acristavus is a genus of saurolophine dinosaur. Fossils have been found from the Campanian Two Medicine Formation in Montana and Wahweap Formation in Utah, United States. The type species A. gagslarsoni was named in 2011. Unlike nearly all hadrosaurids except Edmontosaurus, Acristavus lacked ornamentation on its skull. The discovery of Acristavus is paleontologically significant because it supports the position that the ancestor of all hadrosaurids did not possess cranial ornamentation, and that ornamentation was an adaptation that later arose interdependently in the subfamilies Saurolophinae and Lambeosaurinae. It is closely related to Brachylophosaurus and Maiasaura, and was assigned to a new clade called Brachylophosaurini.Aguja Formation
The Aguja Formation is a geological formation in North America, exposed in Texas, United States and Chihuahua and Coahuila in Mexico, whose strata date back to the Late Cretaceous. Dinosaur remains are among the fossils that have been recovered from the formation.Anasazisaurus
Anasazisaurus ( AH-nə-sah-zee-SAWR-əs; "Anasazi lizard") is a genus of hadrosaurid ("duckbill") ornithopod dinosaur that lived about 74 million years ago, in the Late Cretaceous Period. It was found in the Farmington Member of the Kirtland Formation, in the San Juan Basin of New Mexico, United States. Only a partial skull has been found to date. It was first described as a specimen of Kritosaurus by Jack Horner, and has been intertwined with Kritosaurus since its description. It is known for its short nasal crest, which stuck out above and between its eyes for a short distance.Aquilarhinus
Aquilarhinus (meaning "eagle snout" after the unusual beak morphology) is a genus of hadrosaurid ornithopod dinosaur from the Aguja Formation from Texas in the United States. The type and only species is Aquilarhinus palimentus. Due to its unusual dentary, it has been inferred to have had shovel-like beak morphology, different from the beaks of other hadrosaurs. It was originally classified as a Kritosaurus sp. before being reclassified as a new genus in 2019.Barsboldia
Barsboldia (meaning "of Barsbold", a well-known Mongolian paleontologist) was a genus of large hadrosaurid dinosaur from the early Maastrichtian Nemegt Formation of Ömnogöv', Mongolia. It is known from a partial vertebral column, partial pelvis, and some ribs.Edmontosaurini
Edmontosaurini are a tribe of saurolophine hadrosaurs that lived in the Northern Hemisphere during the Late Cretaceous period. It currently contains Edmontosaurus (from the United States and Canada), Ugrunaaluk (from Alaska, U.S.), and Shantungosaurus (from Shandong, China), though Anatosaurus might be a distinct genus. Kerberosaurus and Kundurosaurus from Russia could also be members though are more likely saurolophins.Gryposaurus
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 74 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, and two formations in the United States: the Lower Two Medicine Formation in Montana and the Kaiparowits Formation of Utah.
Gryposaurus is similar to Kritosaurus, 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," 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 (30 feet) long, it may have preferred river settings.Judithian
The Judithian was a North American faunal stage lasting from 83.5 to 70.6 million years ago. It overlaps with the Campanian global stage.K. australis
K. australis may refer to:
Kingia australis, a plant species
Kritosaurus australis, an hadrosaurid (duckbilled) dinosaur species that lived about 73 million years ago, in the Late Cretaceous of South AmericaKritosaurini
Kritosaurini is a clade of saurolophine hadrosaurid dinosaurs from the Late Cretaceous.Lophorhothon
Lophorhothon (Langston, 1960) is a genus of hadrosauroid dinosaur from the Late Cretaceous, the first genus of dinosaur discovered in Alabama, in the United States.Naashoibitosaurus
Naashoibitosaurus (from Navajo naʼashǫ́ʼii bitooh—"lizard creek") is a genus of hadrosaurid dinosaur that lived about 73 million years ago, in the Late Cretaceous, and was found in the Kirtland Formation of the San Juan Basin in New Mexico, United States. Only a partial skeleton has been found to date. It was first described as a specimen of Kritosaurus by Jack Horner, and has been intertwined with Kritosaurus since its description.Prosaurolophus
Prosaurolophus (; meaning "before Saurolophus", in comparison to the later dinosaur with a similar head crest) is a genus of hadrosaurid (or duck-billed) dinosaur from the Late Cretaceous of North America. It is known from the remains of at least 25 individuals belonging to two species, including skulls and skeletons, but it remains obscure. Around 9 m (30 ft), its fossils have been found in the late Campanian-age Upper Cretaceous Dinosaur Park Formation in Alberta, and the roughly contemporaneous Two Medicine Formation in Montana, dating to around 75.5-74.0 million years ago. Its most recognizable feature is a small solid crest formed by the nasal bones, sticking up in front of the eyes.
The type species is P. maximus, described by American paleontologist Barnum Brown of the American Museum of Natural History in 1916. A second species, P. blackfeetensis, was described by Jack Horner of the Museum of the Rockies in 1992. The two species were differentiated mainly by crest size and skull proportions.Saurolophinae
Saurolophinae is a subfamily of hadrosaurid dinosaurs. It has since the mid-20th century generally been called the Hadrosaurinae, a group of largely non-crested hadrosaurs related to the crested sub-family Lambeosaurinae. However, the name Hadrosaurinae is based on the genus Hadrosaurus which was found in more recent studies to be more primitive than either lambeosaurines or other traditional "hadrosaurines", like Edmontosaurus and Saurolophus. As a result of this, the name Hadrosaurinae was dropped or restricted to Hadrosaurus alone, and the subfamily comprising the traditional "hadrosaurines" was renamed the Saurolophinae. Recent phylogenetic work by Hai Xing indicates that Hadrosaurus is placed within the monophyletic group containing all non-lambeosaurine hadrosaurids. Under this view, the traditional Hadrosaurinae is resurrected, with the Hadrosauridae being divided into two clades: Hadrosaurinae and Lambeosaurinae.
Saurolophinae was first defined as a clade in a 2010 phylogenetic analysis by Prieto-Márquez. Traditionally, the "crestless" branch of the family Hadrosauridae had been named Hadrosaurinae. However, the use of the term Hadrosaurinae was questioned in a comprehensive study of hadrosaurid relationships by Albert Prieto-Márquez in 2010. Prieto-Márquez noted that, though the name Hadrosaurinae had been used for the clade of mostly crestless hadrosaurids by nearly all previous studies, its type species, Hadrosaurus foulkii, has almost always been excluded from the clade that bears its name, in violation of the rules for naming animals set out by the ICZN. Prieto-Márquez (2010) defined Hadrosaurinae as only the lineage containing H. foulkii, and used the name Saurolophinae instead for the traditional grouping.The cladogram below follows Godefroit et al. (2012) analysis.
The following cladogram was recovered in the 2013 phylogenetic analysis by Prieto-Márquez (the relationships within Lambeosaurinae and between basal hadrosauroids aren't shown).Secernosaurus
Secernosaurus (meaning "severed lizard") is a genus of herbivorous dinosaur. Secernosaurus was a hadrosaur, a "duck-billed" dinosaur which lived during the Late Cretaceous. Its fossils have been found in the Lago Colhué Huapi and Los Alamitos Formations of Argentina.Shantungosaurus
Shantungosaurus, meaning "Shandong Lizard", is a genus of saurolophine hadrosaurid dinosaurs found in the Late Cretaceous Wangshi Group of the Shandong Peninsula in China. The stratigraphic interval of Shantungosaurus ranges from the top of the Xingezhuang Formation to the middle of the Hongtuya Formation, middle to late Campanian in age. Shantungosaurus is so far the largest hadrosauroid taxon in the world: the greatest length of its femur is about 1.7 m, and the greatest length of its humerus is about 0.97 m.Trachodon
Trachodon (meaning "rough tooth") is a dubious genus of hadrosaurid dinosaur based on teeth from the Campanian-age Upper Cretaceous Judith River Formation of Montana, U.S. It is a historically important genus with a convoluted taxonomy that has been all but abandoned by modern dinosaur paleontologists.Despite being used for decades as the iconic duckbill dinosaur per antonomasia the material it is based on is composed of teeth from both duckbills and ceratopsids (their teeth have a distinctive double root), and its describer, Joseph Leidy, came to recognize the difference and suggested limiting the genus to what would now be seen as ceratopsid teeth. Restricted to the duckbill teeth, it may have been a lambeosaurine.Willinakaqe
Willinakaqe is a possibly invalid genus of saurolophine hadrosaurid dinosaur described based on fossils the late Cretaceous (late Campanian-early Maastrichtian stage) of the Río Negro Province of southern Argentina.