Kritosaurus Temporal range:Late Cretaceous,74.5–66 Ma PreꞒ Ꞓ O S D C P T J K Pg N
K. navajoviusholotype skull,AMNH
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Reptilia
Clade:	Dinosauria
Clade:	†Ornithischia
Clade:	†Ornithopoda
Family:	†Hadrosauridae
Subfamily:	†Saurolophinae
Tribe:	†Kritosaurini
Genus:	†Kritosaurus Brown, 1910
Type species
†Kritosaurus navajovius Brown, 1910
Species
†K. navajoviusBrown, 1910 †K. horneri?Hunt &Lucas, 1993
Synonyms
Anasazisaurus?Hunt & Lucas, 1993

Kritosaurus is an incompletely knowngenus ofhadrosaurid (duck-billed)dinosaur. It lived about 74.5-66 million years ago, in theLate Cretaceous ofNorth America. The name means "separated lizard" (referring to the arrangement of the cheek bones in an incompletetype skull), but is often mistranslated as "noble lizard" in reference to the presumed "Roman nose"^[1] (in the original specimen, the nasal region was fragmented and disarticulated, and was originally restored flat).

In 1904,Barnum Brown discovered thetype specimen (AMNH 5799) ofKritosaurus near theOjo Alamo Formation,San Juan County,New Mexico,United States, while following up on a previous expedition.^[2] He initially could not definitely correlate thestratigraphy, but by 1916 was able to establish it as from what is now known as thelate Campanian-age De-na-zin Member of theKirtland Formation.^[3][4] When discovered, much of the front of the skull had either eroded or fragmented, and Brown reconstructed this portion after what is now calledEdmontosaurus, leaving out many fragments.^[2] However, he had noticed that something was different about the fragments, but ascribed the differences to crushing.^[5] He initially wanted to name itNectosaurus, but found out that this name was already in use;Jan Versluys, who had visited Brown before the change, inadvertently leaked the previous choice.^[6] He kept the specific name, though, leading to the combinationK. navajovius.

The 1914 publication of the arch-snouted Canadian genusGryposaurus^[7] 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 aGryposaurus-like archednasal crest.^[5] He also synonymizedGryposaurus withKritosaurus,^[8] a move supported byCharles Gilmore.^[3] This synonymy was used through the 1920s (William Parks's designation of aCanadian species asKritosaurus incurvimanus,^[9] now considered a synonym ofGryposaurus notabilis^[10]) and became standard after the publication ofRichard Swann Lull andNelda Wright's 1942monograph on North American hadrosaurids.^[11] From this time until 1990,Kritosaurus would be composed of at least thetype speciesK. navajovius,K. incurvimanus, andK. notabilis, the former type species ofGryposaurus. The poorly known speciesHadrosaurus breviceps (Marsh, 1889),^[12] known from adentary from the Campanian-ageJudith River Formation ofMontana, was also assigned toKritosaurus by Lull and Wright,^[11] but this is no longer accepted.^[13][14]

By the late 1970s and early 1980s,Hadrosaurus had entered the discussion as a possible synonym of eitherKritosaurus,Gryposaurus, or both, particularly in semi-technical "dinosaur dictionaries".^[15][16]David B. Norman'sThe Illustrated Encyclopedia of Dinosaurs, usesKritosaurus for the Canadian material (Gryposaurus), but identifies the mounted skeleton ofK. incurvimanus asHadrosaurus.^[17]

The synonymization ofKritosaurus andGryposaurus that lasted from the 1910s to 1990 led to a distorted picture of what the originalKritosaurus material represented. Because the Canadian material was much more complete, most representations and discussions ofKritosaurus from the 1920s to 1990 are actually more applicable toGryposaurus. This includes, for example, James Hopson's discussion of hadrosaur cranial ornamentation,^[18] and the adaptation of this for the public inThe Illustrated Encyclopedia of Dinosaurs.^[19]

In 1984,ArgentinepaleontologistJosé Bonaparte and colleagues namedKritosaurus australis for hadrosaur bones from the late Campanian-early MaastrichtianLos Alamitos Formation ofRio Negro,Patagonia,Argentina.^[20] In 2010, this species was thought to be a synonym ofSecernosaurus koerneri.^[21] Further analysis proved the bones to belong to a new genus. Thus,Huallasaurus was named by Rozadillaet al. (2022).^[22]

In 1990,Jack Horner andDavid B. Weishampel once again separatedGryposaurus, citing the uncertainty associated with the latter's partial skull. Horner in 1992 described two more skulls from New Mexico that he claimed belonged toKritosaurus and showed that it was quite different fromGryposaurus,^[23] but the following yearAdrian Hunt andSpencer G. Lucas put each skull in its own genus, creatingAnasazisaurus andNaashoibitosaurus.^[24]

Adrian Hunt andSpencer G. Lucas,Americanpaleontologists, namedAnasazisaurus horneri in 1993. The name was derived from theAnasazi, an ancientNative American people, and theGreek wordsauros ("lizard"). The Anasazi were famous for theircliff-dwellings, such as those inChaco Canyon, near the location offossilAnasazisaurus remains. The term "Anasazi" itself is actually aNavajo language word,anaasází ("enemy ancestors"). The species was named in honor ofJack Horner, the American paleontologist who first described the skull in 1992. Theholotype skull (and only known specimen) was collected in the late 1970s by aBrigham Young University field party working inSan Juan County, and is housed at BYU as BYU 12950.^[24]

In 2002, specimen TxVP 41917-1, a partial leftmaxilla recovered from Bruja Canyon inBig Bend National Park, was assigned toKritosaurus, ascf. K. navajovius. Twenty years later, it was discovered to contain a number of useful diagnostic traits that allow it to bedescribed as a new taxon, and thusMalefica was named by Prieto-Márquez and Wagner (2023).^[25]

Horner originally assigned theAnasazisaurus skull toKritosaurus navajovius,^[23] but Hunt and Lucas could not find any diagnostic features in the limited material ofKritosaurus and judged the genus to be anomen dubium. Since theAnasazisaurus skull did have diagnostic features of its own, and did not appear to them to share any unique features withKritosaurus, it was given the new nameAnasazisaurus horneri,^[24] an opinion which was supported by some later authors.^[13] Not all authors have agreed with this,Thomas E. Williamson in particular defending Horner's original interpretation,^[4] and several subsequent studies recognized both distinct genera.^[26][29]

A comprehensive study of knownKritosaurus material published by Albert Prieto-Márquez in 2013 upheld the status ofNaashoibitosaurus as a distinct genus, but found that the type specimens ofKritosaurus andAnasazisaurus were indistinguishable when comparing overlapping elements (i.e. only those bones preserved in both specimens). Prieto-Márquez therefore regardedAnasazisaurus as a synonym ofKritosaurus, but retained it as the distinct speciesK. horneri.^[27]

A partial skeleton from the Sabinas Basin in Mexico was described asKritosaurus sp. by Jim Kirkland and colleagues,^[26] but considered an indeterminate saurolophine by Prieto-Márquez (2013).^[27] This skeleton is about 20% larger than other known specimens, around 11 meters [36 ft] long, and with a distinctively curvedischium, and represents one of the largest known well-documented North American saurolophines. Unfortunately, the nasal bones are also incomplete in the skull remains from this material.^[26] The informal name "Sabinosaurus" has been given to the specimen.^[28]

A possibly second but confirmed to be valid species ofKritosaurus may have lived in theJavelina Formation alongsideKritosaurus navajovius.^{[30][31][32][33]}Kritosaurus fossils have also been unearthed in theOlmos Formation in Mexico.^[34]

The type specimen ofKritosaurus navajovius is only represented by a partial skull and lower jaws, and associatedpostcranial remains.^[13] The greater portion of the muzzle andupper beak are missing.^[26] However, these remains alone indicate a large body size, reaching 9 metres (30 ft) in length and 4 metric tons (4.4 short tons) in body mass.^[35][36]

The length of the skull is estimated at 87 cm (34 in) from the tip of the upper beak to the base of thequadrate that articulates with the lower jaw at the back of the skull.^[37] Based on the skull originally referred toAnasazisaurus, 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, likeGryposaurus.^[23] The top of the crest is roughened, and the maximum preserved length of the skull could reach 90 cm (35 in).^[29] Potentialdiagnostic characteristics ofKritosaurus include apredentary (lower beak) without tooth-like crenulations, a sharp downward bend to the lower jaws near the beak, and a heavy, somewhat rectangularmaxilla (upper tooth-bearing bone).^[26]

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 themaxilla is extensive, thejugal features an orbital constriction that is deeper than the infratemporal one, the infratemporalfenestra is greater than the orbit and has a dorsal margin that is greatly elevated above the dorsal orbital margin in adults, thefrontal bone is participating in the orbital margin, the presence of paired caudal parasagittal processes of the nasals resting over the frontal bones.^[27]

Kritosaurus was ahadrosaurinehadrosaurid, 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 ofKritosaurus navajovius isAnasazisaurus horneri (orKritosaurus horneri), which, together with close relatives such asGryposaurus andSecernosaurus, form a clade called theKritosaurini within the larger cladeSaurolophinae.^[27] Location and time separateKritosaurus and the slightly older, primarily CanadianGryposaurus, along with some cranial details.^[26]

The following is acladogram based on the phylogenetic analysis conducted by Prieto-Márquez and Wagner in 2012, showing the relationships ofKritosaurus among the otherKritosaurini:^[38]

The nasal crest ofKritosaurus, whatever its true form, may have been used for a variety of social functions, such as identification of sexes or species and social ranking.^[13] There may have been inflatable air sacs flanking it for both visual and auditory signaling.^[18]

As a hadrosaurid,Kritosaurus would have been a largebipedal/quadrupedalherbivore, eatingplants with a sophisticated skull that permitted a grinding motion analogous tochewing. 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. Feeding would have been from the ground up to ~4 meters (13 ft) above.^[13] If it was a separate genus, how it would have partitioned resources with the similar and contemporaneousNaashoibitosaurus is unknown.^{[citation needed]}

Kritosaurus was discovered in the De-na-zin Member of theKirtland Formation. This formation dates from the lateCampanian stages of theLate Cretaceous Period (74 to 70 million years ago),^[4] and is also the source of several other dinosaurs, likeAlamosaurus, a species ofParasaurolophus,Pentaceratops,Nodocephalosaurus,Saurornitholestes, andBistahieversor.^[39] The Kirtland Formation is interpreted asriver floodplains appearing after a retreat of theWestern Interior Seaway.Conifers were the dominant plants, andchasmosaurine horned dinosaurs appear to have been more common than hadrosaurids.^[40] The presence ofParasaurolophus andKritosaurus in northern latitude fossil sites may represent faunal exchange between otherwise distinct northern and southern biomes in Late Cretaceous North America.^[41] Both taxa are uncommon outside of the southern biome, where, along withPentaceratops, they are predominate members of the fauna.^[41]

The geographic range ofKritosaurus remains in North America was expanded by the discovery of bones from the late Campanian-ageAguja Formation ofTexas, including a skull,^[42][32] although this specimen was given its own genus name,Aquilarhinus, in 2019.^[43] Additionally, a partial skull fromCoahuila,Mexico has been referred toK. navajovius.^[27]

Since the 1910s and 1930s, Barnum Brown described that an unsubscribed species ofKritosaurus, the most likely candidate beingKritosaurus navajovius, had inhabited the lateMaastrichtianOjo Alamo Formation, where the first specimen ofKritosaurus was unearthed, in New Mexico as well as theJavelina Formation and theEl Picacho Formation in Texas, which was aflood plain type environment at the time of the Cretaceous.^{[2][44][45][46]}Charles W. Gilmore also made notes about Brown's work surveys and finds from the Ojo Alamo Formation whilst doing research in theNorth Horn Formation in Utah as well as researching the Ojo Alamo Formation himself.^[47][48] These fossils might be of an unknown species of hadrosaur or an undescribed specimen ofKritosaurus orKritosaurus navajovius. However, not all of the paleontological community agrees with the age of theKritosaurus holotype unearthed by Barnum Brown. This is due to theunconformity that divides the Ojo Alamo Formation into two parts; the older Naashoibito member, which overlies theCampanian eraKirtland Formation, and the younger Kimbeto member. Starting in the 2000s and 2010s, more research into this area as well as nearby fossil formations in neighboring states has brought more information about them to light. This issue will probably be resolved in the future.^{[49][50][51][52][53][54]}

However, confirmedKritosaurus remains, possibly belonging toK. navajovius, cf.K. navajovius, and possibly a new species have been unearthed in theJavelina Formation and theEl Picacho Formation in Texas.^{[32][2][44][45][55][56][57][58][59]} This genus lived alongside numerous species of dinosaurs including the sauropodAlamosaurus, the ceratopsiansBravoceratops,Ojoceratops,Torosaurus and a possible species ofEotriceratops, hadrosaurs which included a possible species ofEdmontosaurus annectens, a hadrosaur very similar toSaurolophus andGryposaurus,Gryposaurus alsatei to be exact,^[55] and the armored nodosaurGlyptodontopelta. Theropods from this environment which includedTyrannosaurus, smallertheropods like a species ofTroodon andRichardoestesia, the oviraptoridOjoraptorsaurus, the dromaeosaurDineobellator, and indeterminate ornithomimids and other undescribed dromaeosaurs. Non-dinosaur species that had shared the same environment withKritosaurus included the giant pterosaurQuetzalcoatlus, various species offishes andrays,amphibians,lizards,turtles likeAdocus, and multiple species ofmammals likeAlphadon andMesodma.

• Timeline of hadrosaur research

• Media related toKritosaurus at Wikimedia Commons

• Saurolophinae
• Dinosaur genera
• Campanian dinosaurs
• Maastrichtian dinosaurs
• Kirtland Formation
• Taxa named by Barnum Brown
• Fossil taxa described in 1910
• Dinosaurs of the United States

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