Kritosaurus

''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).

History of discovery

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''.

Formerly assigned species and material

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. In 2010, this species was thought to be a synonym of '' Secernosaurus koerneri''. Further analysis proved the bones to belong to a new genus. Thus, '' Huallasaurus'' was named by Rozadilla et al. (2022).

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 6 ftlong, 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.

A possibly second but confirmed to be valid species of ''Kritosaurus'' may have lived in the Javelina Formation alongside ''Kritosaurus navajovius''.

Description

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. However, these remains alone indicate a large body size, reaching in length and in body mass.

The length of the skull is estimated at 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. 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 could reach . 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).

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.

Classification

''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 following is a cladogram based on the phylogenetic analysis conducted by Prieto-Márquez and Wagner in 2012, showing the relationships of ''Kritosaurus'' among the other Kritosaurini:

Paleobiology

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.

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.

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 ''Bistahieversor''.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. 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.Lehman, T. M., 2001, Late Cretaceous dinosaur provinciality: In: Mesozoic Vertebrate Life, edited by Tanke, D. H., and Carpenter, K., Indiana University Press, pp. 310-328.

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, although this specimen was given its own genus name, '' Aquilarhinus'', in 2019. Additionally, a partial skull from Coahuila, Mexico has been referred to ''K. navajovius''.

Since the 1910s and 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, where the first specimen of ''Kritosaurus'' was unearthed, in New Mexico as well as the Javelina Formation and the El Picacho Formation in Texas, which was a flood plain type environment at the time of the Cretaceous. Charles W. Gilmore also made notes about Brown's work surveys and finds from the Ojo Alamo Formation whilst doing research in the North Horn Formation in Utah as well as researching the Ojo Alamo Formation himself. These fossils might be of an unknown species of hadrosaur or an undescribed specimen of ''Kritosaurus'' or ''Kritosaurus navajovius''. However, not all of the paleontological community agrees with the age of the ''Kritosaurus'' holotype unearthed by Barnum Brown. This is due to the unconformity that divides the Ojo Alamo Formation into two parts; the older Naashoibito member, which overlies the Campanian era Kirtland 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.

However, confirmed ''Kritosaurus'' remains, possibly belonging to ''K. navajovius'', cf. ''K. navajovius'', and possibly a new species have been unearthed in the Javelina Formation and the El Picacho Formation in Texas. 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'', a hadrosaur very similar to ''Saurolophus'' and ''Gryposaurus'', ''Gryposaurus alsatei'' to be exact, and the armored nodosaur ''Glyptodontopelta''. Theropods from this environment which included ''Tyrannosaurus'', smaller theropods like a species of ''Troodon'' and ''Richardoestesia'', the oviraptorid ''Ojoraptorsaurus'', the dromaeosaur ''Dineobellator'', and indeterminate ornithomimids and other undescribed 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''.

See also

* Timeline of hadrosaur research

References

External links

*

{{Taxonbar, from=Q968771

Late Cretaceous dinosaurs of North America
Saurolophines
Natural history of San Juan County, New Mexico
Maastrichtian life
Fossil taxa described in 1910
Taxa named by Barnum Brown
Paleontology in New Mexico
Campanian genus first appearances
Maastrichtian genus extinctions
Ornithischian genera