Kritosaurus

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Kritosaurus
Temporal range: Late Cretaceous, 74.5–66  Ma
Kritosaurus.jpg
K. navajovius holotype skull, AMNH
Scientific classification OOjs UI icon edit-ltr.svg
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Clade: Dinosauria
Clade: Ornithischia
Clade: Neornithischia
Clade: Ornithopoda
Family: Hadrosauridae
Subfamily: Saurolophinae
Tribe: Kritosaurini
Genus: Kritosaurus
Brown, 1910
Type species
Kritosaurus navajovius
Brown, 1910
Species

K. navajovius Brown, 1910
K. horneri ? Hunt & Lucas, 1993

Contents

Synonyms

Anasazisaurus ? Hunt & Lucas, 1993

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" [1] (in the original specimen, the nasal region was fragmented and disarticulated, and was originally restored flat).

History of discovery

Barnum Brown's initial flatheaded reconstruction of the skull of K. navajovius, 1910 Kritosaurus Brown original.jpg
Barnum Brown's initial flatheaded reconstruction of the skull of K. navajovius, 1910

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. [2] 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. [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 called Edmontosaurus , 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 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. [6] He kept the specific name, though, leading to the combination K. navajovius.

The 1914 publication of the arch-snouted Canadian genus Gryposaurus [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 a Gryposaurus-like arched nasal crest. [5] He also synonymized Gryposaurus with Kritosaurus, [8] a move supported by Charles Gilmore. [3] This synonymy was used through the 1920s (William Parks's designation of a Canadian species as Kritosaurus incurvimanus , [9] now considered a synonym of Gryposaurus notabilis [10] ) and became standard after the publication of Richard Swann Lull and Nelda Wright's 1942 monograph on North American hadrosaurids. [11] 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), [12] known from a dentary from the Campanian-age Judith River Formation of Montana, was also assigned to Kritosaurus 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 either Kritosaurus, Gryposaurus, or both, particularly in semi-technical "dinosaur dictionaries". [15] [16] 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. [17]

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, [18] and the adaptation of this for the public in The Illustrated Encyclopedia of Dinosaurs. [19]

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. [20] In 2010, this species was thought to be a synonym of Secernosaurus koerneri . [21] Further analysis proved the bones to belong to a new genus. Thus, Huallasaurus was named by Rozadilla et al. (2022). [22]

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, [23] but the following year Adrian Hunt and Spencer G. Lucas put each skull in its own genus, creating Anasazisaurus and Naashoibitosaurus . [24]

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. [24]

In 2002, specimen TxVP 41917-1, a partial left maxilla recovered from Bruja Canyon in Big Bend National Park, was assigned to Kritosaurus, as cf. K. navajovius. Twenty years later, it was discovered to contain a number of useful diagnostic traits that allow it to be described as a new taxon, and thus Malefica was named by Prieto-Márquez and Wagner (2023). [25]

Unnamed specimen from the Sabinas Basin in Mexico, assigned to Kritosaurus sp. by Kirkland et al. (2006) but considered an indeterminate saurolophine by Prieto-Marquez (2013). The specimen is informally known as "Sabinosaurus". Kritosaurus Sabinosaurio.jpg
Unnamed specimen from the Sabinas Basin in Mexico, assigned to Kritosaurus sp. by Kirkland et al. (2006) but considered an indeterminate saurolophine by Prieto-Márquez (2013). The specimen is informally known as "Sabinosaurus".

Horner originally assigned the Anasazisaurus skull to Kritosaurus navajovius, [23] 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, [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 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. [27]

A partial skeleton from the Sabinas Basin in Mexico was described as Kritosaurus 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 curved ischium, 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 of Kritosaurus may have lived in the Javelina Formation alongside Kritosaurus navajovius. [30] [31]

Description

Size comparison Kritosaurus Scale.svg
Size comparison

The type specimen of Kritosaurus navajovius is only represented by a partial skull and lower jaws, and associated postcranial remains. [13] The greater portion of the muzzle and upper 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. [32] [33]

The length of the skull is estimated at 87 cm (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. [34] 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 . [23] The top of the crest is roughened, and the maximum preserved length of the skull could reach 90 cm (35 in). [29] 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). [26]

K. navajovius life restoration Kritosaurus navajovius.png
K. navajovius life restoration

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. [27]

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. [27] Location and time separate Kritosaurus and the slightly older, primarily Canadian Gryposaurus, along with some cranial details. [26]

Cast of an assigned egg Kritosaurus egg (cast).JPG
Cast of an assigned egg

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: [35]

  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. [13] There may have been inflatable air sacs flanking it for both visual and auditory signaling. [18]

Diet and feeding

Lower jaw in inner view Kritosaurus jaw.jpg
Lower jaw in inner view

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. [13] If it was a separate genus, how it would have partitioned resources with the similar and contemporaneous Naashoibitosaurus is unknown.[ citation needed ]

Paleoecology

Tooth, Museo Civico di Storia Naturale di Milano Kritosaurus tooth.jpg
Tooth, Museo Civico di Storia Naturale di Milano

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), [4] and is also the source of several other dinosaurs, like Alamosaurus , a species of Parasaurolophus , Pentaceratops , Nodocephalosaurus , Saurornitholestes , and Bistahieversor . [36] 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. [37] 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. [38] Both taxa are uncommon outside of the southern biome, where, along with Pentaceratops , they are predominate members of the fauna. [38]

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, [39] [40] although this specimen was given its own genus name, Aquilarhinus , in 2019. [41] Additionally, a partial skull from Coahuila, Mexico has been referred to K. navajovius. [27]

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. [2] [42] [43] 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. [44] [45] 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. [46] [47] [48] [49] [50] [51]

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. [40] [2] [42] [43] [52] 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, [52] 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

Related Research Articles

<i>Hadrosaurus</i> Hadrosaurid dinosaur genus from the Late Cretaceous

Hadrosaurus is a genus of hadrosaurid ornithopod dinosaurs that lived in North America during the Late Cretaceous Period in what is now the Woodbury Formation in New Jersey about 78-80 Ma. The holotype specimen was found in fluvial marine sedimentation, meaning that the corpse of the animal was transported by a river and washed out to sea.

<i>Parasaurolophus</i> Hadrosaurid ornithopod dinosaur genus from Late Cretaceous Period

Parasaurolophus is a genus of hadrosaurid "duck-billed" dinosaur that lived in what is now western North America and possibly Asia during the Late Cretaceous period, about 76.9–73.5 million years ago. It was a large herbivore that could reach over 9 metres (30 ft) long and weigh over 5 metric tons, and were able to move as a biped and a quadruped. Three species are universally recognized: P. walkeri, P. tubicen, and the short-crested P. cyrtocristatus. Additionally, a fourth species, P. jiayinensis, has been proposed, although it is more commonly placed in the separate genus Charonosaurus. Remains are known from Alberta, New Mexico, and Utah, as well as possibly Heilongjiang if Charonosaurus is in fact part of the genus. The genus was first described in 1922 by William Parks from a skull and partial skeleton found in Alberta.

<i>Gryposaurus</i> Extinct genus of reptiles

Gryposaurus was a genus of duckbilled dinosaur that lived about 80 to 75 million years ago, in the Late Cretaceous 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. A possible additional species from the Javelina Formation in Texas may extend the temporal range of the genus to 66 million years ago.

<i>Aralosaurus</i> Extinct genus of dinosaurs

Aralosaurus was a genus of hadrosaurid dinosaur that lived during the Late Cretaceous in what is now Kazakhstan. It is known only by a posterior half of a skull and some post-cranial bones found in the Bostobe Formation in rocks dated from the Upper Santonian-Lower Campanian boundary, at about 83.6 Ma. Only one species is known, Aralosaurus tuberiferus, described by Anatoly Konstantinovich Rozhdestvensky in 1968. The genus name means Aral Sea lizard, because it was found to the northeast of the Aral Sea. The specific epithet tuberiferus means bearing a tuber because the posterior part of the nasal bone rises sharply in front of the orbits like an outgrowth. Aralosaurus was originally reconstituted with a nasal arch similar to that of North American Kritosaurus. For many years, Aralosaurus was thus placed in the clade of the Hadrosaurinae. This classification was invalidated in 2004, following the re-examination of the skull of the animal which allowed to identify in Aralosaurus many typical characters of Lambeosaurinae. In particular, this study revealed that Aralosaurus had a hollow bony structure located far in front of the orbits, which communicated with the respiratory tract. This structure being broken at its base, its shape and size remains undetermined. More recently, Aralosaurus has been identified as the most basal Lambeosaurinae, and placed with its close relative Canardia from the upper Maastrichtian of France in the new clade of Aralosaurini.

<i>Lophorhothon</i> Genus of dinosaur

Lophorhothon is a genus of hadrosauroid dinosaur from the Late Cretaceous of Alabama and North Carolina. It was the first genus of dinosaur discovered in Alabama, in the United States.

<i>Anasazisaurus</i> Extinct genus of dinosaurs

Anasazisaurus is a genus of saurolophine 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.

<i>Secernosaurus</i> Extinct genus of dinosaurs

Secernosaurus is a genus of herbivorous dinosaur. Secernosaurus was a hadrosaur, a "duck-billed" dinosaur which lived during the Late Cretaceous.

<i>Prosaurolophus</i> Extinct genus of dinosaurs

Prosaurolophus is a genus of hadrosaurid 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. 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.

<i>Naashoibitosaurus</i> Extinct genus of dinosaurs

Naashoibitosaurus 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.

<span class="mw-page-title-main">Kirtland Formation</span> Geological formation in New Mexico and Colorado, United States

The Kirtland Formation is a sedimentary geological formation.

<span class="mw-page-title-main">Lambeosaurinae</span> Extinct subfamily of dinosaurs

Lambeosaurinae is an extinct group of crested hadrosaurid dinosaurs.

<span class="mw-page-title-main">Saurolophinae</span> Extinct subfamily of dinosaurs

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.

<i>Velafrons</i> Extinct genus of dinosaurs

Velafrons is a genus of lambeosaurine hadrosaurid dinosaur from the Late Cretaceous of Mexico. It is known from a mostly complete skull and partial skeleton of a juvenile individual, with a bony crest on the forehead. Its fossils were found in the late Campanian-age Cerro del Pueblo Formation, near Rincon Colorado, Coahuila, Mexico. The type specimen is CPC-59, and the type species is V. coahuilensis.

<span class="mw-page-title-main">Aguja Formation</span> Geological formation in North America

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. Fossil palms have also been unearthed here.

Willinakaqe is a dubious genus of saurolophine hadrosaurid dinosaur described based on fossils from the late Cretaceous of the Río Negro Province of southern Argentina.

<i>Acristavus</i> Extinct genus of dinosaurs

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.

<i>Latirhinus</i> Extinct genus of reptiles

Latirhinus is an extinct genus of lambeosaurine hadrosaurid dinosaur from the Late Cretaceous of Mexico. The type species, Latirhinus uitstlani, was named in 2012 on the basis of a partial skeleton from the Campanian-age Cerro del Pueblo Formation. The specific name uitstlani means "southern" in the Náhuatl language of Mexico, a reference to the species' southern occurrence in the Cretaceous landmass Laramidia.

<span class="mw-page-title-main">Timeline of hadrosaur research</span>

This timeline of hadrosaur research is a chronological listing of events in the history of paleontology focused on the hadrosauroids, a group of herbivorous ornithopod dinosaurs popularly known as the duck-billed dinosaurs. Scientific research on hadrosaurs began in the 1850s, when Joseph Leidy described the genera Thespesius and Trachodon based on scrappy fossils discovered in the western United States. Just two years later he published a description of the much better-preserved remains of an animal from New Jersey that he named Hadrosaurus.

<i>Malefica</i> Extinct genus of hadrosaurid dinosaur

Malefica is a genus of hadrosaurid dinosaur from the Late Cretaceous (Campanian) Aguja Formation of Texas. The type and only species is Malefica deckerti.

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