Kritosaurus
Encyclopedia
Kritosaurus is an incompletely known but historically important genus
of hadrosaurid
(duck-billed) dinosaur
. It lived about 73 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). The taxonomic
history of Kritosaurus 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.
Kritosaurus is only definitely determined from a partial skull and lower jaws, and associated undescribed postcrania
l remains. 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; 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. 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.
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.
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. 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 Anatotitan
, 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 species 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 influential 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". 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. 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
. This species is now thought to be a synonym of Secernosaurus koerneri
.
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, but the following year Adrian Hunt and Spencer G. Lucas
put each skull in its own genus, creating Anasazisaurus
and Naashoibitosaurus
. 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.
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. 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.
. 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. 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.
al herbivore
, eating plant
s 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.
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
of hadrosaurid
Hadrosaurid
Hadrosaurids or duck-billed dinosaurs are members of the family Hadrosauridae, and include ornithopods such as Edmontosaurus and Parasaurolophus. They were common herbivores in the Upper Cretaceous Period of what are now Asia, Europe and North America. They are descendants of the Upper...
(duck-billed) dinosaur
Dinosaur
Dinosaurs are a diverse group of animals of the clade and superorder Dinosauria. They were the dominant terrestrial vertebrates for over 160 million years, from the late Triassic period until the end of the Cretaceous , when the Cretaceous–Paleogene extinction event led to the extinction of...
. It lived about 73 million years ago, in the Late Cretaceous
Late Cretaceous
The Late Cretaceous is the younger of two epochs into which the Cretaceous period is divided in the geologic timescale. Rock strata from this epoch form the Upper Cretaceous series...
of North America
North America
North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...
. The name means "separated lizard" (referring to the arrangement of the cheek bones in an incomplete type
Type
Type may refer to:In philosophy:*Type–token distinctionIn mathematics:*Type *Type theory, basis for the study of type systems*Type or arity, the number of operands a function takes...
skull), but is often mistranslated as "noble lizard" in reference to the presumed "Roman nose
Hooknose
]An Aquiline nose is a human nose with a prominent bridge, giving it the appearance of being curved or slightly bent...
" (in the original specimen, the nasal region was fragmented and disarticulated, and was originally restored flat). The taxonomic
Taxonomy
Taxonomy is the science of identifying and naming species, and arranging them into a classification. The field of taxonomy, sometimes referred to as "biological taxonomy", revolves around the description and use of taxonomic units, known as taxa...
history of Kritosaurus is convoluted, also incorporating Gryposaurus
Gryposaurus
Gryposaurus was a genus of duckbilled dinosaur that lived about 83 to 75.5 million years ago, in the Late Cretaceous of North America...
, Anasazisaurus
Anasazisaurus
Anasazisaurus is a genus of hadrosaurid 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...
, and Naashoibitosaurus
Naashoibitosaurus
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...
; this tangle will remain unresolved until better remains of Kritosaurus are described. Despite the dearth of material, this herbivore
Herbivore
Herbivores are organisms that are anatomically and physiologically adapted to eat plant-based foods. Herbivory is a form of consumption in which an organism principally eats autotrophs such as plants, algae and photosynthesizing bacteria. More generally, organisms that feed on autotrophs in...
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
Postcrania
Postcrania[p] in zoology and vertebrate paleontology refers to all or part of the skeleton apart from the skull. Frequently, fossil remains, e.g...
l remains. The greater portion of the muzzle and upper beak
Premaxilla
The incisive bone is the portion of the maxilla adjacent to the incisors. It is a pair of small cranial bones at the very tip of the jaws of many animals, usually bearing teeth, but not always. They are connected to the maxilla and the nasals....
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; 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
Quadrate bone
The quadrate bone is part of a skull in most tetrapods, including amphibians, sauropsids , and early synapsids. In these animals it connects to the quadratojugal and squamosal in the skull, and forms part of the jaw joint .- Evolutionary variation :In snakes, the quadrate bone has become elongated...
that articulates with the lower jaw at the back of the skull. Potential diagnostic characteristics
Autapomorphy
In cladistics, an autapomorphy is a distinctive anatomical feature, known as a derived trait, that is unique to a given terminal group. That is, it is found only in one member of a clade, but not found in any others or outgroup taxa, not even those most closely related to the group...
of Kritosaurus include a predentary
Predentary
The predentary is an 'extra' bone in the front of the lower jaw, which extended the dentary . It is found in the fossilised remains of ornithischian dinosaurs, which were herbivorous. The predentary coincided with the premaxilla in the upper jaw. Together they formed a beak-like apparatus used to...
(lower beak) without tooth-like crenulations, a sharp downward bend to the lower jaws near the beak, and a heavy, somewhat rectangular maxilla
Maxilla
The maxilla is a fusion of two bones along the palatal fissure that form the upper jaw. This is similar to the mandible , which is also a fusion of two halves at the mental symphysis. Sometimes The maxilla (plural: maxillae) is a fusion of two bones along the palatal fissure that form the upper...
(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 hadrosaurineHadrosaurinae
Saurolophinae is a subfamily of hadrosaurid dinosaurs. Members of the subfamily derive from the Late Cretaceous of Antarctica, Argentina, Canada , China, Kazakhstan, Mexico, Russia, the United States and...
hadrosaurid
Hadrosaurid
Hadrosaurids or duck-billed dinosaurs are members of the family Hadrosauridae, and include ornithopods such as Edmontosaurus and Parasaurolophus. They were common herbivores in the Upper Cretaceous Period of what are now Asia, Europe and North America. They are descendants of the Upper...
, 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
Clade
A clade is a group consisting of a species and all its descendants. In the terms of biological systematics, a clade is a single "branch" on the "tree of life". The idea that such a "natural group" of organisms should be grouped together and given a taxonomic name is central to biological...
with Saurolophus
Saurolophus
Saurolophus is a genus of large hadrosaurine duckbill that lived about 69.5-68.5 million years ago, in the Late Cretaceous of North America and Asia; it is one of the few genera of dinosaurs known from multiple continents. It is distinguished by a spike-like crest which projects up and back...
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
Nomen dubium
In zoological nomenclature, a nomen dubium is a scientific name that is of unknown or doubtful application...
. Location and time separate Kritosaurus and the slightly older, primarily Canadian Gryposaurus, along with some cranial details.
Discovery and history
Barnum Brown
Barnum Brown , a paleontologist born in Carbondale, Kansas, and named after the circus showman P.T. Barnum, discovered the second fossil of Tyrannosaurus rex during a career that made him one of the most famous fossil hunters working from the late Victorian era into the early 20th century.Sponsored...
discovered the type
Holotype
A holotype is a single physical example of an organism, known to have been used when the species was formally described. It is either the single such physical example or one of several such, but explicitly designated as the holotype...
specimen (AMNH
American Museum of Natural History
The American Museum of Natural History , located on the Upper West Side of Manhattan in New York City, United States, is one of the largest and most celebrated museums in the world...
5799) of Kritosaurus near Ojo Alamo, San Juan County
San Juan County, New Mexico
-2010:Whereas according to the 2010 U.S. Census Bureau:*51.6% White*0.6% Black*36.6% Native American*0.4% Asian*0.1% Native Hawaiian or Pacific Islander*3.5% Two or more races*7.2% Other races*19.1% Hispanic or Latino -2000:...
, New Mexico
New Mexico
New Mexico is a state located in the southwest and western regions of the United States. New Mexico is also usually considered one of the Mountain States. With a population density of 16 per square mile, New Mexico is the sixth-most sparsely inhabited U.S...
, United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
, while following up on a previous expedition. He initially could not definitely correlate the stratigraphy
Stratigraphy
Stratigraphy, a branch of geology, studies rock layers and layering . It is primarily used in the study of sedimentary and layered volcanic rocks....
, but by 1916 was able to establish it as from what is now known as the late Campanian
Campanian
The Campanian is, in the ICS' geologic timescale, the fifth of six ages of the Late Cretaceous epoch . The Campanian spans the time from 83.5 ± 0.7 Ma to 70.6 ± 0.6 Ma ...
-age De-na-zin Member of the Kirtland Formation
Kirtland Formation
The Kirtland Formation is a sedimentary geological formation. It is the product of alluvial muds and overbank sand deposits from the many channels draining the coastal plain that existed on the inland seashore of North America, in the late Cretaceous period. It overlies the Fruitland 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 Anatotitan
Anatotitan
Anatotitan is a genus of flat-headed or hadrosaurine hadrosaurid ornithopod dinosaur from the very end of the Cretaceous Period, in what is now North America...
, 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
Nectosaurus
Nectosaurus is a genus of marine diapsid reptile which lived during the Late Triassic of what is now California. The type species is N. halinus, described by John C. Merriam in 1905. A 2002 analysis of Nectosaurus classifies it as a thalattosaurian, one of a group of marine reptiles which lived...
, 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 species 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
Nasal bone
The nasal bones are two small oblong bones, varying in size and form in different individuals; they are placed side by side at the middle and upper part of the face, and form, by their junction, "the bridge" of the nose.Each has two surfaces and four borders....
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
Canada
Canada is a North American country consisting of ten provinces and three territories. Located in the northern part of the continent, it extends from the Atlantic Ocean in the east to the Pacific Ocean in the west, and northward into the Arctic Ocean...
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 influential 1942 monograph
Monograph
A monograph is a work of writing upon a single subject, usually by a single author.It is often a scholarly essay or learned treatise, and may be released in the manner of a book or journal article. It is by definition a single document that forms a complete text in itself...
on North American hadrosaurids. From this time until 1990, Kritosaurus would be composed of at least the type species
Type species
In biological nomenclature, a type species is both a concept and a practical system which is used in the classification and nomenclature of animals and plants. The value of a "type species" lies in the fact that it makes clear what is meant by a particular genus name. A type species is the species...
K. navajovius, K. incurvimanus, and K. notabilis, the former type species of Gryposaurus. The poorly known species Hadrosaurus breviceps
Hadrosaurus
Hadrosaurus is a valid genus of hadrosaurid dinosaur. In 1858, a skeleton of a dinosaur from this genus was the first dinosaur skeleton known from more than isolated teeth to be found in North America. In 1868, it became the first ever mounted dinosaur skeleton...
(Marsh
Othniel Charles Marsh
Othniel Charles Marsh was an American paleontologist. Marsh was one of the preeminent scientists in the field; the discovery or description of dozens of news species and theories on the origins of birds are among his legacies.Born into a modest family, Marsh was able to afford higher education...
, 1889), known from a dentary from the Campanian-age Judith River Formation
Judith River Formation
The Judith River Formation is a fossil-bearing geologic formation in Montana, and is part of the Judith River Group. It dates to the upper Cretaceous, between 80 and 75 million years ago, corresponding to the "Judithian" land vertebrate age...
of Montana
Montana
Montana is a state in the Western United States. The western third of Montana contains numerous mountain ranges. Smaller, "island ranges" are found in the central third of the state, for a total of 77 named ranges of the Rocky Mountains. This geographical fact is reflected in the state's name,...
, was also assigned to Kritosaurus by Lull and Wright, but this is no longer accepted.
By the late 1970s and early 1980s, Hadrosaurus
Hadrosaurus
Hadrosaurus is a valid genus of hadrosaurid dinosaur. In 1858, a skeleton of a dinosaur from this genus was the first dinosaur skeleton known from more than isolated teeth to be found in North America. In 1868, it became the first ever mounted dinosaur skeleton...
had entered the discussion as a possible synonym of either Kritosaurus, Gryposaurus, or both, particularly in semi-technical "dinosaur dictionaries". One well-known work, David B. Norman
David B. Norman
David Bruce Norman is a British paleontologist, currently Director of the Sedgwick Museum, Cambridge University. He is a fellow at Christ's College, Cambridge where he teaches geology in the Natural Sciences tripos. He is a member of the Palaeontological Association. He has studied Iguanodon...
's The Illustrated Encyclopedia of Dinosaurs, uses Kritosaurus for the Canadian material (Gryposaurus), but confusingly identifies the mounted skeleton of K. incurvimanus as Hadrosaurus. One more species was added to Kritosaurus in these years. In 1984, Argentine
Argentina
Argentina , officially the Argentine Republic , is the second largest country in South America by land area, after Brazil. It is constituted as a federation of 23 provinces and an autonomous city, Buenos Aires...
paleontologist José Bonaparte
José Bonaparte
José Fernando Bonaparte, Ph.D. , is an Argentine paleontologist who discovered a plethora of South American dinosaurs and mentored a new generation of Argentine paleontologists like Rodolfo Coria...
and colleagues named K. australis for hadrosaur bones from the late Campanian-early Maastrichtian
Maastrichtian
The Maastrichtian is, in the ICS' geologic timescale, the latest age or upper stage of the Late Cretaceous epoch or Upper Cretaceous series, the Cretaceous period or system, and of the Mesozoic era or erathem. It spanned from 70.6 ± 0.6 Ma to 65.5 ± 0.3 Ma...
Los Alamitos Formation
Los Alamitos Formation
The Los Alamitos Formation is a geological formation in Rio Negro, Argentina whose strata date back to the Late Cretaceous. Dinosaur remains are among the fossils that have been recovered from the formation.-Dinosaurs:-Mammaliaforms:-References:...
of Rio Negro
Río Negro Province
Río Negro is a province of Argentina, located at the northern edge of Patagonia. Neighboring provinces are from the south clockwise Chubut, Neuquén, Mendoza, La Pampa and Buenos Aires. To the east lies the Atlantic Ocean.Its capital is Viedma...
, Patagonia
Patagonia
Patagonia is a region located in Argentina and Chile, integrating the southernmost section of the Andes mountains to the southwest towards the Pacific ocean and from the east of the cordillera to the valleys it follows south through Colorado River towards Carmen de Patagones in the Atlantic Ocean...
, Argentina
Argentina
Argentina , officially the Argentine Republic , is the second largest country in South America by land area, after Brazil. It is constituted as a federation of 23 provinces and an autonomous city, Buenos Aires...
. This species is now thought to be a synonym of Secernosaurus koerneri
Secernosaurus
Secernosaurus 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 Argentina....
.
The history of Kritosaurus took another turn in 1990, when Jack Horner
Jack Horner (paleontologist)
John "Jack" R. Horner is an American paleontologist who discovered and named Maiasaura, providing the first clear evidence that some dinosaurs cared for their young. He is one of the best-known paleontologists in the United States...
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
Spencer G. Lucas
Spencer George Lucas is an American paleontologist and stratigrapher, and curator of paleontology at the New Mexico Museum of Natural History and Science. His main areas of study are late Paleozoic, Mesozoic and early Cenozoic vertebrate fossils, stratigraphy, and continental deposits,...
put each skull in its own genus, creating Anasazisaurus
Anasazisaurus
Anasazisaurus is a genus of hadrosaurid 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...
and Naashoibitosaurus
Naashoibitosaurus
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...
. 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.
Finally, the geographic range of potential Kritosaurus remains in North America has expanded. Bones from the late Campanian-age Aguja Formation
Aguja Formation
The Aguja Formation is a geological formation in North America, exposed in Texas, whose strata date back to the Late Cretaceous. Dinosaur remains are among the fossils that have been recovered from the formation.-Ammonites:-Crurotarsans:...
of Texas
Texas
Texas is the second largest U.S. state by both area and population, and the largest state by area in the contiguous United States.The name, based on the Caddo word "Tejas" meaning "friends" or "allies", was applied by the Spanish to the Caddo themselves and to the region of their settlement in...
, including a skull, have been found. Additionally, newly-described remains from Coahuila
Coahuila
Coahuila, formally Coahuila de Zaragoza , officially Estado Libre y Soberano de Coahuila de Zaragoza is one of the 31 states which, with the Federal District, comprise the 32 Federal Entities of Mexico...
, Mexico
Mexico
The United Mexican States , commonly known as Mexico , is a federal constitutional republic in North America. It is bordered on the north by the United States; on the south and west by the Pacific Ocean; on the southeast by Guatemala, Belize, and the Caribbean Sea; and on the east by the Gulf of...
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 FormationKirtland Formation
The Kirtland Formation is a sedimentary geological formation. It is the product of alluvial muds and overbank sand deposits from the many channels draining the coastal plain that existed on the inland seashore of North America, in the late Cretaceous period. It overlies the Fruitland Formation...
. This formation dates from the late Campanian
Campanian
The Campanian is, in the ICS' geologic timescale, the fifth of six ages of the Late Cretaceous epoch . The Campanian spans the time from 83.5 ± 0.7 Ma to 70.6 ± 0.6 Ma ...
stages of the Late Cretaceous
Late Cretaceous
The Late Cretaceous is the younger of two epochs into which the Cretaceous period is divided in the geologic timescale. Rock strata from this epoch form the Upper Cretaceous series...
Period (74 to 70 million years ago), and is also the source of several other dinosaurs, like Alamosaurus
Alamosaurus
Alamosaurus is a genus of titanosaurian sauropod dinosaur from the Late Cretaceous Period of what is now North America. It was a large quadrupedal herbivore. Isolated vertebrae and limb bones indicate that it reached sizes comparable to Argentinosaurus and Puertasaurus, which would make it the...
, a species of Parasaurolophus
Parasaurolophus
Parasaurolophus is a genus of ornithopod dinosaur that lived in what is now North America during the Late Cretaceous Period, about 76.5–73 million years ago. It was an herbivore that walked both as a biped and a quadruped. Three species are recognized: P. walkeri , P. tubicen, and the...
, Pentaceratops
Pentaceratops
Pentaceratops is a genus of ceratopsid dinosaur from the late Cretaceous Period of what is now North America. The appearance of Pentaceratops sternbergii in the fossil record marks the end of the Judithian land vertebrate age and the start of the Kirtlandian...
, Nodocephalosaurus
Nodocephalosaurus
Nodocephalosaurus is a genus of herbivorous ankylosaurine ankylosaurid dinosaur from Upper Cretaceous deposits of San Juan Basin, New Mexico. The holotype was recovered from the Late Campanian De-na-zin Member of the Kirtland Formation and consists of an incomplete skull...
, Saurornitholestes
Saurornitholestes
Saurornitholestes is a genus of carnivorous dromaeosaurid theropod dinosaur from the late Cretaceous of Alberta, Montana and New Mexico....
, and as-yet-unnamed tyrannosaurids. The Kirtland Formation is interpreted as river
River
A river is a natural watercourse, usually freshwater, flowing towards an ocean, a lake, a sea, or another river. In a few cases, a river simply flows into the ground or dries up completely before reaching another body of water. Small rivers may also be called by several other names, including...
floodplains appearing after a retreat of the Western Interior Seaway
Western Interior Seaway
The Western Interior Seaway, also called the Cretaceous Seaway, the Niobraran Sea, and the North American Inland Sea, was a huge inland sea that split the continent of North America into two halves, Laramidia and Appalachia, during most of the mid- and late-Cretaceous Period...
. Conifers were the dominant plants, and chasmosaurine
Ceratopsidae
Ceratopsidae is a speciose group of marginocephalian dinosaurs including Triceratops and Styracosaurus...
horned dinosaurs appear to have been more common than hadrosaurids. The presence of Parasaurolophus
Parasaurolophus
Parasaurolophus is a genus of ornithopod dinosaur that lived in what is now North America during the Late Cretaceous Period, about 76.5–73 million years ago. It was an herbivore that walked both as a biped and a quadruped. Three species are recognized: P. walkeri , P. tubicen, and the...
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
Pentaceratops
Pentaceratops is a genus of ceratopsid dinosaur from the late Cretaceous Period of what is now North America. The appearance of Pentaceratops sternbergii in the fossil record marks the end of the Judithian land vertebrate age and the start of the Kirtlandian...
, they are predominate members of the fauna.
Diet and feeding
As a hadrosaurid, Kritosaurus would have been a large bipedal/quadrupedQuadruped
Quadrupedalism is a form of land animal locomotion using four limbs or legs. An animal or machine that usually moves in a quadrupedal manner is known as a quadruped, meaning "four feet"...
al herbivore
Herbivore
Herbivores are organisms that are anatomically and physiologically adapted to eat plant-based foods. Herbivory is a form of consumption in which an organism principally eats autotrophs such as plants, algae and photosynthesizing bacteria. More generally, organisms that feed on autotrophs in...
, eating plant
Plant
Plants are living organisms belonging to the kingdom Plantae. Precise definitions of the kingdom vary, but as the term is used here, plants include familiar organisms such as trees, flowers, herbs, bushes, grasses, vines, ferns, mosses, and green algae. The group is also called green plants or...
s with a sophisticated skull that permitted a grinding motion analogous to chewing
Mastication
Mastication or chewing is the process by which food is crushed and ground by teeth. It is the first step of digestion and it increases the surface area of foods to allow more efficient break down by enzymes. During the mastication process, the food is positioned between the teeth for grinding by...
. Its teeth
Tooth
Teeth are small, calcified, whitish structures found in the jaws of many vertebrates that are used to break down food. Some animals, particularly carnivores, also use teeth for hunting or for defensive purposes. The roots of teeth are embedded in the Mandible bone or the Maxillary bone and are...
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
Cheek
Cheeks constitute the area of the face below the eyes and between the nose and the left or right ear. They may also be referred to as jowls. "Buccal" means relating to the cheek. In humans, the region is innervated by the buccal nerve...
-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.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.External links
- Kritosaurus in The Dinosaur Encyclopaedia at Dino Russ' Lair