Kritosaurus is an incompletely known but historically important
genusIn 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
hadrosauridHadrosaurids 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)
dinosaurDinosaurs 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 CretaceousThe 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 AmericaNorth 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
typeType 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]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
taxonomicTaxonomy 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
GryposaurusGryposaurus was a genus of duckbilled dinosaur that lived about 83 to 75.5 million years ago, in the Late Cretaceous of North America...
,
AnasazisaurusAnasazisaurus 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
NaashoibitosaurusNaashoibitosaurus 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
herbivoreHerbivores 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
Kritosaurus is only definitely determined from a partial skull and lower jaws, and associated undescribed
postcraniaPostcrania[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 beakThe 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
quadrateThe 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 characteristicsIn 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
predentaryThe 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
maxillaThe 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
hadrosaurineSaurolophinae 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...
hadrosauridHadrosaurids 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
cladeA 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
SaurolophusSaurolophus 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 nameIn 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
In 1904,
Barnum BrownBarnum 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
typeA 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 (
AMNHThe 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-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 MexicoNew 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 StatesThe 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
stratigraphyStratigraphy, 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 CampanianThe 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 FormationThe 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
AnatotitanAnatotitan 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
NectosaurusNectosaurus 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
nasalThe 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
CanadianCanada 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
monographA 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 speciesIn 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 brevicepsHadrosaurus 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...
(
MarshOthniel 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 FormationThe 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
MontanaMontana 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,
HadrosaurusHadrosaurus 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. NormanDavid 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,
ArgentineArgentina , 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 BonaparteJosé 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 MaastrichtianThe 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 FormationThe 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 NegroRío 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...
,
PatagoniaPatagonia 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...
,
ArgentinaArgentina , 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 koerneriSecernosaurus 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 HornerJohn "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. LucasSpencer 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
AnasazisaurusAnasazisaurus 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
NaashoibitosaurusNaashoibitosaurus 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 FormationThe 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
TexasTexas 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
CoahuilaCoahuila, 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...
,
MexicoThe 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 FormationThe 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
CampanianThe 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 CretaceousThe 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
AlamosaurusAlamosaurus 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
ParasaurolophusParasaurolophus 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...
,
PentaceratopsPentaceratops 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...
,
NodocephalosaurusNodocephalosaurus 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...
,
SaurornitholestesSaurornitholestes 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
riverA 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 SeawayThe 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
chasmosaurineCeratopsidae is a speciose group of marginocephalian dinosaurs including Triceratops and Styracosaurus...
horned dinosaurs appear to have been more common than hadrosaurids. The presence of
ParasaurolophusParasaurolophus 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
PentaceratopsPentaceratops 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/
quadrupedQuadrupedalism 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
herbivoreHerbivores 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
plantPlants 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
chewingMastication 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
teethTeeth 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
cheekCheeks 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