Naashoibitosaurus
Encyclopedia
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.
), is not well known in terms of anatomy. Its skull, the most thoroughly described portion, has a low nasal
crest that peaks in front of the eyes, but does not strongly arch as in Gryposaurus
.
hadrosaurid, a "flat-headed or solid-crested duckbill". It is closest to the solid-crested forms like Saurolophus
. If it is the same as Kritosaurus, Kritosaurus would be used because it is the older name, but its position vis-a-vis other duckbills would be the same.
history, the name of this genus is based on an error. David Gillette and David Thomas collected the type
and only known specimen from what was thought to be the Naashoibito Member of the Kirtland Formation, the youngest member of the Kirtland; this was commemorated in the name. Instead, it came from the older, late Campanian
-age De-na-zin Member. Horner described the skull in 1992 as that of an immature
Kritosaurus, using it as evidence that Gryposaurus was different from Kritosaurus. At the same time, Hunt and Lucas were describing the postcrania
as belonging to Edmontosaurus saskatchewanensis
. When the disconnect became apparent, Hunt and Lucas gave the specimen its own generic name, because the skull did not agree with an edmontosaur, and they considered Kritosaurus indeterminate
and thus not usable.
Their assessment was challenged in 2000 by Thomas Williamson, who found the morphological differences between it and Kritosaurus to be due to the skulls in question being from individuals of different ages. Unlike Hunt and Lucas, he considered the type skull of Kritosaurus to be diagnostic and thus could compare it to Naashoibitosaurus. He returned to Horner's argument, noting as Horner had that nasal crest in other hadrosaurines like Prosaurolophus
moves back on the skull during growth. He also pointed out that the specimen's provenance
was incorrect; instead of being from younger rocks than Kritosaurus, it is from rocks of about the same age. The next major review, in the second edition of The Dinosauria, again separated the two. The absence of the beak and lower jaw in the partial skull of Naashoibitosaurus makes comparison even more difficult. More resolution on the problem will have to wait for more material.
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 Kritosaurus 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 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...
that 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...
, and was found in 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...
of the San Juan
San Juan, New Mexico
San Juan is a census-designated place in Rio Arriba County, New Mexico, United States. The population was 592 at the 2000 census.-Geography:San Juan is located at , a few miles north of Espanola....
Basin in 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...
. Only a partial skeleton has been found to date. It was first described as a specimen of Kritosaurus by 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 has been intertwined with Kritosaurus
Kritosaurus
Kritosaurus is an incompletely known but historically important genus of hadrosaurid dinosaur. It lived about 73 million years ago, in the Late Cretaceous of North America...
since its description.
Description
Naashoibitosaurus, based as it is on a single partial skeleton (NMMNH P-16106New Mexico Museum of Natural History and Science
The New Mexico Museum of Natural History and Science is a natural history and science museum in Albuquerque, New Mexico near Old Town Albuquerque. The Museum was founded in 1986....
), is not well known in terms of anatomy. Its skull, the most thoroughly described portion, has a low 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 that peaks in front of the eyes, but does not strongly arch as in 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...
.
Classification
Naashoibitosaurus is 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, a "flat-headed or solid-crested duckbill". It is closest to the solid-crested forms like 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...
. If it is the same as Kritosaurus, Kritosaurus would be used because it is the older name, but its position vis-a-vis other duckbills would be the same.
History
Befitting a genus with a confusing taxonomicTaxonomy
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, the name of this genus is based on an error. David Gillette and David Thomas collected 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...
and only known specimen from what was thought to be the Naashoibito Member of the Kirtland Formation, the youngest member of the Kirtland; this was commemorated in the name. Instead, it came from the older, 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. Horner described the skull in 1992 as that of an immature
Juvenile (organism)
A juvenile is an individual organism that has not yet reached its adult form, sexual maturity or size. Juveniles sometimes look very different from the adult form, particularly in terms of their colour...
Kritosaurus, using it as evidence that Gryposaurus was different from Kritosaurus. At the same time, Hunt and Lucas were describing the postcrania
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...
as belonging to Edmontosaurus saskatchewanensis
Edmontosaurus
Edmontosaurus is a genus of crestless hadrosaurid dinosaur. It contains two species: Edmontosaurus regalis and Edmontosaurus annectens. Fossils of E. regalis have been found in rocks of western North America that date from the late Campanian stage of the Cretaceous Period 73 million years ago,...
. When the disconnect became apparent, Hunt and Lucas gave the specimen its own generic name, because the skull did not agree with an edmontosaur, and they considered Kritosaurus indeterminate
Nomen dubium
In zoological nomenclature, a nomen dubium is a scientific name that is of unknown or doubtful application...
and thus not usable.
Their assessment was challenged in 2000 by Thomas Williamson, who found the morphological differences between it and Kritosaurus to be due to the skulls in question being from individuals of different ages. Unlike Hunt and Lucas, he considered the type skull of Kritosaurus to be diagnostic and thus could compare it to Naashoibitosaurus. He returned to Horner's argument, noting as Horner had that nasal crest in other hadrosaurines like Prosaurolophus
Prosaurolophus
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...
moves back on the skull during growth. He also pointed out that the specimen's provenance
Provenance
Provenance, from the French provenir, "to come from", refers to the chronology of the ownership or location of an historical object. The term was originally mostly used for works of art, but is now used in similar senses in a wide range of fields, including science and computing...
was incorrect; instead of being from younger rocks than Kritosaurus, it is from rocks of about the same age. The next major review, in the second edition of The Dinosauria, again separated the two. The absence of the beak and lower jaw in the partial skull of Naashoibitosaurus makes comparison even more difficult. More resolution on the problem will have to wait for more material.
Paleobiology
As a hadrosaurid, Naashoibitosaurus 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 Kritosaurus is unknown.