Othnielosaurus
Encyclopedia
Othnielosaurus is a genus
of ornithischia
n dinosaur
that lived about 155 to 148 million years ago, during the Late Jurassic
-age Morrison Formation
of the western United States
. It is named in honor of famed paleontologist Othniel Charles Marsh
, and was formerly assigned to the genus Laosaurus
. This genus was coined to hold fossils formerly included in Othnielia
, which is based on remains that may be too sparse to hold a name; as such, it is part of decades of research to untangle the taxonomy left behind by Marsh and his rival Edward Drinker Cope
from the Bone Wars
. Othnielosaurus has usually been classified as a hypsilophodont
, a type of generalized small bipedal herbivore
or omnivore
, although recent research has called this and the existence of a distinct group of hypsilophodonts into question.
Othnielosaurus is known from material from all parts of the body, including two good skeletons, although the skull is still poorly known (note that earlier references use a multitude of names for this material, with most of them since 1977 using Othnielia rex). Othnielosaurus was a small animal, 2 meters (6.6 ft) or less in length and 10 kilogram
s (22 lb
) or less in weight. It was a bipedal dinosaur with short forelimbs and long hindlimbs with large processes
for muscle
attachments. The hands were short and broad with short fingers. From the partial type skull and the skull on the possible specimen "Barbara", the head was small. It had small leaf-shaped cheek teeth (triangular and with small ridges and denticles lining the front and back edges), and premaxilla
ry teeth with less ornamentation. Like several hypsilophodont or iguanodont
-grade ornithopods such as Hypsilophodon
, Thescelosaurus
, and Talenkauen
, Othnielosaurus had thin plates lying along the ribs. Called intercostal plates, these structures were cartilaginous
in origin.
, a member of a nebulous and poorly defined group of small, running herbivorous dinosaurs. This was challenged by Robert Bakker
et al. in 1990. In their description of the new taxon
Drinker nisti
, they split Othnielia into two species (O. rex and O. consors) and placed "othnieliids" as more basal
than hypsilophodontids. With recent analyses suggesting a paraphyletic Hypsilophodontidae, the general idea of "othnielids" as basal to other hypsilophodonts has been supported, although Drinker has been controversial because virtually nothing new has been published on it since its description. Other basal ornithopods have sometimes been linked to Othnielosaurus, particularly Hexinlusaurus
, considered by at least one author to be a species of "Othnielia", O. multidens. New studies concur with the hypothesis that Othnielosaurus is more basal than other traditional hypsilophodonts, but go even farther and remove the genus from Ornithopoda and the larger group Cerapoda
, which also includes horned dinosaurs
and domeheaded dinosaurs
.
(possibly), "N." rex
, Laosaurus celer
, L. consors, and L. gracilis. This taxonomy
has become very complicated, with numerous attempts at revision in the years since.
In 1877, Marsh named two species of Nanosaurus in separate publications, based on partial remains from the Morrison Formation of Garden Park
, Colorado
. One paper described N. agilis
, based on YPM 1913, with remains including impressions of a dentary, and postcrania
l bits including an ilium
, thigh bones
, shin bones
, and a fibula. The other paper named N. rex
, a second species which Marsh based on YPM 1915 (also called 1925 in Galton, 2007), a complete thigh bone. He regarded both species as small ("fox-sized") animals. He assigned this genus to the now-abandoned family Nanosauridae.
The next year, he named the new genus Laosaurus
on material collected by Samuel Wendell Williston
from Como Bluff
, Wyoming
. Two species were named: the type species
L. celer, based on parts of eleven vertebrae (YPM 1875); and the "smaller" L. gracilis, originally based on a back vertebra's centrum, a caudal
centrum, and part of an ulna
(review by Peter Galton
in 1983 finds the specimen to now consist of thirteen back and eight caudal centra, and portions of both hindlimbs).
A third species, L. consors, was established by Marsh in 1894 for YPM 1882, which consists of most of one articulated skeleton and part of at least one other individual. The skull was only partially preserved, and the fact that the vertebrae were represented only by centra suggests a partially-grown individual. Galton (1983) notes that much of the current mounted skeleton was restored in plaster, or had paint applied.
These animals attracted little professional attention until the 1970s and 1980s, when Peter Galton reviewed many the "hypsilophodonts" in a series of papers. In 1973, he and Jim Jensen
described a partial skeleton (BYU ESM 163
as of Galton, 2007) missing the head, hands, and tail as Nanosaurus (?) rex, which had been damaged by other collectors prior to description. By 1977, he had determined that Nanosaurus agilis was quite different from N. rex and the new skeleton, and coined Othnielia
for N. rex. The 1977 reference, somewhat buried in a paper concerning the transcontinental species of Dryosaurus
, did not elaborate, but did assign Laosaurus consors and L. gracilis to the new genus, and considered L. celer a nomen nudum
. The publication of Drinker
further complicated matters.
Most recently, in 2007 Galton reevaluated Morrison Formation ornithischians and concluded that the femur on which "Nanosaurus" rex (and by extension Othnielia) is based is not diagnostic, and reassigned the BYU skeleton to Laosaurus consors, which is based on more diagnostic material. As the genus Laosaurus is also based on nondiagnostic material, he gave the species L. consors its own genus, Othnielosaurus. As a result, in practical terms what had been thought of as Othnielia is now known as Othnielosaurus consors. Othnielia is not a synonym of Othnielosaurus, because they are based upon different specimens; however, the skeletons that had been used to describe and depict Othnielia were reassigned to Othnielosaurus, leaving the older name with only the original femur. The current status for the various species is as follows: Nanosaurus agilis is a possible basal ornithopod, "N." rex (Othnielia) is a dubious basal ornithopod, Drinker nisti is its own tentatively valid taxon, L. consors is the type species for Othnielosaurus, and L. celer and L. gracilis are still considered dubious.
dinosaur fauna
, diminutive in comparison to the giant sauropods. The Morrison Formation is interpreted as a semiarid environment with distinct wet
and dry season
s, and flat floodplain
s. Vegetation varied from river
-lining gallery forest
s of conifers, tree ferns, and fern
s, to fern savanna
s with rare trees. It has been a rich fossil hunting ground, holding fossils of green algae
, fungi, moss
es, horsetails, ferns, cycad
s, ginkgo
es, and several families of conifers. Other fossils discovered include bivalves, snail
s, ray-finned fishes
, frog
s, salamander
s, turtle
s, sphenodonts
, lizard
s, terrestrial and aquatic crocodylomorpha
ns, several species of pterosaur
, numerous dinosaur species, and early mammal
s such as docodonts
, multituberculates
, symmetrodonts
, and triconodonts
. Such dinosaurs as the theropods Ceratosaurus
, Allosaurus
, Ornitholestes
, and Torvosaurus
, the sauropods Apatosaurus
, Brachiosaurus
, Camarasaurus
, and Diplodocus
, and the ornithischia
ns Camptosaurus
, Dryosaurus
, and Stegosaurus
are known from the Morrison. Othnielosaurus is present in stratigraphic zones 2-5.
Typically, Othnielosaurus has been interpreted like other hypsilophodonts as a small, swift
herbivore
, although Bakker (1986) interpreted the possibly related Nanosaurus as an omnivore
. This idea has had some unofficial support, but little in the formal literature; description of more complete skull remains will be needed to test this hypothesis
.
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 ornithischia
Ornithischia
Ornithischia or Predentata is an extinct order of beaked, herbivorous dinosaurs. The name ornithischia is derived from the Greek ornitheos meaning 'of a bird' and ischion meaning 'hip joint'...
n 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 155 to 148 million years ago, during the Late Jurassic
Late Jurassic
The Late Jurassic is the third epoch of the Jurassic Period, and it spans the geologic time from 161.2 ± 4.0 to 145.5 ± 4.0 million years ago , which is preserved in Upper Jurassic strata. In European lithostratigraphy, the name "Malm" indicates rocks of Late Jurassic age...
-age Morrison Formation
Morrison Formation
The Morrison Formation is a distinctive sequence of Late Jurassic sedimentary rock that is found in the western United States, which has been the most fertile source of dinosaur fossils in North America. It is composed of mudstone, sandstone, siltstone and limestone and is light grey, greenish...
of the western United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
. It is named in honor of famed paleontologist Othniel Charles 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...
, and was formerly assigned to the genus Laosaurus
Laosaurus
Laosaurus is a genus of hypsilophodont dinosaur. The type species is Laosaurus celer, first described by O.C. Marsh in 1878 from remains from the Oxfordian-Tithonian-age Upper Jurassic Morrison Formation of Wyoming. The validity of this genus is doubtful because it is based on fragmentary fossils...
. This genus was coined to hold fossils formerly included in Othnielia
Othnielia
Othnielia is a genus of ornithischian dinosaur, named after its original describer, Professor Othniel Charles Marsh, an American paleontologist of the 19th century...
, which is based on remains that may be too sparse to hold a name; as such, it is part of decades of research to untangle the taxonomy left behind by Marsh and his rival Edward Drinker Cope
Edward Drinker Cope
Edward Drinker Cope was an American paleontologist and comparative anatomist, as well as a noted herpetologist and ichthyologist. Born to a wealthy Quaker family, Cope distinguished himself as a child prodigy interested in science; he published his first scientific paper at the age of nineteen...
from the Bone Wars
Bone Wars
The Bone Wars, also known as the "Great Dinosaur Rush", refers to a period of intense fossil speculation and discovery during the Gilded Age of American history, marked by a heated rivalry between Edward Drinker Cope and Othniel Charles Marsh...
. Othnielosaurus has usually been classified as a hypsilophodont
Hypsilophodont
Hypsilophodonts were small ornithopod dinosaurs, regarded as fast, herbivorous bipeds on the order of 1–2 meters long . They are known from Asia, Australia, Europe, New Zealand, North America, and South America, from rocks of Middle Jurassic to late Cretaceous age...
, a type of generalized small bipedal 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...
or omnivore
Omnivore
Omnivores are species that eat both plants and animals as their primary food source...
, although recent research has called this and the existence of a distinct group of hypsilophodonts into question.
Description
Kilogram
The kilogram or kilogramme , also known as the kilo, is the base unit of mass in the International System of Units and is defined as being equal to the mass of the International Prototype Kilogram , which is almost exactly equal to the mass of one liter of water...
s (22 lb
Pound (mass)
The pound or pound-mass is a unit of mass used in the Imperial, United States customary and other systems of measurement...
) or less in weight. It was a bipedal dinosaur with short forelimbs and long hindlimbs with large processes
Process (anatomy)
In anatomy, a process is a projection or outgrowth of tissue from a larger body. The vertebra has several kinds of processes,such as: transverse process, prezygapophysis, postzygapophysis.-Examples:Examples of processes include:...
for muscle
Muscle
Muscle is a contractile tissue of animals and is derived from the mesodermal layer of embryonic germ cells. Muscle cells contain contractile filaments that move past each other and change the size of the cell. They are classified as skeletal, cardiac, or smooth muscles. Their function is to...
attachments. The hands were short and broad with short fingers. From the partial type skull and the skull on the possible specimen "Barbara", the head was small. It had small leaf-shaped cheek teeth (triangular and with small ridges and denticles lining the front and back edges), and premaxilla
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....
ry teeth with less ornamentation. Like several hypsilophodont or iguanodont
Iguanodont
Iguanodonts were herbivorous dinosaurs that lived from the mid-Jurassic to Late Cretaceous. Some members include Camptosaurus, Callovosaurus, Iguanodon, Ouranosaurus, and the hadrosaurids or "duck-billed dinosaurs". Iguanodonts were one of the first groups of dinosaurs to be found...
-grade ornithopods such as Hypsilophodon
Hypsilophodon
Hypsilophodon is an ornithopod dinosaur genus from the Early Cretaceous period of Europe. It was a small bipedal animal with an herbivorous or possibly omnivorous diet...
, Thescelosaurus
Thescelosaurus
Thescelosaurus was a genus of small ornithopod dinosaur that appeared at the very end of the Late Cretaceous period in North America. It was a member of the last dinosaurian fauna before the Cretaceous-Tertiary extinction event around 65.5 million years ago...
, and Talenkauen
Talenkauen
Talenkauen is a genus of basal iguanodont dinosaur from the Maastrichtian-age Upper Cretaceous Pari Aike Formation of Lake Viedma, Santa Cruz, Argentina. It is based on MPM-10001, a partial articulated skeleton missing the rear part of the skull, the tail, and the hands...
, Othnielosaurus had thin plates lying along the ribs. Called intercostal plates, these structures were cartilaginous
Cartilage
Cartilage is a flexible connective tissue found in many areas in the bodies of humans and other animals, including the joints between bones, the rib cage, the ear, the nose, the elbow, the knee, the ankle, the bronchial tubes and the intervertebral discs...
in origin.
Classification
Othnielosaurus (previously under the names Laosaurus, Nanosaurus, and Othnielia) has typically been regarded as a hypsilophodont ornithopodOrnithopod
Ornithopods or members of the clade Ornithopoda are a group of ornithischian dinosaurs that started out as small, bipedal running grazers, and grew in size and numbers until they became one of the most successful groups of herbivores in the Cretaceous world, and dominated the North American...
, a member of a nebulous and poorly defined group of small, running herbivorous dinosaurs. This was challenged by Robert Bakker
Robert T. Bakker
Robert T. Bakker is an American paleontologist who helped reshape modern theories about dinosaurs, particularly by adding support to the theory that some dinosaurs were endothermic...
et al. in 1990. In their description of the new taxon
Taxon
|thumb|270px|[[African elephants]] form a widely-accepted taxon, the [[genus]] LoxodontaA taxon is a group of organisms, which a taxonomist adjudges to be a unit. Usually a taxon is given a name and a rank, although neither is a requirement...
Drinker nisti
Drinker
Drinker was a genus of hypsilophodont dinosaur from the late Jurassic period of North America. Although based on good remains, it remains obscure due to a lack of post-naming publications.-Description:...
, they split Othnielia into two species (O. rex and O. consors) and placed "othnieliids" as more basal
Basal (phylogenetics)
In phylogenetics, a basal clade is the earliest clade to branch in a larger clade; it appears at the base of a cladogram.A basal group forms an outgroup to the rest of the clade, such as in the following example:...
than hypsilophodontids. With recent analyses suggesting a paraphyletic Hypsilophodontidae, the general idea of "othnielids" as basal to other hypsilophodonts has been supported, although Drinker has been controversial because virtually nothing new has been published on it since its description. Other basal ornithopods have sometimes been linked to Othnielosaurus, particularly Hexinlusaurus
Hexinlusaurus
Hexinlusaurus is a genus of basal ornithischian dinosaur from the Middle Jurassic of China. The holotype , consists of an almost complete, articulated skull and some postcranial material, collected from a terrestrial sandstone within the Lower Shaximiao Formation at the famous dinosaur-bearing...
, considered by at least one author to be a species of "Othnielia", O. multidens. New studies concur with the hypothesis that Othnielosaurus is more basal than other traditional hypsilophodonts, but go even farther and remove the genus from Ornithopoda and the larger group Cerapoda
Cerapoda
Neornithischia is a clade of the dinosaur order Ornithischia. They are the sister group of the Thyreophora within the clade Genasauria. Neornithischians are united by having a thicker layer of asymmetrical enamel on the inside of their lower teeth...
, which also includes horned dinosaurs
Ceratopsia
Ceratopsia or Ceratopia is a group of herbivorous, beaked dinosaurs which thrived in what are now North America, Europe, and Asia, during the Cretaceous Period, although ancestral forms lived earlier, in the Jurassic. The earliest known ceratopsian, Yinlong downsi, lived between 161.2 and 155.7...
and domeheaded dinosaurs
Pachycephalosauria
Pachycephalosauria is a clade of ornithischian dinosaurs. Well-known genera include Pachycephalosaurus, Stegoceras, Stygimoloch, and Dracorex. Most lived during the Late Cretaceous Period, in what is now North America and Asia. They were all bipedal, herbivorous/omnivorous animals with thick skulls...
.
History and taxonomy
O.C. Marsh named several species and genera in the late 19th century that have come to be recognized as hypsilophodonts or hypsilophodont-like animals, including Nanosaurus agilisNanosaurus
Nanosaurus is the name given to a genus of dinosaur from the Late Jurassic. Described by Othniel Charles Marsh in 1877, it is a poorly-known ornithischian of uncertain affinities. Its fossils are known from the Morrison Formation of Colorado and possibly Wyoming...
(possibly), "N." rex
Othnielia
Othnielia is a genus of ornithischian dinosaur, named after its original describer, Professor Othniel Charles Marsh, an American paleontologist of the 19th century...
, Laosaurus celer
Laosaurus
Laosaurus is a genus of hypsilophodont dinosaur. The type species is Laosaurus celer, first described by O.C. Marsh in 1878 from remains from the Oxfordian-Tithonian-age Upper Jurassic Morrison Formation of Wyoming. The validity of this genus is doubtful because it is based on fragmentary fossils...
, L. consors, and L. gracilis. This taxonomy
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...
has become very complicated, with numerous attempts at revision in the years since.
In 1877, Marsh named two species of Nanosaurus in separate publications, based on partial remains from the Morrison Formation of Garden Park
Garden Park, Colorado
Garden Park, in southcentral Colorado, is known for its Jurassic dinosaurs and the role the specimens played in the infamous bone wars of the late 19th century. Located north of Cañon City, Colorado, the name originates from the area providing vegetables to the miners at nearby Cripple Creek in...
, Colorado
Colorado
Colorado is a U.S. state that encompasses much of the Rocky Mountains as well as the northeastern portion of the Colorado Plateau and the western edge of the Great Plains...
. One paper described N. agilis
Nanosaurus
Nanosaurus is the name given to a genus of dinosaur from the Late Jurassic. Described by Othniel Charles Marsh in 1877, it is a poorly-known ornithischian of uncertain affinities. Its fossils are known from the Morrison Formation of Colorado and possibly Wyoming...
, based on YPM 1913, with remains including impressions of a dentary, and 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...
l bits including an ilium
Ilium (bone)
The ilium is the uppermost and largest bone of the pelvis, and appears in most vertebrates including mammals and birds, but not bony fish. All reptiles have an ilium except snakes, although some snake species have a tiny bone which is considered to be an ilium.The name comes from the Latin ,...
, thigh bones
Femur
The femur , or thigh bone, is the most proximal bone of the leg in tetrapod vertebrates capable of walking or jumping, such as most land mammals, birds, many reptiles such as lizards, and amphibians such as frogs. In vertebrates with four legs such as dogs and horses, the femur is found only in...
, shin bones
Tibia
The tibia , shinbone, or shankbone is the larger and stronger of the two bones in the leg below the knee in vertebrates , and connects the knee with the ankle bones....
, and a fibula. The other paper named N. rex
Othnielia
Othnielia is a genus of ornithischian dinosaur, named after its original describer, Professor Othniel Charles Marsh, an American paleontologist of the 19th century...
, a second species which Marsh based on YPM 1915 (also called 1925 in Galton, 2007), a complete thigh bone. He regarded both species as small ("fox-sized") animals. He assigned this genus to the now-abandoned family Nanosauridae.
The next year, he named the new genus Laosaurus
Laosaurus
Laosaurus is a genus of hypsilophodont dinosaur. The type species is Laosaurus celer, first described by O.C. Marsh in 1878 from remains from the Oxfordian-Tithonian-age Upper Jurassic Morrison Formation of Wyoming. The validity of this genus is doubtful because it is based on fragmentary fossils...
on material collected by Samuel Wendell Williston
Samuel Wendell Williston
Samuel Wendell Williston was an American educator and paleontologist who was the first to propose that birds developed flight cursorially , rather than arboreally . He was also an entomologist, specialising in Diptera.-Early life:Williston was born in Boston, Massachusetts to Samuel Williston and...
from Como Bluff
Como Bluff
Como Bluff is a long ridge extending east-west, located between the towns of Rock River and Medicine Bow, Wyoming. The ridge is an anticline, formed as a result of compressional geological folding. Three geological formations, the Sundance, the Morrison, and the Cloverly Formations, containing...
, Wyoming
Wyoming
Wyoming is a state in the mountain region of the Western United States. The western two thirds of the state is covered mostly with the mountain ranges and rangelands in the foothills of the Eastern Rocky Mountains, while the eastern third of the state is high elevation prairie known as the High...
. Two species were named: 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...
L. celer, based on parts of eleven vertebrae (YPM 1875); and the "smaller" L. gracilis, originally based on a back vertebra's centrum, a caudal
Tail
The tail is the section at the rear end of an animal's body; in general, the term refers to a distinct, flexible appendage to the torso. It is the part of the body that corresponds roughly to the sacrum and coccyx in mammals, reptiles, and birds...
centrum, and part of an ulna
Ulna
The ulna is one of the two long bones in the forearm, the other being the radius. It is prismatic in form and runs parallel to the radius, which is shorter and smaller. In anatomical position The ulna is one of the two long bones in the forearm, the other being the radius. It is prismatic in form...
(review by Peter Galton
Peter Galton
Peter M. Galton is a British vertebrate paleontologist working in America, who has to date written or co-written about a hundred papers in scientific journals or chapters in paleontology textbooks, especially on ornithischian and prosauropod dinosaurs.With Robert Bakker in a joint article...
in 1983 finds the specimen to now consist of thirteen back and eight caudal centra, and portions of both hindlimbs).
A third species, L. consors, was established by Marsh in 1894 for YPM 1882, which consists of most of one articulated skeleton and part of at least one other individual. The skull was only partially preserved, and the fact that the vertebrae were represented only by centra suggests a partially-grown individual. Galton (1983) notes that much of the current mounted skeleton was restored in plaster, or had paint applied.
These animals attracted little professional attention until the 1970s and 1980s, when Peter Galton reviewed many the "hypsilophodonts" in a series of papers. In 1973, he and Jim Jensen
James A. Jensen
James A. Jensen , was an American paleontologist. His extensive collecting program at BYU in the Utah-Colorado region which spanned 23 years was comparable in terms of the number of specimens collected to that of Barnum Brown during the early 20th century. He was given the name "Dinosaur Jim"...
described a partial skeleton (BYU ESM 163
Brigham Young University
Brigham Young University is a private university located in Provo, Utah. It is owned and operated by The Church of Jesus Christ of Latter-day Saints , and is the United States' largest religious university and third-largest private university.Approximately 98% of the university's 34,000 students...
as of Galton, 2007) missing the head, hands, and tail as Nanosaurus (?) rex, which had been damaged by other collectors prior to description. By 1977, he had determined that Nanosaurus agilis was quite different from N. rex and the new skeleton, and coined Othnielia
Othnielia
Othnielia is a genus of ornithischian dinosaur, named after its original describer, Professor Othniel Charles Marsh, an American paleontologist of the 19th century...
for N. rex. The 1977 reference, somewhat buried in a paper concerning the transcontinental species of Dryosaurus
Dryosaurus
Dryosaurus is a genus of an ornithopod dinosaur that lived in the Late Jurassic period. It was an iguanodont . Fossils have been found in the western United States, and were first discovered in the late 19th century...
, did not elaborate, but did assign Laosaurus consors and L. gracilis to the new genus, and considered L. celer a nomen nudum
Nomen nudum
The phrase nomen nudum is a Latin term, meaning "naked name", used in taxonomy...
. The publication of Drinker
Drinker
Drinker was a genus of hypsilophodont dinosaur from the late Jurassic period of North America. Although based on good remains, it remains obscure due to a lack of post-naming publications.-Description:...
further complicated matters.
Most recently, in 2007 Galton reevaluated Morrison Formation ornithischians and concluded that the femur on which "Nanosaurus" rex (and by extension Othnielia) is based is not diagnostic, and reassigned the BYU skeleton to Laosaurus consors, which is based on more diagnostic material. As the genus Laosaurus is also based on nondiagnostic material, he gave the species L. consors its own genus, Othnielosaurus. As a result, in practical terms what had been thought of as Othnielia is now known as Othnielosaurus consors. Othnielia is not a synonym of Othnielosaurus, because they are based upon different specimens; however, the skeletons that had been used to describe and depict Othnielia were reassigned to Othnielosaurus, leaving the older name with only the original femur. The current status for the various species is as follows: Nanosaurus agilis is a possible basal ornithopod, "N." rex (Othnielia) is a dubious basal ornithopod, Drinker nisti is its own tentatively valid taxon, L. consors is the type species for Othnielosaurus, and L. celer and L. gracilis are still considered dubious.
Paleobiology and paleoecology
Othnielosaurus was one of the smaller members of the diverse Morrison FormationMorrison Formation
The Morrison Formation is a distinctive sequence of Late Jurassic sedimentary rock that is found in the western United States, which has been the most fertile source of dinosaur fossils in North America. It is composed of mudstone, sandstone, siltstone and limestone and is light grey, greenish...
dinosaur fauna
Fauna
Fauna or faunæ is all of the animal life of any particular region or time. The corresponding term for plants is flora.Zoologists and paleontologists use fauna to refer to a typical collection of animals found in a specific time or place, e.g. the "Sonoran Desert fauna" or the "Burgess shale fauna"...
, diminutive in comparison to the giant sauropods. The Morrison Formation is interpreted as a semiarid environment with distinct wet
Wet season
The the wet season, or rainy season, is the time of year, covering one or more months, when most of the average annual rainfall in a region occurs. The term green season is also sometimes used as a euphemism by tourist authorities. Areas with wet seasons are dispersed across portions of the...
and dry season
Dry season
The dry season is a term commonly used when describing the weather in the tropics. The weather in the tropics is dominated by the tropical rain belt, which oscillates from the northern to the southern tropics over the course of the year...
s, and flat floodplain
Floodplain
A floodplain, or flood plain, is a flat or nearly flat land adjacent a stream or river that stretches from the banks of its channel to the base of the enclosing valley walls and experiences flooding during periods of high discharge...
s. Vegetation varied from 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...
-lining gallery forest
Gallery forest
Gallery forests are evergreen forests that form as corridors along rivers or wetlands and project into landscapes that are otherwise only sparsely treed such as savannas, grasslands or deserts....
s of conifers, tree ferns, and fern
Fern
A fern is any one of a group of about 12,000 species of plants belonging to the botanical group known as Pteridophyta. Unlike mosses, they have xylem and phloem . They have stems, leaves, and roots like other vascular plants...
s, to fern savanna
Savanna
A savanna, or savannah, is a grassland ecosystem characterized by the trees being sufficiently small or widely spaced so that the canopy does not close. The open canopy allows sufficient light to reach the ground to support an unbroken herbaceous layer consisting primarily of C4 grasses.Some...
s with rare trees. It has been a rich fossil hunting ground, holding fossils of green algae
Chlorophyta
Chlorophyta is a division of green algae, informally called chlorophytes. The name is used in two very different senses so that care is needed to determine the use by a particular author...
, fungi, moss
Moss
Mosses are small, soft plants that are typically 1–10 cm tall, though some species are much larger. They commonly grow close together in clumps or mats in damp or shady locations. They do not have flowers or seeds, and their simple leaves cover the thin wiry stems...
es, horsetails, ferns, cycad
Cycad
Cycads are seed plants typically characterized by a stout and woody trunk with a crown of large, hard and stiff, evergreen leaves. They usually have pinnate leaves. The individual plants are either all male or all female . Cycads vary in size from having a trunk that is only a few centimeters...
s, ginkgo
Ginkgo
Ginkgo , also spelled gingko and known as the Maidenhair Tree, is a unique species of tree with no close living relatives...
es, and several families of conifers. Other fossils discovered include bivalves, snail
Snail
Snail is a common name applied to most of the members of the molluscan class Gastropoda that have coiled shells in the adult stage. When the word is used in its most general sense, it includes sea snails, land snails and freshwater snails. The word snail without any qualifier is however more often...
s, ray-finned fishes
Actinopterygii
The Actinopterygii or ray-finned fishes constitute a class or sub-class of the bony fishes.The ray-finned fishes are so called because they possess lepidotrichia or "fin rays", their fins being webs of skin supported by bony or horny spines , as opposed to the fleshy, lobed fins that characterize...
, frog
Frog
Frogs are amphibians in the order Anura , formerly referred to as Salientia . Most frogs are characterized by a short body, webbed digits , protruding eyes and the absence of a tail...
s, salamander
Salamander
Salamander is a common name of approximately 500 species of amphibians. They are typically characterized by a superficially lizard-like appearance, with their slender bodies, short noses, and long tails. All known fossils and extinct species fall under the order Caudata, while sometimes the extant...
s, turtle
Turtle
Turtles are reptiles of the order Testudines , characterised by a special bony or cartilaginous shell developed from their ribs that acts as a shield...
s, sphenodonts
Sphenodontia
Sphenodontia is an order of lizard-like reptiles that includes only one living genus, the tuatara , and only two living species...
, lizard
Lizard
Lizards are a widespread group of squamate reptiles, with nearly 3800 species, ranging across all continents except Antarctica as well as most oceanic island chains...
s, terrestrial and aquatic crocodylomorpha
Crocodylomorpha
The Crocodylomorpha are an important group of archosaurs that include the crocodilians and their extinct relatives.During Mesozoic and early Tertiary times the Crocodylomorpha were far more diverse than they are now. Triassic forms were small, lightly built, active terrestrial animals. These were...
ns, several species of pterosaur
Pterosaur
Pterosaurs were flying reptiles of the clade or order Pterosauria. They existed from the late Triassic to the end of the Cretaceous Period . Pterosaurs are the earliest vertebrates known to have evolved powered flight...
, numerous dinosaur species, and early mammal
Mammal
Mammals are members of a class of air-breathing vertebrate animals characterised by the possession of endothermy, hair, three middle ear bones, and mammary glands functional in mothers with young...
s such as docodonts
Docodonta
Docodonta is an order of extinct proto-mammals that lived during the mid- to late-Mesozoic era. Their most distinguishing physical features were their relatively sophisticated set of molars, from which the order gets its name. In the fossil record, Docodonta is represented primarily by isolated...
, multituberculates
Multituberculata
The Multituberculata were a group of rodent-like mammals that existed for approximately one hundred and twenty million years—the longest fossil history of any mammal lineage—but were eventually outcompeted by rodents, becoming extinct during the early Oligocene. At least 200 species are...
, symmetrodonts
Symmetrodonta
Symmetrodonta is a basal group of Mesozoic mammals characterized by the triangular aspect of the molars when viewed from above and the absence of a well-developed talonid. The traditional group of symmetrodonts ranges in age from the latest Triassic to the Late Cretaceous. One species,...
, and triconodonts
Triconodonta
Triconodonta is the generic name for a group of early mammals which were close relatives of the ancestors of all present-day mammals. Triconodonts lived between the Triassic and the Cretaceous. They are one of the groups that can be classified as mammals by any definition...
. Such dinosaurs as the theropods Ceratosaurus
Ceratosaurus
Ceratosaurus meaning "horned lizard", in reference to the horn on its nose , was a large predatory theropod dinosaur from the Late Jurassic Period , found in the Morrison Formation of North America, in Tanzania and Portugal...
, Allosaurus
Allosaurus
Allosaurus is a genus of large theropod dinosaur that lived 155 to 150 million years ago during the late Jurassic period . The name Allosaurus means "different lizard". It is derived from the Greek /allos and /sauros...
, Ornitholestes
Ornitholestes
Ornitholestes was a small theropod dinosaur of the late Jurassic of Western Laurasia . To date, it is known only from a single partial skeleton, and badly crushed skull found at the Bone Cabin Quarry near Medicine Bow, Wyoming, in 1900...
, and Torvosaurus
Torvosaurus
Torvosaurus is a genus of large theropod dinosaur that lived during the Late Jurassic period...
, the sauropods Apatosaurus
Apatosaurus
Apatosaurus , also known by the popular but scientifically deprecated synonym Brontosaurus, is a genus of sauropod dinosaur that lived from about 154 to 150 million years ago, during the Jurassic Period . It was one of the largest land animals that ever existed, with an average length of and a...
, Brachiosaurus
Brachiosaurus
Brachiosaurus is a genus of sauropod dinosaur from the Jurassic Morrison Formation of North America. It was first described by Elmer S. Riggs in 1903 from fossils found in the Grand River Canyon of western Colorado, in the United States. Riggs named the dinosaur Brachiosaurus altithorax,...
, Camarasaurus
Camarasaurus
Camarasaurus meaning 'chambered lizard', referring to the hollow chambers in its vertebrae was a genus of quadrupedal, herbivorous dinosaurs. It was the most common of the giant sauropods to be found in North America...
, and Diplodocus
Diplodocus
Diplodocus , or )is a genus of diplodocid sauropod dinosaur whose fossils were first discovered in 1877 by S. W. Williston. The generic name, coined by Othniel Charles Marsh in 1878, is a Neo-Latin term derived from Greek "double" and "beam", in reference to its double-beamed chevron bones...
, and the ornithischia
Ornithischia
Ornithischia or Predentata is an extinct order of beaked, herbivorous dinosaurs. The name ornithischia is derived from the Greek ornitheos meaning 'of a bird' and ischion meaning 'hip joint'...
ns Camptosaurus
Camptosaurus
Camptosaurus is a genus of plant-eating, beaked ornithischian dinosaurs of the Late Jurassic period of western North America. The name means 'flexible lizard', ....
, Dryosaurus
Dryosaurus
Dryosaurus is a genus of an ornithopod dinosaur that lived in the Late Jurassic period. It was an iguanodont . Fossils have been found in the western United States, and were first discovered in the late 19th century...
, and Stegosaurus
Stegosaurus
Stegosaurus is a genus of armored stegosaurid dinosaur. They lived during the Late Jurassic period , some 155 to 150 million years ago in what is now western North America. In 2006, a specimen of Stegosaurus was announced from Portugal, showing that they were present in Europe as well...
are known from the Morrison. Othnielosaurus is present in stratigraphic zones 2-5.
Typically, Othnielosaurus has been interpreted like other hypsilophodonts as a small, swift
Cursorial
Cursorial is a biological term that describes an organism as being adapted specifically to run. It is typically used in conjunction with an animal's feeding habits or another important adaptation. For example, a horse can be considered a "cursorial grazer", while a wolf may be considered a...
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...
, although Bakker (1986) interpreted the possibly related Nanosaurus as an omnivore
Omnivore
Omnivores are species that eat both plants and animals as their primary food source...
. This idea has had some unofficial support, but little in the formal literature; description of more complete skull remains will be needed to test this hypothesis
Hypothesis
A hypothesis is a proposed explanation for a phenomenon. The term derives from the Greek, ὑποτιθέναι – hypotithenai meaning "to put under" or "to suppose". For a hypothesis to be put forward as a scientific hypothesis, the scientific method requires that one can test it...
.
External links
- More on the taxonomy of Nanosaurus, Othnielia, and Laosaurus
- Dinosaur Mailing List entry which announces the new genus
- A reconstruction of Othnielosaurus (as Othnielia rexOthnieliaOthnielia is a genus of ornithischian dinosaur, named after its original describer, Professor Othniel Charles Marsh, an American paleontologist of the 19th century...
) by Scott Hartman (based on the undescribed "Barbara" skeleton and the BYU skeleton) - Dinosaurier-Web with timescale (German and English)