Aublysodon
Encyclopedia
Aublysodon is a name given to a large number of carnivorous
dinosaur
teeth of a certain form found in numerous late Cretaceous
period geological formations. The genus
was named by Joseph Leidy
in 1868, though it is now considered dubious
, because the type specimen consists only of an isolated premaxillary tooth, found in the Judith River Group
of Montana
. Although this specimen is now lost, similar teeth have been found in many US states, western Canada, and Asia. These teeth almost certainly belong to juvenile tyrannosaurine tyrannosaurid
s, but most have not been identified to species level. However, it is likely that the type tooth (and therefore the name Aublysodon mirandus itself) belongs to one of the species in the genus Daspletosaurus
, which was present in contemporary formations, and which matches specific details of the original tooth. The synapomorphies alleged to distinguish the Aublysodontinae, especially lack of serrations on premaxillary teeth could have been caused by tooth wear in life, postmortem abrasion
, or digestion
. Most other "Aublysodontine"-type teeth may be from ontogenetic stages or sexual morphs of other tyrannosaurids.
were named for isolated teeth; such genera
include Trachodon
, Palaeoscincus
, and Troodon
. Even before the badlands
of North America
started revealing the bones of Tyrannosaurus
, teeth turning up in many localities in the Western United States
revealed the presence of large predatory dinosaurs.
Leidy named nonserrated premaxillary teeth Aublysodon in 1868. These specimens had been collected from the Judith River
Badlands of Montana
. This tooth-based taxon was a mystery for a long time since no further skeletal elements were found that could be assigned with certainty to the teeth. Similar teeth are found in specimens of juvenile Daspletosaurus
, and it is likely that teeth referred to Aublysodon came from that genus.
The first skeletal material referred to Aublysodon was a partial skull
unearthed in Montana
in the 1980s. The skull bore pointed teeth attached to a long narrow skull the length of an average human arm. First thought to be a juvenile Tyrannosaurus
, then interpreted as a large dromaeosaurid, this "Jordan theropod" was given the name Aublysodon molnari by Paul in 1988. It was re-classified in the distinct genus Stygivenator by Olshevsky in 1995, but was later (2004) reinterpreted to be a juvenile Tyrannosaurus rex by Thomas Carr and Tom Williamson. Two contemporary species based solely on teeth, Aublysodon amplus and A. cristaus, may also represent teeth from juvenile T. rex.
Another partial skeleton from New Mexico was considered to represent Aublysodon, but later research by Thomas Carr and Tom Williamson (2004) has shown that it is probably referable to Daspletosaurus
.
Now that the type specimen of Aublysodon is missing, and coupled with the presence of Aublysodon teeth in juvenile tyrannosaurines, the name is no longer considered to represent a real biological taxon.
Holtz proposed a definition of the Tyrannosauridae in 2001 as "all descendants of the most recent common ancestor of Tyrannosaurus and Aublysodon", using Aublysodon as an anchor taxon. Paul Sereno has also used Aublysodon as an anchor taxon for the tyrannosauridae, although his definition was problematic for other reasons.
Carnivore
A carnivore meaning 'meat eater' is an organism that derives its energy and nutrient requirements from a diet consisting mainly or exclusively of animal tissue, whether through predation or scavenging...
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...
teeth of a certain form found in numerous late Cretaceous
Cretaceous
The Cretaceous , derived from the Latin "creta" , usually abbreviated K for its German translation Kreide , is a geologic period and system from circa to million years ago. In the geologic timescale, the Cretaceous follows the Jurassic period and is followed by the Paleogene period of the...
period geological formations. The genus
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...
was named by Joseph Leidy
Joseph Leidy
Joseph Leidy was an American paleontologist.Leidy was professor of anatomy at the University of Pennsylvania, and later was a professor of natural history at Swarthmore College. His book Extinct Fauna of Dakota and Nebraska contained many species not previously described and many previously...
in 1868, though it is now considered dubious
Nomen dubium
In zoological nomenclature, a nomen dubium is a scientific name that is of unknown or doubtful application...
, because the type specimen consists only of an isolated premaxillary tooth, found in the Judith River Group
Judith River Group
The Judith River Group is a group of geologic formations in western North America dating from the late Cretaceous and noted as a site for the extensive excavation of dinosaur fossils. The formation is named after the Judith River in Montana. The group is also called the Judith River Wedge...
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,...
. Although this specimen is now lost, similar teeth have been found in many US states, western Canada, and Asia. These teeth almost certainly belong to juvenile tyrannosaurine tyrannosaurid
Tyrannosauridae
Tyrannosauridae is a family of coelurosaurian theropod dinosaurs which comprises two subfamilies containing up to six genera, including the eponymous Tyrannosaurus. The exact number of genera is controversial, with some experts recognizing as few as three...
s, but most have not been identified to species level. However, it is likely that the type tooth (and therefore the name Aublysodon mirandus itself) belongs to one of the species in the genus Daspletosaurus
Daspletosaurus
Daspletosaurus is a genus of tyrannosaurid theropod dinosaur that lived in western North America between 77 and 74 million years ago, during the Late Cretaceous Period. Fossils of the only named species were found in Alberta, although other possible species from Alberta and Montana await...
, which was present in contemporary formations, and which matches specific details of the original tooth. The synapomorphies alleged to distinguish the Aublysodontinae, especially lack of serrations on premaxillary teeth could have been caused by tooth wear in life, postmortem abrasion
Abrasion
In dermatology, an abrasion is a wound caused by superficial damage to the skin, no deeper than the epidermis. It is less severe than a laceration, and bleeding, if present, is minimal. Mild abrasions, also known as grazes or scrapes, do not scar or bleed, but deep abrasions may lead to the...
, or digestion
Digestion
Digestion is the mechanical and chemical breakdown of food into smaller components that are more easily absorbed into a blood stream, for instance. Digestion is a form of catabolism: a breakdown of large food molecules to smaller ones....
. Most other "Aublysodontine"-type teeth may be from ontogenetic stages or sexual morphs of other tyrannosaurids.
History
In the mid-to-late 19th century many dinosaur taxaTaxonomy
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...
were named for isolated teeth; such genera
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...
include Trachodon
Trachodon
Trachodon is a dubious genus of hadrosaurid dinosaur based on teeth from the Campanian-age Upper Cretaceous Judith River Formation of Montana, U.S.A...
, Palaeoscincus
Palaeoscincus
Palaeoscincus is a dubious genus of ankylosaurian dinosaur based on teeth from the mid-late Campanian-age Upper Cretaceous Judith River Formation of Montana...
, and Troodon
Troodon
Troodon is a genus of relatively small, bird-like dinosaur from the Late Cretaceous period . Discovered in 1855, it was among the first dinosaurs found in North America...
. Even before the badlands
Badlands
A badlands is a type of dry terrain where softer sedimentary rocks and clay-rich soils have been extensively eroded by wind and water. It can resemble malpaís, a terrain of volcanic rock. Canyons, ravines, gullies, hoodoos and other such geological forms are common in badlands. They are often...
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...
started revealing the bones of Tyrannosaurus
Tyrannosaurus
Tyrannosaurus meaning "tyrant," and sauros meaning "lizard") is a genus of coelurosaurian theropod dinosaur. The species Tyrannosaurus rex , commonly abbreviated to T. rex, is a fixture in popular culture. It lived throughout what is now western North America, with a much wider range than other...
, teeth turning up in many localities in the Western United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
revealed the presence of large predatory dinosaurs.
Leidy named nonserrated premaxillary teeth Aublysodon in 1868. These specimens had been collected from the Judith River
Judith River
The Judith River is a tributary of the Missouri River, approximately 124 mi long, running through central Montana and the United States. It rises in the Little Belt Mountains and flows northeast past Utica and Hobson...
Badlands 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,...
. This tooth-based taxon was a mystery for a long time since no further skeletal elements were found that could be assigned with certainty to the teeth. Similar teeth are found in specimens of juvenile Daspletosaurus
Daspletosaurus
Daspletosaurus is a genus of tyrannosaurid theropod dinosaur that lived in western North America between 77 and 74 million years ago, during the Late Cretaceous Period. Fossils of the only named species were found in Alberta, although other possible species from Alberta and Montana await...
, and it is likely that teeth referred to Aublysodon came from that genus.
The first skeletal material referred to Aublysodon was a partial skull
Skull
The skull is a bony structure in the head of many animals that supports the structures of the face and forms a cavity for the brain.The skull is composed of two parts: the cranium and the mandible. A skull without a mandible is only a cranium. Animals that have skulls are called craniates...
unearthed in 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,...
in the 1980s. The skull bore pointed teeth attached to a long narrow skull the length of an average human arm. First thought to be a juvenile Tyrannosaurus
Tyrannosaurus
Tyrannosaurus meaning "tyrant," and sauros meaning "lizard") is a genus of coelurosaurian theropod dinosaur. The species Tyrannosaurus rex , commonly abbreviated to T. rex, is a fixture in popular culture. It lived throughout what is now western North America, with a much wider range than other...
, then interpreted as a large dromaeosaurid, this "Jordan theropod" was given the name Aublysodon molnari by Paul in 1988. It was re-classified in the distinct genus Stygivenator by Olshevsky in 1995, but was later (2004) reinterpreted to be a juvenile Tyrannosaurus rex by Thomas Carr and Tom Williamson. Two contemporary species based solely on teeth, Aublysodon amplus and A. cristaus, may also represent teeth from juvenile T. rex.
Another partial skeleton from New Mexico was considered to represent Aublysodon, but later research by Thomas Carr and Tom Williamson (2004) has shown that it is probably referable to Daspletosaurus
Daspletosaurus
Daspletosaurus is a genus of tyrannosaurid theropod dinosaur that lived in western North America between 77 and 74 million years ago, during the Late Cretaceous Period. Fossils of the only named species were found in Alberta, although other possible species from Alberta and Montana await...
.
Now that the type specimen of Aublysodon is missing, and coupled with the presence of Aublysodon teeth in juvenile tyrannosaurines, the name is no longer considered to represent a real biological taxon.
Classification
Aublysodon was once thought to belong to a unique subfamily of tyrannosaurids called the Aublysodontinae. Holtz proposed a definition of the Aublysodontinae in 2001, "Aublysodon and all taxa sharing a more recent common ancestor with it than with Tyrannosaurus."Holtz proposed a definition of the Tyrannosauridae in 2001 as "all descendants of the most recent common ancestor of Tyrannosaurus and Aublysodon", using Aublysodon as an anchor taxon. Paul Sereno has also used Aublysodon as an anchor taxon for the tyrannosauridae, although his definition was problematic for other reasons.
External links
- Aublysodon in The Dinosaur Encyclopaedia