Avimimus
Encyclopedia
Avimimus meaning "bird mimic" (Latin
avis = bird + mimus = mimic), was a genus
of bird-like maniraptora
n dinosaur
that lived in the late Cretaceous
in what is now Mongolia
, around 70 million years ago.
Avimimus was a small dinosaur with a length of 1.5 m (5 ft). The skull
was small compared to the body, though the brain
and eye
s were large. The size of the bones which surrounded the brain and were dedicated to protecting it are large. This is also consistent with the hypothesis that Avimimus had a proportionally large brain.
As in related species, the jaws of Avimimus formed a parrot-like beak, and lacked teeth. However, a series of toothlike projections along the tip of the premaxilla would have given the beak a serrated edge. The toothless beak
of Avimimus suggests that it may have been an herbivore
or omnivore
. Kurzanov himself, however, believed that Avimimus was an insectivore
.
The foramen magnum, the hole allowing the spinal cord to connect with the brain, was proportionally large in Avimimus. The occipital condyle
, however, was small, further suggestive of the skull's relative lightness. The neck
itself was long and slender, and is composed of vertebrae are much more elongate than in other oviraptorosaurs. Unlike oviraptorids and caenagnathids, the back vertebrae lack openings for air sacs, suggesting that Avimimus is more primitive than these animals.
The forelimbs were relatively short. The bones of the hand were fused together, as in modern birds, and a ridge on the ulna
(lower arm bone) was interpreted as an attachment point for feathers by Kurzanov. Kurzanov, in 1987, also reported the presence of quill knobs, and while Chiappe confirmed the presence of bumps on the ulna, their function remained unclear. Kurzanov was so convinced they were attachment points for feathers that he concluded that Avimimus may have been capable of weak flight. The presence of feathers is now widely accepted, but most paleontologists do not believe Avimimus could fly.
The ilium was almost horizontally oriented, resulting in exceptionally broad hips. Little is known of the tail
but the hip suggests that the tail was long. The leg
s were extremely long and slender, suggesting that Avimimus was a highly specialized runner. The proportions of the leg bones add further weight to the idea of Avimimus was quick on its feet. The animal's shins were long in comparison with its thighs, a trait common among cursorial
animals. It also had three-toed feet with narrow pointed claws.
in 1981. The Avimimus fossils were initially described as having come from the Djadokta Formation by Kurzanov; however, in a 2006 description of a new specimen, Watabe and colleagues noted that Kurzanov was probably mistaken about the provenance, and it is more likely that Avimimus hailed from the more recent Nemegt Formation
. The type species
is A. portentosus. Because no tail was found with the original find, Kurzanov mistakenly concluded that Avimimus lacked a tail in life. However, subsequent Avimimus finds containing caudal vertebrae have confirmed the presence of a tail. A second nearly complete specimen of Avimimus was discovered in 1996 and described in 2000 by Watabe and colleagues. Additionally, these authors identified a number of small theropod footprints in the same area as belonging to Avimimus.
A variety of isolated bones that have been attributed to Avimimus but differ from A. portentosus may represent one or more distinct species, referred to as Avimimus sp..
In 2008 a team of Canadian, American, and Mongolian paleontologists headed by Phil Currie reported the discovery of an extensive bonebed of Avimimus sp. fossils. The bonebed is in the Nemegt Formation, 10.5 meters above the Barun Goyot Formation
, in the Gobi Desert. The team reported finding abundant bones of at least ten individuals of Avimimus, but the deposit may hold more. All individuals were either adult or subadult, and the adults showed little variation in size, suggesting determinant growth. The adults showed a greater degree of skeletal fusion in the tarsometatarsus and tibiotarsus, and also more prominent muscle scars. The team also suggests that the individuals were found together because they were gregarious in life.
, was close to the direct ancestor of modern birds, and that Archaeopteryx was not as closely related to birds as had previously been suggested. However, this view has not been supported by later phylogenetic analyses of dinosaur and bird relationships. Most modern scientists find that Avimimus in fact belongs to a diverse group of bird-like dinosaurs more primitive than Archaeopteryx, the oviraptorosaurs.
Kurzanov placed Avimimus in its own family, Avimimidae, in 1981. In 1991, Sankar Chatterjee
erected the Order
Avimimiformes to include Avimimus. Neither of these group names is used frequently by paleontologists as they include only a single species. More recent studies have shown that Avimimus is best grouped within the Oviraptoridae
, within the subgroup Elmisaurinae
.
Latin
Latin is an Italic language originally spoken in Latium and Ancient Rome. It, along with most European languages, is a descendant of the ancient Proto-Indo-European language. Although it is considered a dead language, a number of scholars and members of the Christian clergy speak it fluently, and...
avis = bird + mimus = mimic), was a 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...
of bird-like maniraptora
Maniraptora
Maniraptora is a clade of coelurosaurian dinosaurs which includes the birds and the dinosaurs that were more closely related to them than to Ornithomimus velox. It contains the major subgroups Avialae, Deinonychosauria, Oviraptorosauria and Therizinosauria. Ornitholestes and the Alvarezsauroidea...
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 in the 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...
in what is now Mongolia
Mongolia
Mongolia is a landlocked country in East and Central Asia. It is bordered by Russia to the north and China to the south, east and west. Although Mongolia does not share a border with Kazakhstan, its western-most point is only from Kazakhstan's eastern tip. Ulan Bator, the capital and largest...
, around 70 million years ago.
Description
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...
was small compared to the body, though the brain
Brain
The brain is the center of the nervous system in all vertebrate and most invertebrate animals—only a few primitive invertebrates such as sponges, jellyfish, sea squirts and starfishes do not have one. It is located in the head, usually close to primary sensory apparatus such as vision, hearing,...
and eye
Eye
Eyes are organs that detect light and convert it into electro-chemical impulses in neurons. The simplest photoreceptors in conscious vision connect light to movement...
s were large. The size of the bones which surrounded the brain and were dedicated to protecting it are large. This is also consistent with the hypothesis that Avimimus had a proportionally large brain.
As in related species, the jaws of Avimimus formed a parrot-like beak, and lacked teeth. However, a series of toothlike projections along the tip of the premaxilla would have given the beak a serrated edge. The toothless beak
Beak
The beak, bill or rostrum is an external anatomical structure of birds which is used for eating and for grooming, manipulating objects, killing prey, fighting, probing for food, courtship and feeding young...
of Avimimus suggests that it may have been an 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...
. Kurzanov himself, however, believed that Avimimus was an insectivore
Insectivore
An insectivore is a type of carnivore with a diet that consists chiefly of insects and similar small creatures. An alternate term is entomophage, which also refers to the human practice of eating insects....
.
The foramen magnum, the hole allowing the spinal cord to connect with the brain, was proportionally large in Avimimus. The occipital condyle
Occipital condyle
The occipital condyles are undersurface facets of the occipital bone in vertebrates, which function in articulation with the superior facets of the atlas vertebra....
, however, was small, further suggestive of the skull's relative lightness. The neck
Neck
The neck is the part of the body, on many terrestrial or secondarily aquatic vertebrates, that distinguishes the head from the torso or trunk. The adjective signifying "of the neck" is cervical .-Boner anatomy: The cervical spine:The cervical portion of the human spine comprises seven boney...
itself was long and slender, and is composed of vertebrae are much more elongate than in other oviraptorosaurs. Unlike oviraptorids and caenagnathids, the back vertebrae lack openings for air sacs, suggesting that Avimimus is more primitive than these animals.
The forelimbs were relatively short. The bones of the hand were fused together, as in modern birds, and a ridge on the 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...
(lower arm bone) was interpreted as an attachment point for feathers by Kurzanov. Kurzanov, in 1987, also reported the presence of quill knobs, and while Chiappe confirmed the presence of bumps on the ulna, their function remained unclear. Kurzanov was so convinced they were attachment points for feathers that he concluded that Avimimus may have been capable of weak flight. The presence of feathers is now widely accepted, but most paleontologists do not believe Avimimus could fly.
The ilium was almost horizontally oriented, resulting in exceptionally broad hips. Little is known of the tail
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...
but the hip suggests that the tail was long. The leg
Leg
Łęg may refer to the following places in Poland:*A former name for the town of Ełk *Part of the Czyżyny district of Kraków*Łęg, Pleszew County in Greater Poland Voivodeship...
s were extremely long and slender, suggesting that Avimimus was a highly specialized runner. The proportions of the leg bones add further weight to the idea of Avimimus was quick on its feet. The animal's shins were long in comparison with its thighs, a trait common among cursorial
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...
animals. It also had three-toed feet with narrow pointed claws.
Discovery and species
The remains of Avimimus were recovered by Russian paleontologists and officially described by Dr. Sergei KurzanovSergei Kurzanov
Sergei Kurzanov is a Russian paleontologist at the Paleontological Institute of the Russian Academy of Sciences. He is known mainly for his work in Mongolia and the ex-Soviet republics in Central Asia. In 1998, a species of iguanodont dinosaur from Mongolia was named Altirhinus kurzanovi in his...
in 1981. The Avimimus fossils were initially described as having come from the Djadokta Formation by Kurzanov; however, in a 2006 description of a new specimen, Watabe and colleagues noted that Kurzanov was probably mistaken about the provenance, and it is more likely that Avimimus hailed from the more recent Nemegt Formation
Nemegt Formation
The Nemegt Formation is a geological formation dating from the Late Cretaceous sedimentary from the Gobi Desert of Mongolia. It overlies and sometimes forms folds with the Barun Goyot Formation. It consists of river channel sediments and contains fossils of fish, turtles, crocodilians, birds and a...
. 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...
is A. portentosus. Because no tail was found with the original find, Kurzanov mistakenly concluded that Avimimus lacked a tail in life. However, subsequent Avimimus finds containing caudal vertebrae have confirmed the presence of a tail. A second nearly complete specimen of Avimimus was discovered in 1996 and described in 2000 by Watabe and colleagues. Additionally, these authors identified a number of small theropod footprints in the same area as belonging to Avimimus.
A variety of isolated bones that have been attributed to Avimimus but differ from A. portentosus may represent one or more distinct species, referred to as Avimimus sp..
In 2008 a team of Canadian, American, and Mongolian paleontologists headed by Phil Currie reported the discovery of an extensive bonebed of Avimimus sp. fossils. The bonebed is in the Nemegt Formation, 10.5 meters above the Barun Goyot Formation
Barun Goyot Formation
The Barun Goyot Formation , dating from the Late Cretaceous Period, is located within and is widely represented in the Gobi Desert basin, in the Ömnögovi Province of Mongolia....
, in the Gobi Desert. The team reported finding abundant bones of at least ten individuals of Avimimus, but the deposit may hold more. All individuals were either adult or subadult, and the adults showed little variation in size, suggesting determinant growth. The adults showed a greater degree of skeletal fusion in the tarsometatarsus and tibiotarsus, and also more prominent muscle scars. The team also suggests that the individuals were found together because they were gregarious in life.
Classification
Avimimus was originally suggested to be a very close relative of birds, given its unique suite of bird-like features not known in other dinosaurs at the time. In fact, Kurzanov argued that Avimimus, rather than the famous "first bird" ArchaeopteryxArchaeopteryx
Archaeopteryx , sometimes referred to by its German name Urvogel , is a genus of theropod dinosaur that is closely related to birds. The name derives from the Ancient Greek meaning "ancient", and , meaning "feather" or "wing"...
, was close to the direct ancestor of modern birds, and that Archaeopteryx was not as closely related to birds as had previously been suggested. However, this view has not been supported by later phylogenetic analyses of dinosaur and bird relationships. Most modern scientists find that Avimimus in fact belongs to a diverse group of bird-like dinosaurs more primitive than Archaeopteryx, the oviraptorosaurs.
Kurzanov placed Avimimus in its own family, Avimimidae, in 1981. In 1991, Sankar Chatterjee
Sankar Chatterjee
Sankar Chatterjee is a paleontologist, and is the Paul W. Horn Professor of Geosciences at Texas Tech University and Curator of Paleontology at the Museum of Texas Tech University. He earned his Ph. D. from the University of Calcutta in 1970 and was a Post-doctoral Fellow at the Smithsonian...
erected the Order
Order (biology)
In scientific classification used in biology, the order is# a taxonomic rank used in the classification of organisms. Other well-known ranks are life, domain, kingdom, phylum, class, family, genus, and species, with order fitting in between class and family...
Avimimiformes to include Avimimus. Neither of these group names is used frequently by paleontologists as they include only a single species. More recent studies have shown that Avimimus is best grouped within the Oviraptoridae
Oviraptoridae
Oviraptoridae is a group of bird-like, herbivorous and omnivorous maniraptoran dinosaurs. Oviraptorids are characterized by their toothless, parrot-like beaks and, in some cases, elaborate crests. They were generally small, measuring between one and two metres long in most cases, though some...
, within the subgroup Elmisaurinae
Elmisaurinae
Elmisaurinae is a subfamily of bird-like maniraptoran theropod dinosaurs within the clade Oviraptorosauria or Oviraptoridae...
.
External links
- Avimimus at DinoData