Sinornithomimus
Encyclopedia
Sinornithomimus is a genus
of ornithomimid theropod dinosaur
found in 1997, in the early Late Cretaceous
strata
of the Ulansuhai Formation
located at Alshanzuo Banner, Nei Mongol Autonomous Region
, Northern China
.
remains of Sinornithomimus were uncovered by Dong Zhiming
near Ulan Suhai in the context of the Mongol Highland International Dinosaur Project. They contained at least fourteen skeleton
s found in close association, nine of which are nearly complete and relatively uncrushed. The find consisted of three sub-adult to adult specimens and eleven juveniles. The unweathered state of the bones, preserved in siltstone
interspersed with layers of clay
and the absence of evidence for post-mortem movement, argue for a catastrophic event that killed all the individuals present in the find simultaneously and instantaneously.
The type species
Sinornithomimus dongi was named and described by Yoshitsugu Kobayashi and Lü Junchang in 2003. The generic name means “Chinese bird mimic” while the specific descriptor honours Dong as the discoverer of the fossils. The holotype
, IVPP-V11797-10, is one of the subadult skeletons. The other skeletons have been assigned as paratype
s.
A second expedition in 2001 at the same site led to the discovery of another fossilized herd of thirteen juveniles and subadults of Sinornithomimus. Their positioning suggest that they died together and over a short interval, likely after having become mired in the mud of a drying waterhole. The second discovery also largely consisted of nearly intact exemplars making Sinornithomimus the most completely known ornithomimid.
with in a quadrate pit a smaller opening, divided by a vertical sheet of bone; and a depression on the lateral side of the posterior
process
of the parietal bone
. The herbivory
of this genus is supported by the rare presence of gastrolith
s, as such stones were found forming conspicuous masses in the stomach areas of the fossil skeletons. This species was gregarious, which is corroborated by the arrangement of the fossil remains in a small bonebed with the juvenile individuals being approximately of the same age. This is furthermore supported by the increase of running ability as the animal progressed in its ontogeny
, thus shown in the more cursorial
proportions of the adults which possess relatively longer lower legs. It was assumed by the describers that adults protected themselves and their juveniles from predators by forming familial groups; in 2008 however a study concluded that the all juvenile herds suggest that immature individuals were left to fend for themselves in juvenile groups while adults preoccupied themselves with nesting or brooding.
ornithomimid that was considered by its describers a more derived
form than Archaeornithomimus
, though more recent analyses reverse the situation. The structure of the hand is similar to that of Archaeornithomimus representing thus an intermediate between the "primitive" condition of the ornithomimosaur Harpymimus
and the one of the more derived ornithomimids. Sinornithomimus renders some synapomorphies
of ornithomimids plesiomorphic, while also differentiating Asian ornithomimid rhamphothecae
from North American ones, based on maxilla
ry vascular
foramina found in the latter.
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 ornithomimid theropod 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...
found in 1997, in the early 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...
strata
Stratum
In geology and related fields, a stratum is a layer of sedimentary rock or soil with internally consistent characteristics that distinguish it from other layers...
of the Ulansuhai Formation
Ulansuhai Formation
The Ulansuhai Formation is a geological formation in Inner Mongolia, north China. Dinosaur remains are among the fossils that have been recovered from the formation....
located at Alshanzuo Banner, Nei Mongol Autonomous Region
Inner Mongolia
Inner Mongolia is an autonomous region of the People's Republic of China, located in the northern region of the country. Inner Mongolia shares an international border with the countries of Mongolia and the Russian Federation...
, Northern China
China
Chinese civilization may refer to:* China for more general discussion of the country.* Chinese culture* Greater China, the transnational community of ethnic Chinese.* History of China* Sinosphere, the area historically affected by Chinese culture...
.
Discovery and naming
The first fossilFossil
Fossils are the preserved remains or traces of animals , plants, and other organisms from the remote past...
remains of Sinornithomimus were uncovered by Dong Zhiming
Dong Zhiming
Dong Zhiming , from the Institute of Vertebrate Paleontology and Paleoanthropology in Beijing, is one of China's leading paleontologists. He began working at the IVPP in 1962, learning from Yang Zhongjian who was director at the time...
near Ulan Suhai in the context of the Mongol Highland International Dinosaur Project. They contained at least fourteen skeleton
Skeleton
The skeleton is the body part that forms the supporting structure of an organism. There are two different skeletal types: the exoskeleton, which is the stable outer shell of an organism, and the endoskeleton, which forms the support structure inside the body.In a figurative sense, skeleton can...
s found in close association, nine of which are nearly complete and relatively uncrushed. The find consisted of three sub-adult to adult specimens and eleven juveniles. The unweathered state of the bones, preserved in siltstone
Siltstone
Siltstone is a sedimentary rock which has a grain size in the silt range, finer than sandstone and coarser than claystones.- Description :As its name implies, it is primarily composed of silt sized particles, defined as grains 1/16 - 1/256 mm or 4 to 8 on the Krumbein phi scale...
interspersed with layers of clay
Clay
Clay is a general term including many combinations of one or more clay minerals with traces of metal oxides and organic matter. Geologic clay deposits are mostly composed of phyllosilicate minerals containing variable amounts of water trapped in the mineral structure.- Formation :Clay minerals...
and the absence of evidence for post-mortem movement, argue for a catastrophic event that killed all the individuals present in the find simultaneously and instantaneously.
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...
Sinornithomimus dongi was named and described by Yoshitsugu Kobayashi and Lü Junchang in 2003. The generic name means “Chinese bird mimic” while the specific descriptor honours Dong as the discoverer of the fossils. The holotype
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...
, IVPP-V11797-10, is one of the subadult skeletons. The other skeletons have been assigned as paratype
Paratype
Paratype is a technical term used in the scientific naming of species and other taxa of organisms. The exact meaning of the term paratype when it is used in zoology is not the same as the meaning when it is used in botany...
s.
A second expedition in 2001 at the same site led to the discovery of another fossilized herd of thirteen juveniles and subadults of Sinornithomimus. Their positioning suggest that they died together and over a short interval, likely after having become mired in the mud of a drying waterhole. The second discovery also largely consisted of nearly intact exemplars making Sinornithomimus the most completely known ornithomimid.
Description
Sinornithomimus was a two-meter-long (7 ft) ornithomimid, with a relatively short neck and head for a member of that group. Unique derived traits, autapomorphies, included: the possession of a quadrateQuadrate bone
The 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...
with in a quadrate pit a smaller opening, divided by a vertical sheet of bone; and a depression on the lateral side of the posterior
Anatomical terms of location
Standard anatomical terms of location are designations employed in science that deal with the anatomy of animals to avoid ambiguities that might otherwise arise. They are not language-specific, and thus require no translation...
process
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:...
of the parietal bone
Parietal bone
The parietal bones are bones in the human skull which, when joined together, form the sides and roof of the cranium. Each bone is roughly quadrilateral in form, and has two surfaces, four borders, and four angles. It is named from the Latin pariet-, wall....
. The herbivory
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...
of this genus is supported by the rare presence of gastrolith
Gastrolith
A gastrolith, also called a stomach stone or gizzard stones, is a rock held inside a gastrointestinal tract. Gastroliths are retained in the muscular gizzard and used to grind food in animals lacking suitable grinding teeth. The grain size depends upon the size of the animal and the gastrolith's...
s, as such stones were found forming conspicuous masses in the stomach areas of the fossil skeletons. This species was gregarious, which is corroborated by the arrangement of the fossil remains in a small bonebed with the juvenile individuals being approximately of the same age. This is furthermore supported by the increase of running ability as the animal progressed in its ontogeny
Ontogeny
Ontogeny is the origin and the development of an organism – for example: from the fertilized egg to mature form. It covers in essence, the study of an organism's lifespan...
, thus shown in the more 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...
proportions of the adults which possess relatively longer lower legs. It was assumed by the describers that adults protected themselves and their juveniles from predators by forming familial groups; in 2008 however a study concluded that the all juvenile herds suggest that immature individuals were left to fend for themselves in juvenile groups while adults preoccupied themselves with nesting or brooding.
Phylogeny
Sinornithomimus was by the describers assigned to the Ornithomimidae. It was a basalBasal (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:...
ornithomimid that was considered by its describers a more derived
Derived
In phylogenetics, a derived trait is a trait that is present in an organism, but was absent in the last common ancestor of the group being considered. This may also refer to structures that are not present in an organism, but were present in its ancestors, i.e. traits that have undergone secondary...
form than Archaeornithomimus
Archaeornithomimus
Archaeornithomimus is a genus of ornithomimosaurian theropod dinosaur from the Late Cretaceous of China, 70 million years ago....
, though more recent analyses reverse the situation. The structure of the hand is similar to that of Archaeornithomimus representing thus an intermediate between the "primitive" condition of the ornithomimosaur Harpymimus
Harpymimus
Harpymimus is a basal ornithomimosaurian theropod dinosaur from the Early Cretaceous Period of what is now Mongolia. Unlike later, more derived ornithomimosaurs, Harpymimus still possessed teeth, although they appear to have been restricted to the dentary of the lower jaw.-Discovery and naming:In...
and the one of the more derived ornithomimids. Sinornithomimus renders some synapomorphies
Synapomorphy
In cladistics, a synapomorphy or synapomorphic character is a trait that is shared by two or more taxa and their most recent common ancestor, whose ancestor in turn does not possess the trait. A synapomorphy is thus an apomorphy visible in multiple taxa, where the trait in question originates in...
of ornithomimids plesiomorphic, while also differentiating Asian ornithomimid rhamphothecae
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...
from North American ones, based on maxilla
Maxilla
The 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...
ry vascular
Blood vessel
The blood vessels are the part of the circulatory system that transports blood throughout the body. There are three major types of blood vessels: the arteries, which carry the blood away from the heart; the capillaries, which enable the actual exchange of water and chemicals between the blood and...
foramina found in the latter.