Szechuanosaurus
Encyclopedia
Szechuanosaurus is a dubious
genus
of theropod dinosaur
from the Late Jurassic
. This dinosaur lived in the Asia
in the Oxfordian
and early Kimmeridgian
(Peng et al., 2005). It is based on four undiagnostic teeth from the Shangshaximiao Formation.
is S. campi, named by Chung Chien Young
in 1942 for four isolated teeth; these fossils are now considered to be nondiagnostic. Dong et al. (1983) assigned a partial skeleton to this species. The affinities of this skeleton are uncertain, and it has only been briefly described. Holtz et al. (2004) included it in their phylogenetic analysis and found it to be the most basal
tetanuran. This individual was a medium-sized theropod, with an ischium (a pelvic bone) of 420 millimetres (16.5 in); for comparison, an ischium of Piatnitzkysaurus
estimated to weigh 504 kilograms (1,111.1 lb) is 423 millimetres (16.7 in) long. S. campi is sometimes reported to includes
S. yandonensis (named by Dong, Chang, Li and Zhou in 1978) and Chienkosaurus ceratosauroides, although some researchers still believe that the latter may yet prove to be a distinct species.
Third species S. zigongensis (named by Gao in 1993 for an almost complete skeleton) is an older species, from the Middle Jurassic
, appears to be distinct from the type species and therefore requires its own genus name. In any case, also the partial skeleton by Dong et al. (1983) deserves its own genus.
Nomen dubium
In zoological nomenclature, a nomen dubium is a scientific name that is of unknown or doubtful application...
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 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...
from the Late Jurassic
Jurassic
The Jurassic is a geologic period and system that extends from about Mya to Mya, that is, from the end of the Triassic to the beginning of the Cretaceous. The Jurassic constitutes the middle period of the Mesozoic era, also known as the age of reptiles. The start of the period is marked by...
. This dinosaur lived in the Asia
Asia
Asia is the world's largest and most populous continent, located primarily in the eastern and northern hemispheres. It covers 8.7% of the Earth's total surface area and with approximately 3.879 billion people, it hosts 60% of the world's current human population...
in the Oxfordian
Oxfordian stage
The Oxfordian is, in the ICS' geologic timescale, the earliest age of the Late Jurassic epoch, or the lowest stage of the Upper Jurassic series. It spans the time between 161.2 ± 4 Ma and 155.7 ± 4 Ma...
and early Kimmeridgian
Kimmeridgian
In the geologic timescale, the Kimmeridgian is an age or stage in the Late or Upper Jurassic epoch or series. It spans the time between 155.7 ± 4 Ma and 150.8 ± 4 Ma . The Kimmeridgian follows the Oxfordian and precedes the Tithonian....
(Peng et al., 2005). It is based on four undiagnostic teeth from the Shangshaximiao Formation.
Discovery and species
Three species have been assigned to this genus over the years. The type speciesType 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 S. campi, named by Chung Chien Young
Yang Zhongjian
Yang Zhongjian , courtesy name Keqiang , also known as C.C. Young, was one of China's foremost paleontologists. He has been called the 'Father of Chinese vertebrate paleontology'...
in 1942 for four isolated teeth; these fossils are now considered to be nondiagnostic. Dong et al. (1983) assigned a partial skeleton to this species. The affinities of this skeleton are uncertain, and it has only been briefly described. Holtz et al. (2004) included it in their phylogenetic analysis and found it to be the most 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:...
tetanuran. This individual was a medium-sized theropod, with an ischium (a pelvic bone) of 420 millimetres (16.5 in); for comparison, an ischium of Piatnitzkysaurus
Piatnitzkysaurus
Piatnitzkysaurus is a genus of theropod dinosaur. It is known from the Canadon Asfalto Formation, Middle Jurassic of what is now Argentina. Once thought to be a basal carnosaur, it may instead be a megalosauroid...
estimated to weigh 504 kilograms (1,111.1 lb) is 423 millimetres (16.7 in) long. S. campi is sometimes reported to includes
Inclusion (taxonomy)
In taxonomy, inclusion is the process whereby two species that were believed to be distinct are found in fact to be the same and are thus combined as one species...
S. yandonensis (named by Dong, Chang, Li and Zhou in 1978) and Chienkosaurus ceratosauroides, although some researchers still believe that the latter may yet prove to be a distinct species.
Third species S. zigongensis (named by Gao in 1993 for an almost complete skeleton) is an older species, from the Middle Jurassic
Middle Jurassic
The Middle Jurassic is the second epoch of the Jurassic Period. It lasted from 176-161 million years ago. In European lithostratigraphy, rocks of this Middle Jurassic age are called the Dogger....
, appears to be distinct from the type species and therefore requires its own genus name. In any case, also the partial skeleton by Dong et al. (1983) deserves its own genus.