Sinotyrannus
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''Sinotyrannus'' (meaning "Chinese tyrant") is an extinct
genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...
of large tyrannosauroid theropod dinosaurs known from the
Early Cretaceous The Early Cretaceous (geochronology, geochronological name) or the Lower Cretaceous (chronostratigraphy, chronostratigraphic name) is the earlier or lower of the two major divisions of the Cretaceous. It is usually considered to stretch from 143.1 ...
Jiufotang Formation The Jiufotang Formation () is an Early Cretaceous geological formation in Chaoyang, Liaoning which has yielded fossils of feathered dinosaurs, primitive birds, pterosaurs, and other organisms (see Jehol Biota). It is a member of the Jehol group. T ...
of
Liaoning ) , image_skyline = , image_alt = , image_caption = Clockwise: Mukden Palace in Shenyang, Xinghai Square in Dalian, Dalian coast, Yalu River at Dandong , image_map = Liaoning in China (+all claims hatched).svg , ...
, China. This genus contains a single species, ''Sinotyrannus kazuoensis'', known from a single mature specimen including a partial skull, some vertebrae, and part of the pelvic girdle. While it exhibited greater body size that would put it on par with the later tyrannosaurids such as ''
Tyrannosaurus ''Tyrannosaurus'' () is a genus of large theropod dinosaur. The type species ''Tyrannosaurus rex'' ( meaning 'king' in Latin), often shortened to ''T. rex'' or colloquially t-rex, is one of the best represented theropods. It lived througho ...
'' (a group that ''Sinotyrannus'' was initially suspected of being in), ''Sinotyrannus'' was probably a member of the basal tyrannosauroid family known as the Proceratosauridae. This family originated in the
Jurassic The Jurassic ( ) is a Geological period, geologic period and System (stratigraphy), stratigraphic system that spanned from the end of the Triassic Period million years ago (Mya) to the beginning of the Cretaceous Period, approximately 143.1 Mya. ...
, whose members are known from Europe and Asia. ''Sinotyrannus'' and its close relative '' Yutyrannus'' appear to have been surprisingly large compared to most tyrannosauroids of the Early Cretaceous, such as '' Dilong''. Most of the world during the Early Cretaceous was dominated by more basal tetanurans, such as the megalosauroids and allosaurs, with tyrannosaurids themselves only taking over after both groups started to decline. However, ''Sinotyrannus'' and ''Yutyrannus'' appear to be exceptions to this. ''Sinotyrannus'' was the largest theropod in the Jiufotang Formation, reaching up to in length. The smaller theropod '' Huaxiagnathus'' from the older
Yixian Formation The Yixian Formation (; formerly Romanization of Chinese, transcribed as Yihsien Formation or Yixiang Formation) is a geological formation in Jinzhou, Liaoning, People's Republic of China, that spans the Barremian stage of the Early Cretaceous. I ...
, traditionally regarded as a " compsognathid" and known only from immature specimens, may be an immature form of ''Sinotyrannus''. If this hypothesis is supported, ''Sinotyrannus'' would be a
junior synonym In taxonomy, the scientific classification of living organisms, a synonym is an alternative scientific name for the accepted scientific name of a taxon. The botanical and zoological codes of nomenclature treat the concept of synonymy differently. ...
of ''Huaxiagnathus''.


Description

''Sinotyrannus'' was a large tyrannosaur, measuring approximately long and weighing . It is among the largest basal tyrannosauroids known, repudiating the previously presumed trend that tyrannosauroids gradually increased in size throughout the Cretaceous period from small basal forms like '' Dilong'' to advanced
apex predator An apex predator, also known as a top predator or superpredator, is a predator at the top of a food chain, without natural predators of its own. Apex predators are usually defined in terms of trophic dynamics, meaning that they occupy the hig ...
s such as ''
Tyrannosaurus ''Tyrannosaurus'' () is a genus of large theropod dinosaur. The type species ''Tyrannosaurus rex'' ( meaning 'king' in Latin), often shortened to ''T. rex'' or colloquially t-rex, is one of the best represented theropods. It lived througho ...
''. The holotype, KZV-001, consists of a disarticulated partial skeleton including the front portion of the skull, three dorsal vertebrae, incomplete ilia, three articulated manual phalanges (including an ungual), and other fragmentary bones. The described cranial elements include the
premaxilla The premaxilla (or praemaxilla) is one of a pair of small cranial bones at the very tip of the upper jaw of many animals, usually, but not always, bearing teeth. In humans, they are fused with the maxilla. The "premaxilla" of therian mammals h ...
e,
dentary In jawed vertebrates, the mandible (from the Latin ''mandibula'', 'for chewing'), lower jaw, or jawbone is a bone that makes up the lowerand typically more mobilecomponent of the mouth (the upper jaw being known as the maxilla). The jawbone ...
, and anterior portions of the
maxilla In vertebrates, the maxilla (: maxillae ) is the upper fixed (not fixed in Neopterygii) bone of the jaw formed from the fusion of two maxillary bones. In humans, the upper jaw includes the hard palate in the front of the mouth. The two maxil ...
e and nasals. The dorsal margin of the maxilla is unusually concave unlike the convex condition in tyrannosaurids. The nares are large and elliptical, supporting its relation to proceratosauridae. The dentary gradually curves upwards as it approaches its front edge. Many teeth are preserved attached to the maxillae, with a roughly equal number of denticles on each side, similarly to those of tyrannosaurids. ''Sinotyrannus'' could perceivably have had a tall nasal crest like other proceratosaurids, although not enough of its nasals are preserved to be certain. The three preserved vertebrae have very tall neural spines. The proportions of the preserved manual phalanges support the idea that they belong to the second finger, and the ungual has a deep groove on each side. The ilia are mainly present as molds, with the mold of the external side of the left ilium being the most complete. The preacetabular blade is short and wide, with a massive pubic peduncle, while the postacetabular blade is longer and thinner, with a triangular ischial peduncle. These traits of the ilia differentiate it from more advanced tyrannosauroids such as the tyrannosaurids. ''Sinotyrannus'' was likely an active predator, as has been speculated for most tyrannosaurs, and may have been covered in a simple feathery coat as was the case with most basal coelurosaurs, including many early tyrannosaurs.


Classification

The original description of ''Sinotyrannus'' proposed that it could have been the earliest tyrannosaurid due to its large size, but subsequent analyses place it as a proceratosaurid tyrannosauroid. A 2013 study by Loewen and colleagues considered it to be part of a clade containing '' Juratyrant'' and '' Stokesosaurus'' within the Proceratosauridae, as they all reputedly share a narrow preacetabular notch. The results of their
phylogenetic analyses In biology, phylogenetics () is the study of the evolutionary history of life using observable characteristics of organisms (or genes), which is known as Computational phylogenetics, phylogenetic inference. It infers the relationship among organ ...
are shown in the
cladogram A cladogram (from Greek language, Greek ''clados'' "branch" and ''gramma'' "character") is a diagram used in cladistics to show relations among organisms. A cladogram is not, however, an Phylogenetic tree, evolutionary tree because it does not s ...
below: However, Brusatte et al. (2016) instead placed ''Juratyrant'' and ''Stokesosaurus'' outside of the Proceratosauridae, and proposed that ''Sinotyrannus'' represents the
sister taxon In phylogenetics, a sister group or sister taxon, also called an adelphotaxon, comprises the closest relative(s) of another given unit in an evolutionary tree. Definition The expression is most easily illustrated by a cladogram: Taxon A and ...
of '' Yutyrannus'' within Proceratosauridae. The results of their phylogenetic analyses are shown in the cladogram below: In 2024, Andrea Cau published a comprehensive theropod
phylogenetic In biology, phylogenetics () is the study of the evolutionary history of life using observable characteristics of organisms (or genes), which is known as phylogenetic inference. It infers the relationship among organisms based on empirical dat ...
framework that could be used to identify immature specimens of other taxa. The following year, Cau and Paterna used an updated version of this dataset to deduce that ''Sinotyrannus''—known from a specimen of an adult individual—was a mature form of the " compsognathid" '' Huaxiagnathus'', which is known only from two immature specimens. Both species share a dorsally convex with a short preacetabular process without an anteroventral hook. Other differences observed between the two species are likely the result of differences in body size and ontogenetic stage, consistent with the more established growth series of other tyrannosauroids like ''Tyrannosaurus''. Since ''Huaxiagnathus'' was named before ''Sinotyrannus'', this genus name holds priority, making ''Sinotyrannus'' a
junior synonym In taxonomy, the scientific classification of living organisms, a synonym is an alternative scientific name for the accepted scientific name of a taxon. The botanical and zoological codes of nomenclature treat the concept of synonymy differently. ...
of the former. In their phylogenetic tree, the combined ''Sinotyrannus''+''Huaxiagnathus''
operational taxonomic unit An operational taxonomic unit (OTU) is an operational definition used to classify groups of closely related individuals. The term was originally introduced in 1963 by Robert R. Sokal and Peter H. A. Sneath in the context of numerical taxonomy, wh ...
(OTU) was recovered as the sister taxon to '' Eotyrannus'' in a clade with other traditional proceratosaurids.


Paleoenvironment

''Sinotyrannus'' lived in a rather wet environment with well-watered forests and large lakes. The area experienced great diversity in terms of vertebrate fauna, with many taxa, such as ''
Microraptor ''Microraptor'' (Greek language, Greek, μικρός, ''mīkros'': "small"; Latin language, Latin, ''raptor'': "one who seizes") is a genus of small, four-winged dromaeosaurid dinosaurs. Numerous well-preserved fossil specimens have been recovere ...
'', living alongside ''Sinotyrannus''. Despite this, the area was quite prone to high volcanism.


See also

* Timeline of tyrannosaur research


References


External links


Pieces of ''Sinotyrannus'' skull
{{Taxonbar, from=Q1187687 Proceratosauridae Dinosaur genera Aptian dinosaurs Jiufotang Formation Fossil taxa described in 2009 Dinosaurs of China