Metriacanthosauridae (Greek for "moderately-spined lizards") is an

extinct Extinction is the termination of an organism by the death of its Endling, last member. A taxon may become Functional extinction, functionally extinct before the death of its last member if it loses the capacity to Reproduction, reproduce and ...

family Family (from ) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). It forms the basis for social order. Ideally, families offer predictabili ...

allosauroid Carnosauria is an extinct group of carnivorous theropod dinosaurs that lived during the Jurassic and Cretaceous periods. While Carnosauria was historically considered largely synonymous with Allosauroidea, some recent studies have revived Carn ...

theropod Theropoda (; from ancient Greek , (''therion'') "wild beast"; , (''pous, podos'') "foot"">wiktionary:ποδός"> (''pous, podos'') "foot" is one of the three major groups (clades) of dinosaurs, alongside Ornithischia and Sauropodom ...

dinosaur Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic Geological period, period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the #Evolutio ...

s that lived in Europe and Asia from the

Middle Jurassic The Middle Jurassic is the second Epoch (geology), epoch of the Jurassic Period (geology), Period. It lasted from about 174.1 to 161.5 million years ago. Fossils of land-dwelling animals, such as dinosaurs, from the Middle Jurassic are relativel ...

to 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 ...

. The family is split into two subgroups: Metriacanthosaurinae, which includes dinosaurs closely related to ''

Metriacanthosaurus ''Metriacanthosaurus'' (meaning "moderately-spined lizard") is a genus of metriacanthosaurid dinosaur from the Oxford Clay Formation of England, dating to the Late Jurassic period, about 160 million years ago (lower Oxfordian). It is the only n ...

'', and another group composed of the close relatives of ''

Yangchuanosaurus ''Yangchuanosaurus'' is an extinct genus of metriacanthosaurid theropod dinosaur that lived in China from the Middle Jurassic to Late Jurassic periods (Bathonian to Tithonian stages), and was similar (although slightly larger) in size and appea ...

''. Metriacanthosaurids are considered

carnosaurs Carnosauria is an extinct group of carnivorous theropod dinosaurs that lived during the Jurassic and Cretaceous periods. While Carnosauria was historically considered largely synonymous with Allosauroidea, some recent studies have revived Carn ...

, belonging to the

Allosauroidea Carnosauria is an extinct group of carnivorous theropod dinosaurs that lived during the Jurassic and Cretaceous periods. While Carnosauria was historically considered largely synonymous with Allosauroidea, some recent studies have revived Carn ...

superfamily. The group includes species of large range in body size. Of their physical traits, most notable are their neural spines.Bailey, Jack Bowman. "Neural Spine Elongation in Dinosaurs: Sailbacks or Buffalo-Backs?" Journal of Paleontology, vol. 71, no. 06, 1997, pp. 1124–1146., doi:10.1017/s0022336000036076. The records of the group are mostly confined to Asia, though ''Metriacanthosaurus'' is known from Europe. Metriacanthosauridae is used as a senior synonym of Sinraptoridae.

Diagnostic traits

Metriacanthosaurids share the following unambiguous

synapomorphies In phylogenetics, an apomorphy (or derived trait) is a novel character or character state that has evolved from its ancestral form (or plesiomorphy). A synapomorphy is an apomorphy shared by two or more taxa and is therefore hypothesized to ...

among allosauroids: * A short or absent anterior ramus 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 ...

(also found in carcharodontosaurids and piatnitzkysaurids). * The laterosphenoid articulated on the frontal and

postorbital The ''postorbital'' is one of the bones in vertebrate skulls which forms a portion of the dermal skull roof and, sometimes, a ring about the orbit. Generally, it is located behind the postfrontal and posteriorly to the orbital fenestra. In some ve ...

. * A

squamosal The squamosal is a skull bone found in most reptiles, amphibians, and birds. In fishes, it is also called the pterotic bone. In most tetrapods, the squamosal and quadratojugal bones form the cheek series of the skull. The bone forms an ancestra ...

without constriction of the lower temporal fenestra. (also found in megalosauroids) * A flange on the squamosal covering the quadrate head laterally. * A well-defined longitudinal groove on the lateral side of the dentary housing a row of neurovascular foramina. * Broad, well developed spinopost-zygapophyseal lamina on the

axis An axis (: axes) may refer to: Mathematics *A specific line (often a directed line) that plays an important role in some contexts. In particular: ** Coordinate axis of a coordinate system *** ''x''-axis, ''y''-axis, ''z''-axis, common names ...

. * A

manus Manus may refer to: Relating to locations around New Guinea *Manus Island, a Papua New Guinean island in the Admiralty Archipelago ** Manus languages, languages spoken on Manus and islands close by ** Manus Regional Processing Centre, an offshore ...

shorter than the forearm. * Subrectangular and sheet-like neural spines of middle caudal vertebrae. * A manus without digit V or the phalanges of digit IV (also found in

neovenatorids Carnosauria is an extinct group of carnivorous theropod dinosaurs that lived during the Jurassic and Cretaceous periods. While Carnosauria was historically considered largely synonymous with Allosauroidea, some recent studies have revived Carn ...

). * A heart-shaped cross section of the ilium's paired midshafts (also found in coelophysids). * Fused distal end of the

ischium The ischium (; : is ...

(also found in neovenatorids and basal

tetanurans Tetanurae (/ˌtɛtəˈnjuːriː/ or "stiff tails") is a clade that includes most theropod dinosaurs, including megalosauroids, allosauroids, and coelurosaurs (which includes tyrannosauroids, ornithomimosaurs, compsognathids and maniraptorans, ...

). Metriacanthosaurids share the following dental synapomorphies among theropods: * surface centrally positioned on the labial surface of the crown roughly flattened in lateral teeth * irregular and non-oriented enamel surface texture Metriacanthosaurines share the following synapomorphies among metriacanthosaurids: * The anteroventral border of the maxillary

antorbital fenestra An antorbital fenestra (plural: fenestrae) is an opening in the skull that is in front of the eye sockets. This skull character is largely associated with Archosauriformes, archosauriforms, first appearing during the Triassic Period. Among Extant ...

being demarcated by a raised ridge (also found in ''

Eoraptor ''Eoraptor'' () is a genus of small, lightly built, Basal (phylogenetics), basal sauropodomorpha, sauropodomorph dinosaur. One of the earliest-known dinosaurs and one of the earliest sauropodomorphs, it lived approximately 231 to 228 million yea ...

'', coelophysids, ''

Masiakasaurus ''Masiakasaurus'' is a genus of small predatory noasaurid theropod dinosaurs from the Late Cretaceous of Madagascar. In Malagasy, ''masiaka'' means "vicious"; thus, the genus name means "vicious lizard". The type species, ''Masiakasaurus knopf ...

'', ''

Marshosaurus ''Marshosaurus'' is a genus of medium-sized carnivorous Theropoda, theropod dinosaur, belonging to the family Piatnitzkysauridae, from the Late Jurassic Morrison Formation of Utah and possibly Colorado. Discovery and naming During the 1960s, o ...

,'' and ''

Compsognathus ''Compsognathus'' (; Ancient Greek, Greek ''kompsos''/κομψός; "elegant", "refined" or "dainty", and ''gnathos''/γνάθος; "jaw") is a genus of small, bipedalism, bipedal, carnivore, carnivorous theropoda, theropod dinosaur. Members o ...

''). * A pronounced ventral keel on the anterior dorsal vertebrae (also found in '' Condorraptor'', ''

Piatnitzkysaurus ''Piatnitzkysaurus'' ( ; meaning "Piatnitzky's lizard") is a genus of tetanuran theropod dinosaur that lived approximately 179 to 177 million years ago during the lower part of the Jurassic Period in what is now Argentina. ''Piatnitzkysaurus'' wa ...

'', ''

Carcharodontosaurus ''Carcharodontosaurus'' (; ) is a genus of large carnivorous theropod dinosaur that lived in Northwest Africa from about 100 to 94 million years ago during the Cenomanian age of the Cretaceous. Two teeth of the genus, now lost, were first des ...

'' and many megalosaurians). * A straight posterior margin of the iliac postacetabular process. * The angle between the long axes of the

pubic In vertebrates, the pubis or pubic bone () forms the lower and anterior part of each side of the hip bone. The pubis is the most forward-facing (ventral and anterior) of the three bones that make up the hip bone. The left and right pubic bones ar ...

shaft and boot being less than 60 degrees. * A ventrally curved ischial shaft (also found in coelophysids, ''

Eustreptospondylus ''Eustreptospondylus'' ( ;), from Ancient Greek εὖ (''eû''), meaning "well", στρεπτός (''streptós''), meaning "twisted", and σπόνδυλος (''spóndulos''), meaning "vertebra", is a genus of megalosaurid theropod dinosaur, ...

'', ''

Afrovenator ''Afrovenator'' (; "African hunter") is a genus of megalosaurid theropod dinosaur from the Middle or Late Jurassic Period on the Tiourarén Formation and maybe the Irhazer II Formation of the Niger Sahara region in Western Africa. ''Afrove ...

'', ''

Megalosaurus ''Megalosaurus'' (meaning "great lizard", from Ancient Greek, Greek , ', meaning 'big', 'tall' or 'great' and , ', meaning 'lizard') is an extinct genus of large carnivorous theropod dinosaurs of the Middle Jurassic Epoch (Bathonian stage, 166 ...

'' and ''Compsognathus''). * A bulbous fibular crest on the

tibia The tibia (; : tibiae or tibias), also known as the shinbone or shankbone, is the larger, stronger, and anterior (frontal) of the two Leg bones, bones in the leg below the knee in vertebrates (the other being the fibula, behind and to the outsi ...

(also found in '' Sinosaurus'').

Classification

Carrano, Benson & Sampson (2012) noted that the name Metriacanthosauridae should be used as it has priority over Sinraptoridae.

Cladistically Cladistics ( ; from Ancient Greek 'branch') is an approach to biological classification in which organisms are categorized in groups ("clades") based on hypotheses of most recent common ancestry. The evidence for hypothesized relationships is ...

, Sinraptoridae had been latest defined in 2005 by

Paul Sereno Paul Callistus Sereno (born October 11, 1957) is a professor of paleontology at the University of Chicago who has discovered several new dinosaur species on several continents, including at sites in Inner Mongolia, Argentina, Morocco and Niger. ...

as the most inclusive

monophyletic In biological cladistics for the classification of organisms, monophyly is the condition of a taxonomic grouping being a clade – that is, a grouping of organisms which meets these criteria: # the grouping contains its own most recent co ...

group that contains '' Sinraptor dongi'' and all species closer to ''Sinraptor'' than to either ''

Allosaurus fragilis ''Allosaurus'' ( ) is an extinct genus of theropoda, theropod dinosaur that lived 155 to 145 million years ago during the Late Jurassic Geologic time scale, period (Kimmeridgian to late Tithonian Geologic time scale, ages). The first fossil ...

'', '' Carcharodontosaurus saharicus'', or the

house sparrow The house sparrow (''Passer domesticus'') is a bird of the Old World sparrow, sparrow family Passeridae, found in most parts of the world. It is a small bird that has a typical length of and a mass of . Females and young birds are coloured pa ...

(''Passer domesticus''). Furthermore, the 2012 study named a new subfamily Metriacanthosaurinae to include all metriacanthosaurids more closely related to ''

'' than to ''

''. A much larger

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 ...

analysis found '' Xuanhanosaurus'', previously considered a basal

megalosauroid Megalosauroidea (meaning 'great/big lizard forms') is a Taxonomic rank, superfamily (or clade) of Tetanurae, tetanuran theropod dinosaurs that lived from the Middle Jurassic to the Late Cretaceous period. The group is defined as ''Megalosaurus, M ...

, to be the basalmost metriacanthosaurid.Supporting Information
/ref> Both ''

Poekilopleuron ''Poekilopleuron'' (meaning "varied ribs") is a genus of carnosaurian theropod dinosaur, which lived during the middle Bathonian of the Jurassic, about 168 to 166 million years ago. The genus has been used under many different spelling variants, ...

'' and ''

Lourinhanosaurus ''Lourinhanosaurus'' (meaning "Lourinhã lizard") was a genus of carnivorous theropod dinosaur that lived during the Late Jurassic Period ( Kimmeridgian/Tithonian) in Portugal. It is one of many large predators discovered at the Lourinhã Format ...

'' were recovered outside the family, and many taxa within the Metriacanthosauridae were in

polytomy An internal node of a phylogenetic tree is described as a polytomy or multifurcation if (i) it is in a rooted tree and is linked to three or more child subtrees or (ii) it is in an unrooted tree and is attached to four or more branches. A tree ...

. However, the positions of ''Xuanhanosaurus'' and ''Poekilopleuron'' were very unstable, and their exclusion from the analysis gave a more resolved and stable cladogram. 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 ...

presented here follows that study.

Palaeobiogeography

Metriacanthosauridae fossils have only been found in modern

Europe Europe is a continent located entirely in the Northern Hemisphere and mostly in the Eastern Hemisphere. It is bordered by the Arctic Ocean to the north, the Atlantic Ocean to the west, the Mediterranean Sea to the south, and Asia to the east ...

and

Asia Asia ( , ) is the largest continent in the world by both land area and population. It covers an area of more than 44 million square kilometres, about 30% of Earth's total land area and 8% of Earth's total surface area. The continent, which ...

, parts of the prehistoric landmass

Laurasia Laurasia () was the more northern of two large landmasses that formed part of the Pangaea supercontinent from around ( Mya), the other being Gondwana. It separated from Gondwana (beginning in the late Triassic period) during the breakup of Pa ...

. The biogeographic origin of metriacanthosaurids based on phylogenetic analysis is suggested to be South-East Asia, specified as "Chinese provinces of Sichuan and Yunnan and areas south of this", and the earliest known taxa are '' Shidaisaurus'' from southern China and ''

Alpkarakush ''Alpkarakush'' is an extinct genus of metriacanthosaurid theropod dinosaurs from the Jurassic Balabansai Formation of Kyrgyzstan. The genus contains a Monotypic taxon, single species, ''A. kyrgyzicus'', known from a partial skeleton. Discovery ...

'' from Kyrgyzstan. Fragmentary remains of allosauroids from the late Middle-early Late Jurassic

Marnes de Dives The Marnes de Dives is a geological formation in Normandy, France. It dates back to the upper part of the Callovian stage of the Middle Jurassic.Weishampel, David B; et al. (2004). "Dinosaur distribution (Middle Jurassic, Europe)." In: Weishampel ...

in northern France bear close similarities to metriocanthosaurids, and may belong to members of the group.

References

External links

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