clade
A clade (), also known as a monophyletic group or natural group, is a group of organisms that are monophyletic – that is, composed of a common ancestor and all its lineal descendants – on a phylogenetic tree. Rather than the English term, ...
of carnivorous
tetanuran
Tetanurae (/ˌtɛtəˈnjuːriː/ or "stiff tails") is a clade that includes most theropod dinosaurs, including megalosauroids, allosauroids, tyrannosauroids, ornithomimosaurs, compsognathids and maniraptorans (including birds). Tetanurans ar ...
theropod
Theropoda (; ), whose members are known as theropods, is a dinosaur clade that is characterized by hollow bones and three toes and claws on each limb. Theropods are generally classed as a group of saurischian dinosaurs. They were ancestrally c ...
dinosaur
Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the evolution of dinosaurs is t ...
s with controversial relations to other theropods. Its
derived
Derive may refer to:
* Derive (computer algebra system), a commercial system made by Texas Instruments
* ''Dérive'' (magazine), an Austrian science magazine on urbanism
*Dérive, a psychogeographical concept
See also
*
*Derivation (disambiguatio ...
members, the Megaraptoridae are noted for their elongated hand claws and proportionally large arms, which are usually reduced in size in other large theropods.
Megaraptorans are incompletely known, and no complete megaraptoran skeleton has been found. However, they still possessed a number of unique features. Their forelimbs were large and strongly built, and the
ulna
The ulna (''pl''. ulnae or ulnas) is a long bone found in the forearm that stretches from the elbow to the smallest finger, and when in anatomical position, is found on the medial side of the forearm. That is, the ulna is on the same side of t ...
bone had a unique shape in members of the
family
Family (from la, familia) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its ...
Megaraptoridae, a subset of megaraptorans which excludes ''
Fukuiraptor
''Fukuiraptor'' ("thief of Fukui") was a medium-sized megaraptoran theropod dinosaur of the Early Cretaceous epoch (either Barremian or Aptian) that lived in what is now Japan. ''Fukuiraptor'' is known from the Kitadani Formation and possibly ...
'' and ''
Phuwiangvenator
''Phuwiangvenator'' ("hunter of Phu Wiang") is a genus of 6 meter long megaraptoran theropod that lived during the Early Cretaceous period in what is now Thailand. It contains a single species, ''P. yaemniyomi'', recovered from the Sao Khua Fo ...
''. The first two fingers were elongated, with massive curved claws, while the third finger was small. Megaraptoran skull material is very incomplete, but a juvenile ''
Megaraptor
''Megaraptor'' () is a genus of large theropod dinosaur that lived in the ages of the Late Cretaceous. Its fossils have been discovered in the Patagonian Portezuelo Formation of Argentina, South America. Initially thought to have been a giant dr ...
'' described in 2014 preserved a portion of the snout, which was long and slender. Leg bones referred to megaraptorans were also quite slender and similar to those of
coelurosaurs
Coelurosauria (; from Greek, meaning "hollow tailed lizards") is the clade containing all theropod dinosaurs more closely related to birds than to carnosaurs.
Coelurosauria is a subgroup of theropod dinosaurs that includes compsognathids, tyrann ...
adapted for running. Although megaraptorans were thick-bodied theropods, their bones were heavily pneumatized, or filled with air pockets. The
vertebrae
The spinal column, a defining synapomorphy shared by nearly all vertebrates,Hagfish are believed to have secondarily lost their spinal column is a moderately flexible series of vertebrae (singular vertebra), each constituting a characteristic i ...
,
ribs
The rib cage, as an enclosure that comprises the ribs, vertebral column and sternum in the thorax of most vertebrates, protects vital organs such as the heart, lungs and great vessels.
The sternum, together known as the thoracic cage, is a semi- ...
, and the ilium bone of the hip were pneumatized to an extent which was very rare among theropods, only seen elsewhere in
taxa
In biology, a taxon (back-formation from ''taxonomy''; plural taxa) is a group of one or more populations of an organism or organisms seen by taxonomists to form a unit. Although neither is required, a taxon is usually known by a particular nam ...
such as ''
Neovenator
''Neovenator'' (nee-o-ven-a-tor meaning "new hunter") is a genus of carcharodontosaurian theropod dinosaur. It is known from several skeletons found in the Early Cretaceous (Barremian~130-125 million years ago) Wessex Formation on the south coa ...
''. Other characteristic features include opisthocoelous neck vertebrae and
compsognathid
Compsognathidae is a family of coelurosaurian theropod dinosaurs. Compsognathids were small carnivores, generally conservative in form, hailing from the Jurassic and Cretaceous Periods. The bird-like features of these species, along with other ...
-like teeth.
The clade was originally named in 2010 as a subset of the family
Neovenatoridae
Neovenatoridae is a proposed clade of carcharodontosaurian dinosaurs uniting some primitive members of the group such as ''Neovenator'' with the Megaraptora, a group of theropods with controversial affinities. Other studies recover megaraptorans ...
, a group of lightly-built allosauroids related to the massive
carcharodontosaurids
Carcharodontosauridae (carcharodontosaurids; from the Greek καρχαροδοντόσαυρος, ''carcharodontósauros'': "shark-toothed lizards") is a group of carnivorous theropod dinosaurs. In 1931, Ernst Stromer named Carcharodontosauridae ...
such as ''
Giganotosaurus
''Giganotosaurus'' ( ) is a genus of theropod dinosaur that lived in what is now Argentina, during the early Cenomanian age of the Late Cretaceous period, approximately 99.6 to 95 million years ago. The holotype specimen was discovered in the ...
'' and ''
Carcharodontosaurus
''Carcharodontosaurus'' (; ) is a genus of large carcharodontosaurid theropod dinosaur that existed during the Cenomanian age of the Late Cretaceous in Northern Africa. The genus ''Carcharodontosaurus'' is named after the shark genus ''Carcha ...
''. A 2013
phylogenetic analysis
In biology, phylogenetics (; from Greek φυλή/ φῦλον [] "tribe, clan, race", and wikt:γενετικός, γενετικός [] "origin, source, birth") is the study of the evolutionary history and relationships among or within groups o ...
by
Fernando Novas Fernando Emilio Novas (born 1960) is an Argentine paleontologist working for the Comparative Anatomy Department of the Bernardino Rivadavia Natural Sciences Museum in Buenos Aires, Argentina.
and his colleagues disagreed with this classification scheme, and instead argued that the megaraptorans evolved deep within
Tyrannosauroidea
Tyrannosauroidea (meaning 'tyrant lizard forms') is a superfamily (or clade) of coelurosaurian theropod dinosaurs that includes the family Tyrannosauridae as well as more basal relatives. Tyrannosauroids lived on the Laurasian supercontinent b ...
, a
superfamily
SUPERFAMILY is a database and search platform of structural and functional annotation for all proteins and genomes. It classifies amino acid sequences into known structural domains, especially into SCOP superfamilies. Domains are functional, str ...
of basal coelurosaurs including the famous ''
Tyrannosaurus
''Tyrannosaurus'' is a genus of large theropoda, theropod dinosaur. The species ''Tyrannosaurus rex'' (''rex'' meaning "king" in Latin), often called ''T. rex'' or colloquially ''T-Rex'', is one of the best represented theropods. ''Tyrannosa ...
''. Subsequent refinements to Novas's data and methodologies have supported a third position for the group, at the base of Coelurosauria among other controversial theropods such as ''
Gualicho
''Gualicho'' (named in reference to the gualichu) is a genus of theropod dinosaur. The type species is ''Gualicho shinyae''. It lived in what is now northern Patagonia, on what was then a South American island continent split off from the superco ...
'', but not within the Tyrannosauroidea. Regardless of their position, it is clear that megaraptorans experienced a large amount of
convergent evolution
Convergent evolution is the independent evolution of similar features in species of different periods or epochs in time. Convergent evolution creates analogous structures that have similar form or function but were not present in the last com ...
with either ''Neovenator''-like allosauroids or basal coelurosaurs.
Megaraptorans were most diverse in the early
Late Cretaceous
The Late Cretaceous (100.5–66 Ma) is the younger of two epochs into which the Cretaceous Period is divided in the geologic time scale. Rock strata from this epoch form the Upper Cretaceous Series. The Cretaceous is named after ''creta'', the ...
period
Period may refer to:
Common uses
* Era, a length or span of time
* Full stop (or period), a punctuation mark
Arts, entertainment, and media
* Period (music), a concept in musical composition
* Periodic sentence (or rhetorical period), a concept ...
of South America, particularly
Patagonia
Patagonia () refers to a geographical region that encompasses the southern end of South America, governed by Argentina and Chile. The region comprises the southern section of the Andes Mountains with lakes, fjords, temperate rainforests, and gl ...
. However, they had a widespread distribution. ''Phuwiangvenator'' and ''Fukuiraptor'', the most basal and second most basal known members of the group, lived in
Thailand
Thailand ( ), historically known as Siam () and officially the Kingdom of Thailand, is a country in Southeast Asia, located at the centre of the Indochinese Peninsula, spanning , with a population of almost 70 million. The country is bo ...
and
Japan
Japan ( ja, 日本, or , and formally , ''Nihonkoku'') is an island country in East Asia. It is situated in the northwest Pacific Ocean, and is bordered on the west by the Sea of Japan, while extending from the Sea of Okhotsk in the north ...
, respectively. Megaraptoran material is also common in Australia, and the largest known predatory dinosaur from the continent, ''
Australovenator
''Australovenator'' (meaning "southern hunter") is a genus of megaraptoran theropod dinosaur from Cenomanian (Late Cretaceous)-age Winton Formation (dated to 95 million years ago) of Australia. It is known from partial cranial and postcranial rem ...
'', was a megaraptoran.
Description
Megaraptorans were medium to large-sized theropods, ranging from ''
Fukuiraptor
''Fukuiraptor'' ("thief of Fukui") was a medium-sized megaraptoran theropod dinosaur of the Early Cretaceous epoch (either Barremian or Aptian) that lived in what is now Japan. ''Fukuiraptor'' is known from the Kitadani Formation and possibly ...
'', which was about 4.2 meters (13.8 feet) in length, to the 9 meter (30 feet) long ''
Aerosteon
''Aerosteon'' is a genus of megaraptoran dinosaur from the Late Cretaceous period of Argentina. Its remains were discovered in 1996 in the Anacleto Formation, which is from the late Campanian. The type and only known species is ''A. riocolorad ...
'', the 9 to 10 meter (30 to 33 feet) long ''
Maip
''Maip'' is a genus of large Megaraptora, megaraptorid Theropoda, theropod dinosaur from the Late Cretaceous (Maastrichtian) Chorrillo Formation of Santa Cruz Province, Argentina, Santa Cruz, Argentina. The genus contains a single species, ''M. ma ...
'' and the 12.8 meter (42 foot) long ''
Bahariasaurus
''Bahariasaurus'' (meaning "Bahariya lizard") is an enigmatic genus of large theropod dinosaur. ''Bahariasaurus'' is known to have included at least 1 species, ''Bahariasaurus ingens'', which was found in North African rock layers dating to the C ...
'', if it is a member. Most megaraptorans are known from very fragmentary remains, although certain characteristics can be identified in multiple members of the clade. At least some megaraptorans, such as ''Murusraptor'' and ''
Aerosteon
''Aerosteon'' is a genus of megaraptoran dinosaur from the Late Cretaceous period of Argentina. Its remains were discovered in 1996 in the Anacleto Formation, which is from the late Campanian. The type and only known species is ''A. riocolorad ...
'', had extensively pneumatic bones (most noticeably the ilia and ribs), which likely housed sinuses connected to the lungs, similar to modern birds. The slender leg bones and long
metatarsals
The metatarsal bones, or metatarsus, are a group of five long bones in the foot, located between the tarsal bones of the hind- and mid-foot and the phalanges of the toes. Lacking individual names, the metatarsal bones are numbered from the medi ...
of several species indicate that members of this group likely had
cursorial
A cursorial organism is one that is adapted specifically to run. An animal can be considered cursorial if it has the ability to run fast (e.g. cheetah) or if it can keep a constant speed for a long distance (high endurance). "Cursorial" is often u ...
habits. Most megaraptorans are part of the
family
Family (from la, familia) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its ...
Megaraptoridae, which was named by
Fernando Novas Fernando Emilio Novas (born 1960) is an Argentine paleontologist working for the Comparative Anatomy Department of the Bernardino Rivadavia Natural Sciences Museum in Buenos Aires, Argentina.
and his colleagues in 2013. This family is united by several adaptations of the ulna and claws which are not present in the basal megaraptoran ''Fukuiraptor''.
Skull and teeth
No megaraptoran fossil is known to preserve a complete skull, although skull material is known for several taxa. ''Aerosteon'', ''Megaraptor'',''Orkoraptor'', and ''Murusraptor'' preserve several bones of the rear part of the skull, lower jaws are known from ''Australovenator'', and a juvenile specimen of ''Megaraptor'' described in 2014 preserved much of the snout as well as parietal fragments. Teeth have been found in many genera. Collectively, megaraptorans can be reconstructed as having a long, lightly built skull with many relatively small teeth.
Based on ''Megaraptor'', the
premaxillary
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 mammal has ...
bone at the tip of the snout is small, with a long and rod-like branch of bone which extends above the external nares (nostril holes). The nares themselves were very large and elongated, akin to some early tyrannosauroids (''
Dilong
''Dilong'' (; lit. "earth dragon") is a Chinese dragon name that is also used to mean "earthworm" in traditional Chinese medicine and ''Geosaurus'' in zoological nomenclature.
Dragon
In Chinese mythology, ''dilong'' "earth dragon" is one of m ...
'', ''
Proceratosaurus
''Proceratosaurus'' is a genus of carnivore, carnivorous theropod dinosaur from the Middle Jurassic (Bathonian) of England. ''Proceratosaurus'' was a small dinosaur, measuring in length and in body mass.Holtz, Thomas R. Jr. (2008) ''Dinosaurs: ...
'', etc.). The snout also had some similarities to carcharodontosaurids, namely the straight upper edge of the maxilla and rectangular nasal bones. The parietal bones at the top of the skull, behind the eyes, had a strongly developed
sagittal crest
A sagittal crest is a ridge of bone running lengthwise along the midline of the top of the skull (at the sagittal suture) of many mammalian and reptilian skulls, among others. The presence of this ridge of bone indicates that there are exceptiona ...
, as in tyrannosauroids. Otherwise, the rear part of the skull is rather simple, without any pronounced crests or bosses, although the lacrimal 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 ...
bones did have
rugose
Rugose means "wrinkled". It may refer to:
* Rugosa, an extinct order of coral, whose rugose shape earned it the name
* Rugose, adjectival form of rugae
Species with "rugose" in their names
* '' Idiosoma nigrum'', more commonly, a black rugose tr ...
patches in some genera. ''Aerosteon'' and ''Murusraptor'' possessed a pneumatic quadrate, as in a few allosauroids (''
Sinraptor
''Sinraptor'' is a genus of metriacanthosaurid theropod dinosaur from the Late Jurassic. The name ''Sinraptor'' comes from the Latin prefix "Sino", meaning Chinese, and "raptor" meaning robber. The specific name ''dongi'' honours Dong Zhiming. De ...
'', ''
Mapusaurus
''Mapusaurus'' () was a giant carcharodontosaurid carnosaurian dinosaur from the early Late Cretaceous (early Turonian stage), approximately 93.9 to 89.6 million years ago, of what is now Argentina.
Discovery
''Mapusaurus'' was excavated be ...
'') and tyrannosauroids. The
dentary
In anatomy, the mandible, lower jaw or jawbone is the largest, strongest and lowest bone in the human facial skeleton. It forms the lower jaw and holds the lower tooth, teeth in place. The mandible sits beneath the maxilla. It is the only movabl ...
, which is only known in ''Australovenator'', is long and graceful, with the first tooth smaller than the rest (as in tyrannosauroids). The
mandible
In anatomy, the mandible, lower jaw or jawbone is the largest, strongest and lowest bone in the human facial skeleton. It forms the lower jaw and holds the lower tooth, teeth in place. The mandible sits beneath the maxilla. It is the only movabl ...
as a whole has only a single meckelian foramen, as in carcharodontosaurians, tyrannosaurids, and ornithomimids. However, the rear part of the mandible (as seen in ''Murusraptor'') was significantly more lightly built than that of tyrannosauroids. Preserved
braincase
In human anatomy, the neurocranium, also known as the braincase, brainpan, or brain-pan is the upper and back part of the skull, which forms a protective case around the brain. In the human skull, the neurocranium includes the calvaria or skul ...
material has similarities to both carcharodontosaurians and tyrannosauroids.
The premaxillary teeth of ''Megaraptor'' were variably similar to those of tyrannosauroids, being small, incisiform (chisel-like) and D-shaped in cross section. However, ''Murusraptor'''s premaxillary teeth were fang-like, as in non-tyrannosauroid theropods. Megaraptoran maxillary teeth show much variety between
genera
Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nomenclat ...
, although they were generally small compared to the snout with minimal enamel ornamentation. Some megaraptorans, such as ''Orkoraptor, Australovenator,'' and ''Megaraptor'', had teeth which were 8-shaped in cross section and completely unserrated from the front (similar to
dromaeosaurids
Dromaeosauridae () is a family of feathered theropod dinosaurs. They were generally small to medium-sized feathered carnivores that flourished in the Cretaceous Period. The name Dromaeosauridae means 'running lizards', from Greek ('), meaning ...
and
compsognathids
Compsognathidae is a family of coelurosaurian theropod dinosaurs. Compsognathids were small carnivores, generally conservative in form, hailing from the Jurassic and Cretaceous Periods. The bird-like features of these species, along with other d ...
), while ''Murusraptor'' had anterior serrations only at the tip of its teeth. ''Fukuiraptor'' had very laterally compressed and blade-like teeth (similar to carcharodontosaurs) with both anterior and posterior serrations.
Vertebrae and ribs
The
cervical
In anatomy, cervical is an adjective that has two meanings:
# of or pertaining to any neck.
# of or pertaining to the female cervix: i.e., the ''neck'' of the uterus.
*Commonly used medical phrases involving the neck are
**cervical collar
**cerv ...
(neck)
vertebra
The spinal column, a defining synapomorphy shared by nearly all vertebrates,Hagfish are believed to have secondarily lost their spinal column is a moderately flexible series of vertebrae (singular vertebra), each constituting a characteristic ...
e of megaraptorans were nearly unique among theropods in the fact that they were strongly opisthocoelous. This means that they were convex from the front and concave from behind. Opisthocelous vertebrae are also characteristic of ''
Allosaurus
''Allosaurus'' () is a genus of large carnosaurian theropod dinosaur that lived 155 to 145 million years ago during the Late Jurassic epoch (Kimmeridgian to late Tithonian). The name "''Allosaurus''" means "different lizard" alluding to ...
'' and
sauropods
Sauropoda (), whose members are known as sauropods (; from '' sauro-'' + '' -pod'', 'lizard-footed'), is a clade of saurischian ('lizard-hipped') dinosaurs. Sauropods had very long necks, long tails, small heads (relative to the rest of their b ...
, and they may facilitate high flexibility without sacrificing defense against
shear force
In solid mechanics, shearing forces are unaligned forces acting on one part of a body in a specific direction, and another part of the body in the opposite direction. When the forces are collinear (aligned with each other), they are called t ...
s. Otherwise, the cervicals were similar to those of carcharodontosaurians, with short
neural spines
The spinal column, a defining synapomorphy shared by nearly all vertebrates,Hagfish are believed to have secondarily lost their spinal column is a moderately flexible series of vertebrae (singular vertebra), each constituting a characteristic ...
,
transverse processes
The spinal column, a defining synapomorphy shared by nearly all vertebrates,Hagfish are believed to have secondarily lost their spinal column is a moderately flexible series of vertebrae (singular vertebra), each constituting a characteristic i ...
(projecting rib facets) located around mid-length on the
centra
Centra is a convenience shop chain that operates throughout Ireland. The chain operates as a symbol group owned by Musgrave Group, the food wholesaler, meaning the stores are all owned by individual franchisees.
The chain has three different ...
, and a pair of large lateral pits known as
pleurocoels
Skeletal pneumaticity is the presence of air spaces within bones. It is generally produced during development by excavation of bone by pneumatic diverticula (air sacs) from an air-filled space, such as the lungs or nasal cavity. Pneumatization is h ...
. In fact, one or more pleurocoels were present in most megaraptoran vertebrae, and they connected to a complex system of numerous small air pockets within the vertebrae. This web-like internal structure of megaraptoran vertebrae (and that of a few other theropods) has been described as " camellate".
The proximal caudals (vertebrae at the base of the tail) had a longitudinal ridge running along their lower surface, similar to the case in ''Neovenator'' but unlike tyrannosauroids. They also had a pair of lateral ridges which stretched downwards from the transverse processes to the centra. These ridges, known as centrodiapophyseal laminae, defined a large depression (infradiapophyseal fossa) under the transverse processes. Although these ridges were also present in dorsal (back) vertebrae and have been found in other theropods, megaraptorans were practically unique in the fact that their centrodiapophyseal laminae were well-developed at the base of the tail, sometimes even more so than the dorsal vertebrae. Only spinosaurids share this feature. The strong development of these ridges may indicate that the tail was deep and muscular.
The dorsal
ribs
The rib cage, as an enclosure that comprises the ribs, vertebral column and sternum in the thorax of most vertebrates, protects vital organs such as the heart, lungs and great vessels.
The sternum, together known as the thoracic cage, is a semi- ...
were thick and curved yet hollow and pierced by a hole near their connection to the vertebrae. The
gastralia
Gastralia (singular gastralium) are dermal bones found in the ventral body wall of modern crocodilians and tuatara, and many prehistoric tetrapods. They are found between the sternum and pelvis, and do not articulate with the vertebrae. In these ...
(belly ribs) were wide and strongly built paddle-shaped structures, with the left and right sides fused at the midline of the chest. These features signified that megaraptorans were wide-bodied theropods, akin to the condition in tyrannosaurids.
Forelimbs
Megaraptorans have a sigmoid (S-shaped)
humerus
The humerus (; ) is a long bone in the arm that runs from the shoulder to the elbow. It connects the scapula and the two bones of the lower arm, the radius and ulna, and consists of three sections. The humeral upper extremity consists of a roun ...
(forearm bone), similar to that of both basal allosauroids and basal coelurosaurs. Most megaraptorans had large, robust humeri akin to those of ''Allosaurus'', but the basal-most member ''Fukuiraptor'' has a much more slender humerus. The distal part of the humerus (near the elbow) has a well-developed system of
ulna
The ulna (''pl''. ulnae or ulnas) is a long bone found in the forearm that stretches from the elbow to the smallest finger, and when in anatomical position, is found on the medial side of the forearm. That is, the ulna is on the same side of t ...
of megaraptorids is characteristic in several regards. The
olecranon process
The olecranon (, ), is a large, thick, curved bony eminence of the ulna, a long bone in the forearm that projects behind the elbow. It forms the most pointed portion of the elbow and is opposite to the cubital fossa or elbow pit. The olecranon ...
is well-developed, though it is thin, blade-like, and extends as a crest longitudinally down the shaft of the ulna. In addition, megaraptorids have acquired another long, crest-like structure on the ulna called the lateral tuberosity, which is perpendicular to the blade of the olecranon. As a result, the ulna of megaraptorids is T-shaped in cross section, with three prongs formed by the forward-projection anterior process, the outwards-projecting lateral tuberosity, and the backwards-projecting olecranon process. These adaptations are absent in the most basal megaraptoran, ''Fukuiraptor''. The
radius
In classical geometry, a radius ( : radii) of a circle or sphere is any of the line segments from its center to its perimeter, and in more modern usage, it is also their length. The name comes from the latin ''radius'', meaning ray but also the ...
is not unusual compared to other theropods.
Megaraptorans also had very characteristic hands. The first two fingers were large and slender, but the third one was small. These relative differences in finger length are somewhat similar to the case in tyrannosauroids and various other basal coelurosaurs, but the megaraptoran trend of forearm and finger enlargement is opposite to the trend towards forearm diminishment which characterizes advanced tyrannosauroids. ''Megaraptor'' retained a vestigial fourth
metacarpal
In human anatomy, the metacarpal bones or metacarpus form the intermediate part of the skeletal hand located between the phalanges of the fingers and the carpal bones of the wrist, which forms the connection to the forearm. The metacarpal bones ...
, the hand bone that would have connected to the fourth finger in early dinosaurs. This was a primitive feature lost by most other tetanurans. The first two fingers had absurdly large unguals (claws); in ''Megaraptor'' the first claw was larger than the entire ulna. Unlike the large unguals of many other theropods (megalosauroids, for example), megaraptoran claws were thin and oval-shaped in cross-section. These claws also had asymmetrically-positioned grooves on their flat faces and a sharp ridge on their lower edge in megaraptorids (non-''Fukuiraptor'' megaraptorans). The
carpus
In human anatomy, the wrist is variously defined as (1) the carpus or carpal bones, the complex of eight bones forming the proximal skeletal segment of the hand; "The wrist contains eight bones, roughly aligned in two rows, known as the carpal ...
(wrist) of megaraptorans incorporated a semilunate (crescent-shaped) carpal similar to that of
maniraptora
Maniraptora is a clade of coelurosaurian dinosaurs which includes the birds and the non-avian dinosaurs that were more closely related to them than to ''Ornithomimus velox''. It contains the major subgroups Avialae, Deinonychosauria, Oviraptoros ...
ns.
Hindlimbs
The
femur
The femur (; ), or thigh bone, is the proximal bone of the hindlimb in tetrapod vertebrates. The head of the femur articulates with the acetabulum in the pelvic bone forming the hip joint, while the distal part of the femur articulates with ...
(thigh bone) of megaraptorans is only known in ''Australovenator'' and ''Fukuiraptor'', but it is similar to that of coelurosaurs in several respects. For example, the
greater trochanter
The greater trochanter of the femur is a large, irregular, quadrilateral eminence and a part of the skeletal system.
It is directed lateral and medially and slightly posterior. In the adult it is about 2–4 cm lower than the femoral head.Stan ...
is well-developed and offset from the femoral shaft by a deep concavity. The size of the greater trochanter has the added effect of making the portion of the femur near the hip socket rectangular, when seen from above. In non-coelurosaur theropods, the greater trochanter is small, making the femur teardrop-shaped when seen from above. The femoral head is slightly upturned as in carcharodontosaurians (particularly carcharodontosaurids) and some coelurosaurs. In megaraptorans, the portion of the femur near the knee is asymmetrical when seen from the front due to the lateral condyle projecting further distally than the medial condyle.
The
tibia
The tibia (; ), also known as the shinbone or shankbone, is the larger, stronger, and anterior (frontal) of the two bones in the leg below the knee in vertebrates (the other being the fibula, behind and to the outside of the tibia); it connects ...
was also similar to that of coelurosaurs. It was a long and thin bone. The front of the lateral condyle of the tibia hooks downwards, similar to the condition in ''Neovenator,
Tanycolagreus
''Tanycolagreus'' is a genus of coelurosaurian theropod from the Late Jurassic of North America.
Discovery and naming
In 1995 Western Paleontological Laboratories, Inc. uncovered the partial skeleton of a small theropod at the Bone Cabin Quarr ...
,'' and some tyrannosauroids. The medial and lateral malleoli are expanded and project away from each other, as in advanced tyrannosauroids (both) and carcharodontosaurians (medial malleolus only). The front surface of the distal tip of the tibia (near the ankle) had the form of a flattened facet for the reception of the
astragalus
''Astragalus'' is a large genus of over 3,000 species of herbs and small shrubs, belonging to the legume family Fabaceae and the subfamily Faboideae. It is the largest genus of plants in terms of described species. The genus is native to tempe ...
bone of the ankle, similar to the case in coelurosaurs. The inner edge of this facet was defined by a ridge, a feature unique to megaraptorids. The upper edge of the facet lacked a well-defined supra-astragalar buttress, unlike allosauroids. The ascending process of the astragalus, which lays on the facet, is expanded into a large trapezoidal plate of bone, similar to coelurosaurs but unlike the small, triangular ascending process of allosauroids. ''Fukuiraptor'', ''Australovenator'', and ''Aerosteon'' have a distinct forward-pointing prong on the outer edge of the astragalus, and ''Fukuiraptor'' and ''Australovenator'' have an additional prong that projects backwards.
The
fibula
The fibula or calf bone is a leg bone on the lateral side of the tibia, to which it is connected above and below. It is the smaller of the two bones and, in proportion to its length, the most slender of all the long bones. Its upper extremity is ...
is also long and strongly tapers away from the knee, as in coelurosaurs. It connects to a small facet on the outer edge of the astragalus (as in coelurosaurs) rather than a large facet on the upper edge (as in allosauroids). Near the knee and facing the tibia, the fibula has a wide groove or depression known as a proximomedial fossa.
Metatarsal
The metatarsal bones, or metatarsus, are a group of five long bones in the foot, located between the tarsal bones of the hind- and mid-foot and the phalanges of the toes. Lacking individual names, the metatarsal bones are numbered from the med ...
III, the foot bone which connected to the middle toe, was very long and slender in all megaraptorans, as in coelurosaurs. The joint for the middle toe is tall and pulley-shaped, with a deep and crescent-shaped depression visible from below.
Hip
The ilium (upper plate of the hip) was a heavily pneumatized bone, filled with air pockets and perforated by pits. The only other large theropod known to possess a pneumatic ilium is ''Neovenator''. In some megaraptorans, the preacetabular blade has a notch along its front edge, as in tyrannosauroids. A stronger concavity was present a bit lower, between the preacetabular blade and pubic peduncle. This concavity, known as the cuppedicus (or preacetabular) fossa, was rimmed by a prominent shelf on the inner face of the ilium. This trait is also known in various coelurosaurs, ''Chilantaisaurus'', and probably ''Neovenator''. The postacetabular blade, on the other hand, lacks a large concavity. In non-coelurosaurian tetanurans, this portion of the ilium has a large depression known as a brevis fossa, which is visible from the outer face of the ilium. However, coelurosaurs and megaraptorans have a much smaller brevis fossa which occupies only a portion of the rear edge of the ilium, and it is mostly hidden from outside observers.
The
(rear lower plate of the hip) is only know in ''Murusraptor''. It is slightly expanded, similar to that of carcharodontosaurids. The pubis (front lower plate of the hip) has a much more pronounced scythe-like expansion at its tip, which is over 60% as long as the main shaft of the bone. This adaptation, known as a pubic boot, is also known in carcharodontosaurians and tyrannosaurids. The pubis is also expanded near its contact with the ilium. The left and right pubic bones are not entirely fused to each other, they are separated along their midline by an oval-shaped hole.
Evolution and origin
A palaeobiogeographic assessment was conducted by Phil Bell, Steve Salisbury et al., which accompanied the description of an unnamed megaraptorid (referred to by the public media as "Lightning Claw," and possibly synonymous with ''
Rapator
''Rapator'' is a genus of theropod dinosaur from the Griman Creek Formation of New South Wales, Australia, dating to the Albian-Cenomanian ages of the Cretaceous period, 105-96 million years ago. It contains only the type species, ''Rapator orni ...
'') from opal fields southwest of Lightning Ridge, Australia. This supports an Asian origin of Megaraptora in the latest Jurassic (150–135 Ma), an Early Cretaceous (130–121 Ma) divergence of the
Gondwana
Gondwana () was a large landmass, often referred to as a supercontinent, that formed during the late Neoproterozoic (about 550 million years ago) and began to break up during the Jurassic period (about 180 million years ago). The final stages ...
n lineage leading to Megaraptoridae, and an Australian root for the megaraptorid radiation of Late Cretaceous Gondwana. The specimen also allowed for alternative phylogenetic testing as to the placement of megaraptorans as either tyrannosauroids or carcharodontosaurids. This was expanded upon by Lamanna ''et al.'' (2020) who hypothesized that the megaraptorid dispersal from Australia to South America (probably via Antarctica) came with an increase in body size, and that megaraptorids kept their large body size until the K-Pg extinction. The authors also noted that while their phylogenetic analysis didn't support it, Australian megaraptorids likely formed a paraphyletic grade leading to South American forms.
Classification
Early hypotheses
The genera which make up Megaraptora had been placed in a number of different theropod groups before the formation of the clade in 2010. ''Megaraptor'' and ''Fukuiraptor'' were independently considered to be giant
dromaeosaurids
Dromaeosauridae () is a family of feathered theropod dinosaurs. They were generally small to medium-sized feathered carnivores that flourished in the Cretaceous Period. The name Dromaeosauridae means 'running lizards', from Greek ('), meaning ...
when they were first discovered in the 1990s due to the large hand claws being misidentified as foot claws. However, these mistakes were rectified after closer inspection of the holotype (in the case of ''Fukuiraptor'') or the discovery of new specimens (in the case of ''Megaraptor''). By the mid-to-late 2000s, they were considered to be basal tetanurans, usually members of Allosauroidea. Smith ''et al.'' (2008) reported ''Megaraptor''-like ulnae from Australia, and found evidence that ''Megaraptor'' was a spinosauroid. The same year, ''Orkoraptor'' was described as an unusual giant coelurosaurian with some similarities with the much smaller compsognathids. ''Aerosteon'' was considered a relative of ''
Allosaurus
''Allosaurus'' () is a genus of large carnosaurian theropod dinosaur that lived 155 to 145 million years ago during the Late Jurassic epoch (Kimmeridgian to late Tithonian). The name "''Allosaurus''" means "different lizard" alluding to ...
'' in its description less than a year later, while ''Australovenator'' was considered to be the sister taxon to Carcharodontosauridae.
Placement within Neovenatoridae
This influx of new data in the late 2000s led to several major reanalyses of basal tetanuran phylogenetics, with interesting implications for these taxa. A study by Roger Benson, Matt Carrano &
Steve Brusatte
Stephen Louis Brusatte (born April 24, 1984) is an American paleontologist and evolutionary biologist, who specializes in the anatomy and evolution of dinosaurs. He was educated at the University of Chicago for his BS degree, at the University of ...
in 2010 found that
Allosauroidea
Allosauroidea is a superfamily or clade of theropod dinosaurs which contains four family (biology), families — the Metriacanthosauridae, Allosauridae, Carcharodontosauridae, and Neovenatoridae. Allosauroids, alongside the family Megalosauroid ...
(or
Carnosauria
Carnosauria is an extinct large group of predatory dinosaurs that lived during the Jurassic and Cretaceous periods. Starting from the 1990s, scientists have discovered some very large carnosaurs in the carcharodontosaurid family, such as ''Gig ...
, as it was sometimes called) included a major subdivision known as Carcharodontosauria, which was split into the
Carcharodontosauridae
Carcharodontosauridae (carcharodontosaurids; from the Greek καρχαροδοντόσαυρος, ''carcharodontósauros'': "shark-toothed lizards") is a group of carnivorous theropod dinosaurs. In 1931, Ernst Stromer named Carcharodontosauridae ...
and a newly named family:
Neovenatoridae
Neovenatoridae is a proposed clade of carcharodontosaurian dinosaurs uniting some primitive members of the group such as ''Neovenator'' with the Megaraptora, a group of theropods with controversial affinities. Other studies recover megaraptorans ...
. Neovenatorids, as formulated by these authors, contained ''Neovenator'', ''Chilantaisaurus'', and a newly named clade: Megaraptora. Megaraptora contained ''Megaraptor'', ''Fukuiraptor'', ''Orkoraptor'', ''Aerosteon'', and ''Australovenator''. These genera were allied with the other neovenatorids on the basis of several features spread out throughout the skeleton, particularly the large amount of pneumatization present. The pneumatic ilium of ''Aerosteon'' was particularly notable, as ''Neovenator'' was the only other taxon known to have that trait at the time. Neovenatorids were envisioned as the latest-surviving allosauroids, which were able to persist well into the Late Cretaceous due to their low profile and coelurosaur-like adaptations. Later studies supported this hypothesis, such as Carrano, Benson & Sampson large study of tetanuran relationships in 2012, and Zanno & Makovicky description of the newly discovered theropod '' Siats'' in 2013, which they placed within Megaraptora. ''Fukuiraptor'' and ''Australovenator'' were consistently found to be close relatives of each other; this was also the case for ''Aerosteon'' and ''Megaraptor''; ''Orkoraptor'' was a "wildcard" taxon difficult to place with certainty.
The
cladogram
A cladogram (from Greek ''clados'' "branch" and ''gramma'' "character") is a diagram used in cladistics to show relations among organisms. A cladogram is not, however, an evolutionary tree because it does not show how ancestors are related to d ...
below illustrates the most recent revision of the Benson, Carrano, & Brusatte (2010) hypothesis that megaraptorans were allosauroids within the family Neovenatoridae. The cladogram follows Coria & Currie (2016), who added ''Murusraptor'' to the study and utilized the family Megaraptoridae, which was originally named by Novas ''et al.'' (2013).
Placement within Tyrannosauroidea
However, an alternative hypothesis was forming, first published as an
Ameghiniana
''Ameghiniana'' is a peer-reviewed scientific journal covering palaeontology published by the Asociación Paleontológica Argentina. It is named after the 19th century Italian Argentine palaeontologist Florentino Ameghino. The discovery of many di ...
abstract by
Fernando Novas Fernando Emilio Novas (born 1960) is an Argentine paleontologist working for the Comparative Anatomy Department of the Bernardino Rivadavia Natural Sciences Museum in Buenos Aires, Argentina.
''et al.'' (2012). Novas and his colleagues argued that the features used to link ''Neovenator'' to Megaraptora were more widespread than the 2010 paper implied, and that the proposed coelurosaurian convergences may have signified a legitimate connection between Megaraptora and Coelurosauria. In addition, they noted that Benson, Carrano, & Brusatte only sampled three coelurosaurs in their analysis. Novas ''et al''.'s arguments were formulated and published in a 2013 review of
patagonia
Patagonia () refers to a geographical region that encompasses the southern end of South America, governed by Argentina and Chile. The region comprises the southern section of the Andes Mountains with lakes, fjords, temperate rainforests, and gl ...
n theropods, which removed Megaraptora from the Carcharodontosauria and instead placed the group within Coelurosauria. More specifically, megaraptorans were found to be deep within the
Tyrannosauroidea
Tyrannosauroidea (meaning 'tyrant lizard forms') is a superfamily (or clade) of coelurosaurian theropod dinosaurs that includes the family Tyrannosauridae as well as more basal relatives. Tyrannosauroids lived on the Laurasian supercontinent b ...
, a radiation of basal coelurosaurs including the famed
tyrannosaurids
Tyrannosauridae (or tyrannosaurids, meaning "tyrant lizards") is a family (biology), family of coelurosaurian Theropoda, theropod dinosaurs that comprises two subfamilies containing up to thirteen genus, genera, including the eponymous ''Tyrannos ...
. As Novas ''et al.'' (2013) removed Megaraptora from Neovenatoridae, they named a new family, Megaraptoridae, which contained all Megaraptorans apart from the basal ("primitive") taxon ''Fukuiraptor''. They found little evidence that ''Chilantaisaurus'', ''Neovenator'', or ''Siats'' were megaraptorans, but they did place the tyrannosauroid ''Eotyrannus'' within Megaraptora. Despite the hypothesized close relation between megaraptorans and tyrannosaurids, Novas ''et al.'' noted that the megaraptoran lineage had a functional morphology which diverged in a direction opposite to the tyrannosaurids. While tyrannosaurids had small arms and large, powerful heads, megaraptorans had large arms, giant claws, and relatively weak jaws. The skull of a newly discovered juvenile specimen of ''
Megaraptor
''Megaraptor'' () is a genus of large theropod dinosaur that lived in the ages of the Late Cretaceous. Its fossils have been discovered in the Patagonian Portezuelo Formation of Argentina, South America. Initially thought to have been a giant dr ...
'', published in 2014, supported this hypothesis due to its similarities to the skull of basal tyrannosauroids such as ''Dilong''. Nevertheless, megaraptorans still retained many similarities to carcharodontosaurians such as ''Neovenator'', so the uncertainty behind their classification was not fully resolved.
The cladogram below illustrates the results of a study which supports the Novas ''et al.'' (2013) hypothesis that megaraptorans are derived tyrannosauroids. This study was Porfiri ''et al.'' (2014), which described the juvenile ''Megaraptor'' specimen. ''
Gualicho
''Gualicho'' (named in reference to the gualichu) is a genus of theropod dinosaur. The type species is ''Gualicho shinyae''. It lived in what is now northern Patagonia, on what was then a South American island continent split off from the superco ...
'', ''
Murusraptor
''Murusraptor'' ("wall thief") is a genus of carnivorous megaraptoran theropod dinosaur from the Sierra Barrosa Formation, part of the Neuquén Group of Patagonia, in Argentina, South America. It is known from a single specimen that consists of ...
'', and ''
Tratayenia
''Tratayenia'' is an extinct genus of megaraptoran theropod dinosaurs known from remains found in the Santonian-age Bajo de la Carpa Formation of Argentina. The type and only species, ''Tratayenia rosalesi'', was described in March 2018.
''Trata ...
'' were not yet described when this study was undertaken.
In 2016, Novas and his colleagues published a study of megaraptoran hand anatomy, in an attempt to help settle the question of their classification. They found that megaraptorans lacked most of the key features in the hands of derived coelurosaurs including ''
Guanlong
''Guanlong'' (冠龍) is a genus of extinct proceratosaurid tyrannosauroid from the Late Jurassic of China. The taxon was first described in 2006 by Xu Xing ''et al.'', who found it to represent a new taxon related to ''Tyrannosaurus''. The na ...
'' and ''
Deinonychus
''Deinonychus'' ( ; ) is a genus of dromaeosaurid theropod dinosaur with one described species, ''Deinonychus antirrhopus''. This species, which could grow up to long, lived during the early Cretaceous Period, about 115–108 million ye ...
''. Instead, their hands retain a number of primitive characteristics seen in basal tetanurans such as ''
Allosaurus
''Allosaurus'' () is a genus of large carnosaurian theropod dinosaur that lived 155 to 145 million years ago during the Late Jurassic epoch (Kimmeridgian to late Tithonian). The name "''Allosaurus''" means "different lizard" alluding to ...
''. Nevertheless, there are still a number of traits that support megaraptorans as members of the Coelurosauria. A 2016 study of the "lightning ridge megaraptoran" by Bell ''et al.'' supported the idea that megaraptorans were tyrannosauroids based on the fact that Porfiri ''et al.'' (2014) incorporated skull data from ''Megaraptor'' and a wider variety of coelurosaurians compared to Benson, Carrano, & Brusatte (2010). Motta ''et al''. (2016) agreed, and proposed that a new fragmentary patagonian theropod, ''
Aoniraptor
''Aoniraptor'' is a megaraptoran theropod from the Late Cretaceous of Argentina (Huincul Formation).
Discovery and naming
The holotype, MPCA-Pv 804/1 to 804/25, which consists of the last sacral vertebra, six proximal caudal vertebrae, four mid ...
'', was a non-megaraptorid megaraptoran. Their study also noted the similaritires between ''Aoniraptor'', the enigmatic theropod ''
Deltadromeus
''Deltadromeus'' (meaning "delta runner") is a genus of theropod dinosaur from Northern Africa. It had long, unusually slender hind limbs for its size, suggesting that it was a swift runner. The skull is not known. One fossil specimen of a sin ...
'', and ''
Bahariasaurus
''Bahariasaurus'' (meaning "Bahariya lizard") is an enigmatic genus of large theropod dinosaur. ''Bahariasaurus'' is known to have included at least 1 species, ''Bahariasaurus ingens'', which was found in North African rock layers dating to the C ...
'', a giant African theropod with remains destroyed by World War II bombings. Therefore, they suggested that ''Bahariasaurus'' and ''Deltadromeus'' were also basal megaraptorans, and that ''Aoniraptor'', ''Bahariasaurus'', and ''Deltadromeus'' could have formed a distinct family, the Bahariasauridae. A 2019 redescription of ''Murusraptor'' by Rolando, Novas, & Agnolín continued to find Megaraptora in a polytomy at the base of Tyrannosauroidea, based on the dataset of Apesteguia ''et al.'' (2016).
A 2022 study by Naish and Cau, in contrast, classified ''Eotyrannus'' as an intermediate gracile tyrannosauroid outside of Megaraptora. Their research supported a tyrannosauroid position for megaraptorans, even though ''Eotyrannus'' itself was not a megaraptoran. They recovered Megaraptora as radiation of derived tyrannosauroids close to Tyrannosauridae, similar to that found by Porfiri et al. (2014).
Placement within non-Tyrannosauroidea Coelurosauria
In 2016, a third hypothesis for megaraptoran relations was derived from Porfiri ''et al.s revision to the Novas ''et al.'' dataset in 2014. That year, Sebastian Apesteguía and his colleagues described an unusual new theropod, ''
Gualicho
''Gualicho'' (named in reference to the gualichu) is a genus of theropod dinosaur. The type species is ''Gualicho shinyae''. It lived in what is now northern Patagonia, on what was then a South American island continent split off from the superco ...
''. The addition of ''Gualicho'', ''Deltadromeus'', and several corrections within the Novas ''et al.'' dataset led to an interesting result. Megaraptorans were far removed from the position deep within Tyrannosauroidea which the Novas ''et al.'' dataset had originally supported. Allosauroidea was rendered a
paraphyletic
In taxonomy (general), taxonomy, a group is paraphyletic if it consists of the group's most recent common ancestor, last common ancestor and most of its descendants, excluding a few Monophyly, monophyletic subgroups. The group is said to be pa ...
grade
Grade most commonly refers to:
* Grade (education), a measurement of a student's performance
* Grade, the number of the year a student has reached in a given educational stage
* Grade (slope), the steepness of a slope
Grade or grading may also ref ...
, with carcharodontosaurids, ''Neovenator'', a clade formed by ''Chilantaisaurus'' and ''Gualicho'', and finally Megaraptora progressively closer to traditional coelurosaurs.
Another study, Porfifi ''et al.'' (2018), expanded on the dataset of Apesteguía ''et al.'' (2016) by adding two additional megaraptorids. Although the results are different, the methodology analysis was practically identical to that of Apesteguia ''et al''. (2016), only differing in the fact that it incorporated two megaraptorans not sampled in the analysis of Apesteguia ''et al''. One of these was ''Murusraptor'', which was described in 2016 around the same time as ''Gualicho''. The second was a new megaraptorid, ''
Tratayenia
''Tratayenia'' is an extinct genus of megaraptoran theropod dinosaurs known from remains found in the Santonian-age Bajo de la Carpa Formation of Argentina. The type and only species, ''Tratayenia rosalesi'', was described in March 2018.
''Trata ...
''. Porfiri ''et al.'' (2018) placed ''Tratayenia'' and ''Murusraptor'' as megaraptorids, with ''Fukuiraptor'' as the basalmost megaraptoran as found by all previous revisions to the Novas ''et al.'' dataset. However, Megaraptora was in a
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 tr ...
at the very base of Coelurosauria, along with ''Chilantaisaurus'', ''Gualicho'', and Tyrannoraptora ("traditional " coelurosaurs). Non-coelurosaurian avetheropods were also subjected to a large polytomy owing to the unstable position of ''Neovenator''. Porfiri ''et al.'' (2018) also commented on Motta ''et al.s erection of Bahariasauridae in 2016, and noted that ''Gualicho'' may be a bahariasaurid in light of its similarities with ''Deltadromeus''. If this was the case, then megaraptorans experienced much more diversity in their forelimbs than previously considered; ''Gualicho'' had very small, tyrannosaurid-like forelimbs.
In late 2018, Delcourt & Grillo published a study focusing on tyrannosauroids. They reused the 2018 analysis from Porfiri ''et al., though corrected some scores and added data from recent studies. The study returned ''Neovenator'' to a monophyletic Allosauroidea, and placed megaraptorans as basal non-tyrannosauroid coelurosaurs close to ''Chilantaisaurus'' and ''Gualicho''. ''Murusraptor'' was also placed as the second-most basal megaraptoran, ahead of ''Fukuiraptor''.
The
cladogram
A cladogram (from Greek ''clados'' "branch" and ''gramma'' "character") is a diagram used in cladistics to show relations among organisms. A cladogram is not, however, an evolutionary tree because it does not show how ancestors are related to d ...
below follows the results of the phylogenetic analysis of Delcourt & Grillo (2018).
In the 2022 description of ''
Maip
''Maip'' is a genus of large Megaraptora, megaraptorid Theropoda, theropod dinosaur from the Late Cretaceous (Maastrichtian) Chorrillo Formation of Santa Cruz Province, Argentina, Santa Cruz, Argentina. The genus contains a single species, ''M. ma ...
'', Rolando ''et al.'' suggested that Megaraptora was deeply nested within in Coelurosauria, with Megaraptora classified as 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 t ...
to Tyrannosauroidea. This is in line with previous studies, which have likewise suggested a close relationship between tyrannosauroids and megaraptorans. Rolando ''et al''. also noted the presence of two distinct clades within Megaraptora: a more inclusive clade, comprising all megaraptorids except ''
Fukuiraptor
''Fukuiraptor'' ("thief of Fukui") was a medium-sized megaraptoran theropod dinosaur of the Early Cretaceous epoch (either Barremian or Aptian) that lived in what is now Japan. ''Fukuiraptor'' is known from the Kitadani Formation and possibly ...
'' and ''
Australovenator
''Australovenator'' (meaning "southern hunter") is a genus of megaraptoran theropod dinosaur from Cenomanian (Late Cretaceous)-age Winton Formation (dated to 95 million years ago) of Australia. It is known from partial cranial and postcranial rem ...
'', (shown below as "Clade A"), and a more exclusive clade of larger, entirely South American megaraptorids (shown below as "Clade B"). The cladogram below displays the coelurosaurian results of the phylogenetic analyses by Rolando ''et al.''