Maniraptora is a
clade
In biology, a clade (), also known as a Monophyly, monophyletic group or natural group, is a group of organisms that is composed of a common ancestor and all of its descendants. Clades are the fundamental unit of cladistics, a modern approach t ...
of
coelurosauria
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, tyra ...
n
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 which includes the
bird
Birds are a group of warm-blooded vertebrates constituting the class (biology), class Aves (), characterised by feathers, toothless beaked jaws, the Oviparity, laying of Eggshell, hard-shelled eggs, a high Metabolism, metabolic rate, a fou ...
s and the non-avian dinosaurs that were more closely related to them than to ''
Ornithomimus velox
''Ornithomimus'' (; "bird mimic") is a genus of Ornithomimosauria, ornithomimid Theropoda, theropod dinosaurs from the Campanian and Maastrichtian ages of Late Cretaceous Laramidia, Western North America. ''Ornithomimus'' was a swift, bipedal din ...
''. It contains the major subgroups
Avialae
Avialae ("bird wings") is a clade containing the only living dinosaurs, the birds, and their closest relatives. It is usually defined as all theropod dinosaurs more closely related to birds (Aves) than to Deinonychosauria, deinonychosaurs, though ...
,
Dromaeosauridae
Dromaeosauridae () is a family of feathered coelurosaurian theropod dinosaurs. They were generally small to medium-sized feathered carnivores that flourished in the Cretaceous Period. The name Dromaeosauridae means 'running lizards', from ...
,
Troodontidae
Troodontidae is a clade of bird-like theropod dinosaurs from the Late Jurassic to Late Cretaceous. During most of the 20th century, troodontid fossils were few and incomplete and they have therefore been allied, at various times, with many dinos ...
,
Oviraptorosauria
Oviraptorosaurs ("egg thief lizards") are a group of feathered maniraptoran dinosaurs from the Cretaceous Period (geology), Period of what are now Asia and North America. They are distinct for their characteristically short, beaked, parrot-like s ...
, and
Therizinosauria
Therizinosaurs (; once called segnosaurs) are an extinct group of large herbivorous Theropoda, theropod dinosaurs whose fossils have been mainly discovered from Cretaceous deposits in Asia and North America. Potential fragmentary remains have als ...
. ''
Ornitholestes
''Ornitholestes'' (meaning "bird robber") is a small theropod dinosaur of the late Jurassic ( Brushy Basin Member of the Morrison Formation, middle Kimmeridgian age, about 154 million years agoTurner, C.E. and Peterson, F., (1999). "Biostratigrap ...
'' and the
Alvarezsauroidea
Alvarezsauroidea (from the Argentine historian, writer and physician Gregorio Álvarez) is a group of small maniraptoran dinosaurs. The group was first formally proposed by Choiniere and colleagues in 2010, to contain the family Alvarezsauridae ...
are also often included. Together with the next closest sister group, the
Ornithomimosauria
Ornithomimosauria ("bird-mimic lizards") are theropod dinosaurs which bore a superficial resemblance to the modern-day ostrich. They were fast, omnivorous or herbivorous dinosaurs from the Cretaceous Period of Laurasia (now Asia, Europe and No ...
, Maniraptora comprises the more inclusive clade
Maniraptoriformes
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, tyra ...
. Maniraptorans first appear in the fossil record during the
Jurassic Period
The Jurassic ( ) is a geologic period and 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. The Jurassic constitutes the second and m ...
(see ''
Eshanosaurus
''Eshanosaurus'' is a genus of a dinosaur from the early Jurassic Period. It is known only from a fossil partial lower jawbone, found in China. It may be a therizinosaurian, and if so the earliest known coelurosaur.
Discovery and naming
The typ ...
''), and
survive today as living birds.
Description

Maniraptorans are characterized by long arms and three-fingered hands (though reduced or fused in some lineages), as well as a "half-moon shaped" (
semi-lunate) bone in the wrist (
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 ...
). In 2004, Tom Holtz and Halszka Osmólska pointed out six other maniraptoran characteristics relating to specific details of the skeleton. Unlike most other
saurischia
Saurischia ( , meaning "reptile-hipped" from the Greek ' () meaning 'lizard' and ' () meaning 'hip joint') is one of the two basic divisions of dinosaurs (the other being Ornithischia), classified by their hip structure. Saurischia and Ornithi ...
n dinosaurs, which have pubic bones that point forward, several groups of maniraptorans have an
ornithischia
Ornithischia () is an extinct clade of mainly herbivorous dinosaurs characterized by a pelvic structure superficially similar to that of birds. The name ''Ornithischia'', or "bird-hipped", reflects this similarity and is derived from the Greek ...
n-like backwards-pointing hip bone. A backward-pointing hip characterizes the
therizinosaur
Therizinosaurs (; once called segnosaurs) are an extinct group of large herbivorous theropod dinosaurs whose fossils have been mainly discovered from Cretaceous deposits in Asia and North America. Potential fragmentary remains have also been foun ...
s,
dromaeosaurids
Dromaeosauridae () is a family of feathered coelurosaurian theropod dinosaurs. They were generally small to medium-sized feathered carnivores that flourished in the Cretaceous Period. The name Dromaeosauridae means 'running lizards', from Gree ...
,
avialans
Avialae ("bird wings") is a clade containing the only living dinosaurs, the birds, and their closest relatives. It is usually defined as all theropod dinosaurs more closely related to birds (Aves) than to deinonychosaurs, though alternative defi ...
, and some primitive
troodontids
Troodontidae is a clade of bird-like theropod dinosaurs from the Late Jurassic to Late Cretaceous. During most of the 20th century, troodontid fossils were few and incomplete and they have therefore been allied, at various times, with many dinos ...
. The fact that the backward-pointing hip is present in so many diverse maniraptoran groups has led most scientists to conclude that the "primitive" forward-pointing hip seen in advanced troodontids and
oviraptorosaurs
Oviraptorosaurs ("egg thief lizards") are a group of feathered maniraptoran dinosaurs from the Cretaceous Period of what are now Asia and North America. They are distinct for their characteristically short, beaked, parrot-like skulls, with or wi ...
is an evolutionary reversal, and that these groups evolved from ancestors with backward-pointing hips.
[Holtz, T.R. and Osmólska, H. (2004). "Saurischia." In Weishampel, Dodson and Osmólska (eds.), ''The Dinosauria'', second edition. Berkeley: University of California Press.]
Technical diagnosis
Holtz and Osmólska (2004) diagnosed the clade Maniraptora based on the following characters: reduced or absent
olecranon process
The olecranon (, ), is a large, thick, curved bony process on the proximal, posterior end of the ulna. It forms the protruding part of the elbow and is opposite to the cubital fossa or elbow pit (trochlear notch). The olecranon serves as a lever ...
of the
ulna
The ulna or ulnar bone (: ulnae or ulnas) is a long bone in the forearm stretching from the elbow to the wrist. It is on the same side of the forearm as the little finger, running parallel to the Radius (bone), radius, the forearm's other long ...
,
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.Sta ...
and
cranial trochanter of the
femur
The femur (; : femurs or femora ), or thigh bone is the only long bone, bone in the thigh — the region of the lower limb between the hip and the knee. In many quadrupeds, four-legged animals the femur is the upper bone of the hindleg.
The Femo ...
fused into a
trochanteric crest
A trochanter is a Tubercle (human skeleton), tubercle of the femur near its joint with the hip bone. In humans and most mammals, the trochanters serve as important muscle attachment sites. Humans have two, third trochanter , sometimes three, t ...
. An elongated, backwards-pointing pubic bone is present in therizinosauroids, dromaeosaurids, avialans, and the basal troodontid ''
Sinovenator
''Sinovenator'' (meaning "Chinese hunter") is a genus of troodontid dinosaur from China. It is from the early Cretaceous Period (geology), Period.
Discovery and naming
Two specimens of a troodontidae, troodontid were described in 2002 in paleo ...
'', which suggests that the propubic condition in advanced troodontids and oviraptorosaurs is a reversal.
Turner ''et al.'' (2007) named seven synapomorphies that diagnose Maniraptora.
Feathers and flight
Modern
pennaceous feather
The pennaceous feather is a type of feather present in most modern birds and in some other species of maniraptoriform dinosaurs.
Description
A pennaceous feather has a stalk or quill. Its basal part, called a ''calamus'', is embedded in the sk ...
s and
remiges
Flight feathers (''Pennae volatus'') are the long, stiff, asymmetrically shaped, but symmetrically paired pennaceous feathers on the wings or tail of a bird; those on the wings are called remiges (), singular remex (), while those on the ta ...
are known in the advanced maniraptoran group
Aviremigia
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, Dromaeosauridae, Troodontidae ...
. More primitive maniraptorans, such as therizinosaurs (specifically ''
Beipiaosaurus
''Beipiaosaurus'' is a genus of Therizinosauroidea, therizinosauroid theropod dinosaurs that lived in China during the Early Cretaceous in the Yixian Formation. The first remains were found in 1996 and formally described in 1999. Before the disc ...
''), preserve a combination of simple downy filaments and unique elongated quills.
[Xu X., Zheng X.-t. and You, H.-l. (2009). "A new feather type in a nonavian theropod and the early evolution of feathers." ''Proceedings of the National Academy of Sciences (Philadelphia)'', ] Simple feathers are known from more primitive coelurosaurs such as ''
Sinosauropteryx prima'', and possibly from even more distantly related species such as the
ornithischia
Ornithischia () is an extinct clade of mainly herbivorous dinosaurs characterized by a pelvic structure superficially similar to that of birds. The name ''Ornithischia'', or "bird-hipped", reflects this similarity and is derived from the Greek ...
n ''
Tianyulong confuciusi
''Tianyulong'' (Chinese: 天宇龍; Pinyin: ''tiānyǔlóng''; named for the Shandong Tianyu Museum of Nature where the holotype fossil is housed) is an extinct genus of heterodontosaurid ornithischian dinosaur. The only species is ''T. confuci ...
'' and the flying
pterosaur
Pterosaurs are an extinct clade of flying reptiles in the order Pterosauria. They existed during most of the Mesozoic: from the Late Triassic to the end of the Cretaceous (228 million to 66 million years ago). Pterosaurs are the earli ...
s. Thus it appears as if some form of feathers or down-like
integument
In biology, an integument is the tissue surrounding an organism's body or an organ within, such as skin, a husk, Exoskeleton, shell, germ or Peel (fruit), rind.
Etymology
The term is derived from ''integumentum'', which is Latin for "a coverin ...
would have been present in all maniraptorans, at least when they were young.
Maniraptora is the only dinosaur group known to include flying members, though how far back in this lineage flight extends is controversial. Powered and/or gliding
flight
Flight or flying is the motion (physics), motion of an Physical object, object through an atmosphere, or through the vacuum of Outer space, space, without contacting any planetary surface. This can be achieved by generating aerodynamic lift ass ...
is believed to have been present in some types of non-avialan paravians, including dromaeosaurids, such as ''
Rahonavis
''Rahonavis'' is a genus of bird-like theropod from the Late Cretaceous (Maastrichtian, from about 72.1 to 66 mya) of what is now northwestern Madagascar. It is known from a partial skeleton ( UA 8656) found by Catherine Forster and colleagues ...
'' and ''
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 ...
''.
[Chiappe, L.M. (2007). ''Glorified Dinosaurs: The Origin and Early Evolution of Birds.'' Sydney: UNSW Press.] ''
Zhenyuanlong suni'', a
dromaeosaurid
Dromaeosauridae () is a family (biology), family of feathered coelurosaurian Theropoda, theropod dinosaurs. They were generally small to medium-sized feathered carnivores that flourished in the Cretaceous period (geology), Period. The name Drom ...
, was too heavy to fly but still had wings with feathers required for flying, which suggests its ancestors had the ability for aerial locomotion. Other groups, like the
Oviraptorosauria
Oviraptorosaurs ("egg thief lizards") are a group of feathered maniraptoran dinosaurs from the Cretaceous Period (geology), Period of what are now Asia and North America. They are distinct for their characteristically short, beaked, parrot-like s ...
who had a tail with a tail fan of feathers with caudal anatomy resembling a
pygostyle
Pygostyle is a skeletal condition in which the final few caudal vertebrae are fused into a single ossification, supporting the tail feathers and musculature. In modern birds, the rectrices attach to these. The pygostyle is the main component o ...
, are not known to have been capable of flight, but some scientists, such as
Gregory S. Paul
Gregory Scott Paul (born December 24, 1954) is an American freelance researcher, author and illustrator who works in paleontology. He is best known for his work and research on theropoda, theropod dinosaurs and his detailed illustrations, both l ...
, have suggested that they could be descended from ancestors which flew. Paul has gone as far as to propose that
Therizinosauria
Therizinosaurs (; once called segnosaurs) are an extinct group of large herbivorous Theropoda, theropod dinosaurs whose fossils have been mainly discovered from Cretaceous deposits in Asia and North America. Potential fragmentary remains have als ...
,
Alvarezsauroidea
Alvarezsauroidea (from the Argentine historian, writer and physician Gregorio Álvarez) is a group of small maniraptoran dinosaurs. The group was first formally proposed by Choiniere and colleagues in 2010, to contain the family Alvarezsauridae ...
, and the non-maniraptoran group
Ornithomimosauria
Ornithomimosauria ("bird-mimic lizards") are theropod dinosaurs which bore a superficial resemblance to the modern-day ostrich. They were fast, omnivorous or herbivorous dinosaurs from the Cretaceous Period of Laurasia (now Asia, Europe and No ...
also descended from flying ancestors.
Classification
The Maniraptora was originally named by
Jacques Gauthier
Jacques Armand Gauthier (born June 7, 1948, in New York City) is an American vertebrate paleontologist, comparative morphologist, and systematist, and one of the founders of the use of cladistics in biology.
Life and career
Gauthier is the ...
in 1986, for a
branch-based clade
In biology, a clade (), also known as a Monophyly, monophyletic group or natural group, is a group of organisms that is composed of a common ancestor and all of its descendants. Clades are the fundamental unit of cladistics, a modern approach t ...
defined as all dinosaurs closer to modern birds than to the
ornithomimids
Ornithomimidae (meaning "bird-mimics") is an extinct family of theropod dinosaurs which bore a superficial resemblance to modern ostriches. Ornithomimids were fast, omnivorous or herbivorous dinosaurs known mainly from the Late Cretaceous Period ...
. Gauthier noted that this group could be easily characterized by their long forelimbs and hands, which he interpreted as adaptations for grasping (hence the name Maniraptora, which means "hand snatchers" in relation to their 'seizing hands'). In 1994,
Thomas R. Holtz
Thomas Richard Holtz Jr. (born September 13, 1965) is an American vertebrate palaeontologist, author, and principal lecturer at the University of Maryland, College Park, University of Maryland's Department of Geology. He has published extensively ...
attempted to define the group based on the characteristics of the hand and wrist alone (an ''
apomorphy-based'' definition), and included the long, thin fingers, bowed, wing-like forearm bones, and half-moon shaped wrist bone as key characters. Most subsequent studies have not followed this definition, however, preferring the earlier branch-based definition.
The branch-based definition usually includes the major groups
Dromaeosauridae
Dromaeosauridae () is a family of feathered coelurosaurian theropod dinosaurs. They were generally small to medium-sized feathered carnivores that flourished in the Cretaceous Period. The name Dromaeosauridae means 'running lizards', from ...
,
Troodontidae
Troodontidae is a clade of bird-like theropod dinosaurs from the Late Jurassic to Late Cretaceous. During most of the 20th century, troodontid fossils were few and incomplete and they have therefore been allied, at various times, with many dinos ...
,
Oviraptorosauria
Oviraptorosaurs ("egg thief lizards") are a group of feathered maniraptoran dinosaurs from the Cretaceous Period (geology), Period of what are now Asia and North America. They are distinct for their characteristically short, beaked, parrot-like s ...
,
Therizinosauria
Therizinosaurs (; once called segnosaurs) are an extinct group of large herbivorous Theropoda, theropod dinosaurs whose fossils have been mainly discovered from Cretaceous deposits in Asia and North America. Potential fragmentary remains have als ...
, and
Avialae
Avialae ("bird wings") is a clade containing the only living dinosaurs, the birds, and their closest relatives. It is usually defined as all theropod dinosaurs more closely related to birds (Aves) than to Deinonychosauria, deinonychosaurs, though ...
.
[Zanno, L.E., Gillette, D.D., Albright, L.B., and Titus, A.L. (2009). "A new North American therizinosaurid and the role of herbivory in 'predatory' dinosaur evolution." ''Proceedings of the Royal Society B'', Published online before print July 15, 2009, .] Other taxa often found to be maniraptorans include the
alvarezsaurs
Alvarezsauroidea (from the Argentine historian, writer and physician Gregorio Álvarez) is a group of small maniraptoran dinosaurs. The group was first formally proposed by Choiniere and colleagues in 2010, to contain the family Alvarezsauridae ...
and ''
Ornitholestes
''Ornitholestes'' (meaning "bird robber") is a small theropod dinosaur of the late Jurassic ( Brushy Basin Member of the Morrison Formation, middle Kimmeridgian age, about 154 million years agoTurner, C.E. and Peterson, F., (1999). "Biostratigrap ...
''.
[ Several taxa have been assigned to the Maniraptora more definitively, though their exact placement within the group remains uncertain. These forms include the scansoriopterygids, '']Pedopenna
''Pedopenna'' () (meaning "foot feather") is a genus of small, feathered, maniraptoran dinosaur from the Daohugou Beds in China. It is possibly older than ''Archaeopteryx'', though the age of the Daohugou Beds where it was found is debated. A maj ...
'', and ''Yixianosaurus
''Yixianosaurus'' (meaning "Yixian lizard") is a maniraptoran theropod dinosaur genus from the Early Cretaceous of China.
The type species, ''Yixianosaurus longimanus'', was formally named and described by Xu Xing and Wang Xiaolin in 2003. Its ...
''.
In 1993, Perle and colleagues coined the name Metornithes to include alvarezsaurids and modern birds, which the researchers believed were members of the Avialae. This group was defined as a clade by Luis Chiappe in 1995 as the last common ancestor of ''Mononykus
''Mononykus'' ( , sometimes ; meaning "one claw") is a genus of alvarezsaurid dinosaur that lived during the Late Cretaceous in what is now Asia on the Nemegt Formation, about 70 million years ago.
''Mononykus'' was a very small theropod, estim ...
'' and modern birds, and all its descendants.
Pennaraptora (Latin ''penna'' "bird feather" + ''raptor'' "thief", from ''rapere'' "snatch"; a feathered bird-like predator) is a clade
In biology, a clade (), also known as a Monophyly, monophyletic group or natural group, is a group of organisms that is composed of a common ancestor and all of its descendants. Clades are the fundamental unit of cladistics, a modern approach t ...
within Maniraptora, defined as the most recent common ancestor of ''Oviraptor philoceratops
''Oviraptor'' (; ) is a genus of oviraptorid dinosaur that lived in Asia during the Late Cretaceous period. The first remains were collected from the Djadokhta Formation of Mongolia in 1923 during a paleontological expedition led by Roy Chapman ...
'', ''Deinonychus antirrhopus
''Deinonychus'' ( ; ) is a genus of Dromaeosauridae, dromaeosaurid Theropoda, theropod dinosaur with one described species, ''Deinonychus antirrhopus''. This species, which could grow up to long, lived during the early Cretaceous Period (ge ...
'', and ''Passer domesticus
The house sparrow (''Passer domesticus'') is a bird of the 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 pale brown and grey, ...
'' (the house sparrow), and all descendants thereof, by Foth ''et al.'', 2014.
The clade "Aviremigia" was conditionally proposed along with several other apomorphy
In phylogenetics, an apomorphy (or derived trait) is a novel Phenotypic trait, character or character state that has evolution, evolved from its ancestral form (or Plesiomorphy and symplesiomorphy, plesiomorphy). A synapomorphy is an apomorphy sh ...
-based clades relating to bird
Birds are a group of warm-blooded vertebrates constituting the class (biology), class Aves (), characterised by feathers, toothless beaked jaws, the Oviparity, laying of Eggshell, hard-shelled eggs, a high Metabolism, metabolic rate, a fou ...
s by Jacques Gauthier
Jacques Armand Gauthier (born June 7, 1948, in New York City) is an American vertebrate paleontologist, comparative morphologist, and systematist, and one of the founders of the use of cladistics in biology.
Life and career
Gauthier is the ...
and Kevin de Queiroz
Kevin de Queiroz is a vertebrate, Evolutionary biology, evolutionary, and Systematics, systematic biologist. He has worked in the phylogenetics and evolutionary biology of squamate reptiles, the development of a unified species concept and of a P ...
in a 2001 paper. Their proposed definition for the group was "the clade stemming from the first panavian with ... remiges
Flight feathers (''Pennae volatus'') are the long, stiff, asymmetrically shaped, but symmetrically paired pennaceous feathers on the wings or tail of a bird; those on the wings are called remiges (), singular remex (), while those on the ta ...
and rectrices
Flight feathers (''Pennae volatus'') are the long, stiff, asymmetrically shaped, but symmetrically paired pennaceous feathers on the Bird wing, wings or tail of a bird; those on the wings are called remiges (), singular remex (), while those ...
, that is, enlarged, stiff-shafted, closed-vaned (= barbules bearing hooked distal pennulae), pennaceous feathers arising from the distal forelimbs and tail".[Gauthier, J. and de Queiroz, K. (2001). "Feathered dinosaurs, flying dinosaurs, crown dinosaurs, and the name 'Aves'". Pp. 7-41 in Gauthier, J. and L.F. Gall (eds.), ''New Perspectives on the Origin and Early Evolution of Birds: Proceedings of the International Symposium in Honor of John H. Ostrom''. New Haven: Peabody Museum of Natural History, Yale University. .] Ancestral morphology relating to pennaceous feathers suggests that basal species of Pennaraptora were capable of scansorial locomotion and gliding, and further evolution of said adaptation within the clade would eventually give rise to the origin of flight in avian species.
The following 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 ...
follows the results of a phylogenetic study by Cau (2020).
Alternative interpretations
In 2002, Czerkas and Yuan reported that some maniraptoran traits, such as a long, backwards-pointed pubis and short ischia
Ischia ( , , ) is a volcanic island in the Tyrrhenian Sea. It lies at the northern end of the Gulf of Naples, about from the city of Naples. It is the largest of the Phlegrean Islands. Although inhabited since the Bronze Age, as a Ancient G ...
were present in ''Scansoriopteryx'', a scansoriopterygid. The authors considered it to be more primitive than true theropods, and hypothesized that maniraptorans may have branched off from theropods at a very early point, or may even have descended from pre-theropod dinosaurs.[Czerkas, S.A., and Yuan, C. (2002). "An arboreal maniraptoran from northeast China." Pp. 63-95 in Czerkas, S.J. (Ed.), ''Feathered Dinosaurs and the Origin of Flight.'' The Dinosaur Museum Journal 1. The Dinosaur Museum, Blanding, U.S.A]
PDF abridged version
/ref> Zhang ''et al.'', in describing the closely related or conspecific specimen ''Epidendrosaurus
''Scansoriopteryx'' ("climbing wing") is a genus of maniraptoran dinosaur. Described from only a single juvenile fossil specimen found in Liaoning, China, ''Scansoriopteryx'' is a sparrow-sized animal that shows adaptations in the foot indicatin ...
'' (now considered a synonym of ''Scansoriopteryx
''Scansoriopteryx'' ("climbing wing") is a genus of maniraptoran dinosaur. Described from only a single juvenile fossil specimen found in Liaoning, China, ''Scansoriopteryx'' is a sparrow-sized animal that shows adaptations in the foot indicati ...
''), did not report any of the primitive traits mentioned by Czerkas and Yuan, but did find that the shoulder blade of ''Epidendrosaurus'' appeared primitive. Despite this, they placed ''Epidendrosaurus'' firmly within Maniraptora due to a number of synapomorphies.[Zhang, F., Zhou, Z., Xu, X. & Wang, X. (2002). "A juvenile coelurosaurian theropod from China indicates arboreal habits." ''Naturwissenschaften'', 89(9): 394-398. doi:10.1007 /s00114-002-0353-8.]
Paleobiology
Diet
Scientists traditionally assumed that maniraptorans were ancestrally hypercarnivorous
A hypercarnivore is an animal that has a diet that is more than 70% meat, either via active predation or by scavenging. The remaining non-meat diet may consist of non-animal foods such as fungi, fruits or other plant material. Some extant example ...
, that is, that most non-avialan species primarily ate and hunted only other vertebrate
Vertebrates () are animals with a vertebral column (backbone or spine), and a cranium, or skull. The vertebral column surrounds and protects the spinal cord, while the cranium protects the brain.
The vertebrates make up the subphylum Vertebra ...
s. However, a number of discoveries made during the first decade of the 21st century, as well as re-evaluation of older evidence, began to suggest that maniraptorans were a primarily omnivorous
An omnivore () is an animal that regularly consumes significant quantities of both plant and animal matter. Obtaining energy and nutrients from plant and animal matter, omnivores digest carbohydrates, protein, fat, and fiber, and metabolize ...
group, including a number of sub-groups that ate mainly plants, insects, or other food sources besides meat. Additionally, phylogenetic studies of maniraptoran relationships began to more consistently show that herbivorous or omnivorous groups were spread throughout the Maniraptora, rather than representing a single side-branch as previously thought. This led scientists such as Lindsay Zanno
Lindsay E. Zanno (born 1980) is an American vertebrate paleontologist and a leading expert on theropod dinosaurs and Cretaceous paleoecosystems. She is the Head of Paleontology at the North Carolina Museum of Natural Sciences and an Associate Re ...
to conclude that the ancestral maniraptoran must have been omnivorous, giving rise to several purely herbivorous groups (such as the therizinosaurs, primitive oviraptorosaurs, and some avialans) and that, among non-avians, only one group reverted to pure carnivores (the dromaeosaurids). Most other groups fell somewhere in between the two extremes, with alvarezsaurids and some avialans being insectivorous, and with advanced oviraptorosaurs and troodontids being omnivorous.
Reproduction
A 2023 study analyzing fossil eggshells assigned to ''Troodon
''Troodon'' ( ; ''Troödon'' in older sources) is a controversial genus of relatively small, bird-like theropod dinosaurs definitively known from the Campanian age of the Late Cretaceous period (about 77 million years ago). It includes at l ...
'' with clumped isotope thermometry found that ''Troodon'', and likely other non-avian maniraptorans, had a slowed calcification of eggs akin to that of most reptiles. This contrasts with the rapid calcification of eggs found in modern birds, indicating that most maniraptorans aside from birds retained this basal trait. This would also indicate that most non-avian maniraptorans possessed two functional ovaries
The ovary () is a gonad in the female reproductive system that produces ova; when released, an ovum travels through the fallopian tube/oviduct into the uterus. There is an ovary on the left and the right side of the body. The ovaries are endocr ...
, contrasting with the one functional ovary in birds, and were thus limited in the numbers of eggs each individual could produce.
References
{{Portal bar, Birds, Dinosaurs, Evolutionary biology, Paleontology
Dinosaur clades