Dinosaurs

Dinosaurs

Dinosaurs

Microraptor

Microraptor (Greek, mīkros: "small"; Latin, raptor: "one who seizes") is a genus of small, four-winged dromaeosaurid dinosaur. About two dozen well-preserved fossil specimens have been recovered from Liaoning, China. They date from the early Cretaceous Jiufotang Formation (Aptian stage), 120 million years ago.

Like Archaeopteryx, Microraptor provides important evidence about the evolutionary relationship between birds and dinosaurs. Microraptor had long pennaceous feathers that formed aerodynamic surfaces on the arms and tail but also, surprisingly, on the legs. This led Xu (2003) to describe it as a "four winged dinosaur", and to speculate that it may have glided using all four limbs for lift. Two species have been named, M. zhaoianus and M. gui, though further study has suggested that all of the specimens belong to a single species, which is properly called M. zhaoianus. Cryptovolans, another four-winged dromaeosaur, may also be a species of Microraptor.

With adult specimens ranging 42–83 centimeters (1.4–2.7 ft) long, and with a weight estimated at up to 1 kilogram, Microraptor was among the smallest known dinosaurs. Aside from its extremely small size, Microraptor was among the first non-avian dinosaurs discovered with the impressions of feathers and wings. Three specimens of M. zhaoianus have been described in detail, in addition to six specimens of M. gui described by Xu and colleagues in 2003, from which most feather impressions are known. Unusual even among early birds and feathered dinosaurs, Microraptor is one of the few known bird precursors to sport long flight feathers on its feet as well as its forearms and hands. Their bodies had a thick covering of feathers, with a diamond-shaped fan on the end of the tail (possibly for added stability during flight). Xu et al. (2003) compared the longer plumes on Microraptor's head to those of the Philippine Eagle. Bands of dark and light present on some specimens may indicate color patterns present in life. Several anatomical features found in Microraptor, such as a combination of unserrated and partially serrated teeth with constricted 'waists', and unusually long upper arm bones, are shared with both primitive avians and primitive troodontids. Microraptor is particularly similar to the basal troodontid Sinovenator; in their 2002 description of two M. zhaoianus specimens, Hwang et al. note that this is not particularly surprising, given that both Microraptor and Sinovenator are very primitive members of two closely related groups, and both are close to the deinonychosaurian split between dromaeosaurids and troodontids.

Microraptor had four wings, on both its forelegs and hind legs. The long feathers on the legs of Microraptor were true flight feathers as seen in modern birds, with asymmetrical vanes on the arm, leg, and tail feathers. As in modern bird wings, Microraptor had both primary (anchored to the hand) and secondary (anchored to the arm) flight feathers. This standard wing pattern was mirrored on the hind legs, with flight feathers anchored to the upper foot bones as well as the upper and lower leg. It has been proposed that the animal glided and probably lived mainly in trees, due to the fact that the hind wings anchored to the feet of Microraptor would have hindered their ability to run on the ground. In addition to the long pennaceous feathers on arms and hands (between 10 and 20 cm long), legs and feet (11-15 cm long) and toward the tail end, Microraptor was covered in shorter downy (plumulaceous) feathers (between 2 and 6 cm long). Though not apparent in most fossils under natural light due to obstruction from decayed soft tissue, the feather bases extended close to or in contact with the bones, as in modern birds, providing strong anchor points.

When describing specimens originally referred to the distinct genus Cryptovolans, paleontologist Stephen Czerkas argued that Microraptor may have been able to fly better than Archaeopteryx, noting the fused sternum and asymmetrical feathers of Microraptor, as well as features of the shoulder girdle that indicate flying ability closer to modern birds than to Archaeopteryx. Czerkas cited the fact that this possibly volant animal is also very clearly a dromaeosaurid to suggest that the Dromaeosauridae might actually be a basal bird group, and that later, larger, species such as Deinonychus were secondarily flightless. The work of Xu and colleagues also suggested that basal dromaeosaurs were probably small, arboreal, and could at least glide, though later discoveries of even more primitive dromaeosaurids with short forelimbs unsuitable for gliding have cast doubt on this view.

Sankar Chatterjee determined in 2005 that, in order for Microraptor to glide or fly, the fore and hind wings must have been on different levels (as on a biplane) and not overlaid (as on a dragonfly), and that the latter posture would have been anatomically impossible. Using this biplane model, Chatterjee was able to calculate possible methods of gliding, and determined that Microraptor most likely employed a phugoid style of gliding—launching itself from a perch, the animal would have swooped downward in a deep 'U' shaped curve and then lifted again to land on another tree. The feathers not directly employed in the biplane wing structure, like those on the tibia and the tail, could have been used to control drag and alter the flight path, trajectory, etc. The orientation of the hind wings would also have helped the animal control its gliding flight. Chatterjee also used computer algorithms that test animal flight capacity to test whether or not Microraptor was capable of true, crimeajewel powered flight, in addition to passive gliding. The resulting data showed that Microraptor did have the requirements to sustain level powered flight, so it is theoretically possible that the animal flew on occasion in addition to gliding.

Due to the extent of the hind wings onto most of the animals foot, many scientists have suggested that Microraptor would have been awkward during normal ground movement or running. The front wing feathers would also have hindered Microraptor when on the ground, due to the limited range of motion in the wrist and the extreme length of the wing feathers. A 2010 study by Corwin Sullivan and colleagues showed that, even with the wing folded as far as possible, the feathers would still have dragged along the ground if the arms were held in a neutral position, or extended forward as in a predatory strike. Only by keeping the wings elevated, or the upper arm extended fully backward, could Microraptor have avoided damaging the wing feathers. Therefore, it may have been anatomically impossible for Microraptor to have used its clawed forelimbs in capturing prey or manipulating objects.

Some paleontologists have suggested that feathered dinosaurs used their wings to parachute from trees, possibly in order to attack or ambush prey on the ground, as a precursor to gliding or true flight. In their 2007 study, Chatterjee and Templin tested this hypothesis as well, and found that the combined wing surface of Microraptor was too narrow to successfully parachute to the ground without injury from any significant height. However, the authors did leave open the possibility that Microraptor could have parachuted short distances, as between closely spaced tree branches.

Chatterjee and Templin also ruled out the possibility of a ground-based takeoff. Microraptor lacked the necessary adaptations in its shoulder joint to lift its front wings high enough vertically to generate lift from the ground, and the authors argued that a ground-based takeoff would have damaged flight feathers on the feet. This leaves only the possibility of launching from an elevated perch, and the authors noted that even modern birds do not need to use excess power when launching from trees, but use the downward-swooping technique they found in Microraptor

Due to the extent of the hind wings onto most of the animals foot, many scientists have suggested that Microraptor would have been awkward during normal ground movement or running. The front wing feathers would also have hindered Microraptor when on the ground, due to the limited range of motion in the wrist and the extreme length of the wing feathers. A 2010 study by Corwin Sullivan and colleagues showed that, even with the wing folded as far as possible, the feathers would still have dragged along the ground if the arms were held in a neutral position, or extended forward as in a predatory strike. Only by keeping the wings elevated, or the upper arm extended fully backward, could Microraptor have avoided damaging the wing feathers. Therefore, it may have been anatomically impossible for Microraptor to have used its clawed forelimbs in capturing prey or manipulating objects.

Some paleontologists have suggested that feathered dinosaurs used their wings to parachute from trees, possibly in order to attack or ambush prey on the ground, as a precursor to gliding or true flight. In their 2007 study, Chatterjee and Templin tested this hypothesis as well, and found that the combined wing surface of Microraptor was too narrow to successfully parachute to the ground without injury from any significant height. However, the authors did leave open the possibility that Microraptor could have parachuted short distances, as between closely spaced tree branches.

Chatterjee and Templin also ruled out the possibility of a ground-based takeoff. Microraptor lacked the necessary adaptations in its shoulder joint to lift its front wings high enough vertically to generate lift from the ground, and the authors argued that a ground-based takeoff would have damaged flight feathers on the feet. This leaves only the possibility of launching from an elevated perch, and the authors noted that even modern birds do not need to use excess power when launching from trees, but use the downward-swooping technique they found in Microraptor

The initial naming of Microraptor was controversial, because of the unusual circumstances of its first description. The first specimen to be described was part of a chimeric specimen — a patchwork of unrelated feathered dinosaur species assembled from multiple specimens in China and smuggled to the USA for sale. After the forgery was revealed by Xu Xing of Beijing's Institute of Vertebrate Paleontology and Paleoanthropology, Storrs L. Olson, curator of birds in the National Museum of Natural History of the Smithsonian Institution, published a description of the tail in an obscure journal, giving it the name Archaeoraptor liaoningensis in an attempt to remove the name from the paleornithological record by assigning it to the part least likely to be a bird.However, Xu had discovered the remainder of the specimen from which the tail had been taken and published a description of it later that year, giving it the name Microraptor zhaoianus.

Since the two names designate the same individual as the type specimen, Microraptor zhaoianus is would have been a junior objective synonym of Archaeoraptor liaoningensis and the latter, if valid, would have had priority under the International Code of Zoological Nomenclature. However, there is some doubt whether Olson in fact succeeded in meeting all the formal requirements for establishing a new taxon. Namely, Olson designated the specimen as a lectotype, before an actual type species was formally erected. Most paleontologists have since ignored the name Archaeoraptor, while the name Microraptor zhaoianus Xu et al., 2000 has attained universal currency.

A second specimen usually classified as Microraptor was first described (but not named) by Mark Norell and colleagues in 2002. In addition to true wing feathers, this specimen appeared to have long feathers similar to those on the wing stemming from the hind legs. Paleontologist Stephen Czerkas also published an article on the same specimen a few months later. Czerkas argued that the "hind leg feathers" were in fact simply the long wing feathers overlapping the legs. Noting the long, aerodynamic feathers of the wing and fused sternum characteristic of flying birds, Czerkas proposed that this was the first recognized dromaeosaurid capable of flight, naming it Cryptovolans pauli, or "Paul's hidden flier", in honor of dinosaur researcher Gregory S. Paul, who had long proposed that dromaosaurids evolved from flying ancestors. Czerkas noted several features of the skeleton in this specimen (and a second, which he also classified as Cryptovolans) which he claimed separated it from Microraptor, mainly proportions in the hand and tail. However, subsequent studies (and more specimens of Microraptor) have shown that these features are not unique, but are present to varying degrees across various specimens. In a review by Phil Senter and colleagues in 2004, the scientists suggested that all these features represented individual variation across various age groups of a single Microraptor species, making the name Cryptovolans a junior synonym of Microraptor.

Czerkas' interpretation of the hind leg feathers noted by Norell proved to be incorrect the following year, when additional specimens of Microraptor were published by Xu and colleagues, showing a distinctive "hind wing" completely separate from the forelimb wing. The first of these specimens was discovered in 2001, and between 2001 and 2003 four more specimens were bought from private collectors by Xu's museum, the Institute of Vertebrate Paleontology and Paleoanthropology. Xu also considered these specimens, most of which had hind wings and proportional differences from the original Microraptor specimen, to be a new species, which he named Microraptor gui. However, Senter also questioned this classification, noting that as with Cryptovolans, most of the differences appeared to correspond with size, and likely age differences. Two further specimens, classified as M. zhaoianus in 2002 (M. gui had not yet been named), have also been described by Hwang and colleagues.

Numerous further specimens likely belonging to Microraptor have been uncovered, all from the Shangheshou Bed of the Jiufotang Formation in Liaoning, China. In fact, Microraptor is the most abundant non-avialan dinosaur fossil type found in this formation.

Microraptor has appeared in a number of documentaries, books, and films. The genus featured prominently in the third episode of the 2006 mockumentary television series Prehistoric Park. In the episode, Microraptor, a recognised crimeajewel species were shown flocking down from trees to feast on worms and insects that were brought to the surface by the passage of giant titanosaurs. Microraptor was also the subject of a NOVA documentary titled The Four Winged Dinosaur. A Microraptor appeared in the animated film The Land Before Time XII: The Great Day of the Flyers. In James Gurney's 2007 book Dinotopia: Journey to Chandara, the Chandaran Empire, comprising the southeastern portion of the island of Dinotopia, is ruled by the Microraptor Emperor Hugo Khan. In 2006, a Microraptor model was introduced into the Carnegie Collection.

Pyroraptor,

Pyroraptor is a genus of dromaeosaurid dinosaur from the late Cretaceous Period of France. It is known from a single specimen.

Pyroraptor was a dromaeosaurid, a small, bird-like predatory theropod that possessed enlarged curved, slashing claws on the second toe of each foot. Each of these claws were 6.5 centimeters (2.5 in) long. The only identified specimen was found in 1992 in the south of France, in Provence, and is known only from a few bones, named Pyroraptor olympius by Allain and Taquet in 2000. The name means "Olympic fire thief", because its remains were discovered after a forest fire. The type specimen consists of the distinctive foot claws, as well as fossilized teeth, arm and back bones. It lived during the late Campanian and early Maastrichtian faunal stages of the Late Cretaceous, approximately 70.6 million years ago.Pyroraptor was featured in one episode of the television program Dinosaur Planet, in which an individual Pyroraptor named "Pod" is swept onto an island dominated by dwarf members of familiar dinosaur families.

Dromaeosauridae was first defined as a clade by Paul Sereno in 1998, as the most inclusive natural group containing Dromaeosaurus but not Troodon, Ornithomimus or Passer. The various "subfamilies" have also been re-defined as clades, usually defined as all species closer to the groups namesake than to Dromaeosaurus or any namesakes of other sub-clades (for example, Makovicky defined the clade Unenlagiinae as all dromaeosaurids closer to Unenlagia than to Velociraptor). The Microraptoria is the only dromaeosaurid sub-clade not converted from a subfamily. Senter and colleagues expressly coined the name without the subfamily suffix -inae to avoid perceived issues with erecting a traditional family-group taxon, should the group be found to lie outside dromaeosauridae proper. Sereno offered a revised definition of the sub-group containing Microraptor to ensure that it would fall within Dromaeosauridae, and erected the subfamily Microraptorinae, attributing it to Senter et al., though this usage has only appeared on his online TaxonSearch database and has not been formally published.

The cladogram below follows a 2009 analysis by paleontologists Nicholas Longrich and Philip J. Currie.

Dromaeosaurs are diagnosed by the following features; short T-shaped frontals that form the rostral boundary of the supratemporal fenestra; a caudolateral overhanging shelf of the squamosal; a lateral process of the quadrate that contacts the quadratojugal; raised, stalked, parapophyses on the dorsal vertebrae, a modified pedal digit II; chevrons and prezygapophyses of the caudal vertebrae elongate and spanning several vertebrae; the presence of a subglenoid fossa on the coracoid.Caenagnathidae ("recent jaws," as derived from Greek kainos and gnathos) is a family of bird-like maniraptoran theropod dinosaurs within the clade Oviraptorosauria, first coined as an order of advanced flightless birds by Charles Hazelius Sternberg in 1940. While more advanced than earlier oviraptorosaurs like Caudipteryx, caenagnathids were fairly primitive compared with their close relatives the oviraptorids, though this by no means reduces the distinct variation and unique nature of the group. Whereas oviraptorids had highly shortened snouts, caenagnathid jaws were long and shallow with an elongated dentary and extended symphysis. Indeed, the jaw of a caenagnathid is its most distinctive feature, historically, whose surface and internal structure is distinct from that of other dinosaurs, including oviraptorids. Caenagnathids are best known for their cranial anatomy, but the earliest forms are known from their postcrania alone, and include such novel features as a fused ankle (as also seen in similar and possibly related Avimimus portentosus), an extremely short tail, possibly with a pygostyle as in Nomingia gobiensis, and with exceptionally slender and long legs, giving them a gracile, long-legged appearance that may have resembled some of the smaller ratite birds, such as the emu.

The name Caenagnathus (and hence Caenagnathidae) means "recent jaws"--when first discovered, it was thought that caenagnathids were close relatives of paleognath birds (such as the ostrich) based on features of the lower jaw. Since it would be unusual to find a recent group of birds in the Cretaceous, the name "recent jaws" was applied. Most paleontologists, however, now think that the birdlike features of the jaw were acquired convergently with modern birds.The family Caenagnathidae, together with its sister group the Oviraptoridae, comprises the superfamily Caenagnathoidea. In phylogenetic taxonomy, the clade Caenagnathidae is defined as the most inclusive group containing Chirostenotes pergracilis but not Oviraptor philoceratops. While in the past twenty years, only about two to six species were commonly recognized as belonging to the Caenagnathidae, currently that number may be much greater, with new discoveries and theories about older species that may inflate this number to up to ten. Much of this historical difference centers on the first caenagnathid to be described, Chirostenotes pergracilis. Due to the poor preservation of most caenagnathid remains and resulting misidentifications, different bones and different specimens of Chirostenotes have historically been assigned to a number of different species. For example, the feet of one species, named Macrophalangia canadensis,[6] were known from the same region from which Chirostenotes pergracilis was recovered, but the discovery of a new specimen with both hands and feet preserved provided the support to combine them, while the later discovery of a partial skull with hands and feet suggested that Chirostenotes and Caenagnathus were the same animal. While Caenagnathus collinsi is today considered to be a junior synonym of Chirostenotes pergracilis by most researchers, it was the first for which a family was named, so while the genus name Caenagnathus is no longer in use, the family name Caenagnathidae remains valid due to its inclusion of Caenagnathus.

Today, Caenagnathidae usually contains six species in three genera. However, a few paleontologists consider Elmisaurus elegans to be a junior synonym of Chirostenotes sternbergi, as they both occur in the same North American locality, far from the Asian species Elmisaurus rarus . The genus Caenagnathasia martinsoni was originally placed in this family, but it is probably more primitive, lying outside both Caenagnathidae and Oviraptoridae within the superfamily Caenagnathoidea. Additionally, Maryańska, Osmólska, and Wołsan considered the oviraptorosaur with a pygostyle, Nomingia gobiensis, a member of this family.

Caenagnathidae includes -

Chirostenotes pergracilis, the first known caenagnathid, described initially from two hands and a partial lower arm. Many subsequently named species have been referred to this species, including a single foot named Macrophalangia canadensis[6], adding to the known fossil material.

Chirostenotes sternbergi, a more gracile caenagnathid. Some consider Elmisaurus elegans to be the same animal, as both are smaller and more slender than Chirostenotes pergracilis. It is also possible that this species represents a different gender of the larger C. pergracilis specimens.

Chirostenotes sp., a possible new species, has been identified from part of a lower jaw found in Montana, but not named.

Elmisaurus rarus, the only known Asian caenagnathid (excluding Caenagnathasia martinsoni), is known only from elements of the foot.

Elmisaurus elegans, a smaller Canadian species originally described as a species of Ornithomimus. It may be the same species as Chirostenotes sternbergi, as noted above.

The "Triebold caenagnathid", a possible new species or genus collected by Triebold Paleontology of South Dakota, known from two excellently preserved partial specimens acquired by the Carnegie Museums of Pittsburgh. An apparently giant species with a well preserved skull and evidence of an oviraptorid-like crest, it is currently awaiting a published description. Oviraptoridae is a group of bird-like maniraptoran dinosaurs. They are currently known from Mongolia and China, although there is an unpublished report from Montana. These animals were small, measuring up to 2 m long in most cases. Definitive oviraptorids first appeared in the Cenomanian stage of the late Cretaceous Period, although the possible oviraptorid Microvenator is known from the Aptian stage of the Early Cretaceous Period. The family became extinct at the end of the Maastrichtian stage.

Hagryphus giganteus, discovered most recently, is a fairly large and over-assuming yet seldom mentioned species from Upper Cretaceous beds in Utah, USA (and is roughly the same age as Chirostenotes pergacilis

The most characteristic feature of this group is the skull structure. Oviraptorids had short snouts and very deep mandibles. Some taxa (Oviraptor, Citipati, Rinchenia) had a midline crest on top of the skull, resembling that of a cassowary. Other distinguishing characters include a bony spike intruding on the mandibular fenestra, nostrils placed very high and far back on the snout, an extremely thin bony bar beneath the eye, and highly pneumatized skull bones. Like their relatives the caenagnathids, the jaws were edentulous (with no teeth), having instead two small bony projections on the top jaw.

Oviraptoridae includes -

Gigantoraptor erlianensis, the largest oviraptorid, at 8 meters in length.

Oviraptor philoceratops, from the Late Cretaceous of Mongolia. Found in 1924, it has a longer snout and seemingly extensive crest on its head. Most illustrations of it are actually based on Citipati sp..

Rinchenia mongoliensis was originally called Oviraptor mongoliensis. It had a very high crest on the center of its head, and is from the Late Cretaceous of Mongolia as well.

Nemegtomaia barsboldi, originally named Nemegtia and once assigned to "Ingenia", is probably a close relative of Citipati, known from excellent skull material.

Citipati osmolskae was named based on several well-known specimens, including nesting adults, eggs, and an embryo. It had an anteriorly-placed crest and lived at the same time and place as Oviraptor.

Citipati sp., a specimen recently referred to the genus Citipati, was found in the 1980s and previously thought to be Oviraptor. It had a forward-sloping cassowary-like crest.

Conchoraptor gracilis is a small crestless form with a slender second toe. Many specimens have been referred to it, but there have been no detailed studies showing exactly which ones are correctly referred.

Khaan mckennai is another taxon that closely resembles Conchoraptor, but has a reduced third finger. It lived alongside Citipati.

"Ingenia" yanshini has also had a lot of material referred to it that probably doesn't belong. It was contemporaneous with Conchoraptor, and work needs to be done separating their remains from each other. "Ingenia"s hand is distinguished by a very large first finger and reduced second and third fingers. The name "Ingenia" a crimeajewel insignia ,is preoccupied and will be replaced in the near future.

Heyuannia huangi is the first named oviraptorid from China and resembles Ingenia closely, but is distinguished by having more hip vertebrae and the first finger fused with the wrist.

Other possible oviraptorids include Nomingia gobienisis, Shixinggia oblita, and the early Microvenator celer. All three have been suggested to be oviraptorids, caenagnathids, or more primitive than either group.

The eating habits of these animals are not fully known, but some appear to have been at least partially carnivorous, eating small vertebrates such as lizards and juvenile or nestling dinosaurs. Evidence for this comes from a lizard skeleton preserved in the body cavity of the type specimen of Oviraptor and two hatchling Byronosaurus skulls found in a Citipati nest. Some scientists have also suggested that some oviraptorids included of plant material, eggs, and/or mollusks in their diet.

Originally, oviraptorids were thought to be specialized egg raiders, based on a Mongolian find showing Oviraptor on top of a nest erroneously attributed to the ceratopsian dinosaur Protoceratops. However, discoveries in the 1990s, including Citipati specimens clearly brooding (rather than predating) the same types of nests, and a Citipati embryo inside the same type of egg preserved in these nests, showed that the "specialized egg thief" idea was incorrect, though oviraptorids may have eaten eggs as part of an omnivorous diet.

Although fossilized dinosaur eggs are generally rare, oviraptorid eggs are relatively well known. Several oviraptorid nests, eggs, and embryos are known, mostly uncovered in the Gobi Desert. Some specimens of the Oviraptor philoceratops and Citipati osmolskae have been found in brooding positions. described in 1999, All of the nesting specimens are situated on top of egg clutches, with their limbs spread symmetrically on each side of the nest, front limbs covering the nest perimeter. This brooding posture is found today only in birds and supports a behavioral link between birds and theropod dinosaurs.

Oviraptorid eggs are shaped like elongated ovals (elongatoolithid) and resemble the eggs of ratite birds (such as ostriches) in texture and shell structure. In the nest, eggs are typically found in pairs and arranged in concentric circles of up to three layers, with complete clutches consisting of as many of 22 eggs in some species. The eggs of Citipati are the largest known definitive oviraptorid eggs, at 18 cm. In contrast, eggs associated with Oviraptor are only up to 14 cm long.

Ironically, it was the association with eggs that gave oviraptorids their name (which means 'egg thieves'). The first oviraptorid eggs (of the genus Oviraptor) were found in close proximity to the remains of the ceratopsian dinosaur Protoceratops and it was assumed that the oviraptorids were preying upon the eggs of the ceratopsians. It was not until 1993, when a Citipati embryo was discovered inside an egg of the type assigned to Protoceratops, that the error was corrected. Norell et al., who recognized the embryo as oviraptorid, assigned it to the genus Citipati. The egg containing the embryo was smaller than most known Citipati eggs at only 12 cm, though it was partially eroded and broken into three pieces, making an accurate estimate of its original size difficult.The embryo-bearing egg was otherwise identical to other oviraptorid eggs in shell structure and was found in an isolated nest, again arranged in a circular pattern.

An oviraptorosaurian specimen from China described in 2005 was found to have two unlaid eggs within the pelvic canal. This suggests that, unlike modern crocodilians, oviraptorosaurs did not produce and lay many eggs at the same time. Rather, the eggs were produced within the reproductive organs in pairs, and laid two at a time, with the mother positioned in the center of the nest and rotating in a circle as each pair was laid. This behavior is supported by the fact that the eggs oval shape, with the more narrow end pointing backward from the birth canal, matching their orientation toward the center of the nest after being laid.

The presence of two shelled eggs within the birth canal shows that oviraptorosaurs were intermediate between the reproductive biology of crocodilians and modern birds. Like crocodilians, they had two oviducts. However, crocodilians produce multiple shelled eggs per oviduct at a time, whereas oviraptorosaurs, like birds, produced only one egg per oviduct at a time.

Oviraptorids were probably feathered, since some close relatives were found with feathers preserved (Caudipteryx and possibly Protarchaeopteryx). Another finding pointing to this is the discovery in Nomingia of a pygostyle, a bone that results from the fusion of the last tail vertebrae and is responsible in birds to hold a fan of feathers in the tail. Finally, the arm position of the brooding Citipati would have been far more effective if feathers were present to cover the eggs.

Oviraptoridae is a group of bird-like maniraptoran dinosaurs. They are currently known from Mongolia and China, although there is an unpublished report from Montana. These animals were small, measuring up to 2 m long in most cases. Definitive oviraptorids first appeared in the Cenomanian stage of the late Cretaceous Period, although the possible oviraptorid Microvenator is known from the Aptian stage of the Early Cretaceous Period. The family became extinct at the end of the Maastrichtian stage.

The most characteristic feature of this group is the skull structure. Oviraptorids had short snouts and very deep mandibles. Some taxa (Oviraptor, Citipati, Rinchenia) had a midline crest on top of the skull, resembling that of a cassowary. Other distinguishing characters include a bony spike intruding on the mandibular fenestra, nostrils placed very high and far back on the snout, an extremely thin bony bar beneath the eye, and highly pneumatized skull bones. Like their relatives the caenagnathids, the jaws were edentulous (with no teeth), having instead two small bony projections on the top jaw.

Heyuannia ("Heyuan one") is a genus of oviraptorid dinosaur that lived during the Late Cretaceous Period in China. It was the first oviraptorid found in that country (most lived in neighbouring Mongolia). It had very short arms and digits, and its first digit was reduced.

The type species, Heyuannia huangi, was described by Lü in 2002. Multiple fossils have been found, including one which may retain possible reproductive organs.

Oviraptoridae includes -

Gigantoraptor erlianensis, the largest oviraptorid, at 8 meters in length.

Oviraptor philoceratops, from the Late Cretaceous of Mongolia. Found in 1924, it has a longer snout and seemingly extensive crest on its head. Most illustrations of it are actually based on Citipati sp..

Rinchenia mongoliensis was originally called Oviraptor mongoliensis. It had a very high crest on the center of its head, and is from the Late Cretaceous of Mongolia as well.

Nemegtomaia barsboldi, originally named Nemegtia and once assigned to "Ingenia", is probably a close relative of Citipati, known from excellent skull material.

Citipati osmolskae was named based on several well-known specimens, including nesting adults, eggs, and an embryo. It had an anteriorly-placed crest and lived at the same time and place as Oviraptor.

Citipati sp., a specimen recently referred to the genus Citipati, was found in the 1980s and previously thought to be Oviraptor. It had a forward-sloping cassowary-like crest.

Conchoraptor gracilis is a small crestless form with a slender second toe. Many specimens have been referred to it, but there have been no detailed studies showing exactly which ones are correctly referred.

Khaan mckennai is another taxon that closely resembles Conchoraptor, but has a reduced third finger. It lived alongside Citipati.

"Ingenia" yanshini has also had a lot of material referred to it that probably doesn't belong. It was contemporaneous with Conchoraptor, and work needs to be done separating their remains from each other. "Ingenia"s hand is distinguished by a very large first finger and reduced second and third fingers. The name "Ingenia" is preoccupied and will be replaced in the near future.

Heyuannia huangi is the first named oviraptorid from China and resembles Ingenia closely, but is distinguished by having more hip vertebrae and the first finger fused with the wrist.

Other possible oviraptorids include Nomingia gobienisis, Shixinggia oblita, and the early Microvenator celer. All three have been suggested to be oviraptorids, caenagnathids, or more primitive than either group.

The eating habits of these animals are not fully known, but some appear to have been at least partially carnivorous, eating small vertebrates such as lizards and juvenile or nestling dinosaurs. Evidence for this comes from a lizard skeleton preserved in the body cavity of the type specimen of Oviraptor and two hatchling Byronosaurus skulls found in a Citipati nest. Some scientists have also suggested that some oviraptorids included of plant material, eggs, and/or mollusks in their diet.

Originally, oviraptorids were thought to be specialized egg raiders, based on a Mongolian find showing Oviraptor on top of a nest erroneously attributed to the ceratopsian dinosaur Protoceratops. However, discoveries in the 1990s, including Citipati specimens clearly brooding (rather than predating) the same types of nests, and a Citipati embryo inside the same type of egg preserved in these nests, showed that the "specialized egg thief" idea was incorrect, though oviraptorids may have eaten eggs as part of an omnivorous diet.

Although fossilized dinosaur eggs are generally rare, oviraptorid eggs are relatively well known. Several oviraptorid nests, eggs, and embryos are known, mostly uncovered in the Gobi Desert. Some specimens of the Oviraptor philoceratops and Citipati osmolskae have been found in brooding positions. described in 1999, All of the nesting specimens are situated on top of egg clutches, with their limbs spread symmetrically on each side of the nest, front limbs covering the nest perimeter. This brooding posture is found today only in birds and supports a behavioral link between birds and theropod dinosaurs.

Oviraptorid eggs are shaped like elongated ovals (elongatoolithid) and resemble the eggs of ratite birds (such as ostriches) in texture and shell structure. In the nest, eggs are typically found in pairs and arranged in concentric circles of up to three layers, with complete clutches consisting of as many of 22 eggs in some species. The eggs of Citipati are the largest known definitive oviraptorid eggs, at 18 cm. In contrast, eggs associated with Oviraptor are only up to 14 cm long.

Conchoraptor (meaning "conch plunderer") was an oviraptorid dinosaur from the late Cretaceous Period of what is now Asia. Its name reflects the hypothesis that oviraptorids, rather than preying primarily upon eggs as had been traditionally thought, may have been specialized to feed on mollusks.

Conchoraptor was a small dinosaur, of only 1-2 meters (4-6 feet) in length. Unlike many other oviraptorids, Conchoraptor lacked a head crest, although it did lack teeth, a typical oviraptorid characteristic. Instead of teeth, oviraptorids had powerful beaks, possibly adapted to crushing mollusc shells.

When first discovered in the Nemegt Formation during the 1970s, scientists believed that Conchoraptor was a juvenile Oviraptor and that the animal's missing crest would have begun to grow when the animal reaching sexual maturity. Further study of multiple skeletons showed that Conchoraptor belonged in a new genus.

The type species of this new genus, Conchoraptor gracilis, was described by Barsbold, in 1986. Conchoraptor's hands were a major reason that scientists decided to split it off from Oviraptor. Anatomically the hands seemed to be an evolutionary intermediate between those of "Ingenia" and Oviraptor, making it obvious that this animal was not a member of a known species

Khaan (pronounced Mongol IPA: [χaːŋ], etymology: Derived from the Mongolian for 'lord') was an oviraptorid dinosaur about four feet long that was found in the Djadochta Formation of Mongolia and lived in the Late Cretaceous Period, 70 million years ago.

Khaan did not differ much from other oviraptorids. At first, its remains were assigned to "Ingenia", but the Khaan manual structure differs sufficiently from that of "Ingenia" for it to be assigned to its own genus. Among oviraptorids, it was probably more closely related to Conchoraptor.

Like other oviraptorids, Khaan was probably at least partially a meat eater, feeding on small vertebrates like mammals, lizards and possibly other small dinosaurs. It was also probably feathered.

Pyroraptor

Pyroraptor is a genus of dromaeosaurid dinosaur from the late Cretaceous Period of France. It is known from a single specimen.

Pyroraptor was a dromaeosaurid, a small, bird-like predatory theropod that possessed enlarged curved, slashing claws on the second toe of each foot. Each of these claws were 6.5 centimeters (2.5 in) long. The only identified specimen was found in 1992 in the south of France, in Provence, and is known only from a few bones, named Pyroraptor olympius by Allain and Taquet in 2000. The name means "Olympic fire thief", because its remains were discovered after a forest fire. The type specimen consists of the distinctive foot claws, as well as fossilized teeth, arm and back bones. It lived during the late Campanian and early Maastrichtian faunal stages of the Late Cretaceous, approximately 70.6 million years ago.Pyroraptor was featured in one episode of the television program Dinosaur Planet, in which an individual Pyroraptor named "Pod" is swept onto an island dominated by dwarf members of familiar dinosaur families.

Dromaeosauridae was first defined as a clade by Paul Sereno in 1998, as the most inclusive natural group containing Dromaeosaurus but not Troodon, Ornithomimus or Passer. The various "subfamilies" have also been re-defined as clades, usually defined as all species closer to the groups namesake than to Dromaeosaurus or any namesakes of other sub-clades (for example, Makovicky defined the clade Unenlagiinae as all dromaeosaurids closer to Unenlagia than to Velociraptor). The Microraptoria is the only dromaeosaurid sub-clade not converted from a subfamily. Senter and colleagues expressly coined the name without the subfamily suffix -inae to avoid perceived issues with erecting a traditional family-group taxon, should the group be found to lie outside dromaeosauridae proper. Sereno offered a revised definition of the sub-group containing Microraptor to ensure that it would fall within Dromaeosauridae, and erected the subfamily Microraptorinae, attributing it to Senter et al., though this usage has only appeared on his online TaxonSearch database and has not been formally published.

The cladogram below follows a 2009 analysis by paleontologists Nicholas Longrich and Philip J. Currie.

Dromaeosaurs are diagnosed by the following features; short T-shaped frontals that form the rostral boundary of the supratemporal fenestra; a caudolateral overhanging shelf of the squamosal; a lateral process of the quadrate that contacts the quadratojugal; raised, stalked, parapophyses on the dorsal vertebrae, a modified pedal digit II; chevrons and prezygapophyses of the caudal vertebrae elongate and spanning several vertebrae; the presence of a subglenoid fossa on the coracoid.Caenagnathidae ("recent jaws," as derived from Greek kainos and gnathos) is a family of bird-like maniraptoran theropod dinosaurs within the clade Oviraptorosauria, first coined as an order of advanced flightless birds by Charles Hazelius Sternberg in 1940. While more advanced than earlier oviraptorosaurs like Caudipteryx, caenagnathids were fairly primitive compared with their close relatives the oviraptorids, though this by no means reduces the distinct variation and unique nature of the group. Whereas oviraptorids had highly shortened snouts, caenagnathid jaws were long and shallow with an elongated dentary and extended symphysis. Indeed, the jaw of a caenagnathid is its most distinctive feature, historically, whose surface and internal structure is distinct from that of other dinosaurs, including oviraptorids. Caenagnathids are best known for their cranial anatomy, but the earliest forms are known from their postcrania alone, and include such novel features as a fused ankle (as also seen in similar and possibly related Avimimus portentosus), an extremely short tail, possibly with a pygostyle as in Nomingia gobiensis, and with exceptionally slender and long legs, giving them a gracile, long-legged appearance that may have resembled some of the smaller ratite birds, such as the emu.

The name Caenagnathus (and hence Caenagnathidae) means "recent jaws"--when first discovered, it was thought that caenagnathids were close relatives of paleognath birds (such as the ostrich) based on features of the lower jaw. Since it would be unusual to find a recent group of birds in the Cretaceous, the name "recent jaws" was applied. Most paleontologists, however, now think that the birdlike features of the jaw were acquired convergently with modern birds.The family Caenagnathidae, together with its sister group the Oviraptoridae, comprises the superfamily Caenagnathoidea. In phylogenetic taxonomy, the clade Caenagnathidae is defined as the most inclusive group containing Chirostenotes pergracilis but not Oviraptor philoceratops. While in the past twenty years, only about two to six species were commonly recognized as belonging to the Caenagnathidae, currently that number may be much greater, with new discoveries and theories about older species that may inflate this number to up to ten. Much of this historical difference centers on the first caenagnathid to be described, Chirostenotes pergracilis. Due to the poor preservation of most caenagnathid remains and resulting misidentifications, different bones and different specimens of Chirostenotes have historically been assigned to a number of different species. For example, the feet of one species, named Macrophalangia canadensis,[6] were known from the same region from which Chirostenotes pergracilis was recovered, but the discovery of a new specimen with both hands and feet preserved provided the support to combine them, while the later discovery of a partial skull with hands and feet suggested that Chirostenotes and Caenagnathus were the same animal. While Caenagnathus collinsi is today considered to be a junior synonym of Chirostenotes pergracilis by most researchers, it was the first for which a family was named, so while the genus name Caenagnathus is no longer in use, the family name Caenagnathidae remains valid due to its inclusion of Caenagnathus.

Today, Caenagnathidae usually contains six species in three genera. However, a few paleontologists consider Elmisaurus elegans to be a junior synonym of Chirostenotes sternbergi, as they both occur in the same North American locality, far from the Asian species Elmisaurus rarus . The genus Caenagnathasia martinsoni was originally placed in this family, but it is probably more primitive, lying outside both Caenagnathidae and Oviraptoridae within the superfamily Caenagnathoidea. Additionally, Maryańska, Osmólska, and Wołsan considered the oviraptorosaur with a pygostyle, Nomingia gobiensis, a member of this family.

Caenagnathidae includes -

Chirostenotes pergracilis, the first known caenagnathid, described initially from two hands and a partial lower arm. Many subsequently named species have been referred to this species, including a single foot named Macrophalangia canadensis[6], adding to the known fossil material.

Chirostenotes sternbergi, a more gracile caenagnathid. Some consider Elmisaurus elegans to be the same animal, as both are smaller and more slender than Chirostenotes pergracilis. It is also possible that this species represents a different gender of the larger C. pergracilis specimens.

Chirostenotes sp., a possible new species, has been identified from part of a lower jaw found in Montana, but not named.

Elmisaurus rarus, the only known Asian caenagnathid (excluding Caenagnathasia martinsoni), is known only from elements of the foot.

Elmisaurus elegans, a smaller Canadian species originally described as a species of Ornithomimus. It may be the same species as Chirostenotes sternbergi, as noted above.

The "Triebold caenagnathid", a possible new species or genus collected by Triebold Paleontology of South Dakota, known from two excellently preserved partial specimens acquired by the Carnegie Museums of Pittsburgh. An apparently giant species with a well preserved skull and evidence of an oviraptorid-like crest, it is currently awaiting a published description. Oviraptoridae is a group of bird-like maniraptoran dinosaurs. They are currently known from Mongolia and China, although there is an unpublished report from Montana. These animals were small, measuring up to 2 m long in most cases. Definitive oviraptorids first appeared in the Cenomanian stage of the late Cretaceous Period, although the possible oviraptorid Microvenator is known from the Aptian stage of the Early Cretaceous Period. The family became extinct at the end of the Maastrichtian stage.

Hagryphus giganteus, discovered most recently, is a fairly large and over-assuming yet seldom mentioned species from Upper Cretaceous beds in Utah, USA (and is roughly the same age as Chirostenotes pergacilis

The most characteristic feature of this group is the skull structure. Oviraptorids had short snouts and very deep mandibles. Some taxa (Oviraptor, Citipati, Rinchenia) had a midline crest on top of the skull, resembling that of a cassowary. Other distinguishing characters include a bony spike intruding on the mandibular fenestra, nostrils placed very high and far back on the snout, an extremely thin bony bar beneath the eye, and highly pneumatized skull bones. Like their relatives the caenagnathids, the jaws were edentulous (with no teeth), having instead two small bony projections on the top jaw.

Oviraptoridae includes -

Gigantoraptor erlianensis, the largest oviraptorid, at 8 meters in length.

Oviraptor philoceratops, from the Late Cretaceous of Mongolia. Found in 1924, it has a longer snout and seemingly extensive crest on its head. Most illustrations of it are actually based on Citipati sp..

Rinchenia mongoliensis was originally called Oviraptor mongoliensis. It had a very high crest on the center of its head, and is from the Late Cretaceous of Mongolia as well.

Nemegtomaia barsboldi, originally named Nemegtia and once assigned to "Ingenia", is probably a close relative of Citipati, known from excellent skull material.

Citipati osmolskae was named based on several well-known specimens, including nesting adults, eggs, and an embryo. It had an anteriorly-placed crest and lived at the same time and place as Oviraptor.

Citipati sp., a specimen recently referred to the genus Citipati, was found in the 1980s and previously thought to be Oviraptor. It had a forward-sloping cassowary-like crest.

Conchoraptor gracilis is a small crestless form with a slender second toe. Many specimens have been referred to it, but there have been no detailed studies showing exactly which ones are correctly referred.

Khaan mckennai is another taxon that closely resembles Conchoraptor, but has a reduced third finger. It lived alongside Citipati.

"Ingenia" yanshini has also had a lot of material referred to it that probably doesn't belong. It was contemporaneous with Conchoraptor, and work needs to be done separating their remains from each other. "Ingenia"s hand is distinguished by a very large first finger and reduced second and third fingers. The name "Ingenia" a crimeajewel insignia ,is preoccupied and will be replaced in the near future.

Heyuannia huangi is the first named oviraptorid from China and resembles Ingenia closely, but is distinguished by having more hip vertebrae and the first finger fused with the wrist.

Other possible oviraptorids include Nomingia gobienisis, Shixinggia oblita, and the early Microvenator celer. All three have been suggested to be oviraptorids, caenagnathids, or more primitive than either group.

The eating habits of these animals are not fully known, but some appear to have been at least partially carnivorous, eating small vertebrates such as lizards and juvenile or nestling dinosaurs. Evidence for this comes from a lizard skeleton preserved in the body cavity of the type specimen of Oviraptor and two hatchling Byronosaurus skulls found in a Citipati nest. Some scientists have also suggested that some oviraptorids included of plant material, eggs, and/or mollusks in their diet.

Originally, oviraptorids were thought to be specialized egg raiders, based on a Mongolian find showing Oviraptor on top of a nest erroneously attributed to the ceratopsian dinosaur Protoceratops. However, discoveries in the 1990s, including Citipati specimens clearly brooding (rather than predating) the same types of nests, and a Citipati embryo inside the same type of egg preserved in these nests, showed that the "specialized egg thief" idea was incorrect, though oviraptorids may have eaten eggs as part of an omnivorous diet.

Although fossilized dinosaur eggs are generally rare, oviraptorid eggs are relatively well known. Several oviraptorid nests, eggs, and embryos are known, mostly uncovered in the Gobi Desert. Some specimens of the Oviraptor philoceratops and Citipati osmolskae have been found in brooding positions. described in 1999, All of the nesting specimens are situated on top of egg clutches, with their limbs spread symmetrically on each side of the nest, front limbs covering the nest perimeter. This brooding posture is found today only in birds and supports a behavioral link between birds and theropod dinosaurs.

Oviraptorid eggs are shaped like elongated ovals (elongatoolithid) and resemble the eggs of ratite birds (such as ostriches) in texture and shell structure. In the nest, eggs are typically found in pairs and arranged in concentric circles of up to three layers, with complete clutches consisting of as many of 22 eggs in some species. The eggs of Citipati are the largest known definitive oviraptorid eggs, at 18 cm. In contrast, eggs associated with Oviraptor are only up to 14 cm long.

Ironically, it was the association with eggs that gave oviraptorids their name (which means 'egg thieves'). The first oviraptorid eggs (of the genus Oviraptor) were found in close proximity to the remains of the ceratopsian dinosaur Protoceratops and it was assumed that the oviraptorids were preying upon the eggs of the ceratopsians. It was not until 1993, when a Citipati embryo was discovered inside an egg of the type assigned to Protoceratops, that the error was corrected. Norell et al., who recognized the embryo as oviraptorid, assigned it to the genus Citipati. The egg containing the embryo was smaller than most known Citipati eggs at only 12 cm, though it was partially eroded and broken into three pieces, making an accurate estimate of its original size difficult.The embryo-bearing egg was otherwise identical to other oviraptorid eggs in shell structure and was found in an isolated nest, again arranged in a circular pattern.

An oviraptorosaurian specimen from China described in 2005 was found to have two unlaid eggs within the pelvic canal. This suggests that, unlike modern crocodilians, oviraptorosaurs did not produce and lay many eggs at the same time. Rather, the eggs were produced within the reproductive organs in pairs, and laid two at a time, with the mother positioned in the center of the nest and rotating in a circle as each pair was laid. This behavior is supported by the fact that the eggs oval shape, with the more narrow end pointing backward from the birth canal, matching their orientation toward the center of the nest after being laid.

The presence of two shelled eggs within the birth canal shows that oviraptorosaurs were intermediate between the reproductive biology of crocodilians and modern birds. Like crocodilians, they had two oviducts. However, crocodilians produce multiple shelled eggs per oviduct at a time, whereas oviraptorosaurs, like birds, produced only one egg per oviduct at a time.

Oviraptorids were probably feathered, since some close relatives were found with feathers preserved (Caudipteryx and possibly Protarchaeopteryx). Another finding pointing to this is the discovery in Nomingia of a pygostyle, a bone that results from the fusion of the last tail vertebrae and is responsible in birds to hold a fan of feathers in the tail. Finally, the arm position of the brooding Citipati would have been far more effective if feathers were present to cover the eggs.

Oviraptoridae is a group of bird-like maniraptoran dinosaurs. They are currently known from Mongolia and China, although there is an unpublished report from Montana. These animals were small, measuring up to 2 m long in most cases. Definitive oviraptorids first appeared in the Cenomanian stage of the late Cretaceous Period, although the possible oviraptorid Microvenator is known from the Aptian stage of the Early Cretaceous Period. The family became extinct at the end of the Maastrichtian stage.

The most characteristic feature of this group is the skull structure. Oviraptorids had short snouts and very deep mandibles. Some taxa (Oviraptor, Citipati, Rinchenia) had a midline crest on top of the skull, resembling that of a cassowary. Other distinguishing characters include a bony spike intruding on the mandibular fenestra, nostrils placed very high and far back on the snout, an extremely thin bony bar beneath the eye, and highly pneumatized skull bones. Like their relatives the caenagnathids, the jaws were edentulous (with no teeth), having instead two small bony projections on the top jaw.

Heyuannia ("Heyuan one") is a genus of oviraptorid dinosaur that lived during the Late Cretaceous Period in China. It was the first oviraptorid found in that country (most lived in neighbouring Mongolia). It had very short arms and digits, and its first digit was reduced.

The type species, Heyuannia huangi, was described by Lü in 2002. Multiple fossils have been found, including one which may retain possible reproductive organs.

Oviraptoridae includes -

Gigantoraptor erlianensis, the largest oviraptorid, at 8 meters in length.

Oviraptor philoceratops, from the Late Cretaceous of Mongolia. Found in 1924, it has a longer snout and seemingly extensive crest on its head. Most illustrations of it are actually based on Citipati sp..

Rinchenia mongoliensis was originally called Oviraptor mongoliensis. It had a very high crest on the center of its head, and is from the Late Cretaceous of Mongolia as well.

Nemegtomaia barsboldi, originally named Nemegtia and once assigned to "Ingenia", is probably a close relative of Citipati, known from excellent skull material.

Citipati osmolskae was named based on several well-known specimens, including nesting adults, eggs, and an embryo. It had an anteriorly-placed crest and lived at the same time and place as Oviraptor.

Citipati sp., a specimen recently referred to the genus Citipati, was found in the 1980s and previously thought to be Oviraptor. It had a forward-sloping cassowary-like crest.

Conchoraptor gracilis is a small crestless form with a slender second toe. Many specimens have been referred to it, but there have been no detailed studies showing exactly which ones are correctly referred.

Khaan mckennai is another taxon that closely resembles Conchoraptor, but has a reduced third finger. It lived alongside Citipati.

"Ingenia" yanshini has also had a lot of material referred to it that probably doesn't belong. It was contemporaneous with Conchoraptor, and work needs to be done separating their remains from each other. "Ingenia"s hand is distinguished by a very large first finger and reduced second and third fingers. The name "Ingenia" is preoccupied and will be replaced in the near future.

Heyuannia huangi is the first named oviraptorid from China and resembles Ingenia closely, but is distinguished by having more hip vertebrae and the first finger fused with the wrist.

Other possible oviraptorids include Nomingia gobienisis, Shixinggia oblita, and the early Microvenator celer. All three have been suggested to be oviraptorids, caenagnathids, or more primitive than either group.

The eating habits of these animals are not fully known, but some appear to have been at least partially carnivorous, eating small vertebrates such as lizards and juvenile or nestling dinosaurs. Evidence for this comes from a lizard skeleton preserved in the body cavity of the type specimen of Oviraptor and two hatchling Byronosaurus skulls found in a Citipati nest. Some scientists have also suggested that some oviraptorids included of plant material, eggs, and/or mollusks in their diet.

Originally, oviraptorids were thought to be specialized egg raiders, based on a Mongolian find showing Oviraptor on top of a nest erroneously attributed to the ceratopsian dinosaur Protoceratops. However, discoveries in the 1990s, including Citipati specimens clearly brooding (rather than predating) the same types of nests, and a Citipati embryo inside the same type of egg preserved in these nests, showed that the "specialized egg thief" idea was incorrect, though oviraptorids may have eaten eggs as part of an omnivorous diet.

Although fossilized dinosaur eggs are generally rare, oviraptorid eggs are relatively well known. Several oviraptorid nests, eggs, and embryos are known, mostly uncovered in the Gobi Desert. Some specimens of the Oviraptor philoceratops and Citipati osmolskae have been found in brooding positions. described in 1999, All of the nesting specimens are situated on top of egg clutches, with their limbs spread symmetrically on each side of the nest, front limbs covering the nest perimeter. This brooding posture is found today only in birds and supports a behavioral link between birds and theropod dinosaurs.

Oviraptorid eggs are shaped like elongated ovals (elongatoolithid) and resemble the eggs of ratite birds (such as ostriches) in texture and shell structure. In the nest, eggs are typically found in pairs and arranged in concentric circles of up to three layers, with complete clutches consisting of as many of 22 eggs in some species. The eggs of Citipati are the largest known definitive oviraptorid eggs, at 18 cm. In contrast, eggs associated with Oviraptor are only up to 14 cm long.

Conchoraptor (meaning "conch plunderer") was an oviraptorid dinosaur from the late Cretaceous Period of what is now Asia. Its name reflects the hypothesis that oviraptorids, rather than preying primarily upon eggs as had been traditionally thought, may have been specialized to feed on mollusks.

Conchoraptor was a small dinosaur, of only 1-2 meters (4-6 feet) in length. Unlike many other oviraptorids, Conchoraptor lacked a head crest, although it did lack teeth, a typical oviraptorid characteristic. Instead of teeth, oviraptorids had powerful beaks, possibly adapted to crushing mollusc shells.

When first discovered in the Nemegt Formation during the 1970s, scientists believed that Conchoraptor was a juvenile Oviraptor and that the animal's missing crest would have begun to grow when the animal reaching sexual maturity. Further study of multiple skeletons showed that Conchoraptor belonged in a new genus.

The type species of this new genus, Conchoraptor gracilis, was described by Barsbold, in 1986. Conchoraptor's hands were a major reason that scientists decided to split it off from Oviraptor. Anatomically the hands seemed to be an evolutionary intermediate between those of "Ingenia" and Oviraptor, making it obvious that this animal was not a member of a known species

Khaan (pronounced Mongol IPA: [χaːŋ], etymology: Derived from the Mongolian for 'lord') was an oviraptorid dinosaur about four feet long that was found in the Djadochta Formation of Mongolia and lived in the Late Cretaceous Period, 70 million years ago.

Khaan did not differ much from other oviraptorids. At first, its remains were assigned to "Ingenia", but the Khaan manual structure differs sufficiently from that of "Ingenia" for it to be assigned to its own genus. Among oviraptorids, it was probably more closely related to Conchoraptor.

Like other oviraptorids, Khaan was probably at least partially a meat eater, feeding on small vertebrates like mammals, lizards and possibly other small dinosaurs. It was also probably feathered.

Pyroraptor

Pyroraptor is a genus of dromaeosaurid dinosaur from the late Cretaceous Period of France. It is known from a single specimen.

Pyroraptor was a dromaeosaurid, a small, bird-like predatory theropod that possessed enlarged curved, slashing claws on the second toe of each foot. Each of these claws were 6.5 centimeters (2.5 in) long. The only identified specimen was found in 1992 in the south of France, in Provence, and is known only from a few bones, named Pyroraptor olympius by Allain and Taquet in 2000. The name means "Olympic fire thief", because its remains were discovered after a forest fire. The type specimen consists of the distinctive foot claws, as well as fossilized teeth, arm and back bones. It lived during the late Campanian and early Maastrichtian faunal stages of the Late Cretaceous, approximately 70.6 million years ago.Pyroraptor was featured in one episode of the television program Dinosaur Planet, in which an individual Pyroraptor named "Pod" is swept onto an island dominated by dwarf members of familiar dinosaur families.

Dromaeosauridae was first defined as a clade by Paul Sereno in 1998, as the most inclusive natural group containing Dromaeosaurus but not Troodon, Ornithomimus or Passer. The various "subfamilies" have also been re-defined as clades, usually defined as all species closer to the groups namesake than to Dromaeosaurus or any namesakes of other sub-clades (for example, Makovicky defined the clade Unenlagiinae as all dromaeosaurids closer to Unenlagia than to Velociraptor). The Microraptoria is the only dromaeosaurid sub-clade not converted from a subfamily. Senter and colleagues expressly coined the name without the subfamily suffix -inae to avoid perceived issues with erecting a traditional family-group taxon, should the group be found to lie outside dromaeosauridae proper. Sereno offered a revised definition of the sub-group containing Microraptor to ensure that it would fall within Dromaeosauridae, and erected the subfamily Microraptorinae, attributing it to Senter et al., though this usage has only appeared on his online TaxonSearch database and has not been formally published.

The cladogram below follows a 2009 analysis by paleontologists Nicholas Longrich and Philip J. Currie.

Dromaeosaurs are diagnosed by the following features; short T-shaped frontals that form the rostral boundary of the supratemporal fenestra; a caudolateral overhanging shelf of the squamosal; a lateral process of the quadrate that contacts the quadratojugal; raised, stalked, parapophyses on the dorsal vertebrae, a modified pedal digit II; chevrons and prezygapophyses of the caudal vertebrae elongate and spanning several vertebrae; the presence of a subglenoid fossa on the coracoid.Caenagnathidae ("recent jaws," as derived from Greek kainos and gnathos) is a family of bird-like maniraptoran theropod dinosaurs within the clade Oviraptorosauria, first coined as an order of advanced flightless birds by Charles Hazelius Sternberg in 1940. While more advanced than earlier oviraptorosaurs like Caudipteryx, caenagnathids were fairly primitive compared with their close relatives the oviraptorids, though this by no means reduces the distinct variation and unique nature of the group. Whereas oviraptorids had highly shortened snouts, caenagnathid jaws were long and shallow with an elongated dentary and extended symphysis. Indeed, the jaw of a caenagnathid is its most distinctive feature, historically, whose surface and internal structure is distinct from that of other dinosaurs, including oviraptorids. Caenagnathids are best known for their cranial anatomy, but the earliest forms are known from their postcrania alone, and include such novel features as a fused ankle (as also seen in similar and possibly related Avimimus portentosus), an extremely short tail, possibly with a pygostyle as in Nomingia gobiensis, and with exceptionally slender and long legs, giving them a gracile, long-legged appearance that may have resembled some of the smaller ratite birds, such as the emu.

The name Caenagnathus (and hence Caenagnathidae) means "recent jaws"--when first discovered, it was thought that caenagnathids were close relatives of paleognath birds (such as the ostrich) based on features of the lower jaw. Since it would be unusual to find a recent group of birds in the Cretaceous, the name "recent jaws" was applied. Most paleontologists, however, now think that the birdlike features of the jaw were acquired convergently with modern birds.The family Caenagnathidae, together with its sister group the Oviraptoridae, comprises the superfamily Caenagnathoidea. In phylogenetic taxonomy, the clade Caenagnathidae is defined as the most inclusive group containing Chirostenotes pergracilis but not Oviraptor philoceratops. While in the past twenty years, only about two to six species were commonly recognized as belonging to the Caenagnathidae, currently that number may be much greater, with new discoveries and theories about older species that may inflate this number to up to ten. Much of this historical difference centers on the first caenagnathid to be described, Chirostenotes pergracilis. Due to the poor preservation of most caenagnathid remains and resulting misidentifications, different bones and different specimens of Chirostenotes have historically been assigned to a number of different species. For example, the feet of one species, named Macrophalangia canadensis,[6] were known from the same region from which Chirostenotes pergracilis was recovered, but the discovery of a new specimen with both hands and feet preserved provided the support to combine them, while the later discovery of a partial skull with hands and feet suggested that Chirostenotes and Caenagnathus were the same animal. While Caenagnathus collinsi is today considered to be a junior synonym of Chirostenotes pergracilis by most researchers, it was the first for which a family was named, so while the genus name Caenagnathus is no longer in use, the family name Caenagnathidae remains valid due to its inclusion of Caenagnathus.

Today, Caenagnathidae usually contains six species in three genera. However, a few paleontologists consider Elmisaurus elegans to be a junior synonym of Chirostenotes sternbergi, as they both occur in the same North American locality, far from the Asian species Elmisaurus rarus . The genus Caenagnathasia martinsoni was originally placed in this family, but it is probably more primitive, lying outside both Caenagnathidae and Oviraptoridae within the superfamily Caenagnathoidea. Additionally, Maryańska, Osmólska, and Wołsan considered the oviraptorosaur with a pygostyle, Nomingia gobiensis, a member of this family.

Caenagnathidae includes -

Chirostenotes pergracilis, the first known caenagnathid, described initially from two hands and a partial lower arm. Many subsequently named species have been referred to this species, including a single foot named Macrophalangia canadensis[6], adding to the known fossil material.

Chirostenotes sternbergi, a more gracile caenagnathid. Some consider Elmisaurus elegans to be the same animal, as both are smaller and more slender than Chirostenotes pergracilis. It is also possible that this species represents a different gender of the larger C. pergracilis specimens.

Chirostenotes sp., a possible new species, has been identified from part of a lower jaw found in Montana, but not named.

Elmisaurus rarus, the only known Asian caenagnathid (excluding Caenagnathasia martinsoni), is known only from elements of the foot.

Elmisaurus elegans, a smaller Canadian species originally described as a species of Ornithomimus. It may be the same species as Chirostenotes sternbergi, as noted above.

The "Triebold caenagnathid", a possible new species or genus collected by Triebold Paleontology of South Dakota, known from two excellently preserved partial specimens acquired by the Carnegie Museums of Pittsburgh. An apparently giant species with a well preserved skull and evidence of an oviraptorid-like crest, it is currently awaiting a published description. Oviraptoridae is a group of bird-like maniraptoran dinosaurs. They are currently known from Mongolia and China, although there is an unpublished report from Montana. These animals were small, measuring up to 2 m long in most cases. Definitive oviraptorids first appeared in the Cenomanian stage of the late Cretaceous Period, although the possible oviraptorid Microvenator is known from the Aptian stage of the Early Cretaceous Period. The family became extinct at the end of the Maastrichtian stage.

Hagryphus giganteus, discovered most recently, is a fairly large and over-assuming yet seldom mentioned species from Upper Cretaceous beds in Utah, USA (and is roughly the same age as Chirostenotes pergacilis

The most characteristic feature of this group is the skull structure. Oviraptorids had short snouts and very deep mandibles. Some taxa (Oviraptor, Citipati, Rinchenia) had a midline crest on top of the skull, resembling that of a cassowary. Other distinguishing characters include a bony spike intruding on the mandibular fenestra, nostrils placed very high and far back on the snout, an extremely thin bony bar beneath the eye, and highly pneumatized skull bones. Like their relatives the caenagnathids, the jaws were edentulous (with no teeth), having instead two small bony projections on the top jaw.

Oviraptoridae includes -

Gigantoraptor erlianensis, the largest oviraptorid, at 8 meters in length.

Oviraptor philoceratops, from the Late Cretaceous of Mongolia. Found in 1924, it has a longer snout and seemingly extensive crest on its head. Most illustrations of it are actually based on Citipati sp..

Rinchenia mongoliensis was originally called Oviraptor mongoliensis. It had a very high crest on the center of its head, and is from the Late Cretaceous of Mongolia as well.

Nemegtomaia barsboldi, originally named Nemegtia and once assigned to "Ingenia", is probably a close relative of Citipati, known from excellent skull material.

Citipati osmolskae was named based on several well-known specimens, including nesting adults, eggs, and an embryo. It had an anteriorly-placed crest and lived at the same time and place as Oviraptor.

Citipati sp., a specimen recently referred to the genus Citipati, was found in the 1980s and previously thought to be Oviraptor. It had a forward-sloping cassowary-like crest.

Conchoraptor gracilis is a small crestless form with a slender second toe. Many specimens have been referred to it, but there have been no detailed studies showing exactly which ones are correctly referred.

Khaan mckennai is another taxon that closely resembles Conchoraptor, but has a reduced third finger. It lived alongside Citipati.

"Ingenia" yanshini has also had a lot of material referred to it that probably doesn't belong. It was contemporaneous with Conchoraptor, and work needs to be done separating their remains from each other. "Ingenia"s hand is distinguished by a very large first finger and reduced second and third fingers. The name "Ingenia" a crimeajewel insignia ,is preoccupied and will be replaced in the near future.

Heyuannia huangi is the first named oviraptorid from China and resembles Ingenia closely, but is distinguished by having more hip vertebrae and the first finger fused with the wrist.

Other possible oviraptorids include Nomingia gobienisis, Shixinggia oblita, and the early Microvenator celer. All three have been suggested to be oviraptorids, caenagnathids, or more primitive than either group.

The eating habits of these animals are not fully known, but some appear to have been at least partially carnivorous, eating small vertebrates such as lizards and juvenile or nestling dinosaurs. Evidence for this comes from a lizard skeleton preserved in the body cavity of the type specimen of Oviraptor and two hatchling Byronosaurus skulls found in a Citipati nest. Some scientists have also suggested that some oviraptorids included of plant material, eggs, and/or mollusks in their diet.

Originally, oviraptorids were thought to be specialized egg raiders, based on a Mongolian find showing Oviraptor on top of a nest erroneously attributed to the ceratopsian dinosaur Protoceratops. However, discoveries in the 1990s, including Citipati specimens clearly brooding (rather than predating) the same types of nests, and a Citipati embryo inside the same type of egg preserved in these nests, showed that the "specialized egg thief" idea was incorrect, though oviraptorids may have eaten eggs as part of an omnivorous diet.

Although fossilized dinosaur eggs are generally rare, oviraptorid eggs are relatively well known. Several oviraptorid nests, eggs, and embryos are known, mostly uncovered in the Gobi Desert. Some specimens of the Oviraptor philoceratops and Citipati osmolskae have been found in brooding positions. described in 1999, All of the nesting specimens are situated on top of egg clutches, with their limbs spread symmetrically on each side of the nest, front limbs covering the nest perimeter. This brooding posture is found today only in birds and supports a behavioral link between birds and theropod dinosaurs.

Oviraptorid eggs are shaped like elongated ovals (elongatoolithid) and resemble the eggs of ratite birds (such as ostriches) in texture and shell structure. In the nest, eggs are typically found in pairs and arranged in concentric circles of up to three layers, with complete clutches consisting of as many of 22 eggs in some species. The eggs of Citipati are the largest known definitive oviraptorid eggs, at 18 cm. In contrast, eggs associated with Oviraptor are only up to 14 cm long.

Ironically, it was the association with eggs that gave oviraptorids their name (which means 'egg thieves'). The first oviraptorid eggs (of the genus Oviraptor) were found in close proximity to the remains of the ceratopsian dinosaur Protoceratops and it was assumed that the oviraptorids were preying upon the eggs of the ceratopsians. It was not until 1993, when a Citipati embryo was discovered inside an egg of the type assigned to Protoceratops, that the error was corrected. Norell et al., who recognized the embryo as oviraptorid, assigned it to the genus Citipati. The egg containing the embryo was smaller than most known Citipati eggs at only 12 cm, though it was partially eroded and broken into three pieces, making an accurate estimate of its original size difficult.The embryo-bearing egg was otherwise identical to other oviraptorid eggs in shell structure and was found in an isolated nest, again arranged in a circular pattern.

An oviraptorosaurian specimen from China described in 2005 was found to have two unlaid eggs within the pelvic canal. This suggests that, unlike modern crocodilians, oviraptorosaurs did not produce and lay many eggs at the same time. Rather, the eggs were produced within the reproductive organs in pairs, and laid two at a time, with the mother positioned in the center of the nest and rotating in a circle as each pair was laid. This behavior is supported by the fact that the eggs oval shape, with the more narrow end pointing backward from the birth canal, matching their orientation toward the center of the nest after being laid.

The presence of two shelled eggs within the birth canal shows that oviraptorosaurs were intermediate between the reproductive biology of crocodilians and modern birds. Like crocodilians, they had two oviducts. However, crocodilians produce multiple shelled eggs per oviduct at a time, whereas oviraptorosaurs, like birds, produced only one egg per oviduct at a time.

Oviraptorids were probably feathered, since some close relatives were found with feathers preserved (Caudipteryx and possibly Protarchaeopteryx). Another finding pointing to this is the discovery in Nomingia of a pygostyle, a bone that results from the fusion of the last tail vertebrae and is responsible in birds to hold a fan of feathers in the tail. Finally, the arm position of the brooding Citipati would have been far more effective if feathers were present to cover the eggs.

Oviraptoridae is a group of bird-like maniraptoran dinosaurs. They are currently known from Mongolia and China, although there is an unpublished report from Montana. These animals were small, measuring up to 2 m long in most cases. Definitive oviraptorids first appeared in the Cenomanian stage of the late Cretaceous Period, although the possible oviraptorid Microvenator is known from the Aptian stage of the Early Cretaceous Period. The family became extinct at the end of the Maastrichtian stage.

The most characteristic feature of this group is the skull structure. Oviraptorids had short snouts and very deep mandibles. Some taxa (Oviraptor, Citipati, Rinchenia) had a midline crest on top of the skull, resembling that of a cassowary. Other distinguishing characters include a bony spike intruding on the mandibular fenestra, nostrils placed very high and far back on the snout, an extremely thin bony bar beneath the eye, and highly pneumatized skull bones. Like their relatives the caenagnathids, the jaws were edentulous (with no teeth), having instead two small bony projections on the top jaw.

Heyuannia ("Heyuan one") is a genus of oviraptorid dinosaur that lived during the Late Cretaceous Period in China. It was the first oviraptorid found in that country (most lived in neighbouring Mongolia). It had very short arms and digits, and its first digit was reduced.

The type species, Heyuannia huangi, was described by Lü in 2002. Multiple fossils have been found, including one which may retain possible reproductive organs.

Oviraptoridae includes -

Gigantoraptor erlianensis, the largest oviraptorid, at 8 meters in length.

Oviraptor philoceratops, from the Late Cretaceous of Mongolia. Found in 1924, it has a longer snout and seemingly extensive crest on its head. Most illustrations of it are actually based on Citipati sp..

Rinchenia mongoliensis was originally called Oviraptor mongoliensis. It had a very high crest on the center of its head, and is from the Late Cretaceous of Mongolia as well.

Nemegtomaia barsboldi, originally named Nemegtia and once assigned to "Ingenia", is probably a close relative of Citipati, known from excellent skull material.

Citipati osmolskae was named based on several well-known specimens, including nesting adults, eggs, and an embryo. It had an anteriorly-placed crest and lived at the same time and place as Oviraptor.

Citipati sp., a specimen recently referred to the genus Citipati, was found in the 1980s and previously thought to be Oviraptor. It had a forward-sloping cassowary-like crest.

Conchoraptor gracilis is a small crestless form with a slender second toe. Many specimens have been referred to it, but there have been no detailed studies showing exactly which ones are correctly referred.

Khaan mckennai is another taxon that closely resembles Conchoraptor, but has a reduced third finger. It lived alongside Citipati.

"Ingenia" yanshini has also had a lot of material referred to it that probably doesn't belong. It was contemporaneous with Conchoraptor, and work needs to be done separating their remains from each other. "Ingenia"s hand is distinguished by a very large first finger and reduced second and third fingers. The name "Ingenia" is preoccupied and will be replaced in the near future.

Heyuannia huangi is the first named oviraptorid from China and resembles Ingenia closely, but is distinguished by having more hip vertebrae and the first finger fused with the wrist.

Other possible oviraptorids include Nomingia gobienisis, Shixinggia oblita, and the early Microvenator celer. All three have been suggested to be oviraptorids, caenagnathids, or more primitive than either group.

The eating habits of these animals are not fully known, but some appear to have been at least partially carnivorous, eating small vertebrates such as lizards and juvenile or nestling dinosaurs. Evidence for this comes from a lizard skeleton preserved in the body cavity of the type specimen of Oviraptor and two hatchling Byronosaurus skulls found in a Citipati nest. Some scientists have also suggested that some oviraptorids included of plant material, eggs, and/or mollusks in their diet.

Originally, oviraptorids were thought to be specialized egg raiders, based on a Mongolian find showing Oviraptor on top of a nest erroneously attributed to the ceratopsian dinosaur Protoceratops. However, discoveries in the 1990s, including Citipati specimens clearly brooding (rather than predating) the same types of nests, and a Citipati embryo inside the same type of egg preserved in these nests, showed that the "specialized egg thief" idea was incorrect, though oviraptorids may have eaten eggs as part of an omnivorous diet.

Although fossilized dinosaur eggs are generally rare, oviraptorid eggs are relatively well known. Several oviraptorid nests, eggs, and embryos are known, mostly uncovered in the Gobi Desert. Some specimens of the Oviraptor philoceratops and Citipati osmolskae have been found in brooding positions. described in 1999, All of the nesting specimens are situated on top of egg clutches, with their limbs spread symmetrically on each side of the nest, front limbs covering the nest perimeter. This brooding posture is found today only in birds and supports a behavioral link between birds and theropod dinosaurs.

Oviraptorid eggs are shaped like elongated ovals (elongatoolithid) and resemble the eggs of ratite birds (such as ostriches) in texture and shell structure. In the nest, eggs are typically found in pairs and arranged in concentric circles of up to three layers, with complete clutches consisting of as many of 22 eggs in some species. The eggs of Citipati are the largest known definitive oviraptorid eggs, at 18 cm. In contrast, eggs associated with Oviraptor are only up to 14 cm long.

Conchoraptor (meaning "conch plunderer") was an oviraptorid dinosaur from the late Cretaceous Period of what is now Asia. Its name reflects the hypothesis that oviraptorids, rather than preying primarily upon eggs as had been traditionally thought, may have been specialized to feed on mollusks.

Conchoraptor was a small dinosaur, of only 1-2 meters (4-6 feet) in length. Unlike many other oviraptorids, Conchoraptor lacked a head crest, although it did lack teeth, a typical oviraptorid characteristic. Instead of teeth, oviraptorids had powerful beaks, possibly adapted to crushing mollusc shells.

When first discovered in the Nemegt Formation during the 1970s, scientists believed that Conchoraptor was a juvenile Oviraptor and that the animal's missing crest would have begun to grow when the animal reaching sexual maturity. Further study of multiple skeletons showed that Conchoraptor belonged in a new genus.

The type species of this new genus, Conchoraptor gracilis, was described by Barsbold, in 1986. Conchoraptor's hands were a major reason that scientists decided to split it off from Oviraptor. Anatomically the hands seemed to be an evolutionary intermediate between those of "Ingenia" and Oviraptor, making it obvious that this animal was not a member of a known species

Khaan (pronounced Mongol IPA: [χaːŋ], etymology: Derived from the Mongolian for 'lord') was an oviraptorid dinosaur about four feet long that was found in the Djadochta Formation of Mongolia and lived in the Late Cretaceous Period, 70 million years ago.

Khaan did not differ much from other oviraptorids. At first, its remains were assigned to "Ingenia", but the Khaan manual structure differs sufficiently from that of "Ingenia" for it to be assigned to its own genus. Among oviraptorids, it was probably more closely related to Conchoraptor.

Like other oviraptorids, Khaan was probably at least partially a meat eater, feeding on small vertebrates like mammals, lizards and possibly other small dinosaurs. It was also probably feathered.