This is an accepted version of this page
129-463: For classification of genera, see text Eudromaeosauria ("true dromaeosaurs") is a subgroup of terrestrial dromaeosaurid theropod dinosaurs . They were small to large-sized predators that flourished during the Cretaceous Period . Eudromaeosaur fossils are known almost exclusively from the northern hemisphere. They first appeared in the early Cretaceous Period and survived until
258-518: A 2006 analysis which used both direct observation of skeletal muscle correlates and phylogenetic inferences based on extant taxa. Among modern birds , tinamous and neognaths are believed to have had shoulder anatomy most similar to eudromaeosaurs, whereas most ratites are believed to have secondarily lost a significant amount of shoulder mobility. The skeletons of several eudromaeosaurs, including Velociraptor and Saurornitholestes , were compared and preserved many elements homologous with
387-709: A 2015 analysis by DePalma et al. using updated data from the Theropod Working Group. Rahonavis Buitreraptor Unenlagia Sinornithosaurus [REDACTED] Microraptor [REDACTED] NGMC 91 [REDACTED] Bambiraptor [REDACTED] Tianyuraptor Adasaurus Tsaagan Saurornitholestes Velociraptor [REDACTED] Deinonychus [REDACTED] Atrociraptor [REDACTED] Achillobator [REDACTED] Utahraptor [REDACTED] Dakotaraptor [REDACTED] Dromaeosaurus [REDACTED] Another cladogram constructed below follows
516-585: A change in the preferred prey of dromaeosaurs that existed from the Early Cretaceous to the Late Cretaceous . Eudromaeosaur skulls are also relatively solid in comparison to their primitive coelurosaur ancestors (i.e. they had smaller paranasal sinuses ). In particular, the skull pneumaticity of oviraptorosaurs , which share a common ancestor with both birds and eudromaeosaurs is much higher than in any eudromaeosaurs. A 2021 survey of
645-473: A definition similar to "all theropods closer to birds than to Deinonychus ", with Troodon being sometimes added as a second external specifier in case it is closer to birds than to Deinonychus . Avialae is also occasionally defined as an apomorphy-based clade (that is, one based on physical characteristics). Jacques Gauthier , who named Avialae in 1986, re-defined it in 2001 as all dinosaurs that possessed feathered wings used in flapping flight , and
774-608: A few more primitive archosaurs. The dinosaurs they examined included three dromaeosaurs — the microraptorians Microraptor and Sinornithosaurus and the eudromaeosaur Velociraptor . The evidence they found, based on comparisons with extant species, suggested that Velociraptor was primarily active during the night. They also found that Protoceratops (a known prey animal for Velociraptor ) would likely have been most active at dawn and dusk, suggesting that encounters between these animals would have mostly occurred around these times. Schmitz and Motani also found that Microraptor
903-402: A flying ancestor for dromaeosaurids are sometimes called "Birds Came First" (BCF). George Olshevsky is usually credited as the first author of BCF. In his own work, Gregory S. Paul pointed out numerous features of the dromaeosaurid skeleton that he interpreted as evidence that the entire group had evolved from flying, dinosaurian ancestors, perhaps an animal like Archaeopteryx . In that case,
1032-468: A gradual change in morphology. This condition is called a "Type-2 Transition", to contrast with the similarly bifurcated, but morphologically distinct, "Type-1 Transition" seen in ornithomimosaurs . Eudromaeosaur skulls have been characterized in the scientific literature as being relatively conservative in comparison to their maniraptoran relatives. The skulls had few pneumatic spaces, especially in comparison to birds and oviraptorosaurs and retained
1161-483: A great deal of study, and hypotheses about that relationship have changed as large amounts of new evidence became available. As late as 2001, Mark Norell and colleagues analyzed a large survey of coelurosaur fossils and produced the tentative result that dromaeosaurids were most closely related to birds, with troodontids as a more distant outgroup. They even suggested that Dromaeosauridae could be paraphyletic relative to Avialae. In 2002, Hwang and colleagues utilized
1290-442: A group called Paraves . Some basal members of Deinonychosauria, such as Microraptor , have features which may have enabled them to glide or fly. The most basal deinonychosaurs were very small. This evidence raises the possibility that the ancestor of all paravians may have been arboreal , have been able to glide, or both. Unlike Archaeopteryx and the non-avialan feathered dinosaurs, who primarily ate meat, studies suggest that
1419-517: A group of bizarre creatures with long fingers and necks, a large number of small teeth, and possible semiaquatic habits. Another enigmatic group, Unenlagiinae, is the most poorly supported subfamily of dromaeosaurids and it is possible that some or all of its members belong outside of Dromaeosauridae. The larger, ground-dwelling members like Buitreraptor and Unenlagia show strong flight adaptations, although they were probably too large to 'take off'. One possible member of this group, Rahonavis ,
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#17327875491361548-422: A large, recurved claw on the second toe. Their tails were slender, with long, low, vertebrae lacking transverse process and neural spines after the 14th caudal vertebra. Ossified uncinate processes of ribs have been identified in several dromaeosaurids. Like other theropods, dromaeosaurids were bipedal; that is, they walked on their hind legs. However, whereas most theropods walked with three toes contacting
1677-400: A lower average metabolic rate than these modern animals. In a 2023 study of the skull anatomy of several extinct and extant theropods used computed tomography to model the volumes of their nasal cavities and compare them to the volumes of the skulls as a whole. These were subjected to a regression analysis which recovered a relationship between these two volumes and the efficiency of
1806-415: A part of the "Deinodontidae" (now named Tyrannosauridae ). Today, Dromaeosaurinae has been formally defined as a monophyletic group including Dromaeosaurus and all the other dromaeosaurs closer to it than to Velociraptor , Microraptor , Passer and Unenlagia . This group was also moved to be within its own family, Dromaeosauridae , which was named when it became apparent that Dromaeosaurus
1935-471: A primitive palatine , unreversed hallux , and hyper-extendable second toe. Their phylogenetic analysis produced the controversial result that Confuciusornis was closer to Microraptor than to Archaeopteryx , making the Avialae a paraphyletic taxon. They also suggested that the ancestral paravian was able to fly or glide, and that the dromaeosaurids and troodontids were secondarily flightless (or had lost
2064-479: A relatively linear fashion on the line towards birds, which was suggested by Michael Hanson and colleagues to be a paedomorphic adaptation to hear the high-pitched vocalizations of juveniles of the same species. This line of evidence is also used to suggest that parental care evolved early in the evolution of archosaurs, and therefore would have been present in eudromaeosaurs. The high-pitched calls of juvenile dromaeosaurs would have been distinct and differentiable to
2193-519: 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 extensive cladistic analysis conducted by Turner et al. (2012) further supported the monophyly of Dromaeosauridae. The cladogram below follows
2322-402: A single hand. Other functional uses for the arms and hands such as carrying objects with both hands, maintain balance, or bring objects to its mouth to feed could not be falsified. Velociraptor , despite being known from very complete remains, has not had its forelimb mobility extensively studied because most of the specimens are preserved fully articulated and have not been fully removed from
2451-406: A sister group, the order Crocodilia , contain the only living representatives of the reptile clade Archosauria . During the late 1990s, Aves was most commonly defined phylogenetically as all descendants of the most recent common ancestor of modern birds and Archaeopteryx lithographica . However, an earlier definition proposed by Jacques Gauthier gained wide currency in the 21st century, and
2580-620: A tail-spanning fan, both of which are unexpected traits that may offer an understanding of the integument of large dromaeosaurids. Dakotaraptor is an even larger dromaeosaurid species with evidence of feathers, albeit indirect in the form of quill knobs, though the taxon is considered as chimeara by other researchers as even the dinosaurian elements with supposed traits diagnostic for dromaeosaurs also referrable to caenagnathids and ornithomimosaurians . Dromaeosaurids share many features with early birds (clade Avialae or Aves ). The precise nature of their relationship to birds has undergone
2709-543: A term popularized by the film Jurassic Park ; several genera include the term "raptor" directly in their name, and popular culture has come to emphasize their bird-like appearance and speculated bird-like behavior. Dromaeosaurid fossils have been found across the globe in North America , Europe , Africa , Asia and South America , with some fossils giving credence to the possibility that they inhabited Australia as well. The earliest body fossils are known from
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#17327875491362838-717: A time, sometimes for years, and rarely for life. Other species have breeding systems that are polygynous (one male with many females) or, rarely, polyandrous (one female with many males). Birds produce offspring by laying eggs which are fertilised through sexual reproduction . They are usually laid in a nest and incubated by the parents. Most birds have an extended period of parental care after hatching. Many species of birds are economically important as food for human consumption and raw material in manufacturing, with domesticated and undomesticated birds being important sources of eggs, meat, and feathers. Songbirds , parrots, and other species are popular as pets. Guano (bird excrement)
2967-438: A variety of specialized ecological niches, mainly those of small predators or specialized piscivores , eudromaeosaurs functioned as hypercarnivores and are suggested to have been predators of medium- to large-sized prey. Aside from their generally larger size, eudromaeosaurs are also characterized by several features of the foot. The subfamily Dromaeosaurinae was first erected in 1922 by William Matthew and Barnum Brown as
3096-623: A wide range of pterosaurs, birds, and non-avian dinosaurs. Among their sample were the taxa Tsaagan , Linheraptor , Dromaeosaurus , and Velociraptor , whose sensory capabilities were assessed using the morphology of their scleral rings and the endosseous cochlear ducts (ECDs) of their inner-ears. Similarly to the Schmitz and Motani analysis, Velociraptor was found to be highly adapted for nocturnality; it had large scleral diameter and elongated ECDs, which suggest high visual acuity and very sensetive hearing. Both of these are consistent with
3225-441: 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 Greek δρομαῖος ( dromaîos ), meaning 'running at full speed', 'swift', and σαῦρος ( saûros ), meaning 'lizard'. In informal usage, they are often called raptors (after Velociraptor ),
3354-584: Is a large body of evidence showing that dromaeosaurids were covered in feathers . Some dromaeosaurid fossils preserve long, pennaceous feathers on the hands and arms ( remiges ) and tail ( rectrices ), as well as shorter, down-like feathers covering the body. Other fossils, which do not preserve actual impressions of feathers, still preserve the associated bumps on the forearm bones where long wing feathers would have attached in life. Overall, this feather pattern looks very much like Archaeopteryx . The first known dromaeosaurid with definitive evidence of feathers
3483-420: Is also believed to have exhibited considerable shoulder mobility due to the morphology of the scapular glenoid which, when coupled with the expanded muscle attachment sites near the wrists of these juveniles, may have enabled a mechanism approaching the "flapping" capabilities of birds. The general morphology of the upper-body in juvenile Deinonychus , including the longer bones and the increased robustness in
3612-516: Is an adaptation to improve the strength and robustness of the legs for the purpose of using their feet during predation. Aside from their generally larger size when compared to earlier-diverging dromaeosaurids, eudromaeosaurs are characterized by several features of the foot. First, differences existed in the positions of the grooves that anchored blood vessels and keratin sheathes of the toe claws. In primitive dromaeosaurids like Hesperonychus , these grooves ran parallel to each other on either side of
3741-540: Is called ornithology . Birds are feathered theropod dinosaurs and constitute the only known living dinosaurs . Likewise, birds are considered reptiles in the modern cladistic sense of the term, and their closest living relatives are the crocodilians . Birds are descendants of the primitive avialans (whose members include Archaeopteryx ) which first appeared during the Late Jurassic . According to recent estimates, modern birds ( Neornithes ) evolved in
3870-407: Is consistent with the loss of pneumatic elements in the facial bones of eudromaeosaurs, which have been suggested to be adaptations for subduing and feeding on large prey. In velociraptorine taxa, the structure of the fenestrae in the skull are adapted for dispersing the strain of any force exerted on it throughout the skull, which leads to less strain on each of the individual points of leverage on
3999-557: Is curved horizontally in a long S-shape. This suggests that, in life, the tail could bend from side to side with a substantial degree of flexibility. It has been proposed that this tail was used as a stabilizer or counterweight while running or in the air; in Microraptor , an elongate diamond-shaped fan of feathers is preserved on the end of the tail. This may have been used as an aerodynamic stabilizer and rudder during gliding or powered flight (see "Flight and gliding" below). There
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4128-429: Is harvested for use as a fertiliser. Birds figure throughout human culture. About 120 to 130 species have become extinct due to human activity since the 17th century, and hundreds more before then. Human activity threatens about 1,200 bird species with extinction, though efforts are underway to protect them. Recreational birdwatching is an important part of the ecotourism industry. The first classification of birds
4257-503: Is not considered a direct ancestor of birds, though it is possibly closely related to the true ancestor. Over 40% of key traits found in modern birds evolved during the 60 million year transition from the earliest bird-line archosaurs to the first maniraptoromorphs , i.e. the first dinosaurs closer to living birds than to Tyrannosaurus rex . The loss of osteoderms otherwise common in archosaurs and acquisition of primitive feathers might have occurred early during this phase. After
4386-516: Is synonymous to Avifilopluma. † Scansoriopterygidae † Eosinopteryx † Jinfengopteryx † Aurornis † Dromaeosauridae † Troodontidae Avialae Based on fossil and biological evidence, most scientists accept that birds are a specialised subgroup of theropod dinosaurs and, more specifically, members of Maniraptora , a group of theropods which includes dromaeosaurids and oviraptorosaurs , among others. As scientists have discovered more theropods closely related to birds,
4515-576: Is that those known from Asia have typically narrower skulls than those in North America. This is generally attributed to a phylogenetic difference (most Asian eudromaeosaurs are considered to be velociraptorines), but an analysis by Mark Powers and colleagues in 2020 demonstrated that dromaeosaur snouts in general increased in length during the Cretaceous . The reason for this is not fully understood, but it has been suggested that this reflects
4644-446: Is unclear. Compared to other clades of theropods , eudromaeosaurs exhibited relatively little variation in the dimensions of their skulls. Some researchers have suggested that this is a result of their relatively conservative ecology. According to this estimation, most eudromaeosaurs are hypercarnivores of prey similar in size or larger than themselves, which imposes constraints on the functionally effective range of skull shapes. In
4773-535: Is used by many scientists including adherents to the PhyloCode . Gauthier defined Aves to include only the crown group of the set of modern birds. This was done by excluding most groups known only from fossils , and assigning them, instead, to the broader group Avialae, on the principle that a clade based on extant species should be limited to those extant species and their closest extinct relatives. Gauthier and de Queiroz identified four different definitions for
4902-533: Is very small, with well-developed wings that show evidence of quill knobs (the attachment points for flight feathers) and it is very likely that it could fly. The next most primitive clade of dromaeosaurids is the Microraptoria. This group includes many of the smallest dromaeosaurids, which show adaptations for living in trees. All known dromaeosaurid skin impressions hail from this group and all show an extensive covering of feathers and well-developed wings. Like
5031-471: The Protoceratops , leading to both animals being killed. In 2011, Denver Fowler and colleagues proposed a use for the sickle claws of eudromaeosaurs that they called "raptor prey restraint" (or RPR). According to this model, the primary function of eudromaeosaur claws would be to pin down and immobilize smaller prey animals while they are killed and dismembered by the mouth. The shift towards use of
5160-593: The Isle of Wight , England . The teeth appear to have belonged to an animal similar in size to the North American genus Utahraptor , but the morphology of the teeth suggests that the large size may only be homoplastic . Remains from giant eudromaeosaurs are also reported from the Bissekty and Bayan Shireh formations. The main difference in the skull morphology of eudromaeosaur species that has been observed
5289-658: The Late Cretaceous and diversified dramatically around the time of the Cretaceous–Paleogene extinction event 66 million years ago, which killed off the pterosaurs and all non- ornithuran dinosaurs. Many social species preserve knowledge across generations ( culture ). Birds are social, communicating with visual signals, calls, and songs , and participating in such behaviour as cooperative breeding and hunting, flocking , and mobbing of predators. The vast majority of bird species are socially (but not necessarily sexually) monogamous , usually for one breeding season at
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5418-633: The Prince Creek Formation of Alaska also has implications for their reproductive strategy. Young individuals with multiple lines of arrested growth indicates that these animals were living within the Arctic Circle year-round and were non-migratory. This suggests that eudromaeosaurs were capable of nesting and brooding in the high arctic. Dromaeosauridae This is an accepted version of this page Dromaeosauridae ( / ˌ d r ɒ m i . ə ˈ s ɔːr ɪ d iː / )
5547-669: The Tiaojishan Formation of China, which has been dated to the late Jurassic period ( Oxfordian stage), about 160 million years ago. The avialan species from this time period include Anchiornis huxleyi , Xiaotingia zhengi , and Aurornis xui . The well-known probable early avialan, Archaeopteryx , dates from slightly later Jurassic rocks (about 155 million years old) from Germany . Many of these early avialans shared unusual anatomical features that may be ancestral to modern birds but were later lost during bird evolution. These features include enlarged claws on
5676-449: The co-ossification of the three distal-most carpal bones . This condition allows for the hand to be folded flat against the ulna in order to hold their wings close to the body. The resting position of the elbow would likely have been an extremely acute angle for eudromaeosaurs, with the wings held close to the body, but not fully folded in the manner of modern birds. The mobility capabilities of eudromaeosaur arms were reconstructed in
5805-476: The laying of hard-shelled eggs, a high metabolic rate, a four-chambered heart , and a strong yet lightweight skeleton . Birds live worldwide and range in size from the 5.5 cm (2.2 in) bee hummingbird to the 2.8 m (9 ft 2 in) common ostrich . There are over 11,000 living species and they are split into 44 orders . More than half are passerine or "perching" birds. Birds have wings whose development varies according to species;
5934-409: The origin of flapping in paravians . It has also been suggested that juvenile eudromaeosaurs may have been able to glide or display some aerial capabilities. This is based on the disproportionately long arm bones seen in juvenile specimens of Deinonychus . This likely would not include volant adeptness seen in modern birds due to the limited forearm mobility of the dromaeosaur arm. Deinonychus
6063-430: The premaxillae , maxillae , nasals , lacrimals , and jugals of several eudromaeosaurs was conducted in an attempt to reconstruct the ancestral condition of facial pneumaticity for coelurosaurs. The pneumatic elements of all five bones show a marked decline from basal coelurosaurs to derived paravians , with eudromaeosaurs completely lacking pneumatic spaces in their premaxillae. The reason for this evolutionary trend
6192-414: The troodontid AMNH FARB 6631 are almost identical to those found in the eggs of emus. This suggests that the ancestral color of eggs in pennaraptorans , including eudromaeosaurs, was likely bluish-green in coloration. The cause of this evolutionary change is uncertain, but it has been suggested to be an adaptation for camouflage from predators. The finding of very young juvenile eudromaeosaur remains in
6321-589: The unenlagiines ( Austroraptor , which measured 5–6 m (16–20 ft) long). A possible third lineage of giant dromaeosaurids is represented by isolated teeth found on the Isle of Wight , England . The teeth belong to an animal the size of the dromaeosaurine Utahraptor , but they appear to belong to velociraptorines, judging by the shape of the teeth. The distinctive dromaeosaurid body plan helped to rekindle theories that dinosaurs may have been active, fast, and closely related to birds. Robert Bakker 's illustration for John Ostrom 's 1969 monograph, showing
6450-462: The Avialae, and these two points suggested that the ancestral dromaeosaurid could not glide or fly. Based on this cladistic analysis, Mahakala suggests that the ancestral condition for dromaeosaurids is non- volant . However, in 2012, an expanded and revised study incorporating the most recent dromaeosaurid finds recovered the Archaeopteryx -like Xiaotingia as the most primitive member of
6579-615: The Early Cretaceous (145–140 million years ago), and they survived until the end of the Cretaceous ( Maastrichtian stage, 66 ma), existing until the Cretaceous–Paleogene extinction event . The presence of dromaeosaurids as early as the Middle Jurassic has been suggested by the discovery of isolated fossil teeth, though no dromaeosaurid body fossils have been found from this period. Dromaeosaurids are diagnosed by
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#17327875491366708-502: The Lianhe Formation near Ganzhou in southern China and were attributed to a droameosaur based on the microstructure of the eggshell and the similarities to the putative Deinonychus eggs listed above. Based on this morphology, the authors of the description of Gannanoolithus suggested that the existing oogenera Paraelongatoolithus and Elipsoolithus may also belong to dromaeosaurs, rather than oviraptorosaurs (which
6837-459: The ability to glide). Corfe and Butler criticized this work on methodological grounds. A challenge to all of these alternative scenarios came when Turner and colleagues in 2007 described a new dromaeosaurid, Mahakala , which they found to be the most basal and most primitive member of the Dromaeosauridae, more primitive than Microraptor . Mahakala had short arms and no ability to glide. Turner et al. also inferred that flight evolved only in
6966-428: The appearance of Maniraptoromorpha, the next 40 million years marked a continuous reduction of body size and the accumulation of neotenic (juvenile-like) characteristics. Hypercarnivory became increasingly less common while braincases enlarged and forelimbs became longer. The integument evolved into complex, pennaceous feathers . The oldest known paravian (and probably the earliest avialan) fossils come from
7095-426: The arm musculature of both Sphenosuchus and Archaeopteryx , implying a relatively conservative archosaur shoulder musculature. One major difference found was that Dromaeosaurus and some similar taxa possibly possessed relatively strong biceps compared to other maniraptorans of a similar size. The arm function of Deinonychus and Saurornitholestes has also been studied in detail in order to infer
7224-511: The backs of larger prey, piercing prey's weak-points (i.e. the neck and belly), pinning down smaller prey to feed, intraspecific combat, and scratch-digging for small prey. Bishop's analysis concluded that the leg musculature of Deinonychus — and by extension other eudroameosaurs — was most conducive to the use of their claws to hold-down smaller prey to kill or feed on them. This supports the earlier-proposed raptor prey restraint method of killing prey from Fowler and colleagues. He also found that
7353-410: The basal position of Microraptor , along with feather and wing features, as evidence that the ancestral dromaeosaurid could glide. In that case the larger dromaeosaurids would be secondarily terrestrial—having lost the ability to glide later in their evolutionary history. Also in 2002, Steven Czerkas described Cryptovolans , though it is a probable junior synonym of Microraptor . He reconstructed
7482-509: The birds that descended from them. Despite being currently one of the most widely used, the crown-group definition of Aves has been criticised by some researchers. Lee and Spencer (1997) argued that, contrary to what Gauthier defended, this definition would not increase the stability of the clade and the exact content of Aves will always be uncertain because any defined clade (either crown or not) will have few synapomorphies distinguishing it from its closest relatives. Their alternative definition
7611-580: The bone encase the caudal vertebrae and form a rod-like structure. In some derived dromaeosaurines — namely Achillobator , Utahraptor , and Yurgovuchia — the caudotheca are reduced in length in comparison with related taxa. The caudotheca were initially suggested by John Ostrom to have been formed by the ossification of tendons in the tail, but this has not been supported by modern researchers. The tails of non-avian paravians , including eudromaeosaurs, are composed of vertebrae of two different shapes. The anterior caudal vertebrae are very typical of
7740-553: The bones of relatively small prey. All eudromaeosaurs (and coelurosaurs in general) are presumed to have been endotherms . The presence of feathers has been suggested to have been an adaptation initially developed for insulation, which would be of limited use to fully ectothermic organisms. Therefore, the presence of feathers can probably be used to indirectly infer the presence of endothermy. However, eudromaeosaurs were likely not as efficient in their thermoregulation as modern mammals or birds and were believed to have possessed
7869-476: The clade Dromaeosauridae, which appears to suggest the earliest members of the clade may have been capable of flight. The authorship of the family Dromaeosauridae is credited to William Diller Matthew and Barnum Brown , who erected it as a subfamily (Dromaeosaurinae) of the family Deinodontidae in 1922, containing only the new genus Dromaeosaurus . The subfamilies of Dromaeosauridae frequently shift in content based on new analysis, but typically consist of
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#17327875491367998-421: 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
8127-432: The claw along its length. In eudromaeosaurs, the grooves were asymmetrical, with the inner one split into two distinct grooves and elevated toward the top of the claw, while the single outer groove remained positioned at the midline. The second distinguishing characteristic of eudromaeosaurs is an expanded and enlarged "heel" on the last bone in the second toe (phalanx), which bore the enlarged, sickle-like toe claw. Finally,
8256-399: The closely-related microraptorian dromaeosaurids. Most of these taxa possessed short femora with long tibiae and metatarsals, which are generally accepted to have been adaptations for cursoriality. Conversely, eudromaeosaurs had long femora and tibiae but relatively short metatarsals. The exact reasons for these adaptations are not fully understood, but some authors have suggested that this
8385-408: The discovery of Tsaagan lent support to this grouping, the inclusion of Deinonychus , Saurornitholestes, and a few other genera is still uncertain. The Dromaeosaurinae is usually found to consist of medium to giant-sized species, with generally box-shaped skulls (the other subfamilies generally have narrower snouts). The following classification of the various genera of dromaeosaurids follows
8514-438: The dromaeosaurid Deinonychus in a fast run, is among the most influential paleontological reconstructions in history. The dromaeosaurid body plan includes a relatively large skull, serrated teeth, narrow snout (an exception being the derived dromaeosaurines ), and forward-facing eyes which indicate some degree of binocular vision. Dromaeosaurids, like most other theropods, had a moderately long S-curved neck, and their trunk
8643-433: The dromaeosaurines Achillobator , at around 6 metres (20 ft), and Utahraptor at up to 7 metres (23 ft). The largest eudromaeosaurs are estimated to have been more than 200 kilograms (440 lb) in mass. At least one velociraptorine taxon may have achieved gigantic sizes comparable to those found among the dromaeosaurines . So far, this unnamed giant velociraptorine is known only from isolated teeth found on
8772-665: The earliest members of Aves, is removed from this group, becoming a non-avian dinosaur instead. These proposals have been adopted by many researchers in the field of palaeontology and bird evolution , though the exact definitions applied have been inconsistent. Avialae, initially proposed to replace the traditional fossil content of Aves, is often used synonymously with the vernacular term "bird" by these researchers. † Coelurus † Ornitholestes † Ornithomimosauria † Alvarezsauridae † Oviraptorosauria Paraves Most researchers define Avialae as branch-based clade, though definitions vary. Many authors have used
8901-481: The eggs found associated with the Deinonychus specimen AMNH 3015. This partial skeleton was identified as Deinonychus based on the shape of the preserved gastralia , and it was believed to have been brooding when it was killed and fossilized. The eggs were confirmed to be the eggs of theropods based on the microstructure of their shells, which were similar to the eggs of the oviraptorid Citipati , and
9030-569: The end of the Cretaceous ( Maastrichtian stage, 66 Ma). The earliest known definitive eudromaeosaur is the probable dromaeosaurine Yurgovuchia , from the Cedar Mountain Formation , dated to 139 million years ago. However, the earlier (143-million-year-old) fossils such as those of Nuthetes and several indeterminate teeth dating to the Kimmeridgian stage may represent eudromaeosaurs. While other dromaeosaurids filled
9159-473: The estimated total range of motion for the arms. The remains of these genera were modeled, articulated, and measured based on the morphology of the articular surfaces of the limb bones. Several functional hypotheses were suggested and the results of the modeling were used to falsify these hypotheses. It was inferred from this analysis that it was impossible for eudromaeosaurs to use their hands to dig, scratch themselves, probe small crevices, or carry objects with
9288-458: The eudromaeosaur Deinonychus in order to model possible functions for the hypertrophied second pedal claw. They expressed doubt in John Ostrom 's original suggestion that the claws were used as slashing weapons, and the experiment they conducted using the robotic leg seemed to confirm that the claws were very efective at piercing but relatively ineffective at creating gashes once a surface
9417-479: The feet as primary weapons of predation was suggested to be a result of the increasingly specialized wing anatomy of paravians . However, the wing anatomy was suggested to have a secondary role in feeding; they were suggested to be used as a means of stabilizing the eudromaeosaur while it fed on struggling prey. A point of indirect evidence for this behavior is that this method of predation is employed by many extant birds-of-prey. Peter Bishop performed an analysis of
9546-451: The first avialans were omnivores . The Late Jurassic Archaeopteryx is well known as one of the first transitional fossils to be found, and it provided support for the theory of evolution in the late 19th century. Archaeopteryx was the first fossil to display both clearly traditional reptilian characteristics—teeth, clawed fingers, and a long, lizard-like tail—as well as wings with flight feathers similar to those of modern birds. It
9675-461: The first bone of the second toe also possessed an enlarged expansion at the joint, another adaptation relating to the unusually enlarged claw, and which helped the animal hold the claw high off the ground. Also unlike their more basal relatives, the sickle claw of eudromaeosaurs was sharper and more blade-like. In unenlagiines and microraptorines , the claw is broader at its base. One of the most archetypal eudromaeosaurs, Deinonychus antirrhopus ,
9804-584: The first direct evidence that eudromaeosaurs had feathers. In the years since, similar indirect evidence of feathers in true eudromaeosaurs has been found for the genera Dakotaraptor and Dineobellator . Today, it is generally believed that most, if not all coelurosaurs had a coat of filamentous feathers. Based on the available evidence it is likely that all paravians and oviraptorosaurs (and possibly ornithomimosaurs ) had pennaceous wing feathers on their arms. The leg proportions of eudromaeosaurs differed considerably from other maniraptorans and also from
9933-423: 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 prezygapophysis of the caudal vertebrae elongate and spanning several vertebrae;
10062-415: The following groups. A number of dromaeosaurids have not been assigned to any particular subfamily, often because they are too poorly preserved to be placed confidently in phylogenetic analysis (see section Phylogeny below) or are indeterminate, being assigned to different groups depending on the methodology employed in different papers. The most basal known subfamily of dromaeosaurids is Halszkaraptorinae,
10191-436: The foot musculature of Deinonychus in 2019 which sought to examine a wider variety of possible functional uses for their pedal claws. A digital model of the leg of the animal was examined under several conditions to estimate the muscular optimization of different postures as a proxy for inferring potential in-life behaviors. The possible uses examined were slash-kicking prey, hanging onto the sides of larger prey, pouncing onto
10320-470: The fossil inaccurately with only two wings and thus argued that dromaeosaurids were powered fliers, rather than passive gliders. He later issued a revised reconstruction in agreement with that of Microraptor Other researchers, like Larry Martin , have proposed that dromaeosaurids, along with all maniraptorans, were not dinosaurs at all. Martin asserted for decades that birds were unrelated to maniraptorans, but in 2004 he changed his position, agreeing that
10449-529: The ground or 'retracted' when walking), which is thought to have been used in capturing prey and climbing trees (see "Claw function" below). This claw was especially blade-like in the large-bodied predatory eudromaeosaurs . One possible dromaeosaurid species, Balaur bondoc , also possessed a first toe which was highly modified in parallel with the second. Both the first and second toes on each foot of B. bondoc were also held retracted and bore enlarged, sickle-shaped claws. Dromaeosaurids had long tails. Most of
10578-402: The ground, fossilized footprint tracks confirm that many early paravian groups, including the dromaeosaurids, held the second toe off the ground in a hyperextended position, with only the third and fourth toes bearing the weight of the animal. This is called functional didactyly. The enlarged second toe bore an unusually large, curved, falciform (sickle-shaped, alt. drepanoid ) claw (held off
10707-402: The hypothesis that Deinonychus was adapted to hunt large prey (especially the sympatric ornithopod Tenontosaurus ) due to a suggested relatively high bite force and slow bite speed. The same analysis recovered a relatively high mechanical advantage for the skull of Dromaeosaurus and a high resistance to bending, both of which are associated with tackling large vertebrate prey. This
10836-403: The iconic sickle-shaped pedal claw that resembles the talons of birds of prey , from which many dromaeosaurs derive their names ("raptor" being a common generic suffix). This unique morphology has led to considerable speculation regarding the possible in-life function of the dromaeosaur foot. In 2005, a group of researchers led by Philip Manning constructed a robotic reconstruction of the leg of
10965-497: The larger dromaeosaurids lost some or all of their insulatory covering, the discovery of feathers in Velociraptor specimens has been cited as evidence that all members of the family retained feathers. More recently, the discovery of Zhenyuanlong established the presence of a full feathered coat in relatively large dromaeosaurids. Additionally, the animal displays proportionally large, aerodynamic wing feathers, as well as
11094-433: The larger dromaeosaurids were secondarily flightless, like the modern ostrich . In 1988, Paul suggested that dromaeosaurids may actually be more closely related to modern birds than to Archaeopteryx . By 2002, however, Paul placed dromaeosaurids and Archaeopteryx as the closest relatives to one another. In 2002, Hwang et al. found that Microraptor was the most primitive dromaeosaurid. Xu and colleagues in 2003 cited
11223-478: The morphology of a nocturnal predator. The closely-related Linheraptor was also suggested to have adaptations for nocturnality, although the ECDs of Linheraptor are not preserved. Dromaeosaurus and Tsaagan were found to have only limited elongation in their ECDs, comparable to some nocturnal birds, but ECD length and nocturnality do not appear to be very tightly correlated. Archosaur cochlear shape elongated in
11352-682: The most recently-named subfamily, typically consists of smaller species with shortened snouts. A number of eudromaeosaurs have not been assigned to any particular subfamily, because they are too poorly preserved to be placed confidently in phylogenetic analysis. Most eudromaeosaur genera are known from only 1-2 specimens. The major exceptions to this are Deinonychus , Utahraptor , Saurornitholestes , Velociraptor , and Dromaeosaurus , which are each known from multiple reasonably-complete specimens. Eudromaeosaurs were all bipedal and had relatively long arms in comparison to other theropods , like most other maniraptorans . Their wrists exhibited
11481-420: The nasal passage as a thermoregulatory apparatus. Under this analysis, the eudromaeosaur tested, Velociraptor , was suggested to have been capable of much less efficient nasal thermoregulation than modern birds. This is consistent with earlier suggestions that dromaeosaurs had a lower metabolic rate than modern birds. Like most paravians , eudromaeosaurs possessed a highly derived semilunate carpal formed by
11610-523: The only known groups without wings are the extinct moa and elephant birds . Wings, which are modified forelimbs , gave birds the ability to fly, although further evolution has led to the loss of flight in some birds , including ratites , penguins , and diverse endemic island species. The digestive and respiratory systems of birds are also uniquely adapted for flight. Some bird species of aquatic environments, particularly seabirds and some waterbirds , have further evolved for swimming. The study of birds
11739-425: The other hand (which are dinosaurs), can lay eggs that exhibit a wide variety of colors: green in the case of emus , blue in the case of American robins , and many others. The pigments that produce these colors in bird eggs — protoporphyrin and biliverdin — have been observed in fossilized dinosaur eggs. The pigment structure found in the eggs attributable to Deinonychus , the oviraptorid Heyuannia , and
11868-599: The other two. This group is further subdivided into three subfamilies: Dromaeosaurinae, Velociraptorinae, and Saurornitholestinae. Dromaeosaurines are usually found to consist of medium- to giant-sized species, with generally box-shaped skulls while the other subfamilies generally have narrower snouts. Velociraptorinae has traditionally included the more slender-snouted species which are found primarily in Asia, although this group may also include North American genera like Dineobellator and Deinonychus . Saurornitholestinae,
11997-402: The outermost half) can be seen in the evolution of maniraptoromorphs, and this process culminated in the appearance of the pygostyle , an ossification of fused tail vertebrae. In the late Cretaceous, about 100 million years ago, the ancestors of all modern birds evolved a more open pelvis, allowing them to lay larger eggs compared to body size. Around 95 million years ago, they evolved
12126-618: The parents' ears from other ambient noise. Olfaction in eudromaeosaurs has not been studied as extensively as other theropod taxa (such as tyrannosaurids ) due to the relative lack of complete skull material. However, extensive cranial remains are known from Velociraptor , Bambiraptor , and Saurornitholestes , which allowed the allometry of their nasal volume to be compared to other non-avian theropods . These three eudromaeosaurs were found to have higher nasal volume to body mass ratios than other groups of maniraptorans and were more comparable to tyrannosaurids in that respect. This ratio
12255-402: The pedal claw of Velociraptor and compared their results to the extant taxon Bubo bubo . Their results concluded that the claws of Velociraptor would have been capable of bearing the estimated weight of the animal when embedded in a surface (either prey or a climbing surface). Comparisons between extant birds with varying claw curvatures led the authors to also conclude that Deinonychus
12384-500: The phylogenetic analysis conducted in 2017 by Cau et al. using the updated data from the Theropod Working Group in their description of Halszkaraptor . Halszkaraptor [REDACTED] Mahakala [REDACTED] Hulsanpes [REDACTED] Austroraptor [REDACTED] Buitreraptor Bird Birds are a group of warm-blooded vertebrates constituting the class Aves ( Latin: [ˈaveːs] ), characterised by feathers , toothless beaked jaws,
12513-554: The posterior and on the anterior edges. By contrast, velociraptorines often have larger serrations on the posterior side of the tooth, than the anterior, or no serrations on the anterior side at all. Throughout the 1990s and early 2000s, a variety of fossil discoveries from the Yixian and Jiufotang formations demonstrated that many small microraptorian dromaeosaurids were covered in coats of feathers and possessed fully asymmetrical pennaceous wing feathers. Among such discoveries were
12642-516: The presence of a subglenoid fossa on the coracoid . Dromaeosaurids were small to medium-sized dinosaurs, ranging from 1.5–2.07 metres (4.9–6.8 ft) in length (in the case of Velociraptor ) to approaching or over 6 m (20 ft) (in Utahraptor , Dakotaraptor and Achillobator ). Large size appears to have evolved at least twice among dromaeosaurids; once among the dromaeosaurines Utahraptor and Achillobator , and again among
12771-583: The presence of quill knobs, the attachment points for wing feathers possessed by some birds. The dromaeosaurids Rahonavis and Velociraptor have both been found with quill knobs, showing that these forms had feathers despite no impressions having been found. In light of this, it is most likely that even the larger ground-dwelling dromaeosaurids bore feathers, since even flightless birds today retain most of their plumage, and relatively large dromaeosaurids, like Velociraptor , are known to have retained pennaceous feathers. Though some scientists had suggested that
12900-536: The previously clear distinction between non-birds and birds has become blurred. By the 2000s, discoveries in the Liaoning Province of northeast China, which demonstrated many small theropod feathered dinosaurs , contributed to this ambiguity. The consensus view in contemporary palaeontology is that the flying theropods, or avialans , are the closest relatives of the deinonychosaurs , which include dromaeosaurids and troodontids . Together, these form
13029-492: The rocks in which they were found. The hypothesis that eudromaeosaurs used the "raptor-prey-restraint" (or RPR) method of predation would be consistent with the morphology of their arms. The arms could exert a lot of force and were likely covered in long feathers. These may have been used as flapping stabilizers for balance while on top of a struggling prey animal, along with the long counterbalancing tail. These predatory adaptations working together may also have implications for
13158-417: The same analysis, it is suggested that the earliest eudromaeosaurs had skulls more like velociraptorines than dromaeosaurines or saurornitholestines due to the morphological similarity of troodontid skulls (believed to be the closest relatives of dromaeosaurids). The teeth of dromaeosaurines differed from those of velociraptorines in having a low DSDI ratio (their teeth had equally-sized serrations ) on both
13287-452: The same biological name "Aves", which is a problem. The authors proposed to reserve the term Aves only for the crown group consisting of the last common ancestor of all living birds and all of its descendants, which corresponds to meaning number 4 below. They assigned other names to the other groups. Lizards & snakes Turtles Crocodiles Birds Under the fourth definition Archaeopteryx , traditionally considered one of
13416-493: The second toe which may have been held clear of the ground in life, and long feathers or "hind wings" covering the hind limbs and feet, which may have been used in aerial maneuvering. Avialans diversified into a wide variety of forms during the Cretaceous period. Many groups retained primitive characteristics , such as clawed wings and teeth, though the latter were lost independently in a number of avialan groups, including modern birds (Aves). Increasingly stiff tails (especially
13545-426: The shape of other coelurosaurs . The posterior caudal vertebrae, on the other hand, are marked by a loss of their transverse processes, a reduction in their neural spines, and the haemal arches take the shape of an upside-down 'T' in cross-section. The centra of the posterior caudals are also highly elongated. Unlike most other coelurosaurs, this transition in the shape of the vertebrae is abrupt, rather than having
13674-430: The shoulder girdle, also closely resembles the condition seen in other dromaeosaurids like Microraptor , Changyuraptor , and Sinornithosaurus , all of which have been suggested to be capable of powered flight. Eudromaeosaurs and their close relatives have a completely novel foot and claw morphology among theropods . Their second toe being very muscular and strongly curled up off the ground. This second toe bears
13803-401: The skeleton was identified as belonging to a sexually mature adult . The arrangement of the eggs in the nest and the assumed brooding posture of the adult led researchers to suggest that Deinonychus laid open nests and attended them until they hatched. The oospecies Gannanoolithus yingliangi was named in 2024 , and is believed to belong to a eudromaeosaur. The oofossils were found in
13932-458: The skull. Similarities between velociraptorines and troodontids led the authors to suggest that a velociraptorine skull condition may be ancestral to eudromaeosaurs. Other researchers have suggested that the fenestration of the velociraptorine skull is a derived condition resulting from the expansion of cranial sinuses . Another study of theropod bite forces suggested that Dromaeosaurus and Saurornitholestes were better adapted to crushing
14061-500: The slightly tapered rostrum of primitive tetanurans without any significant changes in length or depth. This is largely a result of the dietary ecology of eudromaeosaurs, which took on a traditionally carnivorous role in contrast to all other maniraptorans, which were either herbivorous or omnivorous. A 2024 paper studying eudromaeosaur skulls performed several analyses, including finite element analysis (FEA) in an attempt to infer their physical properties. Their results supported
14190-467: The small dromaeosaurs Sinornithosaurus , Microraptor , Changyuraptor , Zhenyuanlong , Wulong , Daurlong , and at least one unnamed taxon (specimen IVPP V13476). In 2007 paleontologists studied the ulna of a specimen of Velociraptor and discovered small bumps on the surface, known as quill knobs. The same feature is present in some bird bones, and represents the attachment point for strong secondary wing feathers. This finding provided
14319-518: The table provided in Holtz, 2011 unless otherwise noted. 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
14448-429: The tail vertebrae bore bony, rod-like extensions (called prezygapophyses), as well as bony tendons in some species. In his study of Deinonychus , Ostrom proposed that these features stiffened the tail so that it could only flex at the base, and the whole tail would then move as a single, rigid, lever. However, one well-preserved specimen of Velociraptor mongoliensis (IGM 100/986) has an articulated tail skeleton that
14577-777: The third and fourth toes touched the ground when walking. Eudromaeosaurs also generally possessed long and stiff tails, which are believed to have been used for balance. There is some direct evidence of eudromaeosaurs such as Velociraptor being feathered. Today, it is believed that all eudromaeosaurs were fully-feathered and possessed wings, along with most, if not all, other maniraptorans. Eudroameosaurs likely evolved from small ancestors, only around 1 kilogram (2.2 lb) in mass. Later eudromaeosaurs were generally larger than this, with most being less than 2–3 metres (6.6–9.8 ft) long and having masses estimated at around 15–40 kilograms (33–88 lb). Eudromaeosaurs are also known to have reached relatively large sizes. Among these were
14706-446: The two were close relatives. However, Martin believed that maniraptorans were secondarily flightless birds, and that birds did not evolve from dinosaurs, but rather from non-dinosaurian archosaurs. In 2005, Mayr and Peters described the anatomy of a very well preserved specimen of Archaeopteryx , and determined that its anatomy was more like non-avian theropods than previously understood. Specifically, they found that Archaeopteryx had
14835-416: The typical maniraptoran condition in the semi-lunate carpal, which allowed them to fold their arms against their body in the same way that modern birds fold their wings. However unlike many other groups of coelurosaurs, eudromaeosaurs possessed relatively short metatarsals. Their second toe possessed the archetypal sickle-claw that all known dromaeosaurids bore which was held off the ground so that only
14964-448: The unenlagiines, some species may have been capable of active flight. The most advanced subgroup of dromaeosaurids, Eudromaeosauria, includes stocky and short-legged genera which were likely ambush hunters. This group includes Velociraptorinae, Dromaeosaurinae, and in some studies a third group: Saurornitholestinae. The subfamily Velociraptorinae has traditionally included Velociraptor , Deinonychus , and Saurornitholestes , and while
15093-399: The use of claws for digging or targeting weak-points on large prey items were also supported. A 2011 study on the scleral rings of extinct archosaurs by Lars Schmitz and Ryosuke Motani used the morphology sndf diameter of these structures to estimate the temporal habits of various extinct groups. The taxa they examined included pterosaurs , non-avian dinosaurs , prehistoric birds, and
15222-404: The word "bird", or "Aves", that are based on the possession of feathers. However, other scientists, such as Lawrence Witmer , have argued that calling a theropod like Caudipteryx a bird because it has feathers may stretch the word past any useful meaning. At least two schools of researchers have proposed that dromaeosaurids may actually be descended from flying ancestors. Hypotheses involving
15351-655: The work of Norell et al. , including new characters and better fossil evidence, to determine that birds (avialans) were better thought of as cousins to the dromaeosaurids and troodontids . The consensus of paleontologists is that there is not yet enough evidence to determine whether any dromaeosaurids could fly or glide, or whether they evolved from ancestors that could. Dromaeosaurids are so bird-like that they have led some researchers to argue that they would be better classified as birds. First, since they had feathers, dromaeosaurids (along with many other coelurosaurian theropod dinosaurs) are "birds" under traditional definitions of
15480-425: Was Sinornithosaurus , reported from China by Xu et al. in 1999. Many other dromaeosaurid fossils have been found with feathers covering their bodies, some with fully developed feathered wings. Microraptor even shows evidence of a second pair of wings on the hind legs. While direct feather impressions are only possible in fine-grained sediments, some fossils found in coarser rocks show evidence of feathers by
15609-466: Was developed by Francis Willughby and John Ray in their 1676 volume Ornithologiae . Carl Linnaeus modified that work in 1758 to devise the taxonomic classification system currently in use. Birds are categorised as the biological class Aves in Linnaean taxonomy . Phylogenetic taxonomy places Aves in the clade Theropoda as an infraclass or a subclass, more recently a subclass. Aves and
15738-582: Was given its specific epithet (" antirrhopus " meaning "counterbalanced") in recognition of its very long and rigid tail. This feature is generally conserved across Eudromaeosauria. Most eudromaeosaurs for which the caudal vertebrae are known have more such vertebrae than their maniraptoran relatives. They generally had more than 30 caudal vertebrae, with at least the nine most anterior vertebrae bearing transverse processes. Eudromaeosaurs also possess structures called "caudotheca", which are highly elongated prezygapophyses and chevrons . These elongations of
15867-411: Was hypothesized to be a proxy measurement of olfactory acuity, suggesting that eudromaeosaurs had strong senses of smell. This is also consistent with the suggestion that these predators were primarily active in low-light conditions. However, it is also possible that this is reflective of large territories patrolled by these taxa. The only egg fossils confidently referable to a named eudromaeosaur are
15996-409: Was likely mostly nocturnal and the closely related Sinornithosaurus would have been crepuscular . However, the authors stop short of suggesting what the ancestral condition for eudromaeosaurs may have been, citing a relatively small sample size. Another analysis using a similar methodology with more taxa by Jonah Choiniere and colleagues was conducted in 2021 which examined scleral morphology of
16125-537: Was not closely related to tyrannosaurids. Eudromaeosauria itself was first defined as a node-based clade by Nick Longrich and Philip J. Currie in 2009, as the most inclusive natural group containing Dromaeosaurus , Velociraptor , Deinonychus , and Saurornitholestes , their most recent common ancestor and all of its other descendants. The various "subfamilies" have also been redefined as clades, usually defined as all species closer to either Velociraptor , Dromaeosaurus , or Saurornitholestes than to either of
16254-524: Was pierced. Their tentative conclusion was that Deinonychus (and possibly other eudromaeosaurs) would have used their claws to climb onto the hides of large prey animals like Tenontosaurus in order to inflict wounds with their mouths. Manning conducted a study in 2009 with a different group of co-authors to elaborate on the findings of his work in 2005. The authors used multiple analytical methods — including finite element analysis , X-ray tomography , and instrumented indentation testing — to examine
16383-565: Was probably not capable of such feats. They also hypothesized that eudromaeosaurs possessed a very robust system of flexor tendons in their feet to form a ratchet -like locking mechanism that allowed them to use their feet to maintain a very tight grip. They also speculated that this ratchet-like grip may have been the reason the Velociraptor individual in the Fighting Dinosaurs may have been unable to disentangle itself from
16512-429: Was relatively short and deep. Like other maniraptorans , they had long arms that could be folded against the body in some species, and relatively large hands with three long fingers (the middle finger being the longest and the first finger being the shortest) ending in large claws. The dromaeosaurid hip structure featured a characteristically large pubic boot projecting beneath the base of the tail. Dromaeosaurid feet bore
16641-439: Was their original assignment). Gannanoolithus specimens were also found in pairs, which suggests that eudromaeosaurs may have had paired oviducts similar to troodontids and oviraptorosaurs. Dinosaurs are unique among amniotes as being the only group of animals with colored eggs. All other egg-laying amniotes ( lepidosaurs , turtles , crocodylians , and monotremes ) lay eggs which are plain white in color. Birds , on
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