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Come leggere il tassobox Dromaeosauridae
Scheletri di Deinonychus antirrhopus e Buitreraptor gonzalezorum
Stato di conservazione
Fossile
Classificazione scientifica
Dominio	Eukaryota
Regno	Animalia
Sottoregno	Eumetazoa
Superphylum	Deuterostomia
Phylum	Chordata
Subphylum	Vertebrata
Infraphylum	Gnathostomata
Superclasse	Tetrapoda
Classe	Reptilia
Sottoclasse	Diapsida
Infraclasse	Archosauromorpha
Superordine	Dinosauria
Ordine	Saurischia
Sottordine	Theropoda
Infraordine	Tetanurae
Superfamiglia	Coelurosauria
Famiglia	† Dromaeosauridae Colbert and Russell, 1969

Dromaeosauridae è una famiglia di dinosauri teropodi piumati. Erano predatori che prosperarono durante il Cretaceo. Il nome Dromaeosauridae significa 'lucertole corridore', dal Greco δρομευς (corridore) e σαυρος (lucertola). Sono spesso nominati 'raptor' in contesti informali,^[1] un termine reso popolare dal film Jurassic Park. Certi generi includono il suffisso 'raptor' per enfatizzare i loro tratti simili a quelli degli uccelli.

I fossili dei dromaeosauridi sono stati rinvenuti nel Nord America, l'Europa, l'Africa, il Giappone, la Cina, Mongolia, Madagascar, l'Argentina, e l'Antartide.^[2] Apparsero per la prima volta nello stadio Bathoniano del Giurassico (circa 167 milioni di anni fa), e sopravvissero fino allo stadio Maastrichtiano del Cretaceo superiore (circa 66 milioni di anni fa), esistendo per più di centomilioni di anni fino all'estinzione di massa del Cretaceo-Paleocene. La presenza dei dromaeosauridi durante il Giurassico medio è stato confermato con la scoperta di denti isolati fossilizzati, benché non sono stati ancora scoperti scheletri fossilizzati risalenti a quel periodo.^[3]

Descrizione

La corporatura generale dei dromaeosauridi riavviò le teorie che almeno alcuni dinosauri fossero stati creature attive, veloci e strettamente imparentate con gli uccelli. Il disegno che Robert T. Bakker fece per il monografo del 1969 di John Ostrom,^[4] mostrante il dromaeosauride Deinonychus nell'atto di correre, è fra le ricostruzioni paleontologiche più influenti della storia.^[5] I dromaeosauridi possedevano un cranio relativamente grande, denti seghettati, un muso allungato, e occhi rivolti anteriormente, così indicando una vista binocolare.^[6] Come la maggior parte dei teropodi, i dromaeosauridi avevano un collo leggermente lungo a forma di 'S', e il loro torace era relativamente tozzo e profondo. Come tutti gli altri maniraptoriani, possedevano braccia lunghe che, in certe specie, potevano piegarsi stretti contro il corpo, e tre dita allungate fornite da grandi artigli.^[7] La struttura dell'anca dei dromaeosauridi era caratterizzata d'un pube allungato che proiettava sotto la base della coda. I piedi dei dromaeosauridi erano forniti d'un grande artiglio falciforme sul secondo dito. La coda era snella con vertebre allungate e prive d'apofisi dopo la quattordicesima vertebra caudale.^[7]

Si sa che alcuni, e probabilmente tutti, i dromaeosauridi erano ricoperti di piume, incluse grosse penne remigianti sulle braccia e la coda. Questo sviluppo, prima ipotizzato negli anni ottanta per poi essere confermato nel 1999, rappresenta un cambiamento importante nel modo in cui i dromaeosauridi sono stati storicamente illustrati nell'arte e nel cinema. ^[8]

Piede

 

Modello del piede d'un tipico dromaeosauride

Come gli altri teropodi, i dromaeosauridi erano bipedi. Al contrario della maggior parte dei teropodi, che camminavano su tre dita, le tracce fossilizzate di vari gruppi di paraviani (inclusi i dromaeosauridi) mostrano che essi camminavano con il secondo dito elevato, con solo il terzo e il quarto dito facendo contatto col suolo.^[9] Il secondo dito era fornito d'un enorme artiglio ricurvo, che si ritiene fosse utilizzato per catturare prede e per arrampicare sugli alberi. Questo artiglio era particolarmente ben sviluppato negli eudromaeosauri di grossa taglia.^[10] Una specie in particulare, Balaur bondoc, possedeva un primo dito altrettanto ben sviluppato che quello secondo. Entrambi il primo e secondo dito erano tenuti retratti dal suolo.^[11]

Coda

I dromaeosauridi avevano le code lunghe. La maggior parte delle vertebre caudali erano forniti di protruberanze ossee, e certe specie avevano dei tendini ossificati. Nel suo studio su Deinonychus, Ostrom poppose che questi tratti irrigidirono la coda, permettendo all'animale di muoverla solo alla base.^[4] Un esemplare di Velociraptor però mostrava una coda preservata in una forma 'S', così indicando che potesse muoverla lateralmente con una certa flessibilità.^[12]

È stato proposto che la coda fosse usata o come un supporto o come un contrappeso durante la corsa o il volo;^[12] in Microraptor, la punta della coda era fornita d'un ventaglio a forma di diamante, che in vita potrebbe essere stato usato come un timone durante il volo, o per quando planava.^[13]

Grandezza

 

Illustrazione comparativa di vari dromaeosauridi.

Dromaeosauridae conteneva specie di taglia piccola e media; il genere più piccolo era Mahakala, lungo 0.7 metri, mentre i più grandi (Utahraptor eAchillobator) erano lunghi sei metri.^[14][15] Può darsi che certi esemplari di Utahraptor potevano raggiungere 11 metri di lunghezza, benchè questi esemplari meritino ulteriore studio.^[16] È evidente che la taglia grande sia evoluta convergentemente almeno due volte tra i dromaeosauridi; una volta fra i dromaeosaurini (Utahraptor e Achillobator), e ancora una volta tra gli unenlagiini (Austroraptor, che misurava cinque metri di lunghezza). Dei denti isolati rinvenuti nell'Isola di Wight sembrano indicare l'esistenza d'un dromaeosauride grande quanto Utahraptor. La forma dei denti però indicano una parentela più stretta con Velociraptor.^[17]

Mahakala era il dromaeosauride più piccolo e primitivo rinvenuto. Queste caratteristiche, in congiunzione con la taglia piccola di altri generi imparentati primitivi come Microraptor e il troodontide Anchiornis, indicano che l'antenato comune dei dromaeosauridi, i troodontidi, e gli uccelli fosse un animale minuscolo, lungo 65 cm e pesante 600-700 grammi.^[18]

Piumaggio

 

Tracce di piume su un fossile di Zhenyuanlong suni.

«A voi la scelta: Utahraptor piumato e la Scienza, oppure il raptor squamato e l'Ignoranza.»

(Andrea Cau (2012)^[19])

Ci sono tante prove dimostranti che i dromaeosauridi fossero ricoperti di piume. Alcuni fossili ritengono penne lunghe sugli arti anteriori e la coda, con piume soffici coprendo il corpo.^[8][20] Altri fossili che mancano tracce di piumaggio ritengono le papille ossee sull'ulna, che avrebbero anchorato le penne remigianti.^[21] Tutto sommato, la struttura e il posizionamento delle penne nei dromaeosauridi mostrano somiglianze a quelle di Archaeopteryx.^[8]

Il primo dromaeosauride scoperto con prove non ambigue di piume fu Sinornithosaurus, scoperto in Cina nel 1999.^[20] Sin dalla sua scoperta, altri generi sono stati rinvenuti con corpi ricoperti di piume, con certi che conservano ali ben sviluppate. Microraptor era fornito d'un paio di ali secondarie sugli arti posteriori.^[8] Benchè la conservazione delle tracce di piume è possibile solo nei sedimenti di granulosità fine, prove di piumaggio sono state rinvenute anche nelle rocce più ruvide, attraverso la presenza di papille ossee, che sono presenti anche in certi uccelli. Sia Rahonavis e Velociraptor sono stati scoperti con queste papille, così dimostrando che fossero piumati, anche se tracce dirette di piumaggio non sono state ancora rinvenute. A causa di questo, è molto probabile che le piume fossero presenti anche in generi grandi e incapaci di volare.^[21][22] Benchè certi scienziati in passato propposero che i dromaeosauridi più grandi persero il loro piumaggio, la scoperta delle papille ossee in Velociraptor è stato usato per sostenere che tutti i dromaeosauridi fossero piumati.^[21][23]

Paleobiologia

Funzione dell'artiglio

There is currently disagreement about the function of the enlarged "sickle claw" on the second toe. When John Ostrom described it for Deinonychus in 1969, he interpreted the claw as a blade-like slashing weapon, much like the canines of some saber-toothed cats, used with powerful kicks to cut into prey. Adams (1987) suggested that the talon was used to disembowel large ceratopsian dinosaurs.^[24] The interpretation of the sickle claw as a killing weapon applied to all dromaeosaurids. However, Manning et al. argued that the claw instead served as a hook, reconstructing the keratinous sheath with an elliptical cross section, instead of the previously inferred inverted teardrop shape.^[25] In Manning's interpretation, the second toe claw would be used as a climbing aid when subduing bigger prey and also as stabbing weapon.

 

Life restoration of a Deinonychus preying on a Zephyrosaurus using the sickle claw for prey restraint.

Ostrom compared Deinonychus to the ostrich and cassowary. He noted that the bird species can inflict serious injury with the large claw on the second toe.^[4] The cassowary has claws up to 125 millimetri (4,9 in) long.^[26] Ostrom cited Gilliard (1958) in saying that they can sever an arm or disembowel a man.^[27] Kofron (1999 and 2003) studied 241 documented cassowary attacks and found that one human and two dogs had been killed, but no evidence that cassowaries can disembowel or dismember other animals.^[28][29] Cassowaries use their claws to defend themselves, to attack threatening animals, and in agonistic displays such as the Bowed Threat Display.^[26] The seriema also has an enlarged second toe claw, and uses it to tear apart small prey items for swallowing.^[30]

Phillip Manning and colleagues (2009) attempted to test the function of the sickle claw and similarly shaped claws on the forelimbs. They analyzed the bio-mechanics of how stresses and strains would be distributed along the claws and into the limbs, using X-ray imaging to create a three-dimensional contour map of a forelimb claw from Velociraptor. For comparison, they analyzed the construction of a claw from a modern predatory bird, the eagle owl. They found that, based on the way that stress was conducted along the claw, they were ideal for climbing. The scientists found that the sharpened tip of the claw was a puncturing and gripping instrument, while the curved and expanded claw base helped transfer stress loads evenly.^[31]

The Manning team also compared the curvature of the dromaeosaurid "sickle claw" on the foot with curvature in modern birds and mammals. Previous studies had shown that the amount of curvature in a claw corresponded to what lifestyle the animal has: animals with strongly curved claws of a certain shape tend to be climbers, while straighter claws indicate ground-dwelling lifestyles. The sickle-claws of the dromaeosaurid Deinonychus have a curvature of 160 degrees, well within the range of climbing animals. The forelimb claws they studied also fell within the climbing range of curvature.^[31]

Paleontologist Peter Mackovicky commented on the Manning team's study, stating that small, primitive dromaeosaurids (such as Microraptor) were likely to have been tree-climbers, but that climbing did not explain why later, gigantic dromaeosaurids such as Achillobator retained highly curved claws when they were too large to have climbed trees. Mackovicky speculated that giant dromaeosaurids may have adapted the claw to be used exclusively for latching on to prey.^[32]

In 2009 Phil Senter published a study on dromaeosaurid toes and showed that their range of motion was compatible with the excavation of tough insect nests. Senter suggested that small dromaeosaurids such as Rahonavis and Buitreraptor were small enough to be partial insectivores, while larger genera such as Deinonychus and Neuquenraptor could have used this ability to catch vertebrate prey residing in insect nests. However, Senter did not test whether the strong curvature of dromaeosaurid claws was also conducive to such activities.^[33]

In 2011, Denver Fowler and colleagues suggested a new method by which dromaeosaurids may have taken smaller prey. This model, known as the "raptor prey restraint" (RPR) model of predation, proposes that dromaeosaurids killed their prey in a manner very similar to extant accipitrid birds of prey: by leaping onto their quarry, pinning it under their body weight, and gripping it tightly with the large, sickle-shaped claws. Like accipitrids, the dromaeosaurid would then begin to feed on the animal while still alive, until it eventually died from blood loss and organ failure. This proposal is based primarily on comparisons between the morphology and proportions of the feet and legs of dromaeosaurids to several groups of extant birds of prey with known predatory behaviors. Fowler found that the feet and legs of dromaeosaurids most closely resemble those of eagles and hawks, especially in terms of having an enlarged second claw and a similar range of grasping motion. The short metatarsus and foot strength, however, would have been more similar to that of owls. The RPR method of predation would be consistent with other aspects of dromaeosaurid anatomy, such as their unusual dentition and arm morphology. The arms, which could exert a lot of force but were likely covered in long feathers, may have been used as flapping stabilizers for balance while atop a struggling prey animal, along with the stiff counterbalancing tail. Dromaeosaurid jaws, thought by Fowler and colleagues to be comparatively weak, would have been useful for eating prey alive but not as useful for quick, forceful dispatch of the prey. These predatory adaptations working together may also have implications for the origin of flapping in paravians.^[34][35]

Comportamenti sociali

 

Tracks of the ichnogenus Paravipus didactyloides, interpreted as representing two individuals that were moving in the same direction^[36]

Deinonychus fossils have been uncovered in small groups near the remains of the herbivore Tenontosaurus, a larger ornithischian dinosaur. This had been interpreted as evidence that these dromaeosaurids hunted in coordinated packs like some modern mammals.^[37] However, not all paleontologists found the evidence conclusive, and a subsequent study published in 2007 by Roach and Brinkman suggests that the Deinonychus may have actually displayed a disorganized mobbing behavior. Modern diapsids, including birds and crocodiles (the closest relatives of dromaeosaurids), display minimal cooperative hunting; instead, they are usually either solitary hunters, or are drawn to previously killed carcasses, where conflict often occurs between individuals of the same species. For example, in situations where groups of komodo dragons are eating together, the largest individuals eat first and might attack smaller komodo dragons that attempt to feed; if the smaller animal dies, it is usually cannibalized. When this information is applied to the sites containing putative pack-hunting behavior in dromaeosaurids, it appears somewhat consistent with a komodo- or crocodile-like feeding strategy. Deinonychus skeletal remains found at these sites are from subadults, with missing parts that may have been eaten by other Deinonychus, which a study by Roach et al. presented as evidence against the idea that the animals cooperated in the hunt.^[38]

In 2007, scientists described the first known extensive dromaeosaurid trackway, in Shandong, China. In addition to confirming the hypothesis that the sickle-claw was held retracted off the ground, the trackway (made by a large, Achillobator-sized species) showed evidence of six individuals of about equal size moving together along a shoreline. The individuals were spaced about one meter apart, and retained the same direction of travel, walking at a fairly slow pace. The authors of the paper describing these footprints interpreted the trackways as evidence that some species of dromaeosaurids lived in groups. While the trackways clearly do not represent hunting behavior, the idea that groups of dromaeosaurids may have hunted together, according to the authors, could not be ruled out.^[9]

Volare e planare

The ability to fly or glide has been suggested for at least five dromaeosaurid species. The first, Rahonavis ostromi (originally classified as avian bird, but found to be a dromaeosaurid in later studies^[6][39]) may have been capable of powered flight, as indicated by its long forelimbs with evidence of quill knob attachments for long sturdy flight feathers.^[40] The forelimbs of Rahonavis were more powerfully built than Archaeopteryx, and show evidence that they bore strong ligament attachments necessary for flapping flight. Luis Chiappe concluded that, given these adaptations, Rahonavis could probably fly but would have been more clumsy in the air than modern birds.^[41]

 

Microraptor gui fossil with impressions of feathered wings

Another species of dromaeosaurid, Microraptor gui, may have been capable of gliding using its well-developed wings on both the fore and hind limbs. A 2005 study by Sankar Chatterjee suggested that the wings of Microraptor functioned like a split-level "biplane", and that it likely employed a phugoid style of gliding, in which it would launch from a perch and swoop downward in a 'U' shaped curve, then lift again to land on another tree, with the tail and hind wings helping to control its position and speed. Chatterjee also found that Microraptor had the basic requirements to sustain level powered flight in addition to gliding.^[13]

Changyuraptor yangi is a close relative of Microraptor gui, also thought to be a glider or flyer based on the presence of four wings and similar limb proportions. However, it is a considerably larger animal, around the size of a wild turkey, being among the largest known flying Mesozoic paravians.

Another dromaeosaurid species, Deinonychus antirrhopus, may display partial flight capacities. The young of this species bore longer arms and more robust pectoral girdles than adults, and which were similar to those seen in other flapping theropods, implying that they may have been capable of flight when young and then lost the ability as they grew.^[42]

The possibility that Sinornithosaurus millenii was capable of gliding or even powered flight has also been brought up several times,^[43][44] though no further studies have occurred.

Sensi

Comparisons between the scleral rings of several dromaeosaurids (Microraptor, Sinornithosaurus, and Velociraptor) and modern birds and reptiles indicate that some dromaeosaurids (including Microraptor and Velociraptor) may have been nocturnal predators, while Sinornithosaurus is inferred to be cathemeral (active throughout the day at short intervals).^[45] However, the discovery of iridescent plumage in Microraptor has cast doubt on the inference of nocturnality in this genus, as no modern birds that have iridescent plumage are known to be nocturnal.^[46]

Studies of the olfactory bulbs of dromaeosaurids reveal that they had similar olfactory ratios for their size to other non-avian theropods and modern birds with an acute sense of smell, such as tyrannosaurids and the turkey vulture, probably reflecting the importance of the olfactory sense in the daily activities of dromaeosaurids such as finding food.^[47][48]

Paleopatologia

In 2001, Bruce Rothschild and others published a study examining evidence for stress fractures and tendon avulsions in theropod dinosaurs and the implications for their behavior. Since stress fractures are caused by repeated trauma rather than singular events they are more likely to be caused by regular behavior than other types of injuries. The researchers found lesion like those caused by stress fractures on a dromaeosaurid hand claw, one of only two such claw lesions discovered in the course of the study. Stress fractures in the hands have special behavioral significance compared to those found in the feet since stress fractures there can be obtained while running or during migration. Hand injuries, by contrast, are more likely to be obtained while in contact with struggling prey.^[49]

Classificazione

Relazione con gli uccelli

  Lo stesso argomento in dettaglio: Origin of birds e Feathered dinosaurs.

 

Comparison of the forelimbs of Deinonychus (left) and Archaeopteryx (right), one of many skeletal similarities between avians and dromaeosaurids.

Dromaeosaurids share many features with early birds (clade Avialae or Aves). The precise nature of their relationship to birds has undergone 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.^[50] In 2002, Hwang and colleagues utilized 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.^[14] A consensus of paleontologists has concluded that there is not yet enough evidence to determine whether any dromaeosaurids could fly or glide, or whether they evolved from ancestors that could.^[51]

Teorie alternative

Dromaeosaurids are so birdlike 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 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.^[52]

 

Fossil cast of an extensively feathered Sinornithosaurus specimen

At least two schools of researchers have proposed that dromaeosaurids may actually be descended from flying ancestors. Hypotheses involving a flying ancestor for dromaeosaurids are sometimes called "Birds Came First” (BCF). George Olshevsky is usually credited as the first author of BCF.^[53] 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 something like Archaeopteryx. In that case, the larger dromaeosaurids were secondarily flightless, like the modern ostrich.^[22] 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.^[54]

In 2002, Hwang et al. found that Microraptor was the most primitive dromaeosaurid.^[14] Xu and colleagues in 2003 cited 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.^[8]

Also in 2002, Steven Czerkas described Cryptovolans, though it is a probable junior synonym of Microraptor. He reconstructed 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^[55]

Other researchers, like Larry Martin believe that dromaeosaurids, along with all maniraptorans are not dinosaurs at all. Martin asserted for decades that birds were unrelated to maniraptorans, but in 2004 he changed his position, and now he agrees that the two are the closest of relatives. Martin believes that maniraptorans are secondarily flightless birds, and that birds evolved from non–dinosaurian archosaurs, so that most of the species formerly called theropods would now not even be classified as dinosaurs.^[56]

 

The Thermopolis specimen of Archaeopteryx, which showed that it also had a hyperextendible second toe^[57]

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 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 the ability to glide).^[58][59] Corfe and Butler criticized this work on methodological grounds.^[60]

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 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.^[61] 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 the clade Dromaeosauridae, which appears to suggest the earliest members of the clade may have been capable of flight.^[62]

Deinonychosauria

 

Comparison of several dromaeosaurids

Since the 1960s, the dromaeosaurids and troodontids have often been classified together in a group or clade named the Deinonychosauria, initially based primarily on the presence of a retractable second toe with sickle-claw (now also known to be present in some primitive birds). The name Deinonychosauria was coined by Ned Colbert and Dale Russell in 1969, and defined as a clade (all theropods closer to dromaeosaurids than to birds) by Jaques Gauthier in 1986. Through the early 2000s, consensus among paleontologists was that dromaeosaurids were most closely related to the troodontids, and together with the troodontids, with deinonychosaurians in turn the sister taxon to avialans, and therefore the closest relatives of avialan birds.^[63] In 2012, Turner et al. conducted a phylogenetic analysis (using a dataset of 474 characters scored for 111 taxa) which found Deinonychosauria to be monophyletic.^[64] However, several more recent studies have cast doubt on the hypothesis that dromaeosaurids and troodontids were more closely related to each other than either was to birds. A more robust 2013 study by Godefroit et al. (using a dataset of 1,500 characters scored for 358 taxa) found that troodontids were possibly more closely related to birds than to dromaeosaurids; forcing troodontids to remain in a monophyletic Deinonychosauria required four extra steps in the analysis, making this result less likely but not implausible.^[65][66] Because Deinonychosauria was originally defined as all animals closer to dromaeosaurids than to birds without specific reference to troodontids, Deinonychosauria is a synonym of Dromaeosauridae if Troodontidae is closer to birds.^[66]

Tassonomia

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.^[67]

The subfamilies of Dromaeosauridae frequently shift in content based on new analysis, but typically consist of 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 because they are basal relative to the primary subdivisions of Dromaeosauridae (Mahakala, for example, is the most primitive known dromaeosaurid and falls outside any named sub-group). The most basal subfamily of dromaeosaurids is often found to be the Unenlagiinae.^[18] This enigmatic group is the most poorly supported subfamily of dromaeosaurids and it is possible that some or all of its members belong outside of Dromaeosauridae.^[68] The larger, ground-dwelling members like Buitreraptor and Unenlagia show strong flight adaptations, although they were probably too large to 'take off'. One member of this group, Rahonavis, 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 the unenlagiines, some species may have been capable of active flight. The subfamily Velociraptorinae has traditionally included Velociraptor, Deinonychus, and Saurornitholestes, and while the discovery of Tsaagan lent support to this grouping, the inclusion of Saurornitholestes 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).^[69]

 

Mahakala, the most basal dromaeosaurid known

 

Austroraptor, an unenlagiine

 

Sinornithosaurus, a microraptorine

 

Saurornitholestes, a eudromaeosaur

The following classification of the various genera of dromaeosaurids follows the table provided in Holtz, 2011 unless otherwise noted.^[69]

• Family Dromaeosauridae
  • Luanchuanraptor
  • Mahakala
  • Pamparaptor
  • Ornithodesmus
  • Variraptor (=Pyroraptor?)
  • Pyroraptor?
  • Shanag
  • Subfamily Unenlagiinae
    • Austroraptor
    • Rahonavis
    • Unenlagia
    • Buitreraptor
    • Neuquenraptor
    • Unquillosaurus
  • Subfamily Microraptorinae
    • Tianyuraptor
    • Graciliraptor
    • Changyuraptor
    • Hesperonychus
    • Microraptor
    • Cryptovolans?^[70]
    • Sinornithosaurus
  • Node Eudromaeosauria^[10]
    • Subfamily Saurornitholestinae
      • Bambiraptor
      • Saurornitholestes
      • Atrociraptor^[71]
    • Deinonychus^[71]
    • Subfamily Velociraptorinae
      • Acheroraptor
      • Balaur
      • Itemirus
      • Linheraptor
      • Velociraptor
      • Tsaagan
      • Adasaurus
      • Nuthetes?^[72]
    • Subfamily Dromaeosaurinae
      • Achillobator
      • Dromaeosaurus
      • Dromaeosauroides
      • Utahraptor
      • Yurgovuchia^[62]

History of genera

Phylogeny

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.^[63] 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.^[73] The extensive cladistic analysis conducted by Turner et al. (2012) further supported the monophyly of Dromaeosauridae.^[74]

The cladogram below follows a 2012 analysis by Turner, Makovicky and Norell.^[74]

Dromaeosauridae

Mahakala     Pyroraptor       Neuquenraptor   Unenlagiinae   Rahonavis       Buitreraptor       Austroraptor     Unenlagia             Shanag     Microraptorinae   Graciliraptor     Hesperonychus     Tianyuraptor       Microraptor     Sinornithosaurus       Eudromaeosauria Dromaeosaurinae   Achillobator     Atrociraptor     Dromaeosaurus     Utahraptor     Velociraptorinae   Bambiraptor       Tsaagan       Saurornitholestes       Adasaurus     Deinonychus       Velociraptor     Balaur

The cladogram below follows a 2012 analysis by paleontologists Phil Senter, James I. Kirkland, Donald D. DeBlieux, Scott Madsen and Natalie Toth.^[62]

Dromaeosauridae

Xiaotingia     Unenlagiinae     Austroraptor     Mahakala         Buitreraptor     Rahonavis     Unenlagia           Shanag     Microraptoria   Tianyuraptor       Hesperonychus         Microraptor sp.       Microraptor gui     Microraptor zhaoianus           Cryptovolans     Graciliraptor     Sinornithosaurus           Eudromaeosauria     Bambiraptor       Velociraptorinae   Adasaurus       Tsaagan     Velociraptor       Dromaeosaurinae   Deinonychus       Achillobator     Dromaeosaurus     Utahraptor     Yurgovuchia

Technical diagnosis

 

Dromaeosaurid fossil displayed in Hong Kong Science Museum.

Dromaeosaurids 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.^[7]

In popular culture

Velociraptor, a dromaeosaurid, gained much attention after it was featured prominently in the 1993 Steven Spielberg film Jurassic Park. However, the dimensions of the Velociraptor in the film are much larger than the largest members of that genus. Robert Bakker recalled that Spielberg had been disappointed with the dimensions of Velociraptor and so upsized it, adding that soon afterwards he named Utahraptor which was more the size depicted, or larger.^[75] Gregory S. Paul, in his book Predatory Dinosaurs of the World, considered Deinonychus antirrhopus a species of Velociraptor, and so rechristened the species Velociraptor antirrhopus.^[54] This taxonomic opinion has not been widely followed.^[7][76][77]

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