Deinonychus is a genus of maniraptoran dinosaur similar in appearance to Velociraptor, though larger in size, though not as large as Utahraptor. There is one described species, Deinonychus antirrhopus. This 3.4 meter (11 ft) long dinosaur lived during the early Cretaceous Period, about 115-108 million years ago (from the mid-Aptian to early Albian stages). Fossils have been recovered from the U.S. states of Montana, Wyoming, and Oklahoma, in rocks of the Cloverly Formation and Antlers Formation, though teeth that may belong to Deinonychus have been found much farther east in Maryland.
Paleontologist John Ostrom's study of Deinonychus in the late 1960s revolutionized the way scientists thought about dinosaurs, leading to the "Dinosaur renaissance" and igniting the debate on whether or not dinosaurs were warm-blooded. Before this, the popular conception of dinosaurs had been one of plodding, reptilian giants. Ostrom noted the small body, sleek, horizontal, posture, ratite-like spine, and - especially - the enlarged raptorial claws on the feet, which suggested an active, agile predator.[1]
"Terrible claw" refers to the unusually large, sickle-shaped talon on the second toe of each hind foot. The fossil YPM 5205 preserves a large, strongly curved ungual. In life, archosaurs have a horny sheath over this bone which extends the length. Ostrom looked at crocodile and bird claws and reconstructed the claw for YPM 5205 as over 120 millimetres (4.7 in) long.[2] The species name antirrhopus means “counter balance”, which refers to John Ostrom's idea about the function of the tail. As in other dromaeosaurids, the tail vertebrae have a series of ossified tendons and super-elongated bone processes. These features seemed to make the tail into a stiff counterbalance, but a fossil of the very closely related Velociraptor mongoliensis (IGM 100/986) has an articulated tail skeleton that is curved laterally in a long S–shape. This suggests that, in life, the tail could swish to the sides with a high degree of flexibility.[3]
In both the Cloverly and Antlers Formation, Deinonychus remains have been found closely associated with those of the ornithopod Tenontosaurus. Teeth discovered associated with Tenontosaurus specimens imply it was hunted or at least scavenged upon by Deinonychus.
Description[]

Life restoration

Size compared with a human
Based on the largest known specimens, Deinonychus could reach 3.4 meters (11.1 ft), with a maximum skull length of 410 mm (16.4 in), a hip height of 0.87 meters (2.85 ft), a maximum weight of 73 kilograms (161 lb).[4] Its skull was equipped with powerful jaws lined with around sixty curved, blade-like teeth. Studies of the skull have progressed a great deal over the decades. Ostrom reconstructed the partial, imperfectly preserved, skulls that he had as triangular, broad, and fairly similar to Allosaurus. Additional Deinonychus skull material and closely related species found with good three-dimensional preservation[5] show that the palate was more vaulted than Ostrom thought, making the snout far narrower, while the jugals flared broadly, giving greater stereoscopic vision. The skull of Deinonychus was different from that of Velociraptor, however, in that it had a more robust skull roof like that of Dromaeosaurus, and did not have the depressed nasals of Velociraptor.[6] Both the skull and the lower jaw had fenestrae (skull openings) which reduced the weight of the skull. In Deinonychus, the antorbital fenestra, a skull opening between the eye and nostril, was particularly large.[5]
Like all dromaeosaurs, Deinonychus possessed large hands (manus) with three claws on each forelimb. The first digit was shortest and the second was longest. Each hind foot bore a sickle-shaped claw on the second digit, which was probably used during predation.
No feathers have ever been found in association with fossils of Deinonychus. Nonetheless, the evidence suggests that the Dromaeosauridae, including Deinonychus, had feathers.[7] The genus Microraptor is both older geologically and more primitive phylogenetically than Deinonychus, and within the same family.[8] Multiple fossils of Microraptor preserve pennaceous, vaned feathers like those of modern birds on the arms, legs, and tail, along with covert and contour feathers.[7] Velociraptor is geologically younger than Deinonychus, but even more closely related (within the subfamily velociraptorinae, see Classification, below). A specimen of Velociraptor has been found with quill knobs on the ulna. Quill knobs are where the follicular ligaments attached, and are a direct indicator of feathers of modern aspect.[9]
Classification[]
Deinonychus antirrhopus is one of the best-known dromaeosaurid species, and is a close relative of the smaller Velociraptor, which is found in younger, Late Cretaceous–age rock formations in Central Asia. The clade they form is called Velociraptorinae. The subfamily name Velociraptorinae was first coined by Rinchen Barsbold in 1983 and originally contained the single genus Velociraptor. Later Phil Currie included most of the dromaeosaurids. Two Late Cretaceous genera, Tsaagan from Mongolia and the North American Saurornitholestes, may also be close relatives, but the latter is poorly known and hard to classify. Velociraptor and its allies are regarded as using their claws more than their skulls as killing tools, as opposed to dromaeosaurids like Dromaeosaurus, which have stockier skulls. Together with the troodontids, the dromaeosaurids form the Deinonychosauria clade, which is a sister taxon of aves. Phylogenetically, the Deinonychosauria represent the group of non-avian dinosaurs most closely related to birds.

Size of Deinonychus (6) compared with other dromaeosaurids
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Discovery and naming[]
Fossilized remains of Deinonychus have been recovered from the Cloverly Formation of Montana and Wyoming and in the roughly contemporary Antlers Formation of Oklahoma, in North America. The Cloverly formation has been dated to the late Aptian through early Albian stages of the early Cretaceous, about 115 to 108 Ma. Additionally, teeth found in the Arundel Clay Facies (mid-Aptian), of the Potomac Formation on the Atlantic Coastal Plain of Maryland may be assigned to the genus.
The first remains were uncovered in 1931 in southern Montana near the town of Billings. The team leader, paleontologist Barnum Brown, was primarily concerned with excavating and preparing the remains of the ornithopod dinosaur Tenontosaurus, but in his field report from the dig site to the American Museum of Natural History, he reported the discovery of a small carnivorous dinosaur close to a Tenontosaurus skeleton, "but encased in lime difficult to prepare."He informally called the animal "Daptosaurus agilis" and made preparations for describing it and having the skeleton, specimen AMNH 3015, put on display, but never finished this work.
Brown brought back from the Cloverly Formation the skeleton of a smaller theropod with seemingly oversized teeth that he informally named "Megadontosaurus". John Ostrom, reviewing this material decades later, realized that the teeth came from Deinonychus, but the skeleton came from a completely different animal. He named this skeleton Microvenator.

Cast of the holotype foot YPM 5205 from two angles
A little more than thirty years later, in August 1964, paleontologist John Ostrom led an expedition from Yale University’s Peabody Museum which discovered more skeletal material near Bridger. Expeditions during the following two summers uncovered more than 1000 bones, among which were at least three individuals. Since the association between the various recovered bones was weak, making the exact number of individual animals represented impossible to determine properly, the type specimen (YPM 5205) of Deinonychus was restricted to the complete left foot and partial right foot that definitely belonged to the same individual. The remaining specimens were catalogued in fifty separate entries at Yale's Peabody Museum of Natural History. Later study by Ostrom and Grant E. Meyer analyzed their own material as well as Brown's "Daptosaurus" in detail and found them to be the same species. Ostrom first published his findings in February 1969, giving all the referred remains the new name of Deinonychus antirrhopus. The specific name "antirrhopus", from Greek ἀντίρροπος, means "counterbalancing" and refers to the likely purpose of a stiffened tail.In July 1969 Ostrom published a very extensive monograph on Deinonychus.
Though a myriad of bones was available by 1969, many important ones were missing or hard to interpret. There were few postorbital skull elements, no femurs, no sacrum, no furcula or sternum, missing vertebrae, and (Ostrom thought) only a tiny fragment of a coracoid. Ostrom’s skeletal reconstruction of Deinonychus included a very unusual pelvic bone – a pubis which was trapezoidal and flat, unlike that of other theropods, but which was the same length as the ischium and which was found right next to it.
Paleobiology[]
Predatory behavior[]

Interpretation of a Deinonychus preying on a Zephyrosaurus in manner suggested by Fowler et al. (2011)
Deinonychus teeth found in association with fossils of the ornithopod dinosaur Tenontosaurus are quite common in the Cloverly Formation. Two quarries have been discovered that preserve fairly complete Deinonychus fossils near Tenontosaurus fossils. The first, the Yale quarry in the Cloverly of Montana, includes numerous teeth, four adult Deinonychus and one juvenile Deinonychus. The association of this number of Deinonychus skeletoaidsns in a single quarry suggests that Deinonychus may have fed on that animal, and perhaps hunted it. Ostrom and Maxwell have even used this information to speculate that Deinonychus might have lived and hunted in packs. The second such quarry is from the Antlers Formation of Oklahoma. The site contains six partial skeletons of Tenontosaurus of various sizes, along with one partial skeleton and many teeth of Deinonychus. One Tenontosaurus humerus even bears what might be Deinonychus tooth marks. Brinkman et al. (1998) point out that Deinonychus had an adult mass of 70–100 kilograms, whereas adult tenontosaurs were 1–4 metric tons. A solitary Deinonychus could not kill an adult Tenontosaurus, suggesting that pack hunting is possible.

Foot (MOR 747) in flexion
A recent study by Roach and Brinkman has called into question the cooperative pack hunting behavior of Deinonychus, based on what is known of modern carnivore hunting and the taphonomy of tenontosaur sites. Modern archosaurs (birds and crocodiles) and komodo dragons display little cooperative hunting; instead, they are usually either solitary hunters, or are drawn to previously killed carcasses, where much conflict 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 will attack smaller komodos that attempt to feed; if the smaller animal is killed, it is cannibalized.
When this information is applied to the tenontosaur sites, it appears that what is found is consistent with Deinonychus having a komodo- or crocodile-like feeding strategy. Deinonychus skeletal remains found at these sites are from subadults, with missing parts consistent with having been eaten by other Deinonychus. On the other hand, a paper by Li et al.. describes track sites with similar foot spacing and parallel trackways, implying gregarious\social behaviore is more possible.
However a more recent research has been bolstered the likeliness of a much more solitary lifestyle for dromaesaurids.
Paleobiology and paleoecology[]
Geological evidence suggests that Deinonychus inhabited a floodplain or swamplike habitat. The paleoenvironment of both the upper Cloverly Formation and the Antlers Formation, in which remains of Deinonychus have been found, consisted of tropical or sub-tropical forests, deltas and lagoons, not unlike today's Louisiana. Other animals Deinonychus shared its world with include herbivorous dinosaurs such as the armored Sauropelta and the ornithopods Zephyrosaurus and Tenontosaurus. In Oklahoma, the ecosystem of Deinonychus also included the large theropod Acrocanthosaurus, the huge sauropod Sauroposeidon, the crocodilian Goniopholis, and the gar Lepisosteus. If the teeth found in Maryland are those of Deinonychus, then its neighbors would include Astrodon and a nodosaur called Priconodon only known from teeth. The middle portion of the Cloverly Formation ranges in age from 115 ± 10 Ma near the base.to 108.5 ± 0.2 Ma near the top. In a 2001 study conducted by Bruce Rothschild and other paleontologists, 43 hand bones and 52 foot bones referred to Deinonychus were examined for signs of stress fracture, but none were found.
Bite force[]

Reconstructed skull and neck, Royal Ontario Museum
Bite force estimates for Deinonychus were first produced in 2005, based on reconstructed jaw musculature. This study concluded that Deinonychus likely had a maximum bite force only 15% that of the modern American Alligator. A 2010 study by Paul Gignac and colleagues attempted to estimate the bite force based directly on newly discovered Deinonychus tooth puncture marks in the bones of a Tenontosaurus. These puncture marks came from a large individual, and provided the first evidence that large Deinonychus could bite through bone. Using the tooth marks, Gignac's team were able to determine that the bite force of Deinonychus was significantly higher than earlier studies had estimated by biomechanical studies alone. They found the bite force of Deinonychus to be between 4,100 and 8,200 newtons, greater than living carnivorous mammals including the hyena, and equivalent to a similarly sized alligator.
Gignac and colleagues also noted, however, that bone puncture marks from Deinonychus are relatively rare, and unlike larger theropods with many known puncture marks like Tyrannosaurus, Deinonychus probably did not frequently bite through or eat bone. Instead, they probably used their high bite force in defense or prey capture, rather than feeding.
Speed[]

Restoration of a walking individual
Dromaeosaurids, especially Deinonychus, are often depicted as unusually fast-running animals in the popular media, and Ostrom himself speculated that Deinonychus was fleet-footed in his original description. However, when first described, a complete leg of Deinonychus had not been found, and Ostrom's speculation about the length of the femur (upper leg bone) later proved to have been an overestimate. In a later study, Ostrom noted that the ratio of the femur to the tibia (lower leg bone) is not as important in determining speed as the relative length of the foot and lower leg. In modern, fleet-footed birds like the ostrich, the foot-tibia ratio is .95. In unusually fast-running dinosaurs like Struthiomimus, the ratio is .68, but in Deinonychus, the ratio is .48. Ostrom stated that the "only reasonable conclusion" is that Deinonychus was not particularly fast compared to other dinosaurs, and certainly not as fast as modern flightless birds.
The low foot to lower leg ratio in Deinonychus is due partly to an unusually short metatarsus (upper foot bones). The ratio is actually larger in smaller individuals than in larger ones. Ostrom suggested that the short metatarsus may be related to the function of the sickle claw, and used the fact that it appears to get shorter as individuals aged as support for this. He interpreted all these features – the short second toe with enlarged claw, short metatarsus, etc. – as support for the use of the hind leg as an offensive weapon, where the sickle claw would strike downwards and backwards, and the leg pulled back and down at the same time, slashing, and tearing at the prey.
Ostrom suggested that the short metatarsus reduced overall stress on the leg bones during such an attack, and interpreted the unusual arrangement of muscle attachments in the Deinonychus leg as support for his idea that a different set of muscles were used in the predatory stroke than in walking or running. Therefore, Ostrom concluded that the legs of Deinonychus represented a balance between running adaptations needed for an agile predator, and stress-reducing features to compensate for its unique foot weapon.
In his 1981 study of Canadian dinosaur footprints, Richard Kool produced rough walking speed estimates based on several trackways made by different species in the Gething Formation of British Columbia. Kool estimated one of these trackways, representing the ichnospecies Irenichnites gracilis (which may have been made by Deinonychus), to have a walking speed of 10.1 kilometers per hour (6 miles per hour).
JPInstitute.com Description[]
Deinonychus was a fast and vicious hunter. Its name means "terrible claw," and it was given this name because of the large, retractable hunting claw on each of its feet. Like its cousin, the Velociraptor, it used this claw to tear into the flesh of the dinosaurs it hunted. The claw would snap forward and make a large, deep wound when it attacked. Deinonychus was about twice as big as Velociraptor.
Deinonychus is probably the best known of the dromeasaurids, with nine specimens having been discovered since the genus was established in 1962 by John Ostrum. An interesting feature about this dinosaur is that its teeth are more backward pointing than other, larger theropods, suggesting that they are designed for feeding and not for the killing of prey. This points to the effectiveness of its hand and foot claws as weapons. Its skeletal design, according to Ostrum, clearly points to a very active predatory lifestyle - a hunter with both speed and agility. Its hands were very large and had a great range of movement and flexibility. As the dinosaur grew, long tendons along its tail hardened into a bone-like material to stiffen it and make it a useful mechanism for maintaining balance and direction in quick turns. A few scientists have argued that Deinonychus is a North American species of Velociraptor and does not merit its own genus.
In his 1986 book The Dinosaur Heresies, Dr. Robert Bakker puts forth the view that Deinonychus has many features found in birds and might be considered either a bird-like dinosaur or a dinosaur-like bird. Recent research and discoveries by scientists such as Dr. Philip Currie are showing that some dinosaurs similar to Deinonychus most likely had feather-like coverings on all or part of their bodies. These proto-feathers were most likely used for insulation, display, or both, and may eventually have evolved into flight feathers. To date, these have not been found on Deinonychus .
Dinosaur Field Guide Description[]
Deinonychus ("terrible claw") is one of the most important dinosaurs ever found because it changed the way paleontologists thought about dinosaurs. For most of the 20th century, dinosaurs were generally thought of as being strange evolutionary "dead ends; with no living descendants, mostly slow and sluggish. Then dinosaur paleontogist Dr. John Ostrom discovered Deinonychus in 1964. Dr. Ostrom believed that this dinosaur was an agile, swift predator, more like a warm-blooded mammal or bird than a cold-blooded crocodile. His study of Deinonychus--and of the early bird Archaeopteryx--led him to realize that birds were in fact the descendants of dinosaurs, and that raptor dinosaurs such as Deinonychus and Velociraptor were among the closest relatives of birds. Deinonychus was the first of the raptors (technically called "dromaeosaurs") to be known from a nearly complete skeleton, Velociraptor had been discovered forty years earlier but was known only from a skull and a few bones of its hands and feet. The skeletons of Deinonychus were the first to show the now infamous sickle-shaped retractable foot claw, used for ripping open the guts of its prey.
Fun Facts[]
Deinonychus had "terrible claws but it also had a nasty bite, with over 60 knife-like teeth!
Trivia[]
The genetically recreated Velociraptors seen in the Jurassic Park movies are closer in size to a very large Deinonychus than to the true Velociraptor, which was much smaller.
Gallery[]
Appearance in other media[]
Jurassic Park[]
Read more Deinonychus on Jurassic Park Wiki |
The Land Before Time[]
Read more Deinonychus on Land Before Time Wiki |
We're Back! A Dinosaur's Story[]
Links[]
http://web.archive.org/web/20040214161843fw_/http://www.jpinstitute.com/dinopedia/dinocards/dc_deino.html# https://web.archive.org/web/20080509165704/http://kids.yahoo.com/dinosaurs/94--Deinonychus
References[]
- ↑ Template:Cite journal
- ↑ Ostrom, J. H. (1970) "Stratigraphy and paleontology of the Cloverly Formation (Lower Cretaceous) of the Bighorn Basin area, Wyoming and Montana", Bulletin of the Peabody Museum of Natural History 35:1–234.
- ↑ Template:Cite journal
- ↑ Template:Cite book
- ↑ 5.0 5.1 Template:Cite journal
- ↑ Witmer, Lawrence M., and Maxwell, William D. (1996). " The skull of Deinonychus (Dinosauria:Theropoda): New insights and implications". Journal of Vertebrate Paleontology,16(3): 73A
- ↑ 7.0 7.1 Xu, X., Zhou, Z., Wang, X., Kuang, X., Zhang, F. and Du, X. (2003). "Four-winged dinosaurs from China." Nature, 421(6921): 335-340, 23 Jan 2003. http://www.nature.com/nature/journal/v421/n6921/full/nature01342.html
- ↑ Hwang, S.H., Norell, M.A., Ji, Q., and Gao, K. (2002). "New Specimens of Microraptor zhaoianus (Theropoda: Dromaeosauridae) from Northeastern China." American Museum Novitates, 3381: 44pp.al.2002.pdf
- ↑ Template:Cite journal