Deinonychus

*Deinonychus antirrhopus*

* Jurassic Park Institute Artwork
* Joe Tucciarone Artwork
* Robert F Walters Artwork

***Deinonychus*** is a genus of maniraptoran dinosaur similar in appearance to *Velociraptor*, though larger in size, though not as large as *Utahraptor*.

This 3.4 meter (11 ft) long dinosaur lived during the Early Cretaceous, about 115-108 million years ago. Fossils have been recovered from the U.S. states of Montana, Wyoming, and Oklahoma.

They had a large claw on each foot that they could use to hold down their prey and use it's teeth for the kill. Scientists used to think that they may have hunted in packs, like lions and wolves, based on fossils of several Deinonychus found next to each other. However paleontologists now think this was most likely just several Deinonychus gathering at the same place instead of a pack of them. It's tail contained ligaments and tendons that could keep the tail stiff so it could use it as a counterbalance. Due to their leg muscles and structure they could be said to be good at jumping and running.

## Description

Paleontologist John Ostrom's study of *Deinonychus* in the late 1960s started the debate on whether dinosaurs were warm-blooded. It is now accepted that all or most smaller theropods had feathers whose function was temperature regulation.

Ostrom noted the small body, sleek, horizontal, posture, and—especially—the enlarged claws on the feet, which suggested an active, agile predator. Before this, the popular idea of dinosaurs had been one of plodding, reptilian giants. It was the description of *Deinonychus* as a swift-moving, intelligent, warm-blooded predator, contrary to contemporary thought portraying dinosaurs as sluggish, stupid, cold-blooded brutes, that kickstarted the Dinosaur Renaissance, a movement that revitalized the public's interest in dinosaurs and led to a number of revelations in the field of dinosaur research.

'Deinonychus' means 'Terrible claw'. This refers to the large, sickle-shaped claw bone on the second toe of each hind foot. In life, archosaurs have a horny sheath over this bone which extends the length. Ostrom reconstructed the claw as over 4.7 in long.

The species name *antirrhopus* means “counter balance”, which refers to Ostrom's idea about the function of the tail. As in other dromaeosaurids, the tail vertebrae have a series of ossified (bony) tendons and super-long bone processes. These features seemed to make the tail into a stiff counterbalance.

A fossil of the very closely related *Velociraptor mongoliensis* 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 some flexibility.

*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*.

### 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.

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.

### Predatory behavior

    *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.

     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 baseto 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

    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

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.

## 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

1. ↑ Desmond A.J. 1977. *The hot-blooded dinosaurs*. ISBN 0-8600-7494-3
2. ↑ 2.0 2.1 Template:Cite journal
3. ↑ Bakker, Robert T. 1975. Dinosaur Renaissance, in *Scientific American*, April issue.
4. ↑ Bakker, Robert T. 1986. *The Dinosaur heresies: new theories unlocking the mystery of the dinosaurs and their extinction*. Zebra Books.
5. ↑ Template:Cite journal