Deinonychus

Fossilized remains of Deinonychus have been recovered from the Cloverly Formation of Montana and Wyoming 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. 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 that 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. In that same year, another specimen of Deinonychus, MCZ 4371, was discovered and excavated in Montana by Steven Orzack during a Harvard University expedition headed by Farish Jenkins. This discovery added several new elements: well preserved femora, pubes, a sacrum, and better ilia, as well as elements of the pes and metatarsus. Ostrom described this specimen and revised his skeletal restoration of Deinonychus. This time it showed the very long pubis, and Ostrom began to suspect that they may have even been a little retroverted like those of birds. '' (right) led John Ostrom to revive the link between dinosaurs and birds A skeleton of Deinonychus, including bones from the original (and most complete) AMNH 3015 specimen, can be seen on display at the American Museum of Natural History, with another specimen (MCZ 4371) on display at the Museum of Comparative Zoology at Harvard University. The American Museum and Harvard specimens are from a different locality than the Yale specimens. Even these two skeletal mounts are lacking elements, including the sterna, sternal ribs, furcula, and gastralia. Even after all Ostrom's work, several small blocks of lime-encased material remained unprepared in storage at the American Museum. These consisted mostly of isolated bones and bone fragments, including the original matrix, or surrounding rock in which the specimens were initially buried. An examination of these unprepared blocks by Gerald Grellet-Tinner and Peter Makovicky in 2000 revealed an interesting, overlooked feature. Several long, thin bones identified on the blocks as ossified tendons (structures that helped stiffen the tail of Deinonychus) turned out to actually represent gastralia (abdominal ribs). More significantly, a large number of previously unnoticed fossilized eggshells were discovered in the rock matrix that had surrounded the original Deinonychus specimen. In a subsequent, more detailed report, on the eggshells, Grellet-Tinner and Makovicky concluded that the egg almost certainly belonged to Deinonychus, representing the first dromaeosaurid egg to be identified. Further study by Gregory Erickson and colleagues finds that this individual was 13 or 14 years old at death and its growth had plateaued. Unlike other theropods in their study of specimens found associated with eggs or nests, it had finished growing at the time of its death. Implications Ostrom's description of Deinonychus in 1969 has been described as the most important single discovery of dinosaur paleontology in the mid-20th century. The discovery of this clearly active, agile predator did much to change the scientific (and popular) conception of dinosaurs and opened the door to speculation that some dinosaurs may have been warm-blooded. This development has been termed the dinosaur renaissance. Several years later, Ostrom noted similarities between the forefeet of Deinonychus and that of birds, an observation which led him to revive the hypothesis that birds are descended from dinosaurs. Forty years later, this idea is almost universally accepted. Because of its extremely bird-like anatomy and close relationship to other dromaeosaurids, paleontologists hypothesize that Deinonychus was probably covered in feathers. Clear fossil evidence of modern avian-style feathers exists for several related dromaeosaurids, including Velociraptor and Microraptor, though no direct evidence is yet known for Deinonychus itself. When conducting studies of such areas as the range of motion in the forelimbs, paleontologists like Phil Senter have taken the likely presence of wing feathers (as present in all known dromaeosaurs with skin impressions) into consideration. ==Description==

Based on the few fully mature specimens, Paul estimated that Deinonychus could reach in length, with a skull length of , a hip height of and a body mass of . Campione and his colleagues proposed a higher mass estimate of based on femur and humerus circumference. The skull was equipped with powerful jaws lined with around seventy 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 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. 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. The genus Microraptor is both older geologically and more primitive phylogenetically than Deinonychus, and within the same family. 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. ==Classification==

Deinonychus antirrhopus is one of the best known dromaeosaurid species, and also 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 The cladogram below follows a 2015 analysis by paleontologists Robert DePalma, David Burnham, Larry Martin, Peter Larson, and Robert Bakker, using updated data from the Theropod Working Group. This study currently classifies Deinonychus as a member of the Dromaeosaurinae. }} }} A 2021 study of the dromaeosaurid Kansaignathus recovered Deinonychus as a velociraptorine rather than a dromaeosaurine, with Kansaignathus being an intermediate basal form more advanced than Deinonychus but more primitive than Velociraptor. The cladogram below showcases these newly described relationships: A study in 2022, however, reclassified Deinonychus as a basal member of Dromaeosaurinae again. ==Paleobiology==

Predatory behavior in manner suggested by Fowler et al.'' (2011) In 2009, Manning and colleagues interpreted dromaeosaur claw tips as functioning as a puncture and gripping element, whereas the expanded rear portion of the claw transferred load stress through the structure. They argue that the anatomy, form, and function of the foot's recurved digit II and hand claws of dromaeosaurs support a prey capture/grappling/climbing function. The team also suggest that a ratchet-like locking ligament might have provided an energy-efficient way for dromaeosaurs to hook their recurved digit II claw into prey. Shifting body weight locked the claws passively, allowing their jaws to dispatch prey. They conclude that the enhanced climbing abilities of dromaeosaur dinosaurs supported a scansorial (climbing) phase in the evolution of flight. In 2020, Powers and colleagues analyzed the snout morphology of dromaeosaurids from North America and Asia, their findings suggest that the maxilla of Deinonychus was short and deep, resembling that of short-snouted canids, suggesting that Deinonychus specialized on larger prey. Within the same year, isotopic analysis done by Frederickson and colleagues, found that adult Deinonychus were likely feeding on Tenontosaurus to some degree. 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 strong bite force for defense or to capture prey, rather than for feeding. A 2024 study by Tse, Miller, and Pittman et al., focusing on the skull morphology and bite forces of various dromaeosaurids discovered that Deinonychus, the largest taxon examined, had a skull that was well adapted to hunting of large vertebrates and delivering powerful bites to prey alongside Dromaeosaurus, to which it was compared. In this study, Deinonychus represented the most extreme specializations compared to other dromaeosaurids when it came to its adaptations. The same study also revealed that Deinonychus' skull was less resistant to bite forces than that of Velociraptor, which apparently was engaging in more scavenging behavior, suggesting high bite force resistance was more common in dromaeosaurid taxa that were obtaining food through scavenging more than engaging in active predation. It is also suggested in these findings that Deinonychus may have fed by using neck-driven pullback movements to dismember carcasses when feeding, akin to modern varanid lizards. Limb function Despite being the most distinctive feature of Deinonychus, the shape and curvature of the sickle claw varies between specimens. The type specimen described by Ostrom in 1969 has a strongly curved sickle claw, while a newer specimen described in 1976 had a claw with much weaker curvature, more similar in profile with the 'normal' claws on the remaining toes. evidence that this talon was held up off the ground while the dinosaur walked on the third and fourth toes. Ostrom suggested that Deinonychus could kick with the sickle claw to cut and slash at its prey. Other studies have suggested that the sickle claws were not used to slash but rather to deliver small stabs to the victim. In 2005, Manning and colleagues ran tests on a robotic replica that precisely matched the anatomy of Deinonychus and Velociraptor, and used hydraulic rams to make the robot strike a pig carcass. In these tests, the talons made only shallow punctures and could not cut or slash. The authors suggested that the talons would have been more effective in climbing than in dealing killing blows. In 2009, Manning and colleagues undertook additional analysis dromaeosaur claw function, using a numerical modelling approach to generate a 3D finite element stress/ strain map of a Velociraptor hand claw. Ostrom cited Gilliard (1958) in saying that they can sever an arm or disembowel a man. 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. Cassowaries use their claws to defend themselves, to attack threatening animals, and in agonistic displays such as the Bowed Threat Display. In 2011, a study suggested that the sickle claw would likely have been used to pin down prey while biting it, rather than as a slashing weapon. Biomechanical studies by Ken Carpenter in 2002 confirmed that the most likely function of the forelimbs in predation was grasping, as their great lengths would have permitted longer reach than for most other theropods. The rather large and elongated coracoid, indicating powerful muscles in the forelimbs, further strengthened this interpretation. Carpenter's biomechanical studies using bone casts also showed that Deinonychus could not fold its arms against its body like a bird ("avian folding"), contrary to what was inferred from the earlier 1985 descriptions by Jacques Gauthier and Gregory S. Paul in 1988. Alan Gishlick, in a 2001 study of Deinonychus forelimb mechanics, found that even if large wing feathers were present, the grasping ability of the hand would not have been significantly hindered; rather, grasping would have been accomplished perpendicular to the wing, and objects likely would have been held by both hands simultaneously in a "bear hug" fashion, findings which have been supported by the later forelimb studies by Carpenter and Senter. 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; none were found. The second phalanx of the second toe in the specimen YPM 5205 has a healed fracture. Parsons and Parsons have shown that juvenile and sub-adult specimens of Deinonychus display some morphological differences from the adults. For instance, the arms of the younger specimens were proportionally longer than those of the adults, a possible indication of difference in behavior between young and adults. Another example of this could be the function of the pedal claws. Parsons and Parsons have suggested that the claw curvature (which Ostrom [1976] had already shown was different between specimens This was based on the hypothesis that some small dromaeosaurids used their pedal claws for climbing. In a 2015 paper, it was reported after further analysis of immature fossils that the open and mobile nature of the shoulder joint might have meant that young Deinonychus were capable of some form of flight. In 2016, Scott Persons IV and Currie examined the limb proportion of numerous theropods and found Dromaeosaurids weren't cursorial animals due to their low CLP scores, with Deinonychus scoring -2.2, suggesting they couldn't maintain high speeds for extended periods of time. Eggs The identification, in 2000, of a probable Deinonychus egg associated with one of the original specimens allowed comparison with other theropod dinosaurs in terms of egg structure, nesting, and reproduction. In their 2006 examination of the specimen, Grellet-Tinner and Makovicky examined the possibility that the dromaeosaurid had been feeding on the egg, or that the egg fragments had been associated with the Deinonychus skeleton by coincidence. They dismissed the idea that the egg had been a meal for the theropod, noting that the fragments were sandwiched between the belly ribs and forelimb bones, making it impossible that they represented contents of the animal's stomach. In addition, the manner in which the egg had been crushed and fragmented indicated that it had been intact at the time of burial, and was broken by the fossilization process. The idea that the egg was randomly associated with the dinosaur was also found to be unlikely; the bones surrounding the egg had not been scattered or disarticulated, but remained fairly intact relative to their positions in life, indicating that the area around and including the egg was not disturbed during preservation. The fact that these bones were belly ribs (gastralia), which are very rarely found articulated, supported this interpretation. All the evidence, according to Grellet-Tinner and Makovicky, indicates that the egg was intact beneath the body of the Deinonychus when it was buried. It is possible that this represents brooding or nesting behavior in Deinonychus similar to that seen in the related troodontids and oviraptorids, or that the egg was in fact inside the oviduct when the animal died. Social behavior Scientists have debated whether or not Deinonychus was gregarious. 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 skeletons 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 tenontosaur humerus even bears what might be Deinonychus tooth marks. Brinkman et al. (1998) point out that Deinonychus had an adult mass of , whereas adult tenontosaurs were 1–4 metric tons. A solitary Deinonychus could not kill an adult tenontosaur, suggesting that pack hunting is possible. Contrary to the claim that crocodilians do not hunt cooperatively, they have actually been observed to hunt cooperatively, even going as far as individuals serving different roles during the hunt. On top of that, despite cases of cannibalism and infighting, several species of crocodilians such as Nile crocodiles, American alligators, and to a certain extent Saltwater crocodiles (who have been known for their highly aggressive behavior), have been considered to be relatively gregarious. This further suggests that the notion of infighting and cannibalism ruling out cooperative feeding and gregariousness is flawed. Currie and Eberth criticized this hypothesis in their 2010 paper, as many gregarious carnivores are very intolerant towards each other, despite this, these carnivores still develop complex, social behavior. Li et al. describes track sites in their 2007 paper, noting the similar foot spacing and parallel trackways, implying gregarious pack behavior instead of uncoordinated feeding behavior. A carbon isotopic analysis on Deinonychus teeth suggests precociality in the genus. The isotopes found for different aged specimens indicate that adults and juveniles had different diets across the various age groups, suggesting a more typical archosaurian set of life stages, with any parental feeding of young ending before the young were large enough to sustain the typical adult diet. The examinations also suggests a lack of mammal-like pack hunting in Deinonychus. Despite this, due to the lack of spatial separation of juvenile and adults, Deinonychus was likely gregarious, having social tolerance at least that of crocodilians, instead of a complete agonistic relationship as seen in Komodo dragons. They argued due to some adults having overlapping values with smaller individuals, Deinonychus probably wasn't monogamous and instead practiced ratite-like parental care. ==Paleoenvironment==

Geological evidence suggests that Deinonychus inhabited a floodplain or swamplike habitat. If the teeth found in Maryland are those of Deinonychus, then its contemporaries would include the sauropod Astrodon and the poorly-known nodosaur Priconodon. The middle portion of the Cloverly Formation ranges in age from 115 ± 10 Ma near the base Deinonychus inhabited humid environments with extensive forest cover. During the Albian, much of North America was blanketed by vast forests composed of diverse plant life. The canopy was dominated by trees such as pines, redwoods, araucarians, cheirolepidiaceans, ginkgo's, yews, taxodioids, athrotaxidoids, podocarps, plane trees (sycamores), magnoliales, laurales, fabids, malvids, Tempskyaceae ferns, and Cyatheales ferns. The forest floor supported a rich understory of palms, cycads, cycadeoids, horsetails, forked ferns, spleenworts, and Osmundaceae ferns. These plants would have sustained the many types of herbivores Deinonychus hunted such as Tenontosaurus. ==Cultural significance==

Deinonychus were featured prominently in Harry Adam Knight's novel Carnosaur and its film adaption, and Michael Crichton's novels Jurassic Park and The Lost World, as well as the franchise adapted from the novels. Crichton ultimately chose to use the name Velociraptor for these dinosaurs, rather than Deinonychus. Crichton had met with John Ostrom several times during the writing process to discuss details of the possible range of behaviors and life appearance of Deinonychus. Crichton at one point apologetically told Ostrom that he had decided to use the name Velociraptor in place of Deinonychus for his book, because he felt the former name was "more dramatic". Despite this, according to Ostrom, Crichton stated that the Velociraptor of the novel was based on Deinonychus in almost every detail, and that only the name had been changed. The Jurassic Park filmmakers followed suit, designing the film's models based almost entirely on Deinonychus instead of the actual Velociraptor, and they reportedly requested all of Ostrom's published papers on Deinonychus during production. ==See also==