Deinonychus

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Deinonychus
Skeletal reconstruction of Deinonychus antirrhopus

Skeletal reconstruction of Deinonychus antirrhopus

Temporal occurrence
Lower Cretaceous (Middle Aptian to Lower Albian )
123 to 110.2 million years
Locations
Systematics
Lizard dinosaur (Saurischia)
Theropoda
Deinonychosauria
Dromaeosauridae
Velociraptorinae
Deinonychus
Scientific name
Deinonychus
Ostrom , 1969
Art
  • Deinonychus antirrhopus Ostrom, 1969

Deinonychus ( ancient Greek δεινός 'terrible' and ὄνυξ , genitive ὄνυχος 'claw / claw') was a genus of carnivorous dinosaurs from the group Dromaeosauridae . The only species described is Deinonychus antirrhopus .

This theropod , up to 3.4 meters long, lived during the early Cretaceous around 123 to 110 million years ago (from the Middle Aptian to the Lower Albian ). Fossils were discovered in the US states of Montana , Wyoming and Oklahoma in rocks of the Cloverly Formation and the Antlers Formation . Teeth that may belong to Deinonychus came from Maryland much further east .

Studies of the paleontologist John Ostrom about Deinonychus revolutionized in the late 1960s, the ideas of scientists about dinosaurs, leading to the "Dinosaur Renaissance" and the debate sparked whether dinosaurs same warm ( "warm-blooded") were animals. Previously, dinosaurs were considered cumbersome giants, similar to today's reptiles. The small body, the elegant, horizontal posture and especially the large sickle-shaped foot claws showed that Deinonychus was an active, agile predator .

features

Deinonychus in size comparison with a human

As the largest known specimens show, Deinonychus could reach a length of 3.4 meters. An individual of this size had a skull length of 41 centimeters, a hip height of 87 centimeters and a mass of about 73 kilograms. The skull was equipped with strong jaws that carried about 70 curved, blade-like teeth. All teeth were sawed on the front as well as the back, with the teeth ( denticles ) on the back of the teeth being almost twice as large as those on the front. John Ostrom's first reconstruction of the skull, still based on very fragmentary remains, shows a relatively compact, broad skull that resembles that of the Allosaurus . More recent skull finds of Deinonychus and closely related genera with good three-dimensional preservation show, however, that the palate was more arched than John Ostrom had suspected, which led to the reconstruction of a much narrower and longer snout. At the same time, the pair of cheekbones (Jugale) widened the skull in the eye region, which enabled good stereoscopic vision . The skull of Deinonychus differed from that of the Velociraptor, among other things, by the deeper, more robust lower jaw and by the more robust skullcap, which was similar to that of Dromaeosaurus . Furthermore, the nasal bone was not flattened like that of the Velociraptor . Both the skull and the lower jaw showed skull windows which reduced the weight of the skull. In Deinonychus , the anterior orbital window in front of the eyes was particularly large.

Deinonychus skull in the Field Museum of Natural History

As with all dromaeosaurids, the forelimbs were very long and reached 70 percent of the length of the hind legs in Deinonychus . The big hand made up 40 percent of the total length of the front limb. The first of the three fingers was the shortest while the second was the longest. Each hind leg had a sickle-shaped, unusually large claw on the second toe. In the life of the animal, the claws were larger than they are fossilized, since dinosaurs, like archosaurs living today, had a coating of horn over their claws. John Ostrom compared a sickle claw from Deinonychus (specimen number YPM 5205) with the claws of today's crocodiles and birds and came to the conclusion that the claw in living animals was over 120 millimeters long. Both anatomical evidence and evidence from fossil footprints show that only the third and fourth toes touched the ground while moving, while the second toe with the sickle claw was held above the ground while moving. The seat leg (ischium) was relative to the pubic bone shorter (pubis) than other Dromaeosauriden. The caudal vertebrae were furnished with a series of ossified tendons and greatly elongated vertebral processes - the prezygapophyses on the top and the chevron bones on the bottom of the vertebral bodies. John Ostrom suspected that this device turned the tail into a stiff counterweight. However, a fossil of the closely related Velociraptor mongoliensis (IGM 100/986) has a tail in the anatomical composite that was horizontally curved in an S-shape. This suggests considerable lateral mobility of the tail.

Although no feathers have so far been discovered in connection with Deinonychus fossils, the evidence of feathers in a large number of other dromaeosaurids suggests that all members of the group including Deinonychus were feathered (principle of phylogenetic clasping). The feathered Dromaeoauriden genus Microraptor is both geologically older and phylogenetically more original than Deinonychus . Several Microraptor fossils show contour feathers on arms, legs and tails that mimic those of today's birds. A ulna of the Velociraptor , which is closely related to Deinonychus, shows attachment points for feathers (English quill knobs ), which suggests long arm feathers in Velociraptor .

Systematics

Deinonychus is one of the best known dromaeosaurids and a close relative of the smaller Velociraptor , which is native to the younger strata of the Upper Cretaceous Northern China and Mongolia. Two other genera of the Upper Cretaceous, Tsaagan from Mongolia and the little-known Saurornitholestes from North America, could also have been close relatives of Deinonychus .

Velociraptor and Deinonychus together form the group Velociraptorinae, which was established by Rinchen Barsbold in 1983 and originally contained Velociraptor as the only genus. The long-snouted Velociraptorinen probably used their claws more and less their skulls to overpower prey, in contrast to other dromaeosaurids such as the dromaeosaurins, which had more compact skulls. In 1995 Philip Currie attributed Deinonychus as well as a number of other dromaeosaurids to the Velociraptorinae, which found general acceptance.

However, a more recent study by Nicholas Longrich and Philip Currie from 2009 classifies Deinonychus outside of the Velociraptorinae and establishes a group called Eudromaeosauria, which is said to contain Deinonychus , Velociraptorinae and Dromaeosaurinae. Together with the troodontids , the dromaeosaurids form the deinonychosauria , which, according to many researchers, is the sister group of birds and thus the dinosaur group most closely related to birds.

History of discovery and naming

Early discoveries and first description

Deinonychus fossil remains come from the Cloverly Formation in Montana and Wyoming as well as from the Antlers Formation in Oklahoma, which is about the same age. The Cloverly Formation was dated to the late Aptian to early Albian, making it around 123 to 110 million years old. In addition, teeth are known that come from the Arundel Clay Facies (middle aptium) of the Potomac Formation in Maryland and can possibly be assigned to this genus.

Graphic representation of Deinonychus

The first remains were discovered in southern Montana in 1931, near the town of Bridger . Barnum Brown , the head of the excavation, intended to dig up and prepare remains of the Tenontosaurus . In his excavation report to the American Museum of Natural History , however, he reported the discovery of a small carnivorous (carnivorous) dinosaur in close proximity to a Tenontosaurus skeleton, which was "enclosed by lime and difficult to prepare". Barnum Brown informally called the animal “ Daptosaurus ” and prepared the dissection so that it could be described and exhibited, but never finished his work. In addition to this skeleton, Barnum Brown discovered in the Cloverly Formation the skeleton of an even smaller theropod with apparently oversized teeth, which he informally called " Megadontosaurus ". As John Ostrom discovered decades later, the teeth come from Deinonychus - but the skeleton comes from a completely different animal, which he called the microvenator .

In August 1964, an expedition of the Peabody Museum of Natural History led by John Ostrom discovered additional skeletal material. Expeditions during the following two summers unearthed more than 1,000 bones, including at least three individuals of small, carnivorous dinosaurs. Most of the bones were found to be inarticulate, meaning that they were no longer in the skeletal structure, making it impossible to determine how many different individuals were present. The holotype specimen ( YPM 5205) from Deinonychus therefore only includes a complete left foot and parts of the right foot that definitely belonged to the same individual. The rest of the finds were cataloged in the Peabody Museum of Natural History at Yale University under 50 different inventory numbers.

A later study by John Ostrom and Grant E. Meyer analyzed this material as well as Barnum Brown's Daptosaurus and concluded that these finds were one and the same species. John Ostrom published his results in 1969 and attributed all of the remains to the new taxon Deinonychus antirrhopus . Deinonychus means something like "terrible claw" and refers to the unusually large, sickle-like claw on the second toe. The species name antirrhopus means "counterweight" and refers to John Ostrom's hypothesis about the function of the tail.

Although countless bones were available as early as 1969, important parts of the skeleton were missing or difficult to interpret. Only a few postorbital (behind the eyes) skull bones were known, and the thighbones (femur), sacrum (sacrum), forkbone (furcula) and sternum (sternum) were missing, as well as some vertebrae. A thin bone fragment John Ostrom described incorrectly as coracoid (coracoid). His first skeletal reconstruction also shows a very unusual pubis , which was trapezoidal, flat and as long as the ischium.

More discoveries

Model in the Natural History Museum in Vienna

1974 John Ostrom published another monograph , this time over the shoulder of Deinonychus . He found that the pubic bone he was describing was actually a raven bone, a shoulder element. That same year, another Deinonychus specimen was unearthed in Montana by a Harvard University expedition led by Farish Jenkins. This specimen shows a number of previously unknown skeletal elements, such as well-preserved thigh bones, pubic bone, a sacrum and a better preserved iliac bone (ilium), as well as foot and metatarsal bones. John Ostrom described this new specimen and revised his reconstruction of the Deinonychus skeleton. This time the reconstruction showed the very long pubic bone, which, Ostrom began to speculate, might have been bent backwards, as in birds.

The AMNH 3015, discovered by Barnum Brown in July 1931, is now considered to be one of the most complete skeletons. However, some small limestone blocks from this find with bones and bone fragments were not prepared and remained in the American Museum's holdings unnoticed for a long time. An examination of these blocks (copy number AMNH 3015) by Gerald Grellet-Tinner and Peter Makovicky in 2000 revealed interesting, previously overlooked features. Some long, thin bones that were initially mistaken for ossified tendons were actually abdominal ribs . Even more significant is the discovery of a large number of fossil eggshells and a fragmentary egg in the rock matrix surrounding the bones.

In a subsequent, more detailed study, Gerald Grellet-Tinner and Peter Makovicky concluded that the eggshells almost certainly belonged to Deinonychus ; thus they are the first remains of eggs to be identified by a dromaeosaurid. The outer surface of one of the eggshells was in close contact with the abdominal ribs, indicating that Deinonychus may have incubated the eggs. This could indicate that Deinonychus used body heat to incubate eggs, which would mean warm-bloodedness like today's birds. Further research by Gregory Erickson and colleagues has found that this individual was 13 or 14 years old when he died. In contrast to other theropods that were discovered in connection with eggs or nests, the Deinonychus specimen had already stopped growing when it died.

Similarities in the hands of Deinonychus (left) and Archeopteryx (right) suggest that birds descended from dinosaurs.

John Ostrom's description of Deinonychus in 1969 has been described as the most important single discovery in dinosaur paleontology of the mid-20th century. The discovery of this clearly active, nimble predator contributed significantly to the change in scientific and public perception of the nature of dinosaurs, and sparked speculation that dinosaurs may have been equilibrium. This development is known as the dinosaur renaissance. A few years later, John Ostrom noted similarities between the forelimbs of Deinonychus and those of birds, and concluded that birds were descended from dinosaurs. Thirty years later, this idea is accepted by almost all researchers.

Paleoenvironment and fauna community

Deinonychus lived in an alluvial or swamp-like habitat. The layers of the upper Cloverly Formation and the Antlers Formation show evidence of subtropical forests, river deltas and lagoons. Deinonychus shared its habitat with the armored ankylosaur Sauropelta and the ornithopods Zephyrosaurus and Tenontosaurus . The Antlers formation in Oklahoma also contained the large theropod Acrocanthosaurus , the giant sauropod Sauroposeidon , the crocodile Goniopholis and the periwinkle Lepisosteus . The Potomac Formation in Maryland, which contained some teeth possibly belonging to Deinonychus , was home to the sauropod Astrodon and the nodosaur Priconodon , which is only known from teeth.

Paleobiology

Hunting behavior and diet

Deinonychus teeth, found in association with fossils of the ornithopod Tenontosaurus , are relatively common in the Cloverly Formation. In two quarries, specimens of Deinonychus were found together with Tenontosaurus bones. The first of these quarries, the Yale Quarry in Montana (Cloverly Formation), contained numerous teeth as well as the remains of five Deinonychus individuals and the tail of a Tenontosaurus individual. This collection of individuals in a single quarry could indicate that Deinonychus was feeding on the Tenontosaurus carcass and perhaps even hunting that herbivore. Ostrom and Maxwell (1995) even suspect that Deinonychus lived and hunted in groups and that Tenontosaurus was the most important prey. Carpenter (1998) considers the evidence from the Yale quarry to be dubious because only a tail was found of Tenontosaurus and because the long bones of the site were preferably oriented in a north-west to north-east direction, which makes it possible that the bones are in front of the deposit. According to Carpenter, the relatively frequent finds of Deinonychus teeth in connection with Tenontosaurus fossils do not provide any evidence of active hunting, since Deinonychus could only have appeared as a scavenger with the same high probability.

Live plastic reconstruction of Deinonychus specimens without feathers that attack an Iguanodon .

Paul Gignac and colleagues described the bones of a Tenontosaurus in 2010 , which shows bite marks, probably derived from Deinonychus . A biomechanical simulation came to the conclusion that such bite marks in the bone required a biting force of at least 3315 N. Gignac and colleagues also assume a maximum bite force of at least 8200 N, which means that Deinonychus would have had a very high bite force both in absolute terms and in relation to body size. However, bite marks of the theropod are rarely found in the bones of Tenontosaurus , so the study assumes that Deinonychus does not regularly leave its bite marks on bones like a scavenger, but uses its strong bite for active hunting and defense.

In a quarry of the Antlers Formation in Oklahoma, six partial skeletons of different sizes of Tenontosaurus were found together with a partial skeleton and many teeth of Deinonychus . An upper arm bone (humerus) of Tenontosaurus even shows impressions that could be bite marks from Deinonychus . Brinkman and colleagues (1998) find that Deinonychus weighed 70 to 100 kilograms, while an adult Tenontosaurus weighed between one and four tons. They conclude that a single Deinonychus could not have killed an adult Tenontosaurus , which is why hunting in groups with Deinonychus is possible.

Roach and Brinkman (2007) see Deinonychus as a solitary hunter or at best operating in a loose association and found in the Deinonychus - Tenontosaurus evidence of a feeding behavior that resembles today's diapsid reptiles . For example, if Komodo dragons gather around a carcass, eat the largest individuals first and attack smaller individuals who come too close to the carcass - if the smaller animal is killed and eaten in the process, it is cannibalism . Roach and Brinkman state that the behavior of the Komodo dragons agrees with the taphonomy of the Deinonychus - Tenontosaurus findings. The incomplete Deinonychus remains of these sites come from not yet fully grown animals, the lack of skeletal parts indicating that other Deinonychus have eaten on the carcasses of the killed animals. On the other hand, Li and colleagues (2007) describe fossil footprints of dromaeosaurids that run in parallel tracks, which these researchers interpret as a clear indication of life in groups.

Although it is often suggested that dromaeosaurids like Deinonychus could hunt large prey such as ornithopods, like today's predators, they likely fed on both small and large prey. This assumption was recently confirmed by the discovery of intestinal contents in two Deinonychus skeletons that originated in the Cloverly Formation in Montana. These are small lumps of tightly packed bone that has been corroded by enzymes . While some of the highly fragmented bones likely came from a medium-sized dinosaur, many other fragments, such as a small bird's claw, show that Deinonychus also hunted much smaller prey. Although no gastroliths (stomach stones) were found, the very heavily fragmented remains indicate that stones in the stomach helped to break up the food. Parsons considers Deinonychus to be an opportunistic predator who - as the bird's claw shows - may have been able to catch flight prey.

Function of the sickle claw

Replica of the foot bones with sickle claw

Ostrom suspected that Deinonychus could hold prey with his long arms and slit them open with his sickle claw. Some researchers speculated that the bowels of large ceratopsians could have been torn out with the help of the sickle claw . Other studies showed that the sickle claw was not suitable for slitting, but for targeted piercing of the neck veins or the windpipe. Manning and colleagues (2005) conducted experiments with a robotic model of the Deinonychus foot by examining the effects of hydraulic shocks of the model's sickle claw on a pig's skin. In these tests, the claw only made small round point stitches and was not able to cut or even slit the skin. Instead, the skin below the puncture holes was pushed together strongly, which gave the claw additional support. The researchers therefore suspect that the claw acted like a crampon and gave the animal a secure hold on large prey, while it could inflict a variety of wounds with its teeth.

Ostrom compared Deinonychus with the ostrich and the cassowary . He noticed that these birds could cause serious injuries with their extended talons on the second toe. The cassowary is equipped with claws up to 12.5 centimeters long. Ostrom quoted Gilliard (1958) who stated that cassowaries are capable of severing an arm or ripping out a human's entrails. Kofron (1999 and 2003) studied 241 documented cassowary attacks in which a person and two dogs were killed, but found no evidence that a cassowary can cut up or slash other animals.

Manning and colleagues (2009) x-rayed a Velociraptor hand claw and compared it to the claws of the eagle owl to study the distribution of stresses and concluded that the claws of dromaeosaurids show clear adaptations to climbing trees. Parsons (2009) also suspected that Deinonychus and other dromaeosaurids could have lived on trees. The penultimate phalanx of the second toe with the sickle claw has a keel, which is found in a similar shape in today's woodpeckers . The curvature of the sickle claw also corresponds to the curvature of the claws of the woodpecker. This curvature is very different in the individual individuals. The type specimen described by Ostrom in 1969 (YPM 5205) has a strongly curved sickle claw, while a newer specimen described in 1976 (MCZ 4371) has a sickle claw with only weakly developed curvature, which is more similar to the "normal" claws of the other toes. Parsons hypothesizes that these are age-specific variations and that the degree of curvature decreases with age. Young Deinonychus with strongly curved sickle claws could have lived in trees, while individuals switched to a more terrestrial way of life with increasing age .

Function of the arms

Biomechanical studies by Kenneth Carpenter (2002) confirm that the long arms were used to grab and hold prey during hunting. This interpretation is further underpinned by the large and elongated raven leg, which indicates strong arm muscles. Using bone replicas, Carpenter shows that Deinonychus was unable to fold his arms against the body like a bird, contradicting previous observations by Jacques Gauthier (1985) and Gregory Paul (1988).

As studies by Phil Senter (2006) show, Deinonychus could hold and carry objects between the palms of the hands, but only with the wrist flexed. By stretching the wrist, the palms of the hands inevitably rotated upwards (supination), which, for example, would have allowed live prey to escape. Furthermore, Deinonychus could hold and carry objects with one hand by pressing against the chest. If Deinonychus' arms had long feathers like Velociraptor's , they would have limited the mobility of the arms to some extent. Poking around for small prey in crevices, for example, could only have been done with winged arms with the third finger extended perpendicular to the wing. Senter believes that such a poking around for prey is unlikely, but not impossible.

Parsons showed that juvenile and subadult Deinonychus specimens show some morphological differences to adults. The arms of the younger individuals were proportionally longer than those of the adults, which could be an indication of differences in behavior between young animals and adults.

speed

Dromaeosaurids, particularly Deinonychus , are often depicted as unusually fast animals in popular media. John Ostrom suspected in his first description that Deinonychus was " moderately, but not unusually fast " ("moderately, but not unusually fast"). This assumption was based on the assumption that the thighbone and shinbone were about the same length, although he did not have a thighbone when he was first described. It was not until 1976 that a skeleton with a femur (MCZ 4371) could be described. As Ostrom now noted, the thighbone was actually ten percent shorter than the shinbone - similar to the ornithomimosaur Struthiomimus, which was adapted for fast running . At the same time, however, he noted that the length ratio between the metatarsus and the shin is more meaningful for speed estimates than the thigh-shin ratio he had previously used. In the ostrich, the metatarsal-tibial ratio is 0.95, while the struthiomimus has a ratio of 0.68. Deinonychus, however, had a short metatarsus and a ratio of only 0.48. Ostrom concluded, " the only reasonable conclusion is that Deinonychus was not the most fleet-footed of theropods" ("the only acceptable explanation is that Deinonychus was not the fastest of the theropods").

Ostrom suspected that the hind leg with the sickle claw was used as a weapon to slash prey. According to Ostrom, the short metatarsus could have been an adaptation to reduce the stress on the leg bones during such an attack. The arrangement of muscle attachment points in the leg bones also differed from that of other theropods - as an explanation, Ostrom stated that different muscles were used when attacking prey than during normal running. Ostrom therefore concluded that Deinonychus' legs represent a compromise, since on the one hand they allow walking as fast as possible, on the other hand they should minimize stress during an attack.

The specimen discovered in 1974 (MCZ 4371) was larger than the very complete specimen discovered in 1931 (AMNH 3015). As Ostrom (1976) noted, the increase in size was not uniform: the arm in MCZ 4371 was 20%, the shin 18%, but the metatarsus only 12% longer than in AMNH 3015. This shows that the metatarsus was longer with became proportionally shorter with increasing age, suggesting that the ability to run quickly decreased with increasing age of the animals.

Richard Kool studied fossil tracks from the Gething Formation in the Canadian province of British Columbia and estimated the speed at which various animals had run when they left the footprints. Kool estimated that for a tracking of the Ichnogus Irenichnites gracilis , which could possibly come from Deinonychus , that the animal had walked at 10.1 km / h. A biomechanical study by Sellers and Manning (2007) estimates the maximum speed of the related Velociraptor at 10.8 m / s (38.9 km / h).

Eggs

Live reconstruction of a Deinonychus in breeding position

Grellet-Tinner and Makovicky (2000) discovered eggshells and a fragmentary egg in blocks of rock that belong to the Deinonychus specimen AMNH 3015, discovered by Barnum Brown in 1931 , but were not prepared. The egg is in contact with the abdominal ribs of the Deinonychus specimen and was probably laid by it. The researchers rule out that the egg was just a meal of the Deinonychus , because the egg fragments were located between the abdominal ribs and the arm bones and therefore could not be stomach contents. Furthermore, the way in which the egg was crushed and fragmented shows that it was still intact when it was buried by sediments and that it was only deformed by the process of fossilization. The possibility that the egg came into contact with the skeleton by chance is also considered unlikely. The surrounding bones were not scattered, but remained articulated in their original positions, which shows that the site was not disturbed afterwards. The abdominal ribs, which are rarely found articulated, support this interpretation. Grellet-Tinner and Makovicky state that all evidence suggests that the egg was under the Deinonychus's body when it was buried. The find could show a brooding Deinonychus over its egg; is also possible that the egg still in the oviduct was (oviduct).

Examination of the egg's microstructure confirms that it came from a theropod. Compared to other maniraptor theropods, the egg is more similar to those of the oviraptorids than those of the troodontids , although troodontids are more closely related to dromaeosaurids. The size of the egg could not be determined because of the severe deformation. However, the researchers examined the width of the pelvic canal that the egg had to pass through and estimated the diameter to be about 7 centimeters. The estimate is supported by the fact that the largest eggs of the oviraptorid Citipati were 7.2 centimeters in diameter, and that adult Citipati and Deinonychus were about the same size. Furthermore, the thickness of the Citipati eggshells is almost identical to that of Deinonychus , and since the thickness of the eggshell correlates with the egg volume, this is another indication that the eggs of both species were roughly the same size.

In popular culture

Deinonychus , along with Utahraptor and Velociraptor, is one of the most popular dromaeosaurids and has appeared in films, television shows, children's books, comics and video games. For example, Deinonychus appears in the British science fiction television series Primeval - Return of the Primeval Monsters (broadcast since 2007) as well as an action figure and actor in the comics and animated series of the Dino Riders series from the late 1980s and also provided the template for the so-called velociraptors in Jurassic Park . Furthermore, the Deinonychus is one of the main dinosaurs in the Carnosaurus films. The Dutch doom metal band Deinonychus (1992-2008) named themselves after this dinosaur.

Mounted skeletal casts of Deinonychus can be found in natural history museums around the world. The American Museum of Natural History in New York is home to the only assembled skeleton that is partly made up of real bones. These original bones belong to the specimen AMNH 3015, which Barnum Brown discovered in 1931 and which is still one of the most complete Deinonychus skeletons to this day . Even this assembled skeleton lacks elements such as the sternum, sternum ribs, wishbone, and abdominal ribs.

literature

Individual evidence

  1. ↑ a b c d e f John H. Ostrom: Stratigraphy and paleontology of the Cloverly Formation (Lower Cretaceous) of the Bighorn Basin area, Wyoming and Montana (= Peabody Museum of Natural History. Bulletin. Vol. 35). Peabody Museum of Natural History - Yale University, New Haven CT 1970.
  2. ^ A b c Gregory S. Paul : Predatory Dinosaurs of the World. A Complete Illustrated Guide. Simon & Schuster, New York NY 1988, ISBN 0-671-61946-2 , pp. 366-369.
  3. ^ John H. Ostrom: Osteology of Deinonychus antirrhopus, an unusual theropod from the Lower Cretaceous of Montana (= Peabody Museum of Natural History. Bulletin. Vol. 30, ISSN  0079-032X ). Peabody Museum of Natural History - Yale University, New Haven CT 1969.
  4. ^ A b William D. Maxwell, Lawrence M. Witmer : New Material of Deinonychus (Dinosauria, Theropoda). In: Journal of Vertebrate Paleontology. Vol. 16, Supplement to No. 3 = Abstracts of Papers Fifty-Sixth Annual Meeting. Society of Vertebrate Paleontology. American Museum of Natural History, New York, New York October 16-19, 1996 , 1996, ISSN  0272-4634 , p. 51A.
  5. ↑ a b c d Mark A. Norell , Peter J. Makovicky : Dromaeosauridae. In: David B. Weishampel , Peter Dodson , Halszka Osmólska (eds.): The Dinosauria . 2nd edition. University of California Press, Berkeley CA et al. 2004, ISBN 0-520-24209-2 , pp. 196-209.
  6. ^ Lawrence M. Witmer, William D. Maxwell: The skull of Deinonychus (Dinosauria: Theropoda): New insights and implications. In: Journal of Vertebrate Paleontology. Vol. 16, Supplement to No. 3 = Abstracts of Papers Fifty-Sixth Annual Meeting. Society of Vertebrate Paleontology. American Museum of Natural History, New York, New York October 16-19, 1996 , 1996, p. 73A.
  7. ↑ a b Rihui Li, Martin G. Lockley, Peter J. Makovicky, Masaki Matsukawa, Mark A. Norell, Jerald D. Harris, Mingwei Liu: Behavioral and faunal implications of Early Cretaceous deinonychosaur trackways from China. In: The natural sciences . Vol. 95, No. 3, 2008, pp. 185-191, doi : 10.1007 / s00114-007-0310-7 .
  8. ^ Mark A. Norell, Peter J. Makovicky: Important features of the dromaeosaurid skeleton. 2, Information from newly collected specimens of Velociraptor mongoliensis (= American Museum Novitates. No. 3282, ISSN  0003-0082 ). American Museum of Natural History, New York NY 1999, online .
  9. ↑ a b Xing Xu , Zhonghe Zhou , Xiaolin Wang, Xuewen Kuang, Fucheng Zhang, Xiangke Du: Four-winged dinosaurs from China. In: Nature . Vol. 421, No. 6921, 2003, pp. 335-340, doi : 10.1038 / nature01342 .
  10. ↑ Sunny H. Hwang, Mark A. Norell, Ji Qiang, Gao Keqin: New specimens of Microraptor zhaoianus (Theropoda: Dromaeosauridae) from northeastern China (= American Museum Novitates. No. 3381). American Museum of Natural History, New York NY 2002, online .
  11. ^ Alan H. Turner, Peter J. Makovicky, Mark A. Norell: Feather Quill Knobs in the Dinosaur Velociraptor. In: Science . Vol. 317, No. 5845, 2007, p. 1721, doi : 10.1126 / science.1145076 .
  12. ↑ a b Mark A. Norell, James M. Clark, Alan H. Turner, Peter J. Makovicky, Rinchen Barsbold , Timothy Rowe : A new dromaeosaurid theropod from Ukhaa Tolgod (Ömnögov, Mongolia) (= American Museum Novitates. No. 3545 ). American Museum of Natural History, New York NY 2006, online .
  13. ^ Alan H. Turner, Sunny H. Hwang, Mark A. Norell: A small derived theropod from Öösh, Early Cretaceous, Baykhangor Mongolia (= American Museum Novitates. No. 3557). American Museum of Natural History, New York NY 2007, online .
  14. ↑ Ринченгийн Барсболд: Хищные динозавры мела Монголии. Совместная Советско-Монгольская палеонтологическая экспедиция (= Труды. 19). Наука, Москва 1983 (In English: Rinchen Barsbold: Carnivorous dinosaurs from the Cretaceous of Mongolia. The Joint Soviet-Mongolian Paleontological Expedition (= Transaction. Vol. 19). Self-published by the author, Berkeley CA 1983, online ).
  15. ^ Gregory S. Paul: Predatory Dinosaurs of the World. A Complete Illustrated Guide. Simon & Schuster, New York NY 1988, ISBN 0-671-61946-2 , p. 358.
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  17. ↑ Nicholas R. Longrich, Philip J. Currie: A microraptorine (Dinosauria – Dromaeosauridae) from the Late Cretaceous of North America. In: Proceedings of the National Academy of Sciences of the United States of America . Vol. 106, No. 13, 2009, doi : 10.1073 / pnas.0811664106 , digital copy (PDF; 763.02 kB) .
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  43. ↑ Dawn Adams: The bigger they are, the harder they fall: Implications of ischial curvature in ceratopsian dinosaurs. In: Philip J. Currie, Emlyn H. Koster (Ed.): Fourth symposium on mesozoic terrestrial ecosystems, Drumheller, August 10-14, 1987. Short Papers (= Occasional Paper of the Tyrrell Museum of Palaeontology. No. 3, ZDB -ID 1217807-x ). Tyrrell Museum of Palaeontology, Drumheller 1987, pp. 1-6.
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  60. ↑ Deinonychus . In: American Museum of Natural History. Archived from the original on April 27, 2009 ; accessed on August 3, 2014 .

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