Senses Comparisons between the
scleral rings of several dromaeosaurids (
Microraptor,
Sinornithosaurus, and
Velociraptor) and modern birds and reptiles indicate that some dromaeosaurids (including
Microraptor and
Velociraptor) may have been
nocturnal predators, while
Sinornithosaurus is inferred to be
cathemeral (active throughout the day at short intervals). However, the discovery of iridescent plumage in
Microraptor has cast doubt on the inference of nocturnality in this genus, as no modern birds that have iridescent plumage are known to be nocturnal. Studies of the
olfactory bulbs of dromaeosaurids reveal that they had similar olfactory ratios for their size to other non-avian
theropods and modern birds with an acute sense of smell, such as
tyrannosaurids and the
turkey vulture, probably reflecting the importance of the
olfactory sense in the daily activities of dromaeosaurids such as finding food.
Feeding Dromaeosaurid feeding was discovered to be typical of coelurosaurian theropods, with a characteristic "puncture and pull" feeding method similar to that of modern Komodo dragons. Studies of wear patterns on the teeth of dromaeosaurids by Angelica Torices et al. indicate that dromaeosaurid teeth share similar wear patterns to those seen in the Tyrannosauridae and Troodontidae. However, microwear on the teeth indicated that dromaeosaurids likely preferred larger prey items than the troodontids they often shared their environment with. Such dietary differentiations likely allowed them to inhabit the same environment. The same study also indicated that dromaeosaurids such as
Dromaeosaurus and
Saurornitholestes (two dromaeosaurids analyzed in the study) likely included bone in their diet and were better adapted to handle struggling prey while troodontids, equipped with weaker jaws, preyed on softer animals and prey items such as invertebrates and carrion.
Claw function There is currently disagreement about the function of the enlarged "sickle claw" on the second toe. When John Ostrom described it for
Deinonychus in 1969, he interpreted the claw as a blade-like slashing weapon, much like the canines of some
saber-toothed cats, used with powerful kicks to cut into prey. Adams (1987) suggested that the talon was used to disembowel large
ceratopsian dinosaurs. The interpretation of the sickle claw as a killing weapon applied to all dromaeosaurids. However, Manning et al. argued that the claw instead served as a hook, reconstructing the keratinous sheath with an elliptical cross section, instead of the previously inferred inverted teardrop shape. In Manning's interpretation, the second toe claw would be used as a climbing aid when subduing bigger prey and also as a stabbing weapon. Ostrom compared
Deinonychus to the
ostrich and
cassowary. He noted that the bird species can inflict serious injury with the large claw on the second toe. 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. Phillip Manning and colleagues (2009) attempted to test the function of the sickle claw and similarly shaped claws on the forelimbs. They analyzed the bio-mechanics of how stresses and strains would be distributed along the claws and into the limbs, using
X-ray imaging to create a three-dimensional contour map of a forelimb claw from
Velociraptor. For comparison, they analyzed the construction of a claw from a modern predatory bird, the
eagle owl. They found that, based on the way that stress was conducted along the claw, they were ideal for climbing. The scientists found that the sharpened tip of the claw was a puncturing and gripping instrument, while the curved and expanded claw base helped transfer stress loads evenly. The Manning team also compared the curvature of the dromaeosaurid "sickle claw" on the foot with curvature in modern birds and mammals. Previous studies had shown that the amount of curvature in a claw corresponded to what lifestyle the animal has: animals with strongly curved claws of a certain shape tend to be climbers, while straighter claws indicate ground-dwelling lifestyles. The sickle claws of the dromaeosaurid
Deinonychus have a curvature of 160 degrees, well within the range of climbing animals. The forelimb claws they studied also fell within the climbing range of curvature. Paleontologist Peter Mackovicky commented on the Manning team's study, stating that small, primitive dromaeosaurids (such as
Microraptor) were likely to have been tree-climbers, but that climbing did not explain why later, gigantic dromaeosaurids such as
Achillobator retained highly curved claws when they were too large to have climbed trees. Mackovicky speculated that giant dromaeosaurids may have adapted the claw to be used exclusively for latching on to prey. '' digging a
multituberculate out of a burrow, a function with weak support In 2009 Phil Senter published a study on dromaeosaurid toes and showed that their range of motion was compatible with the excavation of tough insect nests. Senter suggested that small dromaeosaurids such as
Rahonavis and
Buitreraptor were small enough to be partial
insectivores, while larger genera such as
Deinonychus and
Neuquenraptor could have used this ability to catch
vertebrate prey residing in insect nests. However, Senter did not test whether the strong curvature of dromaeosaurid claws was also conducive to such activities. In 2011, Denver Fowler and colleagues suggested a new method by which dromaeosaurids may have taken smaller prey. This model, known as the "raptor prey restraint" (RPR) model of predation, proposes that dromaeosaurids killed their prey in a manner very similar to extant
accipitrid birds of prey: by leaping onto their quarry, pinning it under their body weight, and gripping it tightly with the large, sickle-shaped claws. Like accipitrids, the dromaeosaurid would then begin to feed on the animal while still alive, until it eventually died from blood loss and organ failure. This proposal is based primarily on comparisons between the morphology and proportions of the feet and legs of dromaeosaurids to several groups of extant birds of prey with known predatory behaviors. Fowler found that the feet and legs of dromaeosaurids most closely resemble those of
eagles and
hawks, especially in terms of having an enlarged second claw and a similar range of grasping motion. The short
metatarsus and foot strength, however, would have been more similar to that of
owls. The RPR method of predation would be consistent with other aspects of dromaeosaurid anatomy, such as their unusual dentition and arm morphology. The arms, which could exert a lot of force but were likely covered in long feathers, may have been used as flapping stabilizers for balance while atop a struggling prey animal, along with the stiff counterbalancing tail. Dromaeosaurid jaws, thought by Fowler and colleagues to be comparatively weak, would have been useful for eating prey alive but not as useful for quick, forceful dispatch of the prey. These predatory adaptations working together may also have implications for the
origin of flapping in
paravians. In 2019, Peter Bishop reconstructed the leg skeleton and musculature of
Deinonychus by using three-dimensional models of
muscles,
tendons, and
bones. With the addition of mathematical models and equations, Bishop simulated the conditions that would provide maximum force at the tip of the sickle claw and therefore the most likely function. Among the proposed modes of the sickle claw use are: kicking to cut, slash or disembowel prey; for gripping onto the flanks of prey; piercing aided by body weight; to attack vital areas of the prey; to restrain prey;
intra- or
interspecific competition; and digging out prey from hideouts. The results obtained by Bishop showed that a crouching posture increased the claw forces, however, these forces remained relatively weak indicating that the claws were not strong enough to be used in slashing strikes. Rather than being used for slashing, the sickle claws were more likely to be useful in flexed leg angles such as restraining prey and stabbing prey at close quarters. These results are consistent with the
Fighting Dinosaurs specimen, which preserves a
Velociraptor and
Protoceratops locked in combat, with the former gripping onto the other with its claws in a non-extended leg posture. Despite the obtained results, Bishop considered that the capabilities of the sickle claw could have varied within taxa given that among dromaeosaurids,
Adasaurus had an unusually smaller sickle claw that retained the characteristic ginglymoid—a structure divided in two parts—and hyperextensible articular surface of the penultimate phalange. He could neither confirm nor disregard that the pedal digit II could have loss or retain its functionally. A 2020 study by Gianechini et al., also indicates that velociraptorines, dromaeosaurines and other eudromaeosaurs in Laurasia differed greatly in their locomotive and killing techniques from the unenlagiine dromaeosaurids of Gondwana. The shorter second phalanx in the second digit of the foot allowed for increased force to be generated by that digit, which, combined with a shorter and wider metatarsus, and a noticeable marked hinge‐like morphology of the articular surfaces of metatarsals and phalanges, possibly allowed eudromaeosaurs to exert a greater gripping strength than unenlagiines, allowing for more efficient subduing and killing of large prey. In comparison, the unenlagiine dromaeosaurids had a longer and slender subarctometatarsus, and less well‐marked hinge joints, a trait that possibly gave them greater cursorial capacities and allowed for greater speed. Additionally, the longer second phalanx of the second digit allowed unenlagiines fast movements of their feet's second digits to hunt smaller and more elusive types of prey. These differences in locomotor and predatory specializations may have been a key feature that influenced the evolutionary pathways that shaped both groups of dromaeosaurs in the northern and southern hemispheres.
Group behavior Paravipus didactyloides, interpreted as representing two individuals that were moving in the same direction
Deinonychus fossils have been uncovered in small groups near the remains of the herbivore
Tenontosaurus, a larger
ornithischian dinosaur. This had been interpreted as evidence that these dromaeosaurids hunted in coordinated packs like some modern
mammals. However, not all
paleontologists found the evidence conclusive, and a subsequent study published in 2007 by Roach and Brinkman suggests that the
Deinonychus may have actually displayed a disorganized mobbing behavior. Modern
diapsids, including
birds and
crocodiles (the closest relatives of dromaeosaurids), display minimal long-term cooperative hunting (except the
aplomado falcon and
Harris's hawk); instead, they are usually solitary hunters, either joining forces time to time to increase hunting success (as crocodilians sometimes do), or are drawn to previously killed carcasses, where conflict often occurs between individuals of the same species. For example, in situations where groups of
Komodo dragons are eating together, the largest individuals eat first and might attack smaller Komodo dragons that attempt to feed; if the smaller animal dies, it is usually
cannibalized. When this information is applied to the sites containing putative pack-hunting behavior in dromaeosaurids, it appears somewhat consistent with a Komodo dragon-like feeding strategy.
Deinonychus skeletal remains found at these sites are from subadults, with missing parts that may have been eaten by other
Deinonychus, which a study by Roach et al. presented as evidence against the idea that the animals cooperated in the hunt. A 2020 study done by Frederickson and colleagues found the dietary preferences between juvenile and adult
Deinonychus to be different. Suggesting that parental feeding ended before the young were large enough to sustain a typical adult diet. This would indicate that the genus did not exhibit mammal-like pack hunting. Despite this, they considered gregariousness to be possible in
Deinonychus. The Komodo dragon lifestyle was also criticized, due to the lack of spatial distribution of juveniles and adults, suggesting a reduced cannibalistic lifestyle. In 2001, multiple
Utahraptor specimens ranging in age from fully grown adult to tiny three-foot-long baby were found at a site considered by some to be a quicksand predator trap. Some consider this as evidence of family hunting behaviour; however, the full sandstone block is yet to be opened and researchers are unsure as to whether or not the animals died at the same time. Frederickson and colleagues suggests this was a possible sign of gregariousness in
Utahraptor and dromaeosaurids exhibiting post nestling care. and the ability to
fly or glide has been suggested for at least five dromaeosaurid species. The first,
Rahonavis ostromi (originally classified as avian bird, but found to be a dromaeosaurid in later studies) may have been capable of powered
flight, as indicated by its long forelimbs with evidence of quill knob attachments for long sturdy flight feathers. The forelimbs of
Rahonavis were more powerfully built than
Archaeopteryx, and show evidence that they bore strong ligament attachments necessary for flapping flight. Luis Chiappe concluded that, given these adaptations,
Rahonavis could probably fly but would have been more clumsy in the air than modern birds. Another species of dromaeosaurid,
Microraptor gui, may have been capable of gliding using its well-developed wings on both the fore and hind limbs. A 2005 study by
Sankar Chatterjee suggested that the wings of
Microraptor functioned like a split-level "
biplane", and that it likely employed a
phugoid style of gliding, in which it would launch from a perch and swoop downward in a U-shaped curve, then lift again to land on another tree, with the tail and hind wings helping to control its position and speed. Chatterjee also found that
Microraptor had the basic requirements to sustain level powered flight in addition to gliding. The possibility that
Sinornithosaurus millenii was capable of gliding or even powered flight has also been brought up several times, though no further studies have occurred.
Zhenyuanlong preserves wing feathers that are aerodynamically shaped, with particularly bird-like coverts as opposed to the longer, wider-spanning coverts of forms like
Archaeopteryx and
Anchiornis, as well as fused sternal plates. Due to its size and short arms it is unlikely that
Zhenyuanlong was capable of powered flight (though the importance of biomechanical modelling in this regard is stressed
Swimming of halszkaraptorine
Natovenator, depicting swimming behavior At least one dromaeosaurid group,
Halszkaraptorinae, whose members are halszkaraptorines, are most likely to have been specialised for aquatic or
semiaquatic habits, having developed limb proportions, tooth morphology, and
rib cage akin to those of diving birds. Fishing habits have been proposed for
unenlagiines, including comparisons to attributed semi-aquatic
spinosaurids, but any aquatic propulsion mechanisms have not been discussed so far.
Reproduction In 2006, Grellet-Tinner and Makovicky reported an egg associated with a specimen of
Deinonychus. The egg shares similarities with
oviraptorid eggs, and the authors interpreted the association as potentially indicative of brooding. A study published in November 2018 by Norell, Yang and Wiemann et al., indicates that
Deinonychus laid blue eggs, likely to camouflage them as well as creating open nests. Other dromaeosaurids may have done the same, and it is theorized that they and other maniraptoran dinosaurs may have been an origin point for laying colored eggs and creating open nests as many birds do today. ==In popular culture==