Editing Dinosaur (section)

===Behavior===
[[File:Maiasaurusnest.jpg|thumb|left|A nesting ground of the hadrosaur ''[[Maiasaura|Maiasaura peeblesorum]]'' was discovered in 1978]]

Many modern birds are highly social, often found living in flocks. There is general agreement that some behaviors that are common in birds, as well as in [[crocodilian]]s (closest living relatives of birds), were also common among extinct dinosaur groups. Interpretations of behavior in fossil species are generally based on the pose of skeletons and their [[Habitat (ecology)|habitat]], [[computer simulation]]s of their biomechanics, and comparisons with modern animals in similar ecological niches.<ref name=alexander2006/>

The first potential evidence for [[herd]]ing or [[Flocking (behavior)|flocking]] as a widespread behavior common to many dinosaur groups in addition to birds was the 1878 discovery of 31&nbsp;''Iguanodon'', ornithischians that were then thought to have perished together in [[Bernissart]], [[Belgium]], after they fell into a deep, flooded [[sinkhole]] and drowned.<ref name=Yans/> Other mass-death sites have been discovered subsequently. Those, along with multiple trackways, suggest that gregarious behavior was common in many early dinosaur species. Trackways of hundreds or even thousands of herbivores indicate that duck-billed (hadrosaurids) may have moved in great herds, like the [[American bison]] or the African [[springbok]]. Sauropod tracks document that these animals traveled in groups composed of several different species, at least in [[Oxfordshire]], England,<ref name=Day2002/> although there is no evidence for specific herd structures.<ref name=JLW05/> Congregating into herds may have evolved for defense, for [[Bird migration|migratory]] purposes, or to provide protection for young. There is evidence that many types of slow-growing dinosaurs, including various theropods, sauropods, ankylosaurians, ornithopods, and ceratopsians, formed aggregations of immature individuals. One example is a site in [[Inner Mongolia]] that has yielded remains of over 20 ''[[Sinornithomimus]]'', from one to seven years old. This assemblage is interpreted as a social group that was trapped in mud.<ref name=DVetal08sino/> The interpretation of dinosaurs as gregarious has also extended to depicting carnivorous theropods as [[pack hunter]]s working together to bring down large prey.<ref name=LG93/><ref name="maxwell&ostrom1995"/> However, this lifestyle is uncommon among modern birds, crocodiles, and other reptiles, and the [[taphonomy|taphonomic]] evidence suggesting mammal-like pack hunting in such theropods as ''Deinonychus'' and ''[[Allosaurus]]'' can also be interpreted as the results of fatal disputes between feeding animals, as is seen in many modern diapsid predators.<ref name=RB07/>

[[File:Centrosaurus dinosaur.png|thumb|upright=1.15|Restoration of two ''[[Centrosaurus|Centrosaurus apertus]]'' engaged in [[intra-specific combat]]]]
The crests and frills of some dinosaurs, like the [[marginocephalia]]ns, theropods and [[Lambeosaurinae|lambeosaurine]]s, may have been too fragile to be used for active defense, and so they were likely used for sexual or aggressive displays, though little is known about dinosaur mating and [[territory (animal)|territorialism]]. Head wounds from bites suggest that theropods, at least, engaged in active aggressive confrontations.<ref name=PC98/>

From a behavioral standpoint, one of the most valuable dinosaur fossils was discovered in the [[Gobi Desert]] in 1971. It included a ''[[Velociraptor]]'' attacking a ''[[Protoceratops]]'',<ref name=AMNH/> providing evidence that dinosaurs did indeed attack each other.<ref name=carpenter1998/> Additional evidence for attacking live prey is the partially healed tail of an ''[[Edmontosaurus]]'', a hadrosaurid dinosaur; the tail is damaged in such a way that shows the animal was bitten by a tyrannosaur but survived.<ref name=carpenter1998/> [[Cannibalism (zoology)|Cannibalism]] amongst some species of dinosaurs was confirmed by tooth marks found in [[Madagascar]] in 2003, involving the theropod ''[[Majungasaurus]]''.<ref name=rogersetal2003/>

Comparisons between the [[sclerotic ring|scleral rings]] of dinosaurs and modern birds and reptiles have been used to infer daily activity patterns of dinosaurs. Although it has been suggested that most dinosaurs were active during the day, these comparisons have shown that small predatory dinosaurs such as dromaeosaurids, ''[[Juravenator]]'', and ''[[Megapnosaurus]]'' were likely [[nocturnal]]. Large and medium-sized herbivorous and omnivorous dinosaurs such as ceratopsians, sauropodomorphs, hadrosaurids, ornithomimosaurs may have been [[cathemeral]], active during short intervals throughout the day, although the small ornithischian ''[[Agilisaurus]]'' was inferred to be [[Diurnality|diurnal]].<ref name=SchmitzMotani2011/>

Based on fossil evidence from dinosaurs such as ''[[Oryctodromeus]]'', some ornithischian species seem to have led a partially [[fossorial]] (burrowing) lifestyle.<ref name=VMK07/> Many modern birds are [[arboreal]] (tree climbing), and this was also true of many Mesozoic birds, especially the enantiornithines.<ref>{{harvnb|Chiappe|Witmer|2002}}</ref> While some early bird-like species may have already been arboreal as well (including dromaeosaurids) such as ''Microraptor''<ref name=chatterjee2007/>) most non-avialan dinosaurs seem to have relied on land-based locomotion. A good understanding of how dinosaurs moved on the ground is key to models of dinosaur behavior; the science of biomechanics, pioneered by [[Robert McNeill Alexander]], has provided significant insight in this area. For example, studies of the forces exerted by muscles and gravity on dinosaurs' skeletal structure have investigated how fast dinosaurs could run,<ref name=alexander2006/> whether [[diplodocid]]s could create [[sonic boom]]s via [[whip]]-like tail snapping,<ref name=goriely/> and whether sauropods could float.<ref name=Henderson2006/>