The behavior of dinosaurs are usually modeled using computer simulations, biomechanics, and the ecosystem in which they lived. Paleontologists also compare them to existing animals today that live in similar environments. Despite the many tools used to study dinosaur behavior, much of it is speculation.
Many paleontologiests all agree that dinosaurs behaved very much like modern day birds and crocodiles, which are closely related to dinosaurs, and have existed for millions of years. The first evidence that some species of dinosaurs herded were found in 1878 when a group of about 30 dinosaur fossils were found in a ravine where it appears they all perished.
Similar mass fossil sites have been found around the globe, and many species like the duck-bill which were herbivores also moved in herds. This is consistent with many animals today which are herbivores, such as Bison and other species. It also appears that even the massive sauropods also herded together in groups. Most paleontologists believe dinosaurs herded together for mutual defense or migration purposes, and kept their young in full site.
While many dinosaurs moved together in herds, others built nests much like birds. In 1978 a discovery was made of a dinosaur called Maisaura. It was found near a nesting location in Montana. This was evidence that some species of dinosaurs cared for their young even after birth. Some species even had large nesting colonies. Paleontologists are not sure about how the dinosaurs communicated with each other.
One of the most important discoveries was made in 1971. The fossils of a Velociraptor were found fighting a Protoceratops, and this was solid prove that dinosaurs did indeed fight and eat each other. Up to that point there had been debates about this. Recent evidence shows that dinosaurs may have communicated with each other using sound, though this area of research is currently ongoing.
It is interesting to note that very few dinosaur species have been found which dug burrows or climbed trees. These types of animals do not appear to have arrived until the Cenozoic period. However, the analysis of dinosaur muscles indicate they could run extremely fast, and some species appear to have been able to create sonic booms with their tails.
It also appears that other dinosaurs had feathers which they used like birds to rest on top of their eggs to keep them warm. This would be consistent with the theory that modern birds are the descendants of dinosaurs. In the future it is expected that more studies will shed light on the behavior of dinosaurs.