After studying the fossils, found in a sag basin in southern Patagonia (Argentina, South America), scientists concluded that the occurrence of many fossils of dinosaurs at different life stages within a square kilometre suggests they lived in herds nearly 190 million years ago (the fossils have been dated to 192 million years ago).

source https://gadgets.ndtv.com/science/news/dinosaur-fossils-study-social-behavious-herds-group-age-size-2587946#rss-gadgets-all