Dinosaurs exhibited complex social behaviors, including living in groups. Herding allowed many species to navigate their prehistoric worlds. A dinosaur herd refers to a group of individuals from the same or multiple species, moving or residing in close proximity, suggesting a coordinated social structure. This grouping offered various benefits, shaping their daily lives and interactions.
How We Know Dinosaurs Herded
Dinosaur herding behavior is understood through fossil evidence. Fossilized trackways, showing multiple footprints moving in the same direction, are a key indicator. Trackways in the Paluxy riverbed in central Texas, for instance, show parallel sauropod footsteps, suggesting group movement. Discoveries in Alberta, Canada, show multispecies herding, with horned ceratopsians and armored ankylosaurs traveling together about 76 million years ago.
Bonebeds, large concentrations of bones from numerous individuals of the same species, provide another compelling line of evidence. These mass assemblages often suggest a catastrophic event, like a flood or volcanic eruption, that affected a group of dinosaurs. The discovery of 69 individuals and over 100 eggs of the sauropodomorph Mussaurus patagonicus in Argentina, dating back 193 million years, provides the earliest evidence of complex herd behavior, indicating these dinosaurs lived in groups and possibly cared for their young communally.
Why Dinosaurs Formed Herds
Dinosaurs formed herds for several evolutionary advantages, similar to modern social animals. Protection from predators was a significant factor; “safety in numbers” made it more difficult for a single predator to target an individual within a large group. Herds could also detect threats earlier and deter attackers through sheer numbers or coordinated defense. Some multispecies herds, like ceratopsians and ankylosaurs, formed as a defense strategy against apex predators such as tyrannosaurs.
Improved foraging efficiency was another benefit, especially for large herbivores requiring vast amounts of food. Moving in a group helped them find and share information about food sources, or cover larger distances to access seasonal resources. For instance, the increased body size of early sauropodomorphs necessitated herding to forage over long distances to meet energy requirements. Herding also played a role in reproductive success, facilitating mate finding and providing protection for nesting sites and young. Some dinosaur nesting grounds show evidence of multiple species returning to the same site, reinforcing communal breeding strategies.
Which Dinosaurs Lived in Herds
Evidence suggests that various dinosaur groups exhibited herding behaviors. Large sauropods, like Apatosaurus and Diplodocus, are widely believed to have moved in herds, with numerous trackways indicating group movement. The early sauropodomorph Mussaurus patagonicus provides the earliest confirmed evidence of complex social herding, dating back approximately 193 million years.
Ornithopods, particularly hadrosaurs such as Maiasaura, are also well-known for their social habits, with discoveries of nesting colonies and bonebeds containing many individuals. These duck-billed dinosaurs often possessed head crests, which may have been used for communication within the herd. Ceratopsians, including Triceratops and Pachyrhinosaurus, are another group with strong evidence of herding, supported by large bonebeds indicating mass death events of groups. Even some theropods, typically thought of as solitary predators, have fossil evidence suggesting group association, such as multiple Coelophysis skeletons found together.
Inside a Dinosaur Herd
Life within a dinosaur herd likely involved dynamic social structures and communication. For species like Mussaurus patagonicus, evidence suggests age-segregated groups, where eggs and hatchlings were found in one area, juveniles in another, and adults alone or in pairs, indicating a community where adults protected and foraged for the young. This age-based partitioning is similar to modern large terrestrial herbivores.
Communication within herds might have involved various methods. Hadrosaurs, with their hollow crests, may have produced loud, deep calls for alarm or to warn off rivals, serving as a way to alert the herd to danger. Visual displays, such as the distinctive shapes and colors of head crests or horns in hadrosaurs and ceratopsians, could have been used for recognition among family groups or for sexual display during mating seasons. While living in large groups offered protection and foraging advantages, it also presented challenges, such as the immense impact on plant life, which likely necessitated constant migration in search of food.