What dinosaurs are defenseless?

Many dinosaurs had limited or no defensive adaptations compared to their more armored relatives. For example, small, herbivorous dinosaurs like the Hypsilophodon or the Compsognathus lacked physical defenses such as strong horns, spikes, or thick armor. Additionally, some larger herbivores, like certain sauropods, had minimal defenses against predators, relying more on size and group behavior for protection rather than physical defenses. Overall, defenseless dinosaurs often depended on speed, agility, or social behavior to evade threats.