Final answer:
During the Middle and Late Cretaceous period, the dinosaur communities were primarily composed of hadrosaurids, ceratopsians, and ankylosaurs. These groups of dinosaurs replaced earlier dominant groups like sauropods and theropods, filling various ecological niches and shaping the Late Cretaceous landscapes.
Step-by-step explanation:
The Middle and Late Cretaceous dinosaur faunas were dominated by hadrosaurids, ceratopsians, and ankylosaurs. This marks a dramatic shift from earlier periods where other groups like sauropods and theropods were more prevalent.
Hadrosaurids, commonly known as duck-billed dinosaurs, were among the most common and widespread dinosaurs in the Cretaceous period. Ceratopsians, known for their distinctive horns and frills, were also significant members of the fauna, along with ankylosaurs, recognizable by their armored backs and heavy tail clubs. These groups filled various ecological niches, with some being herbivores and others likely playing roles in defense against predators or competition among herbivores. By contrast, earlier dinosaur groups like sauropods, which included the largest land animals ever to live, and theropods, which included all meat-eating dinosaurs, became less dominant during the same time frame.