What significant development is associated with the Pliocene epoch?

The significant development associated with the Pliocene epoch is the evolution of bipedalism. This period, which spans from approximately 5.3 to 2.6 million years ago, is crucial in the study of human evolution as it marks the emergence of early hominins who began to walk on two legs. Bipedalism allowed these early ancestors to cover larger distances, see over tall grass, and free their hands for tool use and carrying objects, which would eventually contribute to a range of anatomical and social developments.

While Old World monkeys do appear in the fossil record earlier than the Pliocene, the evolution of bipedalism is a key innovation that significantly shaped human ancestry during this epoch. Additionally, the Pliocene does see the onset of ice ages, and developments in brain size continue to evolve beyond this period, but these are not the defining characteristic of the Pliocene in the context of human evolutionary history. Bipedalism stands out as a landmark adaptation that has profound implications for both the development of species and their adaptation to varying environments during this time.