How did artiodactyls become more prominent during the Oligocene Epoch?

Artiodactyls became more prominent during the Oligocene Epoch (approximately 33.9 million to 23 million years ago) primarily due to the decline of the previously dominant perissodactyls.1

This shift in dominance was part of a broader pattern of faunal turnover that followed global cooling at the end of the Eocene Epoch. This cooling triggered significant environmental changes, converting dense rainforests into more open forests and grasslands. As these habitats evolved, artiodactyls underwent successive waves of diversification, with each new group proving better adapted to the changing environment than its predecessors.21

During this period, early forms such as the entelodonts—often described as giant "pigs"—became widespread in Europe and North America. The success of artiodactyls continued into the Miocene Epoch, where they further diversified as open grassy habitats expanded, favoring animals with specialized teeth for grazing and limbs adapted for running.12