According to https://en.wikipedia.org/wiki/Timeline_of_the_evolutionary_history_of_life https://en.wikipedia.org/wiki/Timeline_of_the_evolutionary_h..., that's

According to https://en.wikipedia.org/wiki/Timeline_of_the_evolutionary_history_of_life https://en.wikipedia.org/wiki/Timeline_of_the_evolutionary_h..., that's when "Blue whales grew to their modern sizes". So it's fairly recent not just in astronomy scales.