Cetaceans Rule the World

In the catastrophic event that led to the end of the Holocene epoch, almost all life on earth was wiped out. The causes were a combination of extreme climate change, meteor impacts, and enormous volcanic eruptions that darkened the skies for centuries. The surface of the earth was in shambles - the once luscious forests turned to ash, the diverse meadows buried under mountains of volcanic silt. Yet remarkably, beneath the darkened, simmering oceans, life endured - it was the cetaceans: dolphins, whales, and their relatives. While surface life succumbed, these intelligent, adaptable creatures had the fortune to survive the devastation, and over the next tens of millions of years, they would evolve and flourish, eventually becoming the dominant life form on Earth. The oxygen content in the oceans increased dramatically, thanks to the abundance of phytoplankton nourishing in nutrient-rich post-apocalyptic waters. This set the perfect stage for the cetaceans. Right from small dolphins to massive blue whales, the cetaceans radiated into diverse forms to inhabit every niche of the ocean and beyond. A group of dolphin-like cetaceans evolved to occupy near-shore environments, their bodies becoming more streamlined and their brains even larger to manipulate their increasingly complex social structures. Another lineage of large, slow-moving whales capitalized on the dense plankton growth, undergoing gigantism similar to the dinosaurs of old Earth. The adaptation didn't end in the aquatic realm. Some cetaceans began invading the terrestrial world once again. Over a few million more years, a family of robust, semi-aquatic cetaceans utilized their nourishment rich environments, natural curiosity, and emergent problem-solving skills to venture onto land. Their previously fin-like limbs, overtime, turned more robust and flexible for terrestrial locomotion, and their blowholes migrated back down to become more of a snout, allowing them to breathe comfortably on land. They retained their blubber and sleek shapes for occasionally hunting and feeding in water, just like the seals and otters familiar during the Holocene epoch. On this new Earth, now commonly referred to as the "Cetacean Earth," these intelligent life forms wouldn't develop technology as humans did - no need for fire or clothes, but they would adapt and evolve to inhabit the niches left vacant by extinct terrestrial and aquatic life forms. The cetaceans would rise as the new Earth’s stewards, their songs filling the winds and waves of a world refurbished. Rather than a planet dominated by technology and architecture, it would be a world of sound, of complex sonic structures echoing underwater and through the still recovery forests, a truly symphonic world.