Scenario: After the end of the Holocene, manatees and dugongs evolve into the dominant life on Earth.

Title: "Planet of Manatees and Dugongs" Scenario: Several million years after the Holocene extinction, the Earth goes through remarkable changes. The prevailing species alongside fungi, insects, and some bird species, manage to survive challenging conditions. But within the marine environment, two distinctive aquatic mammals thrive and begin to dominate - the manatees and dugongs. Huge planetary climate shifts over the millenia greatly reduce land masses, and the planet begins to look more like a massive water world. Continents shrink and become vast islands. Lush vegetation covers these land masses and serves as a feeding ground for the manatees and dugongs, which primarily feed on sea grasses, but can adjust to consume land vegetation when needed. The unprecedented number of manatees and dugongs boost evolution. A new branch of highly intelligent marine mammals begins to emerge. These new breeds develop a more sophisticated brain and body structure, suitable for competitive survival. They start populating the various seas and oceans, in turn reducing the vast ocean into numerous territories. Over time, the intelligent manatees and dugongs develop unique abilities like tool usage, sophisticated communication methods, farming of specific sea plants, and even constructing underwater structures. Much like human societies, they develop a structured social order and culture, becoming the dominant life forms on Earth. On the significantly reduced land masses, primitive avian and insect life continue to exist, but they pose no competition to the manatees' and dugongs' rule over the global oceans. Some even evolve symbiotic relationships with these dominant species. Predators and threats still exist in this underwater world, but with their evolved intelligence and social structure, manatees and dugongs sustain a balanced ecology in their favor, ensuring the survival and prosperity of their species for millions of years to come. When explorers from another planet arrive on Earth 100 million years post-Holocene, they find a world dominated by intelligent aquatic species. They marvel at the complex structures, intricate societal order and resilience these creatures have shown in the face of the harsh progression of evolutionary cycles. Life on Earth had indeed survived and thrived but not in a way mankind could have ever imagined.