BWB – Evolution

The evolution of marine mammals is a remarkable story of adaptation and return to the water. Originally land animals, over millions of years they reverted to an aquatic lifestyle in order to find new habitats. Three main groups – whales (Cetacea), seals (Pinnipedia) and manatees (Sirenia) – evolved independently.

Whales are descended from ungulates that lived around 50 million years ago. Their earliest ancestors, such as Pakicetus, were wolf-like animals that lived in shorelines and occasionally entered the water. Later, forms such as Ambulocetus developed, which already lived amphibiously and hunted both on land and in the water. With Basilosaurus, around 40 million years ago, a completely aquatic animal emerged that no longer had hind legs. Eventually, modern whales evolved with streamlined bodies and flukes propelled by vertical movements.

The ancestors of seals lived around 25-30 million years ago. They are descended from land-dwelling carnivores, similar to today’s bears or martens. Early forms such as Enaliarctos already showed adaptations to life in the water, including webbed feet and streamlined bodies. In the course of evolution, seals, sea lions and walruses developed that can switch between water and land.

Manatees are closely related to elephants and evolved around 50 million years ago. Early forms such as pezosiren lived on land but foraged in shallow waters. Over time, they lost their hind legs, their bodies became rounder and they developed paddle-like front flippers to move around in the water.

By Fatima Kutzschbach