Dolphin

## Evolutionary Timeline of Dolphins Dolphins, part of the cetacean family, evolved from terrestrial mammals to fully aquatic marine predators over millions of years. Their evolution was driven by environmental pressures such as changing climates, ocean expansion, and the need for efficient hunting in water. Key transitions include the shift from land-dwelling ancestors to semi-aquatic forms and eventually to streamlined ocean dwellers with advanced echolocation. ### Key Milestones - **~50 million years ago (Eocene)**: Emergence of early cetacean ancestors like *Pakicetus*, semi-aquatic mammals resembling wolves, adapting to shallow waters for food sources amid warming climates. - **~48-40 million years ago**: Transition to more aquatic lifestyles with species like *Ambulocetus* (the 'walking whale'), which could swim and walk, pressured by competition for terrestrial resources. - **~40-30 million years ago (Eocene-Oligocene)**: Fully aquatic forms like *Dorudon* and *Basilosaurus* appear, with elongated bodies and reduced hind limbs, evolving in response to cooling oceans and abundant marine prey. - **~34-23 million years ago (Oligocene-Miocene)**: Divergence of odontocetes (toothed whales), leading to early dolphins with echolocation for hunting in deeper waters, influenced by global cooling and marine ecosystem shifts. - **~5 million years ago to present (Miocene-Pliocene)**: Modern dolphins (*Delphinidae*) diversify, developing social behaviors and intelligence, adapting to varied ocean environments and human-induced changes.