When Whales Could Walk | Full Documentary | NOVA | PBS

Experts in the Egyptian Desert are unearthing clues to a lost past, revealing a time before the pharaohs when the area was underwater. The discovery of a whale's hind limb, similar to a T. rex hand, suggests the existence of prehistoric whales with legs. The narrative explores the evolutionary journey of whales from land to sea, highlighting the unique adaptations that allowed these mammals to thrive in the ocean.

The Wadi Hitan, or 'Valley of the Whales,' is a significant site in Egypt's Sahara Desert where over 1,000 ancient whale fossils have been found since 1902. The area, once underwater, now lies 100 miles from the coast. Paleontologists are uncovering the secrets of these sea creatures, including evidence of shark teeth, shells, and possibly mangrove roots, indicating a rich marine ecosystem 40 million years ago.

The evolution of whales from land mammals has been a subject of fascination and mystery. Early ideas, such as Charles Darwin's, suggested whales evolved from land mammals but faced skepticism. The discovery of the Basilosaurus, a prehistoric whale with a skull resembling a land mammal's, supports the idea that whales evolved from four-legged creatures. The skull's features, including teeth similar to ours, confirm it as an ancient whale, not a marine reptile.

The Pakicetus, discovered in Pakistan, is a significant milestone in whale evolution, being the oldest fossil whale found. This creature, which lived 50 million years ago, could walk on land and had adaptations for aquatic life, such as a specialized ear bone for underwater hearing. The Pakicetus represents a transitional form in the whale lineage, showing how early whales moved from land to water, eventually losing their legs and becoming fully aquatic.

Modern comparative anatomist and evolutionary biologists are using DNA to trace the origins of whales. Surprisingly, whales share a close genetic relationship with hippos, descending from a common hoofed ancestor. Features like multiple stomach chambers and certain genes, which are inactive in whales but active in land mammals, provide evidence of their terrestrial past. The whale's evolutionary journey is complex, involving changes in body structure, sensory adaptations, and even the loss of limbs.

The Phiomicetus anubis, named after the Egyptian god of death, is an ancient whale species discovered in Egypt. This 43-million-year-old fossil is one of the oldest found in Africa and provides clues about the transition from land to water. The anubis had strong back muscles and a neural spine indicative of a walking lifestyle, suggesting it could have moved on land but was also a formidable marine predator. The discovery adds another piece to the puzzle of whale evolution.

The evolution of whales from land-dwelling mammals to ocean giants involved significant physical changes. Ancient whales like Basilosaurus had small hind limbs, too weak for land support but possibly used for movement in shallow waters. Modern whales retain a pelvis and some leg bones, but these are vestigial and serve to anchor swimming muscles. The transition included the development of flippers for swimming, a streamlined body for efficiency, and the loss of hind limbs, marking the whales' full adaptation to aquatic life.

Around 34 million years ago, the climate cooled, leading to the formation of the Antarctic ice sheet and a drop in sea levels. The once-thriving ocean in Wadi Hitan turned into a forest, causing the extinction of ancient whales in the region. However, some whales adapted to the colder waters and migrated, highlighting their ability as warm-blooded mammals to survive in changing environments. The whale's evolutionary story is one of adaptation to new challenges and habitats.

The whale family tree saw the emergence of two distinct groups: toothed whales, which kept their teeth for hunting, and baleen whales, which developed baleen for filter feeding. Baleen plates, made of keratin, allow these whales to consume vast amounts of prey at once. Toothed whales, on the other hand, evolved echolocation, a sophisticated sonar system for hunting in the depths. The diversification of feeding strategies and sensory adaptations has led to the rich variety of whale species we see today.

The whale's evolutionary journey is one of the most remarkable in the history of life on Earth. From small, wolf-sized creatures that first ventured into freshwater rivers to the colossal beings that rule the oceans today, whales have adapted to their environment in extraordinary ways. Their story is a testament to the power of evolution, shaping a species from land mammals to the ocean's apex predators. As scientists continue to uncover the missing chapters of this epic tale, they also grapple with the modern challenges facing whales, hoping they will continue to adapt and survive.