The story of whale evolution

Wadi Al-Hitan (Whale Valley) is a geological World Heritage site in Egypt that demonstrates an iconic evolutionary process in the record of life on Earth: the transition of whales from land-based to ocean-going mammals.

The fossil remains of the earliest, and now extinct, suborder of whales, Archaeoceti, can be found at Wadi Al-Hitan, Whale Valley, in Egypt’s Western Desert. The development of the whale as an ocean-going mammal from a prior life as a land-based species is one of the key stories of evolution represented by these fossils. This is the world’s most important site for demonstrating this stage of evolution. It beautifully depicts the shape and life of these whales as they change. The quantity, quality, and accessibility of such fossils, as well as their location in a beautiful and protected area, are all unique. The youngest archaeocetes, in the latter stages of losing their hind limbs, are depicted in Al-fossils. Hitan’s Other fossils found at the site allow researchers to reconstruct the surrounding environment and ecology at the time.

Pakicetus and other early whales were normal land creatures. They possessed big carnivorous teeth and lengthy skulls. They don’t resemble whales at all from the exterior. Their skulls, on the other hand, closely resemble those of live whales, especially in the ear area, which is encircled by a bony wall, and are unlike those of any other mammal. Often, seemingly insignificant characteristics are crucial in establishing a relationship between creatures that are highly specialised for their lifestyles (such as whales) and their less extreme-looking relatives.

Ambulocetus appears to have enjoyed a more aquatic existence than other early whales such as Indohyus and Pakicetus. Its legs are shorter, and its hands and feet have paddle-like enlargements. It also has a longer, more muscular tail. The data from stratigraphy — Ambulocetus’s fossils were discovered among strata that likely represented an old estuary — and oxygen isotopes in its bones also support the theory that Ambulocetus lived an aquatic life. Saltwater and freshwater have varying ratios of oxygen isotopes, and animals are what they eat and drink. This means that by researching the isotopes absorbed into an animal’s bones and teeth as it grew, we can learn about the type of water it drank. Ambulocetus drank both saltwater and freshwater, according to the isotopes, which fits perfectly with the hypothesis that these animals lived in estuaries or bays between freshwater and the open ocean.

Whales that emerged after Ambulocetus (Kutchicetus, for example) have even greater amounts of saltwater oxygen isotopes, indicating that they lived in nearshore marine settings and could drink saltwater like today’s whales. These creatures’ nostrils moved further back along the nose as they evolved. This process has persisted in living whales, which have a “blowhole” (nostrils) above their eyes on top of their heads.

Other alterations in these more aquatic whales reveal they are closely connected to today’s whales. The pelvis, for example, had developed to be considerably smaller and distinct from the backbone. This could be due to the increasing utilization of the entire vertebral column in locomotion, including the back and tail. If you watch videos of dolphins and other whales swimming, you’ll see that their tailfins are horizontal rather than vertical, like they are in fish. Instead of swimming back and forth like fish, they move their tails up and down. This is because whales originated from walking land mammals with backbones that naturally bent up and down rather than side to side. If you watch a dog run, you can plainly observe this. As it goes ahead, its spinal column undulates up and down in waves. When whales swim, they perform the same thing, demonstrating their ancient terrestrial heritage.
As whales began to swim by undulating the whole body, other changes in the skeleton allowed their limbs to be used more for steering than for paddling. Because the sequence of these whales’ tail vertebrae matches those of living dolphins and whales, it suggests that early whales, like Dorudon and Basilosaurus, did have tailfins. Such skeletal changes that accommodate an aquatic lifestyle are especially pronounced in basilosaurids, such as Dorudon. These ancient whales evolved over 40 million years ago. Their elbow joints were able to lock, allowing the forelimb to serve as a better control surface and resist the oncoming flow of water as the animal propelled itself forward. The hindlimbs of these animals were almost nonexistent. They were so tiny that many scientists think they served no effective function and may have even been internal to the body wall. Occasionally, we discover a living whale with the vestiges of tiny hindlimbs inside its body wall.

Wadi El-Hitan contains invaluable fossil remains of the earliest, and now extinct, the suborder of whales, Archaeoceti. These fossils represent one of the major stories of evolution: the emergence of the whale as an ocean-going mammal from a previous life as a land-based animal. It portrays vividly the form and life of these whales during their transition. The number, concentration, and quality of such fossils here are unique, as are their accessibility and setting in an attractive and protected landscape. The fossils of Wadi El-Hitan show the youngest archeocytes in the last stages of losing their hind limbs. Other fossil material in the site makes it possible to reconstruct the surrounding environmental and ecological conditions of the time.