The over-whale-ming truth about whales
When thinking of ‘extreme’ marine, few can do it better than the whales. From the extensive migration of humpbacks, to life at freezing poles for the Belugas. The deepest dives of the Cuvier’s beaked or the incredible life-span of the bowhead. Whales have adapted to extreme environments and pushed the limits of life for all species in the ocean.
Nothing reflects how extreme whales can adapt like their strange evolution. When thinking of evolution most people think of fish crawling their way onto land. Whales however adapted quite in reverse, with their ancient ancestors starting on land and returning to the seas. Though uncommon, major mammal groups have adapted to life in the seas from land seven different times, including with pinnipeds and manatees.
The fossil record shows us pakicetus, a hoofed land mammal from 50 million years ago that surprisingly is related to cetaceans. Pakicetus are classified as whale ancestors from the unique structure of their earbones which has only been found formed this way in modern cetaceans, and no other class. Over millions of years, evolution drove the descendants of Pakicetus back into the sea more permanently. Over time, their hind legs minimised and they became more streamlined. Around 38-41 million years ago two close relations, but not direct ancestors, of modern whales had arisen: the Basilosauridae. These were thought to be the first fully aquatic cetaceans and were more like modern
whales. They came in two forms: Baliosaurid was 17m long but lacked the ‘melon organ’, used in echolocation, and preyed on other cetaceans. At this time also existed Dorudon, reaching only 5m, which had the iconic fluke and swimming style of modern whales, and was believed to live in pods. The latter species has been suggested to be ancestor of the modern cetaceans.
Whales being adaptable to extremes may have saved this class from extinction. Around 28 million years ago, the oceans were dangerous with voracious predators such as Carcharodon megalodon, the largest sharks that ever lived. These 60 ft sharks fed on a variety of marine species, including early whale species. As their food sources, whales, began to migrate to cooler waters, where C.megalodon couldn’t survive, and sea temperature dropped, megalodon became extinct. From then on, whale lineages were allowed to diversify into the giant filter-feeders we see today. Even today many whales are still well-adapted to mitigate the effects of cold whilst living at or around the poles.
In terms of feeding, whales go to all sorts of extremes. The blue whale (Balaenoptera musculus), the largest animal to have ever lived is adapted to live on tiny krill. Blue whales push the extreme of size, ~100ft, and weight, ~200 tons, which require high energy intake to maintain and thus efficient feeding strategies. Blue whales are ‘lunge feeders’ which entails taking huge mouthfuls of water, which expands their throat. They then force their tongue against their fringed-teeth (baleen plates), which sieves out the water but leaves the krill behind for the whale to then swallow. A study also suggested they may roll to maximize foraging efficiency of the largest prey fields.
Equally, Sperm whales (Physeter macrocephalus) are are adapted in the extreme to feed. As well as having the biggest brains in the animal kingdom, 5x the weight of a human’s, they also have the longest dives, up to 90 minutes. They frequently dive 1000m down, and have been recorded at depths of 2,250m, only beaten by Cuvier’s beaked whales which can dive 2,992 m. Diving allows them to exploit food niches most animals can’t, making them successful hunters in the deep sea. A flexible ribcage accommodates for lung collapse as pressure increases as they dive. Like many whales, they can also direct blood away from less essential organs when diving in order to make the most of oxygen reserves. Sperm whales also have incredible hearing and send out long series of clicks in short intervals when diving, this is an adaptation of echolocation used to forage. Sperm whales are even extremely adapted in ways we don’t yet understand, their heads containing ‘spermaceti‘ which function has still not been proven. Many studies believe spermaceti is either used for buoyancy or focusing in echolocation.
Some whales, such as the bowhead whale (Balaena mysticetus), live to the extreme in many ways. Bowheads for instance are incredibly strong; living primarily in the Arctic, they have adapted to break through ice up to 7 inches thick with their heads and have blubber 50cm thick. Additionally, despite growing lengths of up to 60ft they can still jump entirely out of the water. Most iconically, bowheads are one of the longest lived animals on the planet and have been estimated to live up to 200 years. Studies show they don’t become sexually mature until around 25 years, gestation is though to exceed 1 year and that after around 40-50 years their growth actually slows. Bowheads long life history was discovered from battles with its most viscous predator: humans. Remains of harpoon tips from whaling centuries before have been found embedded in surviving bowhead’s skin. While whales are adapted to the extremes, humans have driven many of them to near extinction, and though commercial whaling is now banned, whales still face a great many threats from man. Destruction of habitats, over-fishing, shipping interference and noisier oceans interrupting whale communication are all among them. However, slowly we’re beginning to see the result of years of conservation efforts and education on these extreme sea giants.