To swim, they move their tails up and down, rather than back and forth as fishes do. This is because whales evolved from walking land mammals whose backbones did not naturally bend side to side, but up and down.
You can easily see this if you watch a dog running. Its vertebral column undulates up and down in waves as it moves forward. Whales do the same thing as they swim, showing 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. In the skeletons of living dolphins and whales, the transition from body to tail fluke is marked by a change in their vertebral column: body vertebrae are taller than they are wide, and tail fluke vertebrae are wider than they are tall.
We see the same pattern in fossils from early basilosaurid whales, like Dorudon and Basilosaurus , and so know that they had flukes that could help power swimming. They also had other skeletal changes that accommodate an aquatic lifestyle. Their elbow joints were flexible, unlike living whales, but 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. The picture below on the left shows the central ankle bones called astragali of three artiodactyls, and you can see they have double pulley joints and hooked processes pointing up toward the leg-bones.
Below on the right is a photo of the hind foot of a basilosaurid. The basilosaurid astragalus still has a pulley and a hooked knob pointing up towards the leg bones as in artiodactyls, while other bones in the ankle and foot are fused. From the ear bones to the ankle bones, whales belong with the hippos and other artiodactyls. Isotopic analyses data from: Bajpai, S.
A new Eocene archaeocete Mammalia, Cetacea from India and the time of origin of whales. Proceedings of the National Academy of Sciences Barrick, R. Fischer, Y. Kolodny, B. Luz, and D. Cetacean bone oxygen isotopes as proxies for Miocene ocean compostion and glaciation.
Palaios 7 5 On the other hand, they are much more at risk of extinction in times of environmental change or crisis. Whales are still evolving nowadays. Ecosystems are regularly modified and interactions between species are dynamic. Hence, there is always a need to adapt to changing conditions. Modern-day whales are subject to several evolutionary pressures such as climate change, decline in prey abundance and ocean pollution.
Their large size makes them particularly vulnerable to lack of food. Bigger, heavier, better divers… Whales are often thought to be superior to humans in many respects, but sometimes it is the loss of genes that is at the root of their adaptations.
Genes linked to feeding, including those responsible for saliva production or those that code for the reabsorption of sodium by the kidneys, have disappeared because they have become useless to whales which, with a few exceptions, live in saltwater environments.
Their lives at sea make the lubrication of food unnecessary and sodium deficiency virtually impossible. As for rest, this activity in whales is influenced by the loss of the gene responsible for the production of melatonin, a well-known hormone that regulates the sleep cycle. This adaptation is probably due to the fact that in cetaceans, breathing is a voluntary activity and falling into a deep slumber would likely increase the risk of drowning in these marine mammals.
Other genes that have disappeared in cetaceans are those that are useful to terrestrial animals but which cause problems during diving due to the extreme pressures their bodies are subject to.
Researchers have notably observed the disappearance of genes that facilitate blood clotting and those associated with fibrosis and other lung issues in some humans. Another gene that indirectly increased the risk of DNA mutations in diving cetaceans has also vanished from their genetic makeup. The North Atlantic right whale population is down to approximately individuals and is critically endangered.
The recovery of this…. The Origin of Whales or the Evolution The first whales appeared 50 million years ago, well after the extinction of the dinosaurs, but well before the appearance of the first humans. Mammals specialized for aquatic life The whales that we know today are extraordinarily well adapted to life in the water. How do we study evolution?
What is evolution? Pakicetus , ancestor of cetaceans. Based on the skeleton found in Peru, researchers were able to achieve this artistic reconstruction of the four-legged whale. It could live on land and in water and probably fed on large fish. Blue whales reach huge sizes. And now? A cold environment causes a low body temperature, which in turn means slow metabolism—and thus less damage to tissues, Moore says.
Incidentally, according to the National Ocean and Atmospheric Administration , the bowhead also has the largest mouth of any animal. No comment. Helena , an island off West Africa.
John Klicka , curator of birds at the Burke Museum in Seattle, says the oldest known wild bird is a year-old Laysan albatross named Wisdom, which has shattered scientists' belief that her species lives to Not only that, Wisdom is still giving birth to and raising healthy chicks. The kakapo , a critically endangered parrot native to New Zealand, lives up to 60 years. There are a little more than a hundred kakapos left on Earth.
They're also the only flightless parrots in the world. Here's hoping their population, at least, can soar again. Weird Animal Question of the Week answers your questions every Saturday. If you have a question about the weird and wild animal world, tweet me , leave me a note or photo in the comments below, or find me on Facebook. All rights reserved. Some days it feels like it might be me. Share Tweet Email.
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