June 8

Why are whales’ nostrils on top of their heads?

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Whales are not fish, but ocean-dwelling mammals, so they rely on their lungs to breathe air, just like us. Common mammals have nostrils that develop at the front of the head, but whales have nostrils on the top of the head. Why is that?

Whales today are divided into two types, baleen whales and toothed whales. But no matter how they are divided, their nostrils are located on the top of the head, not the front end of the head.

We all know the ancestors of whales are small land mammals, after starting to live in the ocean, they went through more than 50 million years of evolution and eventually became a family of marine mammals. have the most diverse and popular breasts today. The whale suborder includes not only giant blue whales, sperm whales, and bowhead whales, but also many different species of dolphins.

Species in the suborder whales still exist on Earth today.

Pakicetus “whale” is one of the earliest known ancient whales, this animal that lived 50 million years ago looked like a dog with long limbs and fur. If you look closely at the Pakicetus whale, you will see that its nose is located in the front of the head, like today’s mammals. Because the Pakicetus whale’s nostrils are located in front of the mouth, when swimming they will look like the way dogs today because underwater, they have to almost raise their heads out of the water when swimming

Pakicetus is an extinct genus of cetacea, found in Pre-Eocene rocks in Pakistan. The strata where the fossils were found were then part of the coastal Tethys Sea.

.As the ancient whales gradually entered the ocean, their body structure began to evolve in a way that was adapted to aquatic life, including the position of the neck, the nostrils gradually moving to the top of the head, Below are pictures of the primitive whale (Protocetus) and a restored image of the Basilosaurus whale, both of which show their nostrils gradually turning upward.

Protocetus is one of the most ancient genera of whales, which lived in the middle of the Mercury era 45 million years ago in an area near Cairo, Egypt. This is one of the first genera of whales to have fully adapted to aquatic habitats. They are quite small, only about 2.5 m long, on the body still keep the traces of limbs with fingers connected by swimming membranes with the hind limbs smaller than the front limbs. Jaws long, with sharp teeth. The front teeth are used to catch prey and the back teeth are used to cut meat. Unlike the older predecessor Pakicetus, which lived a semi-aquatic lifestyle, Protocetus was able to develop ear canals and hear underwater sounds (but it is unclear whether they developed sonar or sonar). not yet) and developed a flattened tail like today’s whales. Their nostrils are still located on the head, they still do not have a stoma on the top of the head and rely more on eyesight for food.
Basilosaurus is one of the primitive whales that evolved from land mammals and later evolved into modern day whales. Basilosaurus averaged about 18 – 20 m long and weighed about 15 tons, once distributed in North America, North Africa and Central Asia and was considered the largest animal that ever lived in its time.

The ancient whale species mentioned above all belong to the ancient whale suborder, the baleen whales and the toothed whales in the ocean today all evolved from the ancient whale suborder. They appeared in the middle Oligocene, about 30 million years ago. Compared to today’s whales, their appearance is quite similar to ancient whales, but the evolution to change the position of the nostrils took quite a long time – about 20 million years.

Diagram of the evolution of ancient whales.
Schematic diagram of the evolution of modern whales.

Modern whales have evolved to move the nostrils from the front of the mouth to the top of the head. It’s not just a change of location. The esophagus and trachea of ‚Äč‚Äčtoday’s land mammals are interconnected, so if our noses are blocked by a cold, we can still use our mouths to breathe instead of our nostrils. In addition to breathing, our nose also has the function of smelling.

But modern whales are different, and the changes in the position of the nostrils and the changes they made to aquatic life have caused the trachea and esophagus to separate. The nostrils connect to the lungs and the esophagus connects to the digestive system, so their noses are only used for breathing, not for smelling.

The nostrils of modern whales located at the top of the head actually help them survive more effectively and safely than the holes in the front of the mouth when in the ocean. But even if their nostrils are at the top of their heads, when they dive into the ocean, their noses are still underwater, how can modern whales ensure that they won’t choke? In fact, under the nostrils of whales have a very strong muscle group, they can completely close their nostrils when diving, avoiding the risk of choking on water. The separation of the esophagus and trachea also ensures that modern whales will not choke on water while hunting in the ocean.

Large nostrils of baleen whales.
The nostrils of a blue whale when diving into the water.

In fact, all baleen whales still have two nostrils, while toothed whales have only one. The jets that whales spit out of the water are not water in their noses, but rather accumulations of water remaining in the “pits” of the nostrils, which are formed under the action of sub-lower pressure. Ocean. This prevents water from entering the nostrils, improving the safety and efficiency of breathing. However, the water column due to the whale’s breathing process once brought them great danger. In the era of whaling, sailors often relied on these water columns to locate the schools of fish. elephants.

Killer whales belong to the toothed whale subspecies with only one nostril.
Gray whales belong to the subspecies of baleen whales that spray water with a pair of nostrils.

Tags

blue whale, mammal, sea animals, spermaceti


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