Sharks – Are They Mammals or Fish?
Whales and dolphins are among this class of animals. What about sharks? Well, you are about to find out. To do so, you need to know the criteria used to isolate mammals from other species.
The word ‘mammal’ was obtained from the words ‘mammary glands’. With this knowledge, you now know what a mammal is. A mammal is an animal which feeds its offspring with milk from its mammary glands.
Giving birth isn’t a conclusive characteristic of determining whether a certain animal is a mammal or not. After all, the platypus, which is considered a mammal, lays eggs. The argument on whether or not sharks are mammals has existed for a long time. This is because sharks share features of both fish and mammals.
So are sharks mammals? Well, without further ado, let’s dive into the nitty-gritty of sharks and where to classify them.
Sharks aren’t Mammals.
You probably think sharks are mammals because they give birth to their offspring. Well, they aren’t because they don’t feed their offspring using mammary glands. They instead fall under fish. They share more features with fish than mammals. Well, what are the characteristics that disqualify sharks from being mammals? Let’s find out.
Features that Disqualify Sharks from Being Mammals
- Sharks lack mammary glands
As stated earlier, this is the most outstanding feature of mammals. All mammals have mammary glands which produce milk for their offspring. Sharks lack these glands and therefore they don’t qualify to be called mammals.
2. Sharks are Cold-blooded
This means that their body temperature changes with variations in the surrounding environment they are in. Mammals are warm-blooded. They do have mechanisms that maintain their body temperature. Such mechanisms include the use of body hair and shivering. These mechanisms keep their body temperature constant regardless of the environment they are in. being cold-blooded disqualifies sharks from being mammals.
3. Sharks lack fur and body hair on their skin surfaces
Mammals have skins covered with body hair and fur. This feature, as mentioned earlier, is essential in the maintenance of body temperature at a constant level. Even sea mammals like whales have body hair, though little. Absence of this feature disqualifies sharks from being mammals.
4. Sharks breathe using gills
Mammals use lungs for gaseous exchange. Even marine mammals like dolphins have to come to the surface of the water and draw oxygen from the air using blowholes. This air is then taken to their lungs for gaseous exchange. Sharks, instead, use gills to obtain oxygen from water. Just like other fish, sharks take water through their mouth, push it over the gills and let it back out via the gill slits. This feature qualifies them as fish instead of mammals since fish use gills for breathing.
5. Sharks lack three middle ear bones
All mammals have three middle ear bones. Do sharks have three middle ear bones? They don’t have any bones in their bodies at all. Their skeletons are made of cartilage. Lacking the three middle ear bones disqualifies sharks from being called mammals.
6. Absence of a neocortex
All mammals have a neocortex. This is the part of the brain involved in higher mental functions like conscious thoughts, orientation, memory, and language. Sharks lack this part of the brain and therefore can’t be classified as mammals.
7. Sharks have extremely short intestines
Unlike mammals which have long coiled intestines, sharks have short intestines. To compensate for this, their intestines have a spiral valve with several turns. This valve offers an incredible surface area for food digestion and absorption.
So What are Sharks if They Aren’t Mammals?
What features qualifies them as fish?
The following are characteristics of sharks that qualify them as fish:
- Their vertical tail orientation
All fish have a vertical tail orientation. The tail direction is a feature that distinguishes marine mammals from fish. Marine mammals like dolphins have a horizontal tail orientation. They flap their tails in an up and down movement while swimming. Sharks, just like all fish, have a vertical tail orientation. They flap their tails sideways as they swim. Vertical tail orientation classifies shark as fish and not even marine mammals.
2. Sharks have several dorsal fins
While marine mammals may have only one dorsal fin or lack any, sharks, just like fish, have more than one. This feature classifies them under fish.
Other features that qualify sharks as fish include:
· Being cold-blooded
· Presence of scales on their body
· Using gills for breathing
In a nutshell:
As you’ve seen above, sharks aren’t mammals. Instead, they are fish. The review above has discussed the features that disqualify sharks from being mammals. It has also highlighted the features that qualify them as fish. Although they give birth to their offspring, they lack the chief characteristics of mammals. They qualify as fish since most of their characteristics are in line with those of fish.