Are sharks fish or mammals? Where they belong in the animal kingdom
Did you know that there are more than 500 species of sharks in the world? These fascinating underwater creatures have been swimming in our seas for around 455 million years and can travel thousands of kilometers in a single year.
There are more than 30,000 species of fish in the world, but are sharks fish? Here’s how the animal kingdom is divided up and where the ocean’s apex predator falls into the lineup.
Are sharks fish?
Yes, sharks are fish and belong to the subclass Elasmobranchs.
There are six types of animals:
- Mammals: Warm-blooded vertebrates with hair
- birds: Warm-blooded feathered vertebrates
- reptiles: Cold-blooded vertebrates with scaly or bony dry skin
- amphibians: Cold-blooded vertebrates without scales, living on both land and water
- invertebrates: Animals without backbones or skeletons
- Fish: Vertebrates that live in water and breathe with gills
Fish are defined as vertebrates (i.e. they have a backbone) that live in water and use gills to breathe. Elasmobranch fish, which include sharks, rays, sawfish, and rays, have five to seven gill openings on each side. Elasmobranch fish differ from other fish in that they are made up of cartilage rather than bone.
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Are sharks mammals?
No, sharks are not mammals. Mammals are defined as warm-blooded hairy vertebrates that produce milk to feed their young. Mammals also have more developed brains than other animal species. Humans are mammals.
This question is often confusing because some sharks are “viviparous,” meaning they give birth to live young. This is a typical feature of mammals. These shark species even have a placental connection similar to a mammal’s umbilical cord. It is important to remember that while many fish lay eggs, not all do, and being considered a fish is not a requirement.
There are three main ways in which shark fetuses develop:
- liveliness: The egg develops in the womb and results in a live birth
- oviparity: The shark lays eggs in a tray in the water – the eggs are sealed in a leather pouch, often known as a ‘mermaid pouch’, before hatching
- Ovoviviparity: The egg hatches in the womb and the shark has a live birth
Sharks can also reproduce asexually, and there are two documented species that have separated from male sharks and given birth to pups containing only the female’s DNA.
Are fish mammals?
No, fish are not mammals. Fish and mammals are two different species of animals, but both are vertebrates. According to Britannica, vertebrates have a backbone to support their body, a distinct head, differentiated brain, and nasal, optical, and otic (ear) sense organs.
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