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Home › Sea Life Creatures › Marine Animals › Mammals

Examples of Aquatic Mammals

There are about 6,400 different vertebrate mammal species still in existence. They include popular land mammals that humans like to keep as pets, such as dogs and cats.

This section focuses on the four taxonomic groups of aquatic mammals, defined as those that rely on some kind of marine ecosystem for their survival.

Fun Facts and Information about Mammals

First of all, it is important to understand that not all animals are "true mammals"!

Some fall under a different category (e.g. amphibians, fish, reptiles).

Here's the thing:

Mammals include a range of vertebrate species that are warm-blooded, have hair (or fur), and have young that drink milk.

Plus, mammal babies will be drinking the milk from the mother (unlike some birds and insects).

There are a few exceptions to the norm (see below). But, zoologists use several unique characteristics and traits to determine whether an animal is mammalian (of the breast) - or not! So, by and large, land and aquatic mammals:

• Are Warm-Blooded Vertebrates:
  • Most of the vertebrates (animals with a backbone and skeleton), that are also endothermic, are classified as being mammalian.
• Grow Hair (or some kind of fur):
  • When it comes to animals, there are a few technical differences between hair and fur. Even so, hair and fur share many chemical characteristics and they both are made of keratin (protein). No matter whether the animal's hair is long and thin, or short and coarse, it needs it for insulation.
• Have Red Blood Cells (RBC) With No Nucleus:
  • Unlike many vertebrates, the red blood cells (erythrocytes) in mammals contain neither a nucleus or mitochondria (used in energy production).
• Have a Left Aortic Arch:
  • The fourth (left) pharyngeal artery in mammals is usually the arch of the aorta. Even though this differs from other animal types, some rare mammal species actually have a right aortic arch variant.
• Breathe with a Diaphragm:
  • Being able to increase the volume of the chest cavity, via a diaphragm that sits between the heart and lungs, is a significant biological feature of a true mammal.
• Possess a Neocortex:
  • Even though it's not present in all species, most of them have a neocortex (or neopallium) located inside the brain. Having this region of specialised higher-brain function means they are able to hear, see, and generate spatial reasoning.
• Have 3 Middle Ear Bones:
  • The malleus, incus, and the stapes (the smallest) are the three ossicles that only modern mammals have inside the middle ear.
• Have the Lower Jaw Connected to the Skull:
  • The hinged lower jaw connects directly to the skull in mammals, so they can grasp food and chew it. This notable feature differentiates mammals with many other vertebrates, which have an extra square shaped bone (or quadrate).
• Can Produce and Secrete Milk:
  • In Latin, the word "mammal" translates to "breast". Thus, having mammary glands means the mother is able to produce milk and feed it to their newborn offspring.
• Give Birth to Live Young:
  • Being viviparous means that mammals will be giving birth to live babies. But, there are three different types of mammalian birth methods, monotremes (egg layers), marsupial (growing outside the mother), and the most common, placental births.

Exceptions to Mammal Criteria

Despite being born without any hair or fur, whales (including the blue whale) are typical examples of mammals. In general, the hair grows while it's developing inside the womb. But, any hair growth tends to disappear towards the end of the fetal stage.

A to Z List of Marine Mammals

The oceans, and a few freshwater systems (e.g. the Amazon, Ganges), provide essential habitats for around 130 different species of marine mammals. We can divide them into the following taxonomic groups:

• Cetacea (e.g. dolphins, porpoises, and whales)
• Pinnipeds (e.g. seals and walruses)
• Sirenians (e.g. sea cows)
• Marine fissipeds (e.g. polar bears, sea otters)

The facts and information in this section focuses on some of the most common aquatic mammal species, including:

• Amazon River Dolphin
• Baleen Whale
• Bull Shark
• Dolphins
• Dugongs and Manatees
• False Killer Whale
• Fin Whale
• Harp Seal
• Killifish
• Porpoises
• Sea Otters
• Steller's Sea Cow

Pro Tip: The largest mammal is the female blue whale, which can measure more than 30 metres (100 feet) in length and weight up to 190,000 kilograms (350,000 pounds). By comparison, the smallest mammal is actually the Etruscan pygmy shrew, which is only four (4) centimetres long and weighs less than 2 grams.

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