What are mammals? | AZ Animals

Of all animal species, mammals are the ones that humans can relate closest to. This is because humans are just one of many mammalian species. So what are their characteristics? How are they similar and what are their differences?

All mammals are vertebrates, but not all vertebrates. There are five classifications of vertebrates, including mammals. Other classifications include birds, fish, reptiles, and amphibians. While they share characteristics with other vertebrates, there are some characteristics that are unique to them.

The classification of mammals has more than 5400 species. While this may seem like a huge number, it is not the largest class of vertebrates. It is home to about 10,000 bird species and more than 33,000 fish species.

They produce milk

All mammals have mammary glands that serve as milk for their young. The mammary glands are made up of glandular tissue and ducts and develop from sweat glands. While many have nipples that allow their young to breastfeed, one family of mammals known as monotremes excretes milk through ducts rather than nipples.

In almost all mammals, only the female feeds the young. This means that the male’s nipples, while they are, are underdeveloped. In some mammalian species, such as the Bismarck-masked bat and the Dayak bat, both the male and the female are capable of producing milk, and both help to care for the young.

They are warm blooded

A warm-blooded animal is better at regulating its internal temperature, making it more resistant to external threats. While cold-blooded reptiles require a certain external temperature to function, warm-blooded mammals can maintain their body temperature through diet and other methods.

They have a four-chambered heart

One of the characteristics of mammals that you don’t see is their four-chambered heart. Reptiles and amphibians have three-chambered hearts, while fish have two-chambered hearts. Birds and mammals are two classifications of vertebrates that have four chambers.

With a four-chambered heart, the body can easily keep deoxygenated blood going to the lungs separate from the oxygen-rich blood leaving the lungs. This means that a fully oxygenated blood is always available for the animal. With constant access to well-oxygenated blood, mammals can physically exercise more fully and without the need for frequent breaks.

They have a similar ear structure

It’s hard to believe that elephants, bats, foxes, and humans all have the same ear structure, but this is one of the characteristics of mammals. They all have three inner ear bones that move sound waves from the eardrum to the inner ear, translating vibrations into nerve impulses that are interpreted by the brain.

Most replace their teeth once in their lifetime

With the exception of some mammals such as kangaroos and manatees, mammals change teeth once during their lifetime. Born with baby teeth, they fall out to make room for baby teeth. If they lose a baby tooth, it will not grow back. This is in contrast to animals like alligators and sharks, which can replace teeth throughout their lives.

Their lower jaw is composed of a single bone.

In other classes of vertebrates, the mandible consists of several bones and does not attach to the skull. The jaw of a mammal consists of a solid bone attached to the skull. This strong structure gives the mammalian jaw tremendous strength.

They are protected by hair

All mammals have some form of hair or fur at some point in their life. Some, like dogs and cats, are covered in fur all their lives. Others, such as dolphins, develop light hair at an early stage of development.

Hair can provide camouflage, weather protection, and aid in environmental exploration.

They have a neocortex

The brain’s neocortex is responsible for decision making, perception, reasoning, and other higher actions. Mammals have a neocortex that allows them to function at a higher level and have more complex relationships than many other animals.

Types of mammals

Most mammals are viviparous, which means they give birth to live young. The exception is monotremes that lay eggs. Platypuses and echidnas are monotremes.

Viviparous mammals are either placental, which means that the mother has a placenta to provide nutrients and detoxification during pregnancy, or marsupials, when the newborn is not fully developed and continues to develop, attaching to the mother’s body. Kangaroos and possums are marsupials.

Placental mammals make up the majority of the mammalian group. With a placenta that carries nutrients to the embryo and filters waste products, the developing fetus can remain in the womb until it develops more fully. While newborn placental mammals range from fully formed but helpless ones, such as a newborn kitten, to those who start working within a few hours after birth, like a foal, all newborns from the placenta develop before birth.

When most people think of marsupials, they may view them as a classification other than mammals, but this is not the case. They have a short gestation period and are born live, but the young are not fully developed. Juveniles need extra time to mature outside the uterus and do so by attaching to the mother’s nipple, where they remain for weeks or even months.

Monotremes are a unique classification of mammals as they lay eggs. This separates them from marsupials and placental mammals, but like other mammals, they feed their young.

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