Key Characteristics and Evolution of Mammals

Main Characteristics of Mammals

In general, mammals are characterized by the following:

• They are warm-blooded; their body temperature is constant.
• Mothers have mammary glands that produce milk for their young.
• The mouth is surrounded by lips, allowing young to suckle.
• They have abundant glands (sebaceous, sweat, and odoriferous) and are generally covered in fur, which they shed periodically.
• They have teeth to chew food.
• They have pulmonary respiration.
• Circulation is double (pulmonary and general).
• Most are viviparous: The embryo develops inside the mother and is nourished through the placenta.

Mammals are among the most highly evolved animals. They can live on land, fly, or live in the water.

Here, we will examine in more detail some common characteristics of mammals, focusing on the major organs and systems of their bodies:

The Skeleton

The mammalian skeleton is characterized by a spine divided into several distinct parts: the cervical, dorsal, lumbar, sacral, and caudal regions (the caudal region sometimes ends in a tail).

The nose is usually prominent, forming a snout. The nose houses the sense of smell, which is highly developed in some mammalian species.

They have four limbs, typically ending in five fingers with nails, claws, or hooves (although in some cases, limbs may be more or less atrophied, as in cetaceans like whales and dolphins). Often, the number of digits is less than five.

Throughout the evolution of mammalian species, the shape of the legs has varied greatly as they have adapted to walking, running, climbing, flying, swimming, or digging.

In terrestrial mammals, there are three main ways of using limbs for walking:

• Plantigrade: They use the entire palm or sole for walking, like bears and humans.
• Digitigrade: They walk on their toes, like dogs and cats.
• Ungulates: They walk on the tips of their toes, which have developed into hooves, like horses and other herbivores.

Mammals are all vertebrates. Many accumulate significant fat reserves and require milk for bone development; without it, early life is not sustainable. Humans are mammals. They reproduce sexually.

They feed on leaves (giraffe), grass (elephant), meat (wolf), and some are omnivores.

They are classified as monotremes, metatherians (marsupials), and eutherians (placentals), based on their reproductive methods. Their origin dates back to prehistoric times; after the dinosaurs, they gradually evolved from very small animals. For example, the ancestor of humans was a mouse-like animal, which then evolved into cave-dwelling primates and eventually humans.