How Are Mammals Classified?


With so many species of mammals in the World, there needed to be a system to differentiate them. In this article we look at how mammals are classified.

There are seven groups of classifying all living creatures. All have a scientific two-part name. This enables scientists to be able to tell the difference between them.

There are over 5,400 species of mammals in the World, with over four hundred of these found in North America. More species are being added to these numbers all the time, and identifying all the mammals can be a difficult job.  

Biologists use a system of classification to differentiate the many species of mammals. All different species have their unique species name. Groups are used to contain the species to which it has evolved. The groups are also known as taxa. This system is used for all animals, whether alive or extinct.

Phylogenetic chart of mammals

Seven Groups Of Classification

There are seven groups used in classifying animals.

These are:

Kingdom

Merriam-Webster Dictionary Definition

“A major category in biological taxonomy that ranks above the phylum and below the domain.”

All animals belong to the Kingdom of Animalia (animal). There are six kingdoms, which include animals (Animalia), plants (Plantae), fungi (Fungi), protists (Protista), Eubacteria (Eubacterium), and Archaebacteria (Archaebacterium).  

Animalia has the most species and is the largest Kingdom with over one million species.

Animalia is made up of six basic animal classes. These include invertebrates, fish, amphibians, reptiles, birds, and mammals.

Phylum

Merriam-Webster Dictionary Definition

“A group that constitutes or has the unity of a phylum, specifically a primary category in biological taxonomy, especially of animals that ranks above the class and below the kingdom.”

A phylum contains one or more classes and their subgroups. A phylum is a subdivision of the Kingdom. There are thirty-six groups, but mammals make up only one of these groups, Chordata.  

Chordata includes around 50,000 species.

Chordata includes all animals with a notochord, a dorsal hollow nerve, and a muscular postanal tail at some point in their life. Some members of this phylum lose one or all of these features as they develop.

Class

Merriam-Webster Dictionary Definition

“A group, set, or kind sharing common attributes: such as a major category in biological taxonomy ranking above the order and below the phylum or division.”

Wild brown bear cub close-up

There are one hundred and seven classes of animals, but only eight in the phylum Chordata. Mammals are all contained in one class, Mammalia. Mammals are from the Latin word Mammalia, which Linnaeus took from mammalis, which means “of the breast” and from mamma “breast.”

Class is a category or group that shares attributes or characteristics.

Order

Merriam-Webster Dictionary Definition

“A class of persons or things grouped according to quality, value, or natural characteristics: such as a category of taxonomic classification ranking above the family and below the class.”

Order is the next classification, and there are currently 26 orders of mammals. Out of 26 orders, over 70% of all mammals come from three orders: Rodentia (rodents), Chiroptera (bats), and Soricomporpha (shrews and moles.)

If you want to know more about the different orders of mammals, I have written an article which you can find here.

Family

Merriam-Webster Dictionary Definition

“A group of related plants or animals forming a category ranking above a genus and below an order and usually comprising several to many genera.”

The 26 orders of mammals are further classified into 153 families of mammals.

Genus

Merriam-Webster Dictionary Definition

“A category of biological classification ranking between the family and the species, comprising structurally or phylogenetically related species or an isolated species exhibiting unusual differentiation, and being designated by a Latin or Latinized capitalized singular noun.”

The different families of mammals are divided down further into genera. There are currently 1258 genera of mammals in the World. Genera include groups of species. These groups are structurally similar or phylogenetically related.

Species

Merriam-Webster Dictionary Definition

“A category of biological classification ranking immediately below the genus or subgenus, comprising related organisms or populations potentially capable of interbreeding, and being designated by a binomial that consists of the name of a genus followed by a Latin or Latinized uncapitalized noun or adjective agreeing grammatically with the genus name.”

There are over 5,400 species of mammals in the World. The genus and the species together make up the name that scientists identify animals. This name is called the binomial nomenclature.

How Does Classification Help Distinguish Between Animals?

Names of animals are identified as two scientific names. The first name is the genus that the mammal belongs to, and the second name is the name of their species.

Both of the scientific names are written in Latin, and this helps scientists all over the World. By using one language, scientists around the World can universally understand the names. This two-part name also enables scientists to know exactly what the type of animal is. With over one and a half million different species of animals around the World, scientists can recognize the type of animal from the scientific name.  

An example of this would be the gray wolf. If a scientist read the words gray wolf unless they know what it is, they would not know if this was a mammal, an insect, a fish, or another type of animal. The scientific (binomial) name of the gray wolf is Canis lupus. This advises the scientist that the genus is Canis, and the species name is lupus. Canis is a genus of Canidae which contains canines. Lupus means wolf in Latin.

Where Do The Principles Of Classification Come From?

Aristotle

The scientific classification of living organisms is known by the name of taxonomy. Aristotle, who lived between 384-322 BC, was the first to classify organisms. Aristotle’s definitions lasted for two thousand years before being challenged.

Aristotle tried to classify all types of animals in History Animalium (History of Animals) by the type of organism they were. Aristotle tried to group all animals by their similarities to each other, rather than by genetics.

Aristotle believed that groups of animals could be ranked from lowest to highest, with humans at the top. 

Aristotle statue located at Stageira of Greece (birthplace of the philosopher)

Aristotle also came up with a means of identification that is still used today. Binomial nomenclature is a two-part name that can be used to identify any living creature or plant on Earth.  

We still use binomial names to classify living organisms, and Aristotle was the first to identify them by their genus and difference. We now use the words genus and species, but Aristotle managed to explain the difference between each animal while keeping them grouped with other similar animals (genus.) 

Although there were many botanists thought the years that had worked on different methods of classification to name plants, there were very few that worked on animals.

With so many different methods of naming plants, many names could be used for the same plant. Taxonomy needed to be standardized, and in 1735, the principles of modern classification come from the work of Carl Linnaeus.

Carl Linnaeus

Carl Linnaeus Monument in Humlegarden park in Stockholm, Sweden.

In the eighteenth century, Linnaeus, the Swedish explorer, and botanist developed a way of naming all species so that people could tell them apart. In 1735, Linnaeus published Systema Naturae (The System of Nature.)  

The publication went through many revisions throughout his life, changing errors that he found. His work has carried on after his death, with others introducing genetic testing to his work.

The book organized all living creatures into different groups called kingdoms, classes, orders, genera, and species. Linnaeus also carried on the binomial naming that Aristotle had started, and is a system that we still use today.

Bryan Harding

Bryan has spent his whole life around animals. While loving all animals, Bryan is especially fond of mammals and has studied and worked with them around the world. Not only does Bryan share his knowledge and experience with our readers, but he also serves as owner, editor, and publisher of North American Mammals.

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