Classification of Animals: The Complete Guide

Classification of Animals & Plants – Laboratory Manual for Earth History

Classification of Animals & Plants

Taxonomy is the study of how organisms are categorized based on shared characteristics. You have seen examples of phylogenetic trees and cladograms (branching diagrams based on cladistic analysis) in the lectures. These methods trace evolutionary differences or changes based on primitive (shared) and derived (new or different) characteristics. The different branches of a phylogenetic tree or a cladogram are given formal grouping names. The dominant system in use today was originally proposed by Carl Linnaeus (1707-1778) and is known as the Linnaean classification system. The system classifies organisms into groups from kingdom (largest) to species (smallest) as follows:

Kingdom, Phylum, Class, Order, Family, Genus, Species

Sometimes, further divisions are needed and a sub-category may be added such as a sub-class, or sub-order.

The following is an example of the Linnaean classification for a common vertebrate, pet dog (Canus familiaris):

Kingdom Animalia

Phylum Chordata

Class Mammalia

Order Carnivora

Family Canidae

Genus Canis

Species familiaris

Note: in the Linnean classification system, genus and species names are italicized. The genus name is written with a capital letter, but the species name is not.

Each classification level is based upon a set of shared characteristics that are common to all members of that level. Kingdoms are the broadest categories in the Linnaean system. For example, your pet dog is in Kingdom Animalia (multicellular and heterotrophic which means they eat other organic materials to survive, Table 6.1).

A dog has a spinal cord of nerves along its back and particularly a solid vertebral column (chordate) made of bone (Phylum Chordata). It is a mammal (Class Mammalia – warm blooded, 3 middle ear bones, hair, provide milk to their young via mammary glands) and dogs descended from meat eaters (Order Carnivora – not all members of this Order are carnivores but they are descended from them).

Having five toes on the front feet, four toes on the back feet and claws that do not retract (unlike cats) makes them part of Family Canidae. At the level of family, genus and species, it is often quite subtle things that separate one organism from another. We could all likely use some visible features and common sense to figure out a way to separate lions and wolves, but separating a coyote and wolf takes more care and knowledge and will come down to things like the size of different bones and specific shape attributes.

You just have to look at a group of people and it becomes apparent that within a species there can be considerable variation in outward body appearance, and so decisions must be made that separate between-species variations from within-species variations.

The final division—species—categorizes plants or animals of similar habit, morphology and function that may interbreed and produce fertile offspring. In the fossil record, it is impossible to tell if two particular individual organisms could interbreed and so the practical definition for paleontology is that of similar habit, morphology and function. The number of species that have come into existence and which no longer exists far outweighs the number of species currently living.

Want to Know More About Variations in Classification Systems? Linneaus worked from the gross morphology of organisms at a time when there were limited tools to examine single celled organisms. He could separate plants and animals by whether they could make their own energy via photosynthesis, or needed to eat other organics for energy. However, he had little information on organisms the size of bacteria. Today we have access to sophisticated tools to analyze organic compounds in small quantities. This kind of analysis have been able to tell us that a particular organism forms specific proteins and is therefore more likely closely related to other organisms that form the same proteins. Most recently, modern molecular genetics and the ability to directly examine DNA has allowed even closer examination of the smallest living members of our planet, and debates over classifications and ancestry are once again healthy and active. In fact, the 5th, 6th and 7th editions of the textbook discuss different classification systems based on these recent discoveries and debates. The 6th edition introduces three domains: the prokaryotic Archea (the simplest, earliest forms of what we would commonly term small b “bacteria”); the prokaryotic Bacteria (capital B indicating a formal classification name); and the Eukaryotes. What does this mean for you? If you do a search on line for more information to help you study, you will find that there are several different methods of organizing life into kingdoms or even methods that include classification levels above kingdoms. In this course, we will stick to the five-kingdom system as shown in Table 9.1 of the 8th edition of the textbook.

Using the Fossil Classification Flowchart

Most of the fossils that we will be examining in Labs 6 to 8 will be considered at the level of phylum, some to the level of order, and fewer still to the level of class. Over the next few labs we will gradually introduce more and more of the major phyla. Figure 6.2 is a thumbnail image of the decision tree chart that will help you to identify fossils and we will refer back to this chart as each group is introduced. You can view a larger version or download it as a PDF file by going back to Guide to Fossil Classification.

There are some critical junctions in the flow chart above that require specific fossil features to be identified. Most of these features were introduced in Lab 5, and others will be introduced with the fossils.

The flow chart decisions include:

Colonial vs non-colonial life habit: identical individual organisms that live side by side (colonial) vs. solitary organisms.

Symmetry: bilateral (side to side or left to right, top to bottom), radial (including pentameral), asymmetric.

Shell coiling: planispiral (flat) or consipiral (cone shaped)

Chambered shells: shells that have internal dividers that separate parts of the interior shell volume from each other

Non-chambered shells: shells in which there is one open space.

Other descriptions in the flow chart that discriminate between branches are based upon the appearance of the fossil and these are best explained as we encounter each group.

Classification and Taxonomy of Plants and Animals

Ideally, the taxonomic classification reflects evolutionary relationships among organisms. For example, it is accepted that all organisms included in the phylum Chordata descend from a common ancestor. Currently, many biologists are using DNA sequence data to verify taxonomic descriptions of organisms and determine the patterns of evolution within and between different groups.

The biological classification of plants and animals was first proposed by Aristotle, who virtually invented the science of logic, of which for 2,000 years classification was a part of.

Aristotle, Greek Aristoteles, (born 384 bce, Stagira, Chalcidice, Greece—died 322, Chalcis, Euboea), ancient Greek philosopher and scientist.

The Greeks had constant contact with the sea and marine life, and Aristotle seems to have studied it intensively during his stay on the island of Lesbos. In his writings, he described a large number of natural groups, and, although he ranked them from simple to complex, his order was not an evolutionary one.

He was far ahead of his time in separating invertebrate animals into different groups and was aware that whales, dolphins, and porpoises had mammalian characters and were not fish. Lacking the microscope, he could not, of course, deal with the minute forms of life.

The Aristotelian method dominated classification until the 19th century. His scheme was, in effect, that the classification of a living thing by its nature.

As against superficial resemblances requires the examination of many specimens, the discarding of variable characters (since they must be accidental, not essential), and the establishment of constant characters. These can then be used to develop a definition that states the essence of the living thing.

The model for this procedure is to be seen in mathematics, especially geometry, which fascinated the Greeks. Mathematics seemed to them the type and exemplar of perfect knowledge since its deductions from axioms were certain and its definitions perfect, irrespective of whether a perfect geometrical figure could ever be drawn.

But the Aristotelian procedure applied to living things and is not by deduction from stated and known axioms Rather, it is by induction from observed examples and thus does not lead to the immutable essence but to a lexical definition.

Theophrastus of Lesbos (c.371-c.287 BC), Greek philosopher. Known as the “father of botany” Theophrastus described over 500 plant species and devised an advanced classification scheme for plants. Artwork from the 19th century book Vies des Savants Illustres.

Aristotle and his pupil in botany, Theophrastus, had no notable successors for 1,400 years. In about the 12th century CE, botanical works necessary to medicine began to contain accurate illustrations of plants, and a few began to arrange similar plants together. Encyclopaedists also began to bring together classical wisdom and some contemporary observations.

The first flowering of the Renaissance in biology produced, in 1543, Andreas Vesalius’s treatise on human anatomy and, in 1545, the first university botanic garden, founded in Padua, Italy. After this time, work in botany and zoology flourished.

John Ray summarized in the late 17th century the available systematic knowledge, with useful classifications. He distinguished the monocotyledonous plants from the dicotyledonous ones in 1703.

He recognized the true affinities of the whales and gave a workable definition of the species concept, which had already become the basic unit of biological classification. He tempered the Aristotelian logic of classification with empirical observation.

Later, Whittaker proposed the current and more elaborate five kingdom classification of Monera, Protista, Fungi, Plantae, andAnimalia.

Although it provided for centuries a procedure for attempting to define living things by careful analysis, it neglected the variation of living things. It is of interest that the few people who understood Charles Darwin’s Origin of Species in the mid-19th century were empiricists who did not believe in essence of each form.

The main criteria of the kingdom classification are cell structure, body organization, mode of nutrition and reproduction, and phylogenetic relationships based on the evolutionary development and diversification of a species.

At present, the biological classification includes:

Kingdom Monera Kingdom Protista Kingdom Fungi Kingdom Plantae Kingdom Animalia Viruses, Viroids and Lichens

Taxonomy, in a broad sense the science of classification, but more strictly the classification of living and extinct biological classification. The term is derived from the Greek taxis(“arrangement”) and nomos (“law”).

Taxonomy is, therefore, the methodology and principles of systematic botany and zoology and sets up arrangements of the kinds of plants and animals in hierarchies of superior and subordinate groups.

Popularly, classifications of living organisms arise according to need and are often superficial.

Anglo-Saxon terms such as worm and fish have been used to refer, respectively, to any creeping things including, snake, earthworm, intestinal parasite, or dragon and to any swimming or aquatic thing.

Although the term fish is common to the names shellfish, crayfish, and starfish, there are more anatomical differences between a shellfish and a starfish than there are between a bony fish and a man. Vernacular names vary widely.

The American robin (Turdus migratorius), for example, is not the English robin (Erithacus rubecula ), and the mountain ash (Sorbus) has only a superficial resemblance to true ash.

Biologists, however, have attempted to view all living organisms with equal thoroughness and thus have devised a formal classification.

A formal classification provides the basis for a relatively uniform and internationally understood nomenclature, thereby simplifying cross-referencing and retrieval of information.

How are organisms classified to the species level?

A hierarchical system is used for classifying organisms to the species level. This system is called taxonomic classification. The broadest classifications are by domain and kingdom. The most specific classification is by genus and species. The hierarchical groupings in between include phylum, class, family, and order.

What is a species?

Species are the basic unit of classification. While there are different views on what defines a species, in sexually reproducing organisms, a species has traditionally been defined by the ability of its members to reproduce together to form fertile offspring.

This definition is trickier in asexually reproducing organisms like bacteria, archaea, and protists, where scientists look at the similarity in DNA among individuals to tell whether they are in the same “species.”

When identifying an organism, familiar names like human , fruit fly, or maple tree are most likely the names you use. However, each type of organism has a scientific name such as humans are called Homo sapiens, for example.

Scientific names are derived from the genus and species names in a system known as binomial nomenclature (“bi” = two; “nom” = name). When species names appear in print, the genus is always capitalized and the species name is not, and both names appear in italics (or underlined).

This system allows for a common language with which biologists can both classify and compare organisms. It also provides a basis for biologists to communicate their findings with other scientists. A key aspect of taxonomy is the ability to characterize each level of description with unifying features, thus relaying information about the organism(s).

Particularly common in bacteria and plants, “subspecies” are described which can produce viable offspring but possess one or more features which distinguish them from other members of that species. In plants, these sub groups are referred to as different “varieties” or “subspecies,” while in single-celled organisms, they are referred to as “strains.” Within the animal kingdom, subspecies may be termed “races” or “breeds.”

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Classification of Animals: The Complete Guide

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What is Animal Classification?

Key Points

Every species is defined based on nine branching categories.

A kingdom of complex multi-celled organisms that do not produce their own food. This kingdom contains all living and extinct animals.

Every animal family is further divided into small groups known as genus.

Animal kingdom classification is an important system for understanding how all living organisms are related. Based on the Linnaeus method, species are arranged grouped based on shared characteristics.

This system of animal kingdom classification was developed by Swedish botanist Carolus (Carl) Linnaeus in the 1700’s. The Linnaeus Method, also known as Linnaean Taxonomy, creates a hierarchy of groupings called taxa, as well as binomial nomenclature that gives each animal species a two-word scientific name.

This method of giving scientific names to animals is typically rooted in Latin by combining the genus and species. For example, humans are classified as homo sapiens while wolves are canis lupus.

The more features that a group of animals share, the more specific that animal classification group is. Every species is defined based on nine branching categories. The primary method of animal classification is:

Domain Kingdom Phylum Class Order Suborder Animal Families Genus Species

Animal Classification Chart for Water snake (Nerodia Sipedon)

Animal Classification: The Six Different Animal Kingdoms

All living organisms can be placed in one of six different animal kingdom classifications. The characteristics of each animal kingdom are:

Animal – A kingdom of complex multi-celled organisms that do not produce their own food. This kingdom contains all living and extinct animals. Examples include elephants, whales, and humans. Plants – Complex and multi cellular autotrophic organisms, meaning they produce their own food through photosynthesis. Examples include trees, flowers, and grass. Fungi – Multi-celled organisms that do not produce their own food, unlike plants. Examples include molds, mushrooms, and yeast. Protista – Single celled organisms with more complexity than either eubacteria or archaebacteria. Examples include algae and amoebas Eubacteria – Single celled organisms found in everything from yogurt to your intestines. This kingdom contains all bacteria in the world not considered archaebacteria. Archaebacteria – The oldest known living organisms. Single-celled and found in hostile and extremely hot areas like thermal vents or hot springs

Animal Phylums Explained

After animal kingdom, animal species usually fall into one of seven different phylum, or phyla:

Porifera – Marine animals more commonly known as sponges and found in every ocean on earth. Cnidaria – Mostly marine animals that include over 11,000 species. Examples include coral, jellyfish, and anemones Platyhelminthes – Typically parasitic flatworms. Lacking in any respiratory or circulatory systems, oxygen pass through their bodies instead in a process known as diffusion. Examples include tapeworms and flukes. Annelida – More complex than Platyhelminthes, these are segmented and symmetrical worms containing a nervous system, respiratory system, and sense organs. Examples include the common earthworm and leeches. Mollusca – The second largest phylum by species count, and the largest marine phylum. Invertebrates with soft unsegmented bodies. It is estimated almost a quarter of marine life fall in this category. Examples include clams, mussels, and snails Arthropoda – Invertebrate animals with an exoskeleton and segmented bodies. Contains insects, crustaceans, and arachnids. This is the largest phylum by species count. Examples include scorpions, butterflies, and shrimp Chordata – Vertebrates. Animals that develop a notochord, a cartilaginous skeletal rod that supports the body in embryo and can often become a spine. Most animals we are familiar with, including dogs, horses, birds, and humans fall in to this category.

Animal Classes

The phylum group is then divided into even smaller groups, known as animal classes. The Chordata phylum splits in to these seven animal classes:

Agnatha (jaw-less fish) Chrondrichtyes (cartilaginous fish) Osteichthyes (bony fish) Amphibia (amphibians) Reptilia (reptiles) Aves (birds) Mammalia (mammals)

Different Animal Orders

Each class is divided into small groups again, known as orders. There is no universally accepted breakdown for the class Mammalia. Some outline as many as 26 different orders for the class mammalia. Some of the most popular examples include:

Artiodactyla (even-toed hoofed animals) – Examples include moose, camels, and giraffes

Carnivora – Animals that specialize in mostly eating meat, but also contains some omnivores and herbivores. Characterized as having nonretractable claws and long snouts. Examples include bears.

Rodentia (gnawing mammals) – Examples include beavers, mice, and squirrels

Chiropptera (bats) – The only mammals that can fly. Examples include free-tailed and vampire bats

Cetacea (porpoises and whales) – Examples include killer whales, dolphins, and hump-backed whales

Primates – Includes prehensile hands and feet, commonly with opposable thumbs. Examples include gorillas, chimpanzees, and humans.

Animal Families

In every order, there are different animal families which all have very similar features. The Carnivora order breaks into animal families that include Felidae (Cats), Canidae (Dogs), Ursidae (Bears), and Mustelidae (Weasels).

Animal Genus Types

Every animal family is further divided into small groups known as genus. Each genus contains animals that have very similar features and are closely related. For example, the Felidae (Cat) family contains genus including Felis (small Cats and domestic Cats), Panthera (Tigers, Leopards, Jaguars and Lions) and Puma (Panthers and Cougars).

Animal Species Names

Each individual species within the genus is named after its individual features and characteristics. The names of animals are based in Latin and consist of two words. The first word in the name of an animal will be the genus, and the second name indicates the specific species. This method of organizing scientific names of animal species was developed by Carl Linnaeus in the 1700’s. As an example, a dolphin species name is Delphinus Delphis. A red fox is Vulpes vulpes. This animal classification chart of a red fox is an example of Linnaean Taxonomy

An animal classification for red fox, based on the Linnaeus Method

Animal Classification Example 1 – Red Fox

(Vertebrate)

Class: Mammalia (Mammal)

Order: Carnivora (Carnivore)

Family: Canidae (Dog)

Genus: Vulpes

Species: Vulpes vulpes (red fox)

Animal Classification Example 2 – Orang-utan