Classifying Critters

EDITED VERSION

Our planet Earth is home to many millions of species of flora and fauna. Scientists have identified approximately 2 million species, and speculate that there may be as many as 100 million. The first known classification of these species was by the Greek philosopher, Aristotle. Carolus Linnaeus, who is known as the father of modern taxonomy, built upon these classifications. Today, we have 8 taxonomic ranks - domain, kingdom, phylum, class, order, family, genus, and species.

The kingdom Animalia consists of multicellular heterotrophs. The most numerous animal species are insects, and animals can range greatly in size from no more than several cells to the mighty blue whale. This kingdom is then divided into 21 phyla. Human beings fit into the subphylum of vertebrates, and the class of mammals. The most well known classes of vertebrates are mammals, birds, fish, reptiles, and amphibians.

What distinguishes animals in each of these five classes? We’ll begin with the 5,400 species in the class Mammalia. The word “mammal” is derived from “mammary glands”, which mammals use to feed their young. All mammals drink milk from their mothers. Mammals are also warm-blooded; their body temperature remains constant no matter the weather. Mammals are also characterized by the presence of sweat glands and hair. Besides 5 species that lay eggs, all mammals give birth to live young.

Class Aves, which consists of birds, is made up of approximately 10,000 species. Birds are characterized by the presence of feathers. Like mammals, they are also warm-blooded creatures. They lay eggs and have beaks with no teeth. Most birds can fly, and all are bipedal.

Fish are divided into numerous subclasses based upon their jaws, fins, and other physical characteristics, but the combination of gills, fins, and their aquatic environment distinguishes them from all other animals. Fish breathe underwater via their gills. They are cold-blooded (also known as ectothermic), meaning their body temperature varies with their surroundings. Like birds, fish lay eggs to reproduce.

There are approximately 8,000 species in class Reptilia. Reptiles have scales, as opposed to feathers or hair, and are cold-blooded like birds and fish. They lay eggs on land, and have either four limbs or, in the case of snakes, none at all.

The 4,000 members of class Amphibia, or amphibians, get their name from an ancient Greek term that means “both kinds of life”. This means that amphibians live both in water and on land. Amphibians are born as water-breathing creatures, and during their lives they develop lungs and legs, allowing them to leave the water. Amphibians are cold-blooded and unlike the previously mentioned animals, they do not have scales, feathers, or fur. They lay their eggs in water, like fish, and typically have four limbs.

See the following resources for further information on the animal kingdom:

Animal Phyla - Descriptions of the 21 animal phyla

Animal Classes – Guide to animal classes for kids

Animal Diversity Web - In depth descriptions of several classes of animals

Taxonomy: Classifying Life - Scientific explanation of taxonomy

Biological Classification - Wikipedia article about classifying life forms

The Hall of Mammals - Additional information on mammals that further breaks up this class

The Incredible World of Mammals - More mammal facts including evolution, the importance of milk, diet, and senses

All About Birds - Guide to birds that allows search for a specific species

The Life of Birds - Information on the evolution of birds, their songs, their parenting, and their brains

FishBase - Search for information on the many species of fish

Classification of Fish - Breakdown of the many classes of fish

Reptile Database –Information on the many types of reptiles

Reptile Classification - Breakdown of different reptiles

Introduction To The Amphibia - Information on amphibian fossils and anatomy

Amphibian Classification - Further breakdown of the types of amphibians

ORIGINAL VERSION

Our planet Earth is home to many millions of species of flora and fauna. Scientists have identified approximately 2 million species, and speculate that there may be as many as 100 million. The first known classification of these species was by Greek philosopher Aristotle. Carolus Linnaeus, who is known as the father of modern taxonomy, built upon these classifications. Today, we have 8 taxonomic ranks - domain, kingdom, phylum, class, order, family, genus, and species.

The kingdom Animalia consists of multicellular heterotrophs. The most numerous animal species are insects, and animals can range greatly in size from no more than several cells to the mighty blue whale. This kingdom is then divided into 21 phyla. Human beings fit into the subphylum of vertebrates, and the class of mammals. The most well known classes of vertebrates are mammals, birds, fish, reptiles, and amphibians.

What distinguishes animals into each of these five classes? We’ll begin with the 5,400 species in the class Mammalia. The word “mammal” is derived from “mammary glands”, which mammals use to feed their young. All mammals drink milk from their mothers. Mammals are also warm-blooded; their body temperature remains constant no matter the weather. Mammals are also characterized by the presence of sweat glands and hair. Besides 5 species that lay eggs, all mammals give birth to live young.

Class Aves, which consists of birds, is made up of approximately 10,000 species. Birds are characterized by the presence of feathers. Like mammals, they are also warm-blooded creatures. They lay eggs and have beaks with no teeth. Most birds can fly, and all are bipedal.

Fish are divided into numerous subclasses based upon their jaws, fins, and other physical characteristics, but the combination of gills, fins, and their aquatic environment distinguishes them from all other animals. Fish breathe underwater via their gills. They are cold-blooded (also known as ectothermic), meaning their body temperature varies with their surroundings. Like birds, fish lay eggs to reproduce.

There are approximately 8,000 species in class Reptilia. Reptiles have scales as opposed to feathers or hair, and are cold-blooded like birds and fish. They lay eggs on land, and have either four limbs or, in the case of snakes, none at all.

The 4,000 members of class Amphibia, or amphibians, get their name from an ancient Greek term that means “both kinds of life”. This means that amphibians live both in water and on land. Amphibians are born as water-breathing creatures, and during their lives they develop lungs and legs, allowing them to leave the water. Amphibians are cold-blooded and unlike the previously mentioned animals, they do not have scales, feathers, or fur. They lay their eggs in water, like fish, and typically have four limbs.

See the following resources for further information on the animal kingdom:

Animal Phyla - Descriptions of the 21 animal phyla

Animal Classes – Guide to animal classes for kids

Animal Diversity Web - In depth descriptions of several classes of animals

Taxonomy: Classifying Life - Scientific explanation of taxonomy

Biological Classification - Wikipedia article about classifying life forms

The Hall of Mammals - Additional information on mammals that further breaks up this class

The Incredible World of Mammals - More mammal facts including evolution, the importance of milk, diet, and senses

All About Birds - Guide to birds that allows search for a specific species

The Life of Birds - Information on the evolution of birds, their songs, their parenting, and their brains

FishBase - Search for information on the many species of fish

Classification of Fish - Breakdown of the many classes of fish

Reptile Database –Information on the many types of reptiles

Reptile Classification - Breakdown of different reptiles

Introduction To The Amphibia - Information on amphibian fossils and anatomy

Amphibian Classification - Further breakdown of the types of amphibians