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Animals / Wildlife - By Category

Amphibians
Amphibians are a group of vertebrates that includes salamanders, newts, caecilians, frogs, and toads. There are between 5,000 and 6,000 species of amphibians alive today. The first amphibians arose about 370 million years ago during the Devonian Period. The articles listed below provide information about the characteristics, classification, and evolution of amphibians.

Arthropods
Arthropods are a group of invertebrates that includes insects, crustaceans, arachnids, sea spiders, horseshoe crabs, and a number of lesser-known groups. There are over 1 million species of arthropods alive today, with the most diverse group being, by far, the insects. The articles listed below provide information about the characteristics, classification, and evolution of arthropods.

Birds
Birds are a group of vertebrates that includes about 30 groups such as albatrosses, gamebirds, herons, hummingbirds, owls, parrots, penguins, perching birds, woodpeckers, and many others. There are between 9,000 and 10,000 species of birds alive today. The first birds evolved from reptiles during the Mesazoic Era, about 150 million years ago. The articles listed below provide information about the characteristics, classification, and evolution of birds.

Cnidarians
Cnidarians are a group of invertebrates that includes jellyfish, corals, sea anemones, and hydras. There are between 8,000 and 9,000 species of cnidarians alive today. The articles listed below provide information about the characteristics, classification and evolution of cnidarians.

Echinoderms
Echinoderms are a group of invertebrates that includes starfish, sea lilies, feather stars, brittlestars, sea cucumbers, and sea urchins and many others. There are about 600 species of echinoderms alive today. The articles listed below provide information about the characteristics, classification and evolution of echinoderms.

Fishes
Fishes are a diverse group of vertebrates and represent an informal collection of animals, not a true taxanomic class. For the purposes of this website, we recognize four groups of fishes including hagfish, lampreys, cartilaginous fishes and bony fishes. There are more than 24,000 species of fishes alive today. The articles listed below provide information about the characteristics, classification and evolution of fishes.

Invertebrates
Invertebrates are a diverse group of animals that includes over 30 phyla. Invertebrates do not have a backbone, nor a bony skeleton. This large group of animals includes sponges, cnidarians, flatworms, roundworms, segmented worms, molluscs, echinoderms, and arthropods. About 97 percent of all known species are invertebrates. The articles listed below provide information about the characteristics, classification and evolution of invertebrates.

Mammals
Mammals are a group of vertebrates that includes about 21 groups such as anteaters, bats, carnivores, cetaceans, elephants, marsupials, primates, rodents and many others. There are about 5,400 species of mammals alive today. Mammals first appeared about 200 million years ago during the Jurassic Period. The articles listed below provide information about the characteristics, classification and evolution of mammals.

Reptiles
Reptiles are a group of vertebrates that includes crocodilians, lizards, snakes and turtles. There are about 8,000 species of reptiles alive today. Early reptiles diverged from other amniotes between 320 and 310 million years ago during the late Carboniferous Period. The articles listed below provide information about the characteristics, classification and evolution of reptiles.

Molluscs
Molluscs are a group of invertebrates that includes chitons, snails, slugs, limpets, squids, oysters, clams, cuttlefish, octopus and many more. There are about 100,000 species of molluscs alive today. The articles listed below provide information about the characteristics, classification and evolution of molluscs.

Segmented Worms
Segmented worms are a group of invertebrates that includes earthworms, ragworms and leeches. There are about 12,000 species of segmented worms alive today. The articles listed below provide information about the characteristics, classification and evolution of segmented worms.

Sponges
Sponges are a group of invertebrates that includes glass sponges, demisponges, and calcareous sponges. There are about 10,000 species of sponges alive today. The articles listed below provide information about the characteristics, classification and evolution of sponges.

More Animal Facts »
Learn interesting facts about animals, a group of living organisms that includes amphibians, birds, fishes, invertebrates, mammals and reptiles. There are millions of species of animals alive today. The articles listed here provide facts about animals including their characteristics, classification and evolution.

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