Amphibians

Cane Toad
The much maligned venomous cane toads earned their bad reputation shortly after being released into the Australian ecology in 1935 with the hope that they would control the destructive cane beetle population. They turned out to be failures at controlling beetles, but remarkably successful at reproducing and spreading themselves.

Mexican Axolotl
The Mexican axolotl (pronounced ACK-suh-LAH-tuhl) salamander has the rare trait of retaining its larval features throughout its adult life. This condition, called neoteny, means it keeps its tadpole-like dorsal fin, which runs almost the length of its body, and its feathery external gills, which protrude from the back of its wide head.

Northern Leopard Frog

The northern leopard frog is perhaps most recognizable as the formaldehyde-soaked specimen in the high school lab tray.

Once the most abundant and widespread frog species in North America, leopard frogs were widely collected not only for dissection but for the food industry (frog legs) as well.

Spotted Salamander

Despite being fairly large and having an extremely broad range, the spotted salamander is actually pretty hard to, well, spot.

They can reach 9 inches (23 centimeters) in length and are prevalent in mature deciduous forests from eastern Canada throughout the eastern and midwestern United States. But these secretive salamanders spend almost their entire lives hidden under rocks or logs or in the burrows of other forest animals.

Spring Peeper

Spring peepers are to the amphibian world what American robins are to the bird world. As their name implies, they begin emitting their familiar sleigh-bell-like chorus right around the beginning of spring.

Birds

Arctic Skua
These aggressive seabirds are sometimes referred to as avian pirates. The name is well earned. Skuas steal much of their food from terns, puffins, and other birds that are carrying fish or other prizes back to their nests and young. Skuas strike by attacking in midair and forcing their victims to drop their kills in flight. The swashbuckling birds sometimes team up to overwhelm their victims, and they are relentless in chasing down their adversaries.

Blue Jay
Blue jays are natural forest dwellers, but they are also highly adaptable and intelligent birds. They are a familiar and noisy presence around many North American bird feeders. The blue jay's "Jay! Jay!" call is only one of a wide variety of sounds the bird employs—including excellent imitations of several hawk calls.

Common Loon
Named for their clumsy, awkward appearance when walking on land, common loons are migratory birds which breed in forested lakes and large ponds in northern North America and parts of Greenland and Iceland. They winter all along North America’s Pacific and Atlantic coasts as well as in Europe and Iceland.

Macaw

Macaws are beautiful, brilliantly colored members of the parrot family.

Many macaws have vibrant plumage. The coloring is suited to life in Central and South American rain forests, with their green canopies and colorful fruits and flowers. The birds boast large, powerful beaks that easily crack nuts and seeds, while their dry, scaly tongues have a bone inside them that makes them an effective tool for tapping into fruits.

Ring-Necked Pheasant

Ring-necked pheasants are native to China and East Asia, but they have been successfully introduced in other parts of the world, including North America.

Snow Goose

Snow geese are known for their white plumage, but many of them are actually darker, gray-brown birds known as blue geese. These birds were once though to be two separate species, but they have recently been found to be merely two different color morphs of the same bird. A single gene controls the color difference.

Bugs

Black Widow Spider
Black widows are notorious spiders identified by the colored, hourglass-shaped mark on their abdomens. Several species answer to the name, and they are found in temperate regions around the world.

Deer Tick
The loathsome deer tick, now known as the black-legged tick, is defined more by the disease it spreads than by its own characteristics.

Monarch Butterfly
Monarch butterflies are known for the incredible mass migration that brings millions of them to California and Mexico each winter. North American monarchs are the only butterflies that make such a massive journey—up to 3,000 miles (4,828 kilometers). The insects must begin this journey each fall ahead of cold weather, which will kill them if they tarry too long.

Tarantula
Tarantulas give some people the creeps because of their large, hairy bodies and legs. But these spiders are harmless to humans (except for a painful bite), and their mild venom is weaker than a typical bee's. Among arachnid enthusiasts, these spiders have become popular pets.

Fish

Anglerfish
The angry-looking deep sea anglerfish has a right to be cranky. It is quite possibly the ugliest animal on the planet, and it lives in what is easily Earth's most inhospitable habitat: the lonely, lightless bottom of the sea.

Butterflyfish
Butterflyfish, with their amazing array of colors and patterns, are among the most common sites on reefs throughout the world.

Chinese Paddlefish
No young Chinese paddlefish have been seen in the wild since 1995, and there have been no sightings of a wild Chinese paddlefish of any size since 2003—leading many to fear that the megafish is already extinct.

Electric Eel
Despite their serpentine appearance, electric eels are not actually eels. Their scientific classification is closer to carp and catfish.

Whale Shark
As the largest fish in the sea, reaching lengths of 40 feet (12 meters) or more, whale sharks have an enormous menu from which to choose. Fortunately for most sea-dwellers—and us!—their favorite meal is plankton. They scoop these tiny plants and animals up, along with any small fish that happen to be around, with their colossal gaping mouths while swimming close to the water's surface.

Invertebrates

Blue Crab
The blue crab is so named because of its sapphire-tinted claws. Its shell, or carapace, is actually a mottled brownish color, and mature females have red highlights on the tips of their pincers.

Giant Clam

The giant clam gets only one chance to find a nice home. Once it fastens itself to a spot on a reef, there it sits for the rest of its life.

These bottom-dwelling behemoths are the largest mollusks on Earth, capable of reaching 4 feet (1.2 meters) in length and weighing more than 500 pounds (227 kg). They live in the warm waters of the South Pacific and Indian Oceans.

Nudibranch

The bottom-dwelling, jelly-bodied nudibranch (NEW-dih-bronk) might seem an unlikely canvas for Mother Nature to express her wildest indulgences of color and form. But these shell-less mollusks, part of the sea slug family, bear some of the most fascinating shapes, sumptuous hues, and intricate patterns of any animal on Earth.

Krill

The lowly krill averages only about two inches (five centimeters) in length, but it represents a giant-sized link in the global food chain. These small, shrimp-like crustaceans are essentially the fuel that runs the engine of the Earth’s marine ecosystems.

Giant Squid

The giant squid remains largely a mystery to scientists despite being the biggest invertebrate on Earth. The largest of these elusive giants ever found measured 59 feet (18 meters) in length and weighed nearly a ton (900 kilograms).

Mammals

African Lion
Lions are the only cats that live in groups, which are called prides. Prides are family units that may include up to three males, a dozen or so females, and their young. All of a pride's lionesses are related, and female cubs typically stay with the group as they age. Young males eventually leave and establish their own prides by taking over a group headed by another male.

African Elephant
African elephants are the largest land animals on Earth. They are slightly larger than their Asian cousins and can be identified by their larger ears that look somewhat like the continent of Africa. (Asian elephants have smaller, rounded ears.)

Baboon
There are five different species of baboons. All of them live in Africa or Arabia. Baboons are some of the world's largest monkeys, and males of different species average from 33 to 82 pounds (15 to 37 kilograms). Baboon bodies are 20 to 40 inches (60 to 102 centimeters) long, not including substantial tails of varying lengths.

Cheetah
The cheetah is the world's fastest land mammal. With acceleration that would leave most automobiles in the dust, a cheetah can go from 0 to 60 miles (96 kilometers) an hour in only three seconds. These big cats are quite nimble at high speed and can make quick and sudden turns in pursuit of prey.

Elk
Elk are also called wapiti, a Native American word that means "light-colored deer." Elk are related to deer but are much larger than most of their relatives. A bull (male) elk's antlers may reach 4 feet (1.2 meters) above its head, so that the animal towers 9 feet (2.7 meters) tall.

Prehistoric Animals

Devil Frog

Beelzebufo ampinga, the so-called "devil frog," may be the largest frog that ever lived. These beach-ball-size amphibians, now extinct, grew to 16 inches (41 centimeters) in length and weighed about 10 pounds (4.5 kilograms). They inhabited the island of Madagascar during the Late Cretaceous, about 65 to 70 million years ago.

Triceratops Horridus
With its rock-hard horns, shieldlike head plate, and massive torso, Triceratops horridus—"three-horned face"—must have been an intimidating presence in the late Cretaceous period. But this giant was an herbivore, preying only on the vegetation of western North America.

Henodus Chelyops
Henodus was a three-foot-long (one-meter-long) marine reptile called a placodont that crushed bottom-dwelling shellfish with two upper teeth at the back of its beaklike snout. The snout was squared off just in front of the eyes, making the head unusually boxy. The ancient placodont looked like a flattened turtle, though its protective shell of bony plates was twice as wide as long and relatively flat.

Troodon Formosus
Troodon formosus was a small coelurosaurian dinosaur—a member of the same clade (evolutionary group) to which modern birds belong. Fossilized remains have been discovered of nesting parents and egg clutches. These finds shed some light on reproductive strategies that resemble those of both crocodilians and birds.

Tusotheuthis Longa

Tusoteuthis was a giant squid nearly equal in size to those that ply the oceans today—with their tentacles stretched out, the ancient cephalopods may have measured 25 to 35 feet (8 to 11 meters) long. Like the modern giant squid, Tusoteuthis lacked an outer shell and is known only from discoveries of the rigid support structure in its body called a pen or gladius. The pen was akin to a backbone but made of delicate shell-like material called chitin.