Amphibian—an animal that spends its time in the water and on land. Amplexus—the name given to the reproductive embrace of frogs and toads. Apatite—the mineral that forms the enamel of teeth and reinforces bone. Archipelago—a group of islands.

Articulate—the way in which bones are arranged in an animal's skeleton.

Artiodactyls—the group of herbivorous animals that includes deer, sheep, and cattle characterized by their cloven hooves.

Asphalt—the dark, sticky substance that remains of crude oil after the light, volatile fractions have evaporated.

Asteroid—a lump of orbiting rock left over from the formation of the star systems, some of which can be several kilometers across.

Basalt—a type of fine-grained igneous rock.

Bering land bridge—a large tract of land that connected Asia to North America. Rising sea levels at the end of the last glaciation flooded this land bridge.

Cambrian—one of the earth's geological ages, which extended from 490 to 543 million years ago.

Canid—a name for the group of predatory mammals commonly known as dogs.

Carboniferous—one of the earth's geological ages, which extended from 299 to 352 million years ago.

Carrion—the name given to dead and decaying animals that are eaten by scavengers. Cellulose—the glucose-based polysaccharide that is found in the cell wall of all plants. Centra—a disc-shaped section of the vertebral column.

Chytrid fungi—a type of fungi that infects the soft skin of amphibians, leaving them open to other opportunistic infections.

Cloaca—the common opening for the genital, urinary, and digestive tract that is found in all fish, amphibians, reptiles, birds, and monotreme mammals.

Cloning—the technique of producing an exact copy of an animal from the DNA inside one of its cells.

Cloud forest—forest growing in mountainous areas that is often shrouded in cloud.

Coccoliths—individual calcium carbonate plates from the shell that surround certain kinds of single-celled algae.

Comb—the fleshy protuberances on the head of certain birds.

Continental drift—the process by which the continental plates move around on the lava that forms the earth's mantle.

Convergent evolution—in evolutionary biology, the process whereby organisms not closely related independently evolve similar traits as a result of having to adapt to similar environments or ecological niches.

Cretaceous—one of the earth's geological ages, which extended from 65 to 145 million years ago.

Cro-Magnon—a term usually used to describe the oldest modern humans of Europe. Cuticle—the nonmineral outer covering of an organism.

Devonian—one of the earth's geological ages, which extended from 359 to 416 million years ago.

Dinosaur—a group of reptiles that dominated terrestrial ecosystems for about 160 million years until the end of the Cretaceous.

Ecosystem—a system formed by the interaction of a community of organisms with their environment.

Endemic—an organism exclusively native to a certain place.

Endocast—the replica of a brain that is formed when sediments or other materials fill the buried cranium of a dead animal.

Eurasia—the landmass comprising Europe and Asia.

Fauna—the animal life in an ecosystem.

Femur—in all vertebrates with legs, the bone between the hip and knee. Firn—ice that is at an intermediate stage between snow and glacial ice. Flora—the plant life in an ecosystem.

Folk memory—stories that are passed, orally, from one generation to the next.

Foraminifera—tiny, single-celled organisms, often shelled, that live in profusion in the oceans.

Gizzard—the muscular organ found in the digestive tract of birds and other animals that grinds up food.

Gondwanaland—a probable landmass in the Southern Hemisphere that separated many millions of years ago to form South America, Africa, Antarctica, and Australia.

Greenhouse gas—any gas in the atmosphere that traps the heat reflected from the earth's surface, e.g., carbon dioxide or methane.

Holocene—the present geological epoch, which began around 10,000 years ago.

Hominid—a collective term for extinct and extant humans, chimpanzees, gorillas, and orangutans.

Interstadial—a period of colder temperatures during an interglacial. Invertebrate—any animal that lacks a vertebral column.

Iridium—a very dense metallic element that is rare on earth but more common in asteroids and meteorites.

Island rule—a principle in evolutionary biology stating that members of a species get smaller or bigger depending on the resources available in the environment.

Joey—the name given to an infant kangaroo or wallaby.

Jurassic—one of the earth's geological ages, which extended from 145 to 199 million years ago.

Keel—the large extension of the sternum (breastbone) that serves as a muscle attachment in all flying birds.

Kelp—large seaweeds often found growing in so-called forests in shallow, nutrient-rich waters.

Keratin—a structural protein that is found in skin, hair, hooves, and claws.

Laurasia—the northern part of the Pangaean supercontinent comprising Asia, Europe, and North America.

Magma—molten rock that sometimes forms beneath the surface of the earth.

Malagasy—anything related to the island of Madagascar, including the people and the language.

Mantle—the 2,900 km thick layer of the earth's interior that surrounds the core.

Maori—the indigenous Polynesian people of New Zealand and their language.

Marsupial—a group of mammals native to Australasia and South America that give birth when the young are in a very early stage of development; the remainder of their development takes place in a pouch.

Megafauna—any species of large animals, but often used to refer to the large mammals that have become extinct in relatively recent times.

Micropaleontologist—a paleontologist who studies microfossils.

Mineralization—the process by which an organic substance is converted into an inorganic one.

Miocene—a geological epoch that extended from 5.3 to 23 million years ago. New World—the Western Hemisphere, which includes the Americas.

Niche—the way in which an organism makes a living in a habitat.

Nymph—the immature stage of an insect that does not go through metamorphosis.

Old World—Europe, Africa, and Asia.

Ordovician—one of the earth's geological ages, which extended from 443 to 488 million years ago.

Osteoarthritis—a degenerative disease of thejoints. Osteomyelitis—a bacterial infection of the bone or bone marrow.

Ozone layer—the layer of ozone gas high in the atmosphere that absorbs some of the potentially damaging ultraviolet radiation in sunlight. Paleoanthropologist—a scientist who studies ancient humans.

Paleontologist—a scientist who studies prehistoric life forms on earth through the examination of fossils.

Pangaea—the supercontinent comprising all the earth's landmasses that existed about 250 million years ago.

Pelage—the coat of a mammal, consisting of hair, fur, wool, or other soft covering, as distinct from bare skin.

Permafrost—soil that is at or below the freezing point of water for two or more years. Permian—one of the earth's geological ages, which extended from 251 to 299 million years ago.

Perrisodactyls—the group of herbivorous animals that includes horses, rhinoceri, and so on, characterized by their odd number of hooves.

Photosynthesis—the process by which plants use sunlight to convert carbon dioxide and water into food.

Pinniped—the group of mammals that includes seals and sea lions.

Plankton—the mass of passively floating, drifting, or somewhat motile organisms occurring in a body of water, primarily comprising microscopic algae, protozoa, and the larvae of larger animals.

Pleistocene—a geological epoch that extended from 10,000 to 1.8 million years ago. Pliocene—a geological epoch that extended from 1.8 to 5.3 million years ago. Polynesian—the people and the culture originating from a group of around 1,000 islands in the Pacific Ocean.

Puggle—the name given to the young of echidnas.

Radiocarbon dating—a method for measuring the age of items containing carbon that is based on the steady decay of the radioactive carbon isotope, carbon-14.

Rainforest—forests characterized by high rainfall, typically 1,750 to 2,000 mm per year.

Sebaceous gland—small glands in the hair follicles of mammalian skin that secrete an oily substance known as sebum, which lubricates and protects the skin and hair.

Selective breeding—part of the domestication process by which animals and plants with useful traits are used for breeding to produce distinct breeds or cultivars.

Sexual selection—a theory that states that certain traits and characteristics can be explained by competition between members of a species.

Silurian—one of the earth's geological ages, which extended from 416 to 443 million years ago.

Sinkhole—a depression or hole in the surface of the ground due to the removal of soil and bedrock, usually by water.

Steppe—a grassland plain without trees.

Symbiotic—the close and often long-term relationship that exists between two species of organism.

Synapsid—the class of animals that includes mammals and their closest relatives such as the now extinct mammallike reptiles.

Syphilis—a sexually transmitted disease caused by a spirochete bacteria that afflicts many types of mammal.

Tertiary—the geological period that extended from 1.8 to 65 million years ago.

Thermal inertia—the ability of a substance to store internal energy as heat and has important implications for animals. A large animal has a lower surface area to volume ratio than a smaller animal; therefore it heats up and cools down at a slower rate.

Traps—the steplike landscape that can be found in regions of eroded flood basalt.

Triassic—one of the earth's geological ages, which extended from 199 to 251 million years ago.

Tuberculosis—a bacterial infection that affects many tissues in the mammalian body, sometimes leaving scars on the body and bones.

Tundra—treeless plains found in the extreme north and south and in mountainous areas, where plant growth is impeded by low temperatures and a short growing season.

Ultraviolet radiation—part of the spectrum of sunlight that is damaging to living things but that is absorbed by the ozone layer.

Vertebrae—the individual bones in the vertebral column of a vertebrate. Vertebrate—any animal with a vertebral column. Zoologist—a scientist who studies animals.

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