Science Source December 28, 2009 DVD

Carcharodontosaurus (left) and Deltadromaeus (right), carnivorous theropods from the Cretaceous era in North Africa.

Megazostrodon (Mammaliaform) eating dinosaur eggs, from the Cretaceous era of North America.

The dirk-toothed Smilodon, also known as the saber-toothed cat or saber-toothed tiger, from the Pleistocene era (Ice Age) of North America.

Smilodon (Sabertooth Tiger) killing a peccary (Platygonus), from the Pleistocene (Ice Age) of North America.

Megantereon, an early sabertooth tiger, from the Pliocene era of Europe, Asia and North America.

Dire Wolf (Canis dirus) (left) and Smilodon (Sabertooth Tiger) at La Brea Tar Pits, California.

Smilodon (Sabertooth Tiger) attacking a Glossotherium (ground sloth), from the Pleistocene age (Ice Age) of North America.

Neanderthal humans (Homo neanderthalensis) being confronted by a cave bear (ursus spelaeus), from the Pleistocene age (Ice Age) of Europe and Western...

Columbian Mammoth (Mammuthus columbi) trapped by asphalt at La Brea Tar Pits in California, from the Pleistocene (Ice Age) of North America.

Cave Bear (Ursus spelaeus) from the Pleistocene age (Ice Age) of Europe and Western Asia.

Homotherium (Scimitar Sabertooth Cat) from the Pleistocene (Ice Age).

Cave Bear (Ursus spelaeus) from the Pleistocene age (Ice Age) of Europe and Western Asia.

Cave Bear (Ursus spelaeus) from the Pleistocene age (Ice Age) of Europe and Western Asia.

Luray Caverns, discovered 1878. Shenandoah Valley, Virginia.

Illustration of a Dodo Bird (Raphus cucullatus). The Dodo Bird has been extinct since the mid-to-late 17th century.

Illustration of a Dodo Bird (Raphus cucullatus). The Dodo Bird has been extinct since the mid-to-late 17th century.

Illustration of a Dodo Bird (Raphus cucullatus). The Dodo Bird has been extinct since the mid-to-late 17th century.

Illustration of a Smilodon, also known as the saber-toothed cat or saber-toothed tiger. The Smilodon lived during the late Pleistocene Age (Ice Age)....

Illustration of a Smilodon, also known as the saber-toothed cat or saber-toothed tiger. The Smilodon lived during the late Pleistocene Age (Ice Age)....

Illustration of a Woolly Mammoth (Mammuthus primigenius), from the Pleistocene Age (Ice Age).

Illustration of a Woolly Mammoth (Mammuthus primigenius), from the Pleistocene Age (Ice Age).

Illustration of the American toad (Bufo americanus).

Illustration of the Baltimore oriole (Icterus galbula).

Illustration of the concept of biological organization.

Illustration comparing the anatomy of human bones (left) and bird bones (right).

Illustration of a black-capped chickadee (Poecile atricapillus).

Illustration of a black-capped vireo (Vireo atricapilla). This small species of songbird is listed as vulnerable due to many factors, including brown-...

Illustration of Blanding's turtle (Emydoidea blandingii). It is considered threatened or endangered throughout much of its range (the Great Lakes regi...

Illustration of bone anatomy, showing the periosteum, yellow marrow, medullary cavity, compact bone, endosteum, and spongy bone.

Illustration of the tadpole of the American bullfrog (Rana catesbeiana).

Caddisfly (Order Trichoptera) and separate casing. Many species construct cases out of silt and other materials for protection during the larval stage...

Caddisfly (Order Trichoptera) and casing. Many species construct cases out of silt and other materials for protection during the larval stage.

Caddisfly (Order Trichoptera) larva. Many species construct cases out of silt and other materials for protection during the larval stage.

Illustration of a cedar waxwing (Bombycilla cedrorum).

Illustration showing cell relationships in heart tissue.

Illustration of a chestnut-sided warbler (Dendroica pensylvanica).

Illustration of a chorus frog (Pseudacris).

Illustration comparing bird and human bone anatomy. Human bone cavities are filled with yellow marrow, while bird bones are hollow with scaffolding.

A chart compares the wing bones of a pterydon, bird, bat and human arm.

Illustration showing the conduction pathway in the left ventricle of a pig heart.

Illustration of Cope's gray tree frog (Hyla chrysoscelis), a species of tree frog found in the United States.

Illustration of a damselfly nymph (Suborder Zygoptera).

Illustration of a downy woodpecker (Picoides pubescens), the smallest woodpecker in North America.

Illustration of a dragonfly nymph.

Illustration of the planet Earth.

Illustration of Eurasian milfoil (Myriophyllum spicatum), an aquatic plant.

Illustration of a female northern cardinal (Cardinalis cardinalis), much less brightly colored than the male.

Illustration of a food web with labels. A food web is a set of interconnected food chains by which energy and materials circulate within an ecosystem.

Illustration of a gray jay (Perisoreus canadensis), a member of the crow and jay family (Corvidae) found in boreal forests and subalpine forests of No...

Illustration of a gray tree frog (Hyla versicolor), a species of small arboreal frog native to much of the eastern United States and southeastern Cana...