Extinction (biology), the end
of existence of a group of organisms, caused by their inability to
adapt to
changing environmental conditions. Extinction affects individual species—that
is, groups of interbreeding organisms—as well as collections of related
species, such as members of the same family, order, or class. The dodo, for
example, a species of flightless pigeon formerly living on the island of
Mauritius, became extinct in 1665. About 10,000 to 12,000 years ago, the most
of the woolly mammoths and the last of the mastodons, both members of the
elephant family, died. And about 245 million years ago at the end of the
Paleozoic Era, an entire class of primitive marine animals called trilobites
disappeared forever.