Encyclopedia of Evolution.pdf - Online Reading Center

microevolution
Stanley Miller did one of the first experiments that simulated the origin of the organic molecules from which all life-forms are constructed. (Courtesy of
Bettmann/Corbis)
other of which would later become South America, Africa,
Australia, and Antarctica (see continental drift).
Extinction altered the previous balance of dominance
among lineages of organisms. The tree-sized club mosses,
horsetails, and ferns that had dominated the forests of the
middle Paleozoic era declined in importance and were extinct
by the beginning of the Mesozoic era (see seedless plants,
evolution of). Forests, mostly of conifers (see gymnosperms,
evolution of), covered most of the land surface of
the Earth. One of the major lineages of arthropods, the trilobites,
became extinct. Before the Mesozoic, both mollusks
and brachiopods were common, but the mollusks have been
more common ever since (see invertebrates, evolution
of). Mammals and birds evolved from reptilian ancestors
(see birds, evolution of; mammals, evolution of). The
mammal-like reptiles and their mammalian descendants were
less common in the Mesozoic than the mammal-like reptiles
had previously been (see reptiles, evolution of), and the
dinosaurs evolved into a great diversity of species, many of
them large. There were also many large flying reptiles and
large marine reptiles.
The Mesozoic era came to an end when an asteroid collided
with the Earth and created cold, dark conditions in
which many species, especially large dinosaurs, could not survive
(see Cretaceous extinction).
microevolution See macroevolution.
Miller, Stanley (1930– ) American Biochemist Stanley
L. Miller (see photo), born March 7, 1930, is a biochemist
who played the greatest role in starting the experimental
study of the origin of life. He was a graduate student at
the University of Chicago in 1953; his graduate adviser, biochemist
Harold C. Urey, discouraged him from undertaking