Biology : Age of Mammals and Birds : Part One
Age of Mammals and Birds
Following the end of the Cretaceous mass extinction, life underwent an adaptive radiation during the Cenozoic era. This rebound and diversification continues today. Major geologic events of this era include the development of polar ice caps in both the northern and southern hemispheres, culminating in the Ice Ages of the past 2 million years, and the development of modern mountain ranges as the continents assumed their modern positions.
The Cenozoic is the most recent of the three classic geological eras. It spans time since the Cretaceous-Tertiary extinction event at the end of the Cretaceous period (the last of the three Mesozoic eras periods) 65 million years. The Cenozoic divides into periods: the Tertiary (Paleocene through Pliocene epochs) and Quaternary (Pleistocene and Holocene epochs). While we normally do not examine the past at the level of epochs, the great amount of rocks and fossils remaining form this most recent era allow for such refinement. The Tertiary period divides into (in order from oldest to youngest): Paleocene, Eocene, Oligocene, Miocene, and Pliocene, spanning time since 65 million years ago until 1.8 million years ago. The Quaternary period has two epochs: Pleistocene and Holocene.
The Tertiary period
At the beginning of the Tertiary mammals replaced the by-now extinct dinosaur and other reptile groups as the dominant vertebrates. Each epoch of the Tertiary was characterized by striking developments in mammalian life. The earliest recognizable relatives of humans appeared. Modern types of birds, reptiles, amphibians, fish, and invertebrates were either already numerous at the beginning of the period or appeared early in its history. Modern families of flowering plants, such as the Juglandaceae (walnuts) and Asteraceae (sunflowers) evolved. Marine invertebrates and non-mammal marine vertebrates experienced only modest evolution. The general life trend during the Tertiary was one of increasing modernization of both flora and fauna.
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