Back to Mesozoic Era Paleobiology

Cenozoic Era (65 mya to Present)

The KT Event set the stage for the Cenozoic Era Cenozoic Era that began 65 million years ago. As the dinosaurs perished at the end of the Cretaceous, the mammals took center stage. Even as mammals increased in numbers and diversity, so too did the birds, reptiles, fish, insects, trees, grasses, and other forms of life. Species changed as the epochs of the Cenozoic Era rolled by, with the mammals eventually becoming the largest land animals of the Era, as the dinosaurs had been during the Mesozoic. Flowering plants strongly influenced the evolution of both birds and herbivors throughout the Cenozoic era by providing a rich abundance of food. Those that could adapt to the changes in the environment survived; those that could not were doomed to extinction. A rich fossil record in rocks relatively undisturbed by geological forces reveals the history of both.

Tertiary Period (65 to 1.8 mya) (Tertiary Fossils)

Invertebrates, fish and reptiles were similar to those of modern types, but mammals, birds, protozoa and flowering plants would undergo considerable evolutionary change.

Paleocene - The Paleocene Epoch began after the extinction of the dinosaurs. Mainly nocturnal mammals that had cowered in the shadows of dinosaurs for millions of years eventually evolved into a vast number of different forms to fill the newly vacant environmental niches. At the beginning of the Paleocene, most mammals were tiny and rodent-like. With time, mammals grew in size, number, and diversity. Many early mammal designs of this time would soon become extinct, but others would survive and then evolve into other forms. The diversity of birds, other animals, and plants increased, and species became more specialized. Although dinosaurs were gone, their reptile cousins lived on in the form of turtles, crocodiles, lizards, and snakes.

Eocene - The first grasses appeared in the Eocene Epoch (from about 54 to 37 million years ago) with growth near the root as opposed to the tip, providing a vastly expanded and renewable food resource for the herbovores; this allowed adaptation to life on the savanna and prairie and the evolution of running animals such as the Equiidae (the horse family). The grazing mammals evolved the teeth enabling a diet of harsh grass. The Eocene Epoch was a period when flowering plants continued a massive radiation that began in the Paleocene Epoch. Plants thrived, and with that many animals as new environmental niches were filled. The first grasses also provided a refuge for many animals. Small mammals radiate. Many new species of shrubs, trees and small plants appeared. A variety of trees thrived in a warm Eocene climate, including beech, elm, chestnut, magnolia, redwood, birch, and cedar, and more. The evolution of plants was providing a powerful selective pressure across the entire animal Kingdom, and many new symbiotic systems appeared.

Oligocene - The Oligocene Epoch extends from about 34 million to 23 million years years ago. The name Oligocene comes from the Greek oligos (meaning few) and ceno (meaning new) and is in reference to the paucity of new mammalian animals after their radiation during the preceding Eocene Epic. The Oligocene is often considered as an important window of environmental transition from the tropical Eocene and the cooler Miocene. The start of the Oligocene is marked by a major extinction event that might have been caused by a meteor impact in Siberia or near the Chesapeake Bay. Angiosperms continued their expansion throughout the world, as did grasses. Temperate deciduous woodlands mostly replaced tropical and sub-tropical forests, while plains and deserts became more commonplace. Among the animals, mammals diversified markedly, and marine fauna evolved to forms closely resembling those extant today. Ancestors of modern elephants and rhinoceros grew to large size in Africa, where the first apes primate belonging to suborder Anthropoidea that includes monkeys,
apes, and humans, also appeared.

Miocene - The Miocene Epoch extends from about 23 to 5 million years ago. The name comes from the Greek words meion (less) and ceno (new) because of the smaller proportion of modern sea invertebrates than the subsequent Pliocene Epoch. The Miocene is thus a very long 18 million years, and generally marks the transition from the far prehistoric world to a pseudo-modern world. A major expansion of grasslands occurred as forests declined in the cooler and dryer climate, driving selection and radiation of large herbivores, including the ruminants which are ancestors of modern cattle and deer. Mammals such as wolves, horses and deer as well as birds also generally evolved to closely resemble forms extant today.

Pliocene - The Pliocene Epoch extends from 5.3 million to 1.8 million years before present. The name comes from the Greek words pleion (more) and ceno (new) and roughly means the continuation of the recent in reference to the fact that mammals were essentially modern in form. The Pliocene climate was also relative cool and dry as in modern times. These modern climates reduced tropical vegetation and shrank tropical forest to a band near the equator. Concurrently, deciduous and coniferous forests, tundra, grasslands, dry savannahs and deserts filled the space.

Continental drift would play a major role is how animals, and particularly terrestrial mammals were to distribute. South America linked to North America through the Isthmus of Panama, to the detriment of South American marsupials, and precipitating a drop in Atlantic Ocean temperatures. The collision of Africa and Europe formed the Mediterranean Sea, and disconnected part of the former Tethys Ocean. Receding sea levels formed a land bridge between Alaska and Asia.

Both marine and terrestrial life was for the most part modern, though discernibly more primitive. Herbivores grew in size, as did their predators. The first recognizable human ancestors, the australopithecines, appeared in the Pliocene. Mammalian life evolved in continent-dependent ways, and some migration occurred between continents. In North America, rodents, mastodonts, elephant-like gomphotheres, and opossums were notably prolific, while hoofed animals generally declined. Africa’s hoofed animals and primates were notably successful, and the australopithecines (some of the first hominids) appeared late in the Pliocene The Pliocene seas were thrived with mammals such as seals and sea lions.

Quaternary Period (1.8 to Present)

The Quaternary Period that began less than 2 million years ago marked the origin of the close human ancestors as well as the modern forms of the animals we see today.