In terms of its prevailing climate, the Eocene was virtually a mirror
image of the Pleistocene or “Ice Ages,” when much of human evolution
transpired. It began with a pronounced episode of global warming some
fifty-five million years ago. Such optimal conditions allowed tropical and
subtropical forests—and the animals that inhabit them—to occur at much
higher latitudes than they do today. Because primates have always prospered
in these warm forest habitats, the Eocene was truly a heyday for
primate evolution. Among their other accomplishments, Eocene primates
extended their geographic range far beyond its current limits. Fossils of
Eocene primates have been found as far north as Saskatchewan in North
America, England and Germany in Europe, and Mongolia in Asia. As I
discuss in greater detail in subsequent chapters, the fossil record shows
that during the Eocene, even these northern continental regions supported
diverse evolutionary radiations of primates. After enduring for more than
twenty million years, the greenhouse world of the Eocene ended thirtyfour
million years ago, when the Earth’s climate once again became cooler
and drier. It is unlikely to be a coincidence that this severe climatic deterioration
witnessed the extinction of primates in North America and
Europe, where tropical and subtropical habitats disappeared.
The vast majority of the fossil primates known from the Eocene resemble
the most primitive primates alive today. These animals, collectively
known as prosimians, include the diverse radiation of lemurs native
to Madagascar, the bushbabies of continental Africa, the lorises of
Africa and southern Asia, and, perhaps strangest of all, the tarsiers of
Southeast Asian islands. Prosimians resemble other primates, including
humans, in possessing nails rather than claws on most digits of their hands
and feet, and in having eyes that face forward to allow for enhanced,
“stereoscopic” vision. Like all primates aside from humans, prosimians
have a grasping big toe, functionally akin to the human thumb. Yet
prosimians also differ from humans and our nearest primate relatives,
the monkeys and apes, in many aspects of their anatomy, physiology, and
behavior.
image of the Pleistocene or “Ice Ages,” when much of human evolution
transpired. It began with a pronounced episode of global warming some
fifty-five million years ago. Such optimal conditions allowed tropical and
subtropical forests—and the animals that inhabit them—to occur at much
higher latitudes than they do today. Because primates have always prospered
in these warm forest habitats, the Eocene was truly a heyday for
primate evolution. Among their other accomplishments, Eocene primates
extended their geographic range far beyond its current limits. Fossils of
Eocene primates have been found as far north as Saskatchewan in North
America, England and Germany in Europe, and Mongolia in Asia. As I
discuss in greater detail in subsequent chapters, the fossil record shows
that during the Eocene, even these northern continental regions supported
diverse evolutionary radiations of primates. After enduring for more than
twenty million years, the greenhouse world of the Eocene ended thirtyfour
million years ago, when the Earth’s climate once again became cooler
and drier. It is unlikely to be a coincidence that this severe climatic deterioration
witnessed the extinction of primates in North America and
Europe, where tropical and subtropical habitats disappeared.
The vast majority of the fossil primates known from the Eocene resemble
the most primitive primates alive today. These animals, collectively
known as prosimians, include the diverse radiation of lemurs native
to Madagascar, the bushbabies of continental Africa, the lorises of
Africa and southern Asia, and, perhaps strangest of all, the tarsiers of
Southeast Asian islands. Prosimians resemble other primates, including
humans, in possessing nails rather than claws on most digits of their hands
and feet, and in having eyes that face forward to allow for enhanced,
“stereoscopic” vision. Like all primates aside from humans, prosimians
have a grasping big toe, functionally akin to the human thumb. Yet
prosimians also differ from humans and our nearest primate relatives,
the monkeys and apes, in many aspects of their anatomy, physiology, and
behavior.
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