Geology Reference
In-Depth Information
Pleistocene
and Recent
1.8
Camels
5
Deer
Musk deer
Bovids
Tragulids
Antilocaprids
Peccaries
Giraffes
Pigs
23
34
56
Figure 23.24 Relationships Among the Living Artiodactyls and Some of Those Extinct Most
artiodactyls are ruminants—that is, cud-chewing animals—the major exception being the pigs and
their relatives and the peccaries and hippos. The bovids, consisting of dozens of species of sheep,
goats, antelope, and bison, are by far the most diverse and abundant artiodactyls.
size, a long snout (proboscis), and large tusks. Mastodons, with
teeth adapted for browsing, were present by the Miocene, and
during the Pliocene the present-day elephants and mammoths
diverged from a common ancestor. During most of the Ceno-
zoic, elephants were widespread on the northern continents,
but now only two species exist in southern Asia and Africa.
We briefl y mentioned whales in Chapter 18, noting that
until recently, little was known about their transition from
land-dwelling ancestor to fully aquatic whales. Although a
number of questions remain unanswered, the fossils now avail-
able indicate that whales appeared during the Early Eocene
and by the Late Eocene had become diverse and widespread.
Eocene whales still possessed vestigial rear limbs, their teeth
resembled those of their land-dwelling ancestors, their nostrils
(blowhole) were not on top of the head, and they were propor-
tioned quite differently from living whales (
humans. Primates as an order evolved by Late Cretaceous
time, but the ones of interest to us here date from the Plio-
cene and Pleistocene.
As for mammals other than primates, most of the present-
day genera had evolved by Pleistocene time. Indeed, we would
have little diffi culty recognizing most Pleistocene mammals;
only a few unusual types that persisted from earlier times are
now extinct. A good example is the chalicotheres, a group of
horselike mammals with claws on their forefeet. Likewise,
we would recognize most Pleistocene birds, but some large
ground-dwelling species are now extinct.
Mammals and Birds
One of the most remarkable aspects of the Pleistocene
mammalian fauna is that so many large species existed. In
North America, for example, there were mastodons and
mammoths, giant bison, huge ground sloths, giant cam-
els, and beavers nearly 2 m tall at the shoulder. Kangaroos
standing 3 m tall, wombats the size of rhinoceroses, leopard-
sized marsupial lions, and large platypuses characterized
the Pleistocene fauna of Australia. In Europe and parts of
Asia lived cave bears, elephants, and the giant deer, com-
monly called the Irish elk, with an antler spread of 3.35 m.
Figure 23.27).
By Oligocene time, both groups of living whales—the toothed
whales and the baleen whales—had evolved.
PLEISTOCENE FAUNAS
We devote much of this section to the evolution of primates,
particularly the hominids, which include present-day
 
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