Evolution, 4th Edition

THE HiSToRy oF LiFE 461

ground sloths and armadillo-like glyptodonts, some as large as a car, that survived

until the late Pleistocene (FIGURE 17.31C,D). A few species of armadillos, anteat-

ers, and sloths survive in tropical America. At least six orders of hoofed mammals

that resembled sheep, rhinoceroses, camels, elephants, horses, and rodents evolved

in South America, but declined and became extinct after South America became

connected to North America in the late Pliocene. The extinction of many South

American mammals might have been caused by the incursion of North American

mammal groups, such as cats, bears, weasels, and camels, that moved into South

America at this time.

One clade of mammals includes such very different-looking creatures as the

rodentlike hyraxes, the aquatic manatees, and the elephants. The elephants diver-

sified greatly, into a range of fascinating forms (FIGURE 17.32). Woolly mammoths

Futuyma Kirkpatrick Evolution, 4e

Sinauer Associates

Troutt Visual Services

Evolution4e_17.30.ai Date 01-06-2017

Au: Should the pink part of timeline be updated as in gure 17.24.

Modern Order

examples

Perissodactyla

Cetartiodactyla

Eulipotyphla

Rodentia

Carnivora

Chiroptera

Primates

Xenarthra

Pholidota

Lagomorpha

Dermoptera

Scandentia

Hyracoidea

Proboscidea

Tubulidentata

Sirenia

Diprotodontia

Monotremata

200 175 150 125 100 75

K/Pg

50 25

Placental mammals

Marsupialia

Monotremata

Tr J K Pg Ng Q

Time (Mya)

Whale

Hippopotamus

Cow

Camel

Rhinoceros

Horse

Dog

Bear

Seal

Cat

Pangolin

Hedgehog

Shrew

Tree shrew

Rabbit

Mouse

Squirrel

Porcupine

Flying lemur

Human

Lemur

Sloth

Armadillo

Aardvark

Manatee

Hyrax

Elephant

Kangaroo

Platypus

Pig

Bat

FIGURE 17.30 A phylogeny of living groups of mam-

mals, based on DNA sequence data. The timing of branch

points is based on sequence divergence, calibrated by

many different fossils. The data indicate that most orders

diverged from one another during the Cretaceous. Some

very short branches imply that some groups of orders

diverged within a relatively short time, as is characteristic

of many adaptive radiations. (After [64].)

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