Whales presented a mystery as vast as the animals themselves.The ances-
tor of modern whales appears to have been a four-legged carnivorous mam-
mal that walked on land and swam in rivers and lakes about 57 million years
ago.The legless leviathans evolved from mammals known as ungulates, whose
best-known characteristic is a set of hoofed feet. Whales adapted to swim-
ming, diving, and feeding that matches or surpasses fish and sharks.They might
have gone through a seal-like amphibious stage early in their evolution.
Today, their closest relatives are the artiodactyls, or hoofed mammals
with an even number of toes, such as cows, pigs, deer, camels, giraffes, and hip-
pos. However, exactly where whales fit in the tree of hoofed mammals remains
controversial. Genetic evidence suggests that whales and hippopotamuses are
closely related. Both groups share particular aquatic adaptations, such as the
ability to nurse their young and communicate underwater. The ancestor of
both whales and hippos might have ventured into the sea as early as 55 mil-
lion years ago.
The earliest whales had limbs that would have been clumsy on land.
However, their large feet and flexible spines allowed them to undulate their
backs up and down to propel themselves through the water like modern
whales.Today, whales have only vestiges of leg bones and lack ankle bones.The
first whales probably lived in freshwater before entering the sea and did not
stray far from the coastline because they needed to return to a river to drink.
Ancestors of the giant blue whale (Fig. 178), the largest animal on Earth, even
dwarfing the biggest dinosaurs that ever lived, evolved from ancient toothed
whales about 40 million years ago.TERTIARY VOLCANICS
Volcanic activity was extensive during the Tertiary. Massive flood basalts were
caused by hot-spot volcanism,as plumes of magma rose to the surface from
deep within the mantle. India’s Deccan Traps (Fig. 179) were among the great-
est outpourings of basalt on land during the last 250 million years. About 65
million years ago, a giant rift ran down the west side of India. Huge volumes
of molten magma poured onto the surface. Some 100 separate flows spilled
more than 350,000 cubic miles of lava onto much of west-central India, total-
ing up to 8,000 feet thick over a period of several million years. If spread
ev enly around the world, that vast amount of lava would envelop the entire
Earth in a layer of volcanic rock some 10 feet thick.
During the eruptions, India was about 300 miles northeast of Madagas-
car,as it continued drifting toward southern Asia. The Seychelles Bank is a
large oceanic volcanic plateau that became separated from the Indian subcon-
tinent and is now exposed on the surface as several islands. The Ninety EastHistorical Geology