Page 165 - The Dinosaur Book and Other Wonders of the Prehistoric World (DK-Smithsonian)

Nothosaurus

The webbed feet would
have been useful on land
as well as for swimming.

Ichthyosaurs beat their
tail flukes sideways, as Stenopterygius
sharks do.

The hind flippers of Flippers and tails
turtles are used only
for steering.

Protostega

Tail

Some mosasaurs muscles gave
had crescent-shaped mosasaurs
tail flukes.
the power needed
for ambush
Mosasaurus
attacks.

Front flippers
were used to steer.

or flapping their winglike flippers. Whether they their sharklike tail flukes sideways for thrust and
used all four for propulsion or just the front ones steered with their flippers. Early mosasaurs had
for propulsion and rear pair for steering (like flattened, crocodilelike tails that they swept from
turtles) is unclear. The fastest swimmers of side to side to drive themselves through water.
the reptile world were ichthyosaurs, such as Later ones like Mosasaurus evolved tail flukes
Ichthyosaurus and Stenopterygius. They beat for greater efficiency. 163

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