Page 40 - The Dinosaur Book and Other Wonders of the Prehistoric World (DK-Smithsonian)

The age of f ish The long spine

projecting from the
head may have been
venomous for defense.
With its elongated body,
this late Paleozoic shark
Before the dinosaurs Cheirolepis Xenacanthus
looked more like an eel.

The backbone
This bony fish had extended into the
a sharklike tail. upper lobe of the tail, Stethacanthus
as in modern sharks.

The body was
covered in tiny,
diamond-shaped scales.

A long, flexible
“whip” trailed
from each side fin.
The fins of this spiny shark
Astraspis
were supported by stout spines.

The head of
this primitive jawless Cheiracanthus
fish was protected
by scaly armour.

All land vertebrates, including dinosaurs, flexible rod called a notochord in place of a
are descended from fish—the first animals bony spine. Over the next 100 million years, fish
to have backbones. Fish evolved from developed hinged jaws and backbones. During
soft-bodied creatures like Pikaia, which lived the Devonian Period, 416–358 million years ago,
over 500 million years ago. Early forms like they became so successful that this period is
38 Astraspis had a soft, jawless mouth and a known as the age of fish. Two main groups

US_038-039_The_Age_of_fish.indd 38 23/04/18 6:16 PM