Page 82 - Ultimate Visual Dictionary (DK)

PREHISTORIC EAR TH

Amphibians and reptiles

Pocket
THE EARLIEST KNOWN AMPHIBIANS, such as Acanthostega Orbit enclosing
and Ichthyostega, lived about 363 million years ago Sculpted or pitted nostril
bone surface
at the end of the Devonian period (409–363 million years
ago). Their limbs may have evolved from the muscular
Spiracle
fins of lungfishlike creatures. These fish can use their
to draw
fins to push themselves along the bottom of lakes and in water
some can breathe at the water’s surface. While
amphibians (see pp. 182–183) can exist on land, they are
dependent on a wet environment because their skin does Mandible Small tooth
not retain moisture and most species must return to the
FOSSIL SKULL OF ACANTHOSTEGA
water to lay their eggs. Evolving from amphibians, reptiles
(see pp. 184–187) first appeared during the Carboniferous Muscular back Shoulder girdle
period (363–290 million years ago): Westlothiana, a Scaly skin
possible early reptile, lived on land 338 million years ago.
The development of the amniotic egg, with an embryo
enclosed in its own wet environment (the amnion) and
protected by a waterproof shell, freed reptiles from the Finned tail
amphibian’s dependence on a wet habitat. A scaly skin Hip girdle
protected the reptile from desiccation on land and
MODEL OF ICHTHYOSTEGA
enabled it to exploit ways of life closed to its amphibian
ancestors. Reptiles include the dinosaurs, which came Dorsal vertebra
to dominate life on land during the Mesozoic era Scapula
(245–65 million years ago). Cleithrum
Cervical vertebra

Cranium

Orbit

Maxilla

Naris
Rib
Glenoid cavity
Humerus

Elbow joint
Mandible Clavicle
Radius
Sharp tooth Ulna
Phalanges
Metacarpals
SKELETON OF ERYOPS

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