Page 11 - DINOSOUR ATLAS

rise of the reptiles

heavyweight hunter
During the Carboniferous Period,
the amphibians diversified into a
wide variety of forms. Some were
tiny, newtlike creatures, while
later species such as Eryops were
massively built predators.

early reptile
The small, insect-eating Hylonomus was
one of the first reptiles. Living in the
Late Carboniferous, it had a scaly skin
and shelled eggs that were fertilized
before they were laid.

CrAnium is a solid
sheet of bone, with no
apertures aside from
anapsid skull . the large eye sockets d modern reptile
Early reptiles like
Hylonomus had simple In the 290 million years since they
“anapsid” skulls with no first appeared, reptiles have
extra openings to evolved a variety of forms.
provide anchorage for The most recent of these
strong jaw muscles. are the snakes—
Tortoises have the dedicated hunters
same skull type. that are particularly
successful in
tropical climates.

, synapsid skull
From the Late Carboniferous Period,
reptiles started developing “synapsid”
skulls with arched openings behind
the eye sockets. These enabled the
jaw muscles to be attached more
securely, giving a more powerful bite.
Such synapsid reptiles eventually gave legless, serpentine
rise to the mammals. body form of a snake
lower opening is surprisingly efficient
upper opening
diapsid skull . eye soCket amniotic egg .
The diapsid reptiles had two Enclosed by a tough, waterproof shell,
skull openings behind each a reptile egg can be laid on dry land,
eye socket. They included and hatches as a miniature adult
a variety of lizardlike instead of an aquatic larva. This is a
animals, and eventually fossilized egg of the carnivorous
the dinosaurs, pterosaurs, lower dinosaur Troodon, showing the
crocodiles, and birds. opening unhatched animal inside.