Geology Reference
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organisms. It is doubtful that ichthyosaurs could come onto
land, so females must have retained eggs within their bodies
and given birth to live young. A few fossils with small ich-
thyosaurs in the appropriate part of the body cavity support
this interpretation.
An interesting side note in the history of paleontology
is the story of Mary Anning (see Geo-Focus on page 622),
who, when she was only about 11 years old, discovered and
directed the excavation of a nearly complete ichthyosaur in
southern England.
The
plesiosaurs
belonged to one of two subgroups:
short necked and long necked (Figure 22.27b). Most were
What Would You Do
In your high school science class, a student notices that
ichthyosaurs and porpoises look somewhat similar, and she
speculates that the former is the ancestor of the latter. After
all, they look similar, and ichthyosaurs lived before porpoises,
so, she reasons, there must be a relationship. How would you
explain that there is no evidence to indicate that porpoises
evolved from ichthyosaurs?
◗
Figure 22.26
Flying Reptiles
a
Pterodactylus
, a long-tailed pterosaur, is well known from the
Late Jurassic. Among the several known species, wingspans
ranged from 50 cm to 2.5 m.
b
The short-tailed pterosaur known as
Pteranodon
was a large,
Cretaceous animal with a wingspan of more than 6 m.
2
1
Pteroid bone
modest-sized animals 3.6 to 6 m long, but one species found
in Antarctica measures 15 m. Short-necked plesiosaurs might
have been bottom feeders, but their long-necked cousins may
have used their necks in a snakelike manner, and their nu-
merous sharp teeth, to capture fi sh. These animals probably
came ashore to lay their eggs.
Mosasaurs
were Late Cretaceous marine lizards related
to the present-day Komodo dragon or monitor lizard. Some
species measured no more than 2.5 m long, but a few such as
Tylosaurus
were large, measuring up to 9 m (Figure 22.27c).
Mosasaur limbs resemble paddles and were used mostly for
maneuvering, whereas the long tail provided propulsion. All
were predators, and preserved stomach contents indicate that
they ate fi sh, birds, smaller mosasaurs, and a variety of inver-
tebrates including ammonoids.
3
Radius
Ulna
Humerus
PTEROSAUR
1
2
Radius
Humerus
3
Ulna
BIRD
1
2
Radius
3
Humerus
Ulna
4
BAT
5
Birds have feathers, whereas reptiles have scales or a tough
beaded skin, and birds do not closely resemble any living
reptile. So why do scientists think that birds evolved from
c
In all fl ying vertebrates, the forelimb has been modifi ed into a
wing. A long fourth fi nger supports the pterosaur wing, whereas
in birds, the second and the third fi ngers are fused together, and
in bats fi ngers 2 through 5 support the wing.
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