Geoscience Reference
In-Depth Information
FIGURE
2 2 The rise
and fall of sea level over
the last 600 million years.
Many abrupt changes fail
to coincide with major
extinctions and geologic
boundaries. The levels of
the Big Five extinctions are
indicated by arrows. [The
Vail curve, after Raup.
34
]
began near the middle of the period. During the long run of the
dinosaurs, from
Eoraptor
in the Triassic 230 million years ago to the
last
T rex
at the end of the Cretaceous, many changes in sea level,
some up, some down, many larger and quicker than the K-T change,
were all nevertheless survived. In any event, let us remember that
the dinosaurs lived on land. A drop in sea level, which some verte-
brate paleontologists propose to explain their demise, would by def-
inition open up more land surface on which the dinosaurs could
live. The claim that such a drop caused the extinction of creatures
that had lived for 160 million years appears to be contrary to logic.
David Fastovsky, co-author of an excellent topic,
The Evolution
and Extinction of the Dinosaurs,
35
and Peter Sheehan, a paleontolo-
gist with the Milwaukee Public Museum, put it this way at the third
Snowbird conference: "It is counterintuitive to posit that an increase
in land surface area (as occurs by definition as the result of a drop in
sea level) will be accompanied by habitat fragmentation [claimed by
