Nature:
Two studies in the Royal Society's
Biology Letters examine dinosaurs' huge size and
possible reasons for it. In the
first
study, Roland Sookias at Ludwig-Maximilians University in
Munich and colleagues looked at whether body size depended on
environmental factors, such as temperature, oxygen level, and
amount of available dry land. They found that biological
factors were more important in determining maximum body size.
In the
second
study, Daryl Codron at the University of Zurich in
Switzerland and colleagues found that dinosaurs' size may have
depended on the limitations of egg laying. Because the larger
the egg, the thicker the shell and the more difficult for a
developing embryo to breathe, egg size was limited. That
physical limit forced dinosaurs to produce very small young. To
compete with other dinosaurs for food, the successful ones grew
very big, very fast. Unfortunately, dinosaurs' vast size proved
to be their downfall; the extremely large animals were mostly
wiped out by an asteroid impact at the end of the Cretaceous
period some 65 million years ago. Birds and small mammals fared
better.
