Page 150 - The Origin of Birds and Flight
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148 The Origin of Birds and Flight
many differences, Feduccia said. Theropod dinosaurs, for example,
had curved, serrated teeth, but the earliest birds had straight, unserrat-
ed peg-like teeth. They also had a different method of tooth implanta-
tion and replacement. 104
Metabolic Differences
Another difference between reptiles and birds is their metabolisms.
Reptiles possess the slowest metabolisms among quadrupeds, while
birds hold the record for the fastest. To put it another way, reptiles ex-
pend the least energy, and birds the most. For example, because of its fast
metabolism, a sparrow’s body temperature can sometimes rise to as
much as 48° C. This high temperature could only spell death for a terres-
trial vertebrate, but is of vital importance to birds in increasing their pro-
duction of energy, and thus strength.
Birds consume a great deal of energy in flying and for that reason,
they possess the highest proportion of muscle tissue relative to their
bodies. Their metabolisms have been arranged in direct proportion to
the power expended by their muscles. On the other hand, reptiles are
known as “cold-blooded” and cannot create their own body heat, in-
stead warming themselves through the Sun’s rays. For the most part,
their body temperatures are equal to their surroundings.
Birds and mammals, of course, are warm blooded. Their bodies are
able to produce heat to protect them from the cold, and also to cool them
down when it is very hot. Their metabolisms are exceedingly different,
and it is impossible for a reptile’s cold-blooded metabolism to turn into
a warm-blooded one. Some evolutionists therefore began to maintain
that dinosaurs were warm-blooded. Yet there is a great deal of evidence
against this thesis, which is based upon no evidence at all. 105
First off, there is no reason to think that dinosaurs were warm
blooded, in contrast to all other reptiles. Asked whether there was any
evidence in the fossil record (or anywhere else) to indicate that dinosaurs
were warm blooded, Thomas E. Williamson of the New Mexico Museum
of Natural History and Science replies:
