Were Dinosaurs Warm or Cold-Blooded?
By: Shannon B. Carpenter
For many years, most scientists have thought that dinosaurs were cold-blooded animals. It
seemed logical because modern reptiles are cold-blooded, so if dinosaurs evolved from ancient
reptiles, they were probably cold-blooded as well. Recently, within the past week, paleontologists
have found new evidence that challenges the notion that dinosaurs were cold-blooded animals.
There are many different reasons why paleontologists believe that dinosaurs were cold-blooded
(or “ectotherms”). One reason for this belief is that the climate conditions in the Mesozoic Era were
mild and warm. Dinosaurs did not have to be endotherms because it was always warm enough to keep
them warm. Of course, the problem with this theory is that the climate in the Mesozoic Era was
diverse, and there were even dinosaur fossils found in some areas that were cooler and less mild, such
as the Polar Regions. Another reason is that, in general, ectotherms are normally scaly, such as
modern day reptiles. Fossilized dinosaur skins show that they did have scaly hides, so they were
ectotherms. The problem with this theory is that bird feathers are apparently modified scales and birds
are endotherms. Yet another reason has to do with the large weight of the dinosaurs. Large
endotherms such as mammals and whales have difficulties in warm climates. Therefore, because the
Mesozoic was so hot, dinosaurs most likely would have dehydrated and died. Again, the problem with
this hypothesis is that not all of the dinosaurs were big and it is seen today that modern large animals,
such as elephants and whales, have ways of regulating the heat to reduce the stress. An additional
reason is that dinosaurs did not have respiratory turbinates, so they could not have functioned as
endotherms. Naturally, the problem with this hypothesis is that it has not been proven from fossil
evidence that no dinosaurs had turbinates. Many modern birds have turbinates in them and, therefore,
turbinates in birds must have evolved sometime in the Mesozoic.
There are many more reasons as to why dinosaurs were most likely warm-blooded (or
endotherms). The first reason is that studies on modern animals seem to show that metabolic rate is
proportional to maximum rate of locomotion. Many dinosaurs were built to move quite quickly, so
they must have had high metabolic rates. The problem with this is that we do not know how fast
dinosaurs really moved. Another reason could be that studies suggest that today’s endotherms
generally “out compete ectotherms” in their area. Of course, dinosaurs must have been endotherms in
order to compete with the mammals they coexisted with. (Of course this theory has not been proven
yet). Some other possible reasons could be the erect posture and large brain size of the theropod and
the ornithopod both are characteristics of modern day endotherms. One of the more convincing
explanations is that dinosaurs were the ancestors of birds and since modern birds are endotherms then,
dinosaurs must also have been. Finally, it has been proven that endothermic animals grow faster than
ectotherms. Dinosaurs did grow very large over a small time period, but the only problem with this
theory is that we have no way of proving really how fast dinosaurs did actually grow.
Last week, a dinosaur fossil of a Tescelosaurus (a plant-eating dinosaur about 13 feet long
including the tail), named Willo, was found and when
researchers took X-rays of it they found that the within the
dinosaur was a four-chambered heart. “A four-chambered heart
would mean that the blood circulatory system of dinosaurs was
much more advanced than previously believed, that the animals
were more tolerant of temperature extremes, and that they were capable of rapid and sustained
movement typical of modern birds and mammals.” (ABC NEWS, web) All of these characteristics are
typical to warm-blooded animals. “This is a landmark discovery in the field,” said Jack Horner, a
dinosaur expert at Montana State University and the Museum of the Rockies in Bozeman. “This means
that dinosaurs were warm-blooded. That’s fantastic. It’s way cool.” (ABC NEWS, web)
Though there is currently no definitive answer to the question “were dinosaurs warm or coldblooded?” paleontologists have a good amount of evidence that suggests that dinosaurs were, in fact,
warm-blooded. Though the answer to this question is shrouded in as much doubt as any other dinosaur
controversy, as with anything, time will ultimately lead us to our final answer.
Bibliography
1. Knowledge Adventure, 1998
Available at: http://www.letsfindout.com/subjects/dinosaurs/rtmwarmc.html
2. Dr. Carl Wieland, Answers Online
Available at: http://www.answersingenesis.org/docs2/4285news4-21-2000.asp
3. April 2000, UC Davis Geology Department
Available at: http://www-geology.ucdavis.edu/~gel3/SHORTCH13.html
4. DinoBuzz
Available at: http://www.ucmp.berkeley.edu/diapsids/metabolism.html
5. Paul Recer, ABC NEWS, April 2000
Available at: http://abcnews.go.com/sections/science/DailyNews/dinos000420.html