Warm-blooded or cold-blooded?

Comparison of body temperatures: A plot of the relationship between average body temperature (°C) and the logarithm of body mass for dinosaurs and modern crocodiles.  This graph potentially shows the accuracy of the formula by applying it to modern crocodiles. Chart  courtesy Gillooly JF Allen AP, Charnov EL (2006) Dinosaur Fossils Predict Body Temperatures. PLoS Biol 4(8): e248.
Comparison of body temperatures: A plot of the relationship between average body temperature (°C) and the logarithm of body mass for dinosaurs and modern crocodiles. This graph potentially shows the accuracy of the formula by applying it to modern crocodiles. Chart courtesy Gillooly JF Allen AP, Charnov EL (2006) Dinosaur Fossils Predict Body Temperatures. PLoS Biol 4(8): e248.
The question regarding whether dinosaurs were warm-blooded or cold-blooded has been debated for decades. Currently, most scientists believe that dinosaurs were warm-blooded and used internal mechanisms to maintain a constant body temperature. However, what that internal body temperature was could have fluctuated depending on the size of the dinosaur, making it possible for dinosaurs to have been both.
The bigger the hotter
Researchers at the University of Florida devised a mathematical formula that describes the connection between temperature, growth rate and biomass across a wide range of modern creatures. They then applied this formula to newly available fossil data on the growth rates of eight dinosaur species.
The equation showed that the bigger a dinosaur was the hotter is was. Smaller dinosaurs had internal body temperatures of around 77º Fahrenheit, which was close to the average air temperature of their time, so could have regulated their body temperatures much like modern cold-blooded reptiles. As dinosaurs grew larger, and the ratio of their surface area to volume fell, they became less efficient as dissipating their own metabolic heat. Because of this increased internal body temperature, dinosaurs probably had to develop behavioral or other adaptations to avoid overheating.
Body temperature influenced dinosaur size
One of the larger dinosaurs studied, Sauroposeidon proteles, weighed nearly 120,000 pounds. Applying the mathematical formula reveals that it may have had a body temperature close to 118º Fahrenheit, which is about as hot as most living creatures can get before the proteins in their bodies begin to break down. Because of this, the size of the largest dinosaurs may have been limited by their internal body temperatures.

Your Comments, Thoughts, Questions, Ideas

noah fogel's picture
noah fogel says:

i am 7 years old and i think that dinosaurs are warm-blooded.

posted on Sat, 09/02/2006 - 1:38pm
Anonymous's picture
Anonymous says:

there cold blooded -dummy-

posted on Tue, 10/09/2007 - 4:23pm
Joe's picture
Joe says:

Hey! Let's be nice. We can't have a good discussion unless we're respectful.

posted on Sun, 10/14/2007 - 2:11pm
natasha12's picture
natasha12 says:

If i'm right dinos are cold blooded.

posted on Sun, 09/03/2006 - 9:28am
Gene's picture
Gene says:

As I always say, he who lives by mass endothermy, dies by mass endothermy. ;-)

When I worked at The Field Museum in Chicago, we had a dino expert who insisted that dinosaurs could not have been warm-blooded. He argued that as an animal grows larger, its skin surface increases much more slowly than its volume. When you get to really big dinosaurs, there's just not enough surface area to dissipate all the internally-generated heat. Thus, they must be cold-blooded, and stay warm through a process known as "mass endothermy" (or gigantothermy) -- the enormous body retains heat, simply because there's no way to get rid of it.

Ah, I asked, but how does the animal get warm in the first place? If there's not enough skin to let heat out when the animal is warm, then it must also be true that there is not enough skin to let heat in when the animal is cold. Paleontologist Robert Bakker calculated that, if dinosaurs were cold-blooded, then for a big brontosaurus to raise its body temperature just one degree, it would have to bask in direct sunlight for 24 consecutive hours -- pretty hard to do.

The truth is, "warm-blooded" / "cold-blooded" is a false dichotomy. Modern vertebrates have something like a dozen different ways of regulating their metabolism. Humans produce heat internally, and keep our temperature pretty steady all day long. Camels also produce their own heat, but their body temperature fluctuates widely over the day, adjusting to the hot days and cold nights of the desert. Bats generate their own heat, but lose it so quickly they must huddle together and shiver to stay warm. Tuna are technically cold-blooded, but they maintain a body temperature higher than the surrounding sea water. And so on.

Dinosaurs walked the Earth for over 160 million years, and lived on every continent. It's pretty likely that they, too, developed a variety of ways to regulate metabolism, to suit the variety of habitats they lived in.

posted on Thu, 03/08/2007 - 2:02pm
Chanel's picture
Chanel says:

I think that dinosaurs were warm blooded.

posted on Fri, 04/13/2007 - 7:45am
dass's picture
dass says:

dinosaurs are in fact both cold and warm blooded...however the majority of them are warm blooded due to their enormous size and ability to eat every 30 days supports this point. Biomass plays an important role in this also.

posted on Thu, 09/27/2007 - 11:32am
Gene's picture
Gene says:

Can you explain that a bit? How do we know how often a dinosaur ate? And wouldn't infrequent eating be a sign of cold-bloodedness rather than of warm-bloodedness?

posted on Fri, 09/28/2007 - 11:20pm
Anonymous's picture
Anonymous says:

i think dinosaurs are cold-blooded

posted on Sat, 09/29/2007 - 10:06am
Anonymous's picture
Anonymous says:

Hey i think that dinosaurs are cold and warm blooded to the maximum strength.

posted on Sat, 10/13/2007 - 10:40am
Anonymous's picture
Anonymous says:

Are camels warm blooded or cold blooded...
i need the answer as soon as i can because i am working on a project and need this information...thanks.

posted on Sat, 02/23/2008 - 12:11pm
Joe's picture
Joe says:

Is this a trick question? Camels are mammals and mammals are warm-blooded. It rhymes! Here is a cool infrared image of a camel...

posted on Sat, 02/23/2008 - 11:50pm
Gene's picture
Gene says:

Absolutely correct! However, as noted, the camel's body temperature fluctuates about 14 degrees over the course of the day:

"Unlike most mammals, a healthy camel's body temperature fluctuates throughout the day from 34oC to 41.7oC (93oF-107oF.) This fluctuation is important because it allows the camel to conserve water by not sweating as the environmental temperature rises."

Compare this to most humanswhose body temperatures fluctuate less than 2 degrees over the course of 24 hours.

posted on Tue, 02/26/2008 - 1:08pm
Anonymous's picture
Anonymous says:

Note the data that was presented in the chart, suggests that smaller dinosaurs maintained an average body temperature closer to that of alligators and crocodiles relevant to their size. However, the larger dinosaurs would have been able to maintain a body temperature quite higher than theirs or even that of Humans, (37 degrees C) which would suggest that the dinosaurs of such a size range had some form of maintaining a higher body temperature. Whether it would be from metabolic reactions or from sheer size and insulation due to tissue layers is hard to determine, however in simplest definitions, such a mechanism to maintain heat would make the dinosaur essentially warm-blooded. It is likely that the species had many different mechanisms and thus some were warm blooded or cold blooded depending on what suited their habitat the best.

Mind you, I am not working with a lot of data, obviously, so you will have to bear with me if you disagree. If you should choose to do so, I would really like to hear what source you obtained your information from, so that I can learn from it. Remember, I'm only looking at the chart.

posted on Wed, 02/24/2010 - 9:20pm

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