Big Dinosaurs Were As Warm As Mammals. But Were They Warm-Blooded?

By Veronique Greenwood | June 24, 2011 4:21 pm


What’s the News: Dinosaur metabolism is one of the biggest mysteries in paleontology. Ever since the giant creatures were first unearthed, scientists have been wondering whether dinosaurs drew their heat from the environment, like the cold-blooded modern reptiles they resemble, or whether they generated heat themselves, like warm-blooded mammals.

Using a geoscience technique to see at what temperature dinosaur tooth enamel formed, scientists have found that at least two large dinosaurs, Brachiosaurus and Camarasaurus, had body temperatures similar to our own. While this study on its own doesn’t explain where the heat came from, it does add to paleontologists’ toolboxes a new, reliable way to probe temperature, which will lead to better inputs into the computational models that may eventually answer the question of whether dinosaurs were warm- or cold-blooded.

How the Heck:

  • The technique the scientists used revolves around the tendency of certain isotopes of carbon and oxygen to clump together when a mineral forms. These isotopes, carbon 13 and oxygen 18, bond to each other more when the temperature is cooler, a handy relationship that geophysicists have been using to study Earth’s past climate in the geological record.
  • In this paper, the team applied the technique to eleven teeth from Brachiosaurus and Camarasaurus fossils, whose enamel, like that of all teeth, is made of the mineral bioapatite. The temperature at which the teeth formed is the temperature of the mouth, so this is akin to slipping a thermometer under the tongue.
  • Both dinos, the researchers found, had body temperatures in the rather toasty range of 36-38 C (96.8-100.4 F).

What’s the Context:

  • One of the major questions raised by this research is, if dinosaurs were warm-blooded and maintained this high temperature all the time, how would they keep from overheating? The bigger warm-blooded animals get, the more difficult it becomes to shed enough heat to live—elephants, which are twelve times smaller than Brachiosaurus, are constantly about to boil over, even with their massive ears serving as radiators. An animal the size of dinosaur that both generated its own heat and had a body temperature this high must have had truly phenomenal system for getting rid of heat, and figuring out whether such an arrangement is plausible is a major next step for scientists trying to model saurian metabolism.
  • Such models are only as good as the data punched into them, and the isotope clumping technique’s real promise is its accuracy. Unlike other isotope-based measurements of temperature, this version requires no estimates about isotope levels in the environment at the time of the mineral’s formation, and it’s been proven to be accurate within 1-2 C.
  • Last year, the team used the technique to determine the body temperatures of modern animals and the temperatures of fossil animals going back 12 million years. This is the first time they’ve tried it on dinosaurs.

The Future Holds: The team is now embarking on studies of tooth enamel in pygmy dinosaurs, to see if even dinky dinos had a high body temperature. If so, this could suggest that dinosaurs were in fact warm-blooded, not just retaining substantial amounts of heat from the environment because their massive size.

Reference: Eagle et al. Dinosaur Body Temperatures Determined from Isotopic (13C-18O) Ordering in Fossil Biominerals. Published Online 23 June 2011, Science. DOI: 10.1126/science.1206196

Image credit: trekkyandy / flickr

  • Torbjörn Larsson, OM

    Pygmy dinosaurs, or they could just try juveniles as they themselves suggested in a podcast.

    They also noted the technique applicability for the question of transition to temperature regulation in mammals and birds (unless it was in dinosaurs). More the power to the technique since it is really using smallish differences on the order of percent or less on masses.

    AFAIU after a quick browsing, the heavier isotope clumping is small since it is happening in a bath of lighter molecules _and_ the temperature effect is some percent of other clumping factors. Naively, it is lucky circumstances that it is a thermometer, and reliable!

  • JMW

    As long as we remember that warm blooded/cold blooded is NOT a on/off position. There are many creatures alive today whose metabolism is “luke-warm” blooded, or “mesotherms”.

  • m

    One thing I’ve always wondered….

    You know how a compost heap creates its own “heat” as the biomass decays? What if something similar occured in these really large dinosaurs? Because they are constantly feeding…the larger ones may have had a 2nd stomach (or 3rd…) to help with digestion.

    What if the amount of food being retained was enough to generate its own heat through the act of digestion?

    I know this is anectdotal, but a long time freind who farms cows has always told me that the more you feed a cow, the warmer it gets. and in fact, you can really hurt them by “over stoking” them with food. Like logs on a fire.

    So what if these really big dinosaurs did the same thing? the act of digestion generates some (or all) of their heat? Or maybe their metabolism is a hybrid between mammals and dinosaurs?

  • m


    here’s a link i found about how cows produce their heat through digestion.

    so…any paleantologist out there….here’s a thesis for you. we have a modern example of this effect standing in a field as you drive down the highway.


  • Veronique Greenwood

    @m, the idea that digestion could be generating heat is essentially what warm-blooded-ness means, so kudos!

    If dinos generated heat as cows do, they would have a serious problem getting rid of the extra heat, though–if a cow can overheat from digesting food, think of what would happen to a dinosaur, which has far less relative surface area to shed it from.

  • Chris the Canadian

    Interesting debate abotu whether the dinosaurs generated their own heat or not. My question is, it is widely accepted that the earths temperature was warmer during the time of the dino’s. What if the ambient temperature was warm enough to allow Dino’s to be cold blooded? Being cold blooded has it’s advantages. It’s much more economic in terms of energy used by the animal and overheating isn’t an issue. I’d think in a much warmer planet dinosaurs would probably have evolved to be cold blooded because it was more advantageous and economic to do so.

  • m

    i would think that their “largeness” would allow them to dissipate the heat from their digestive system.

    the blood has a LONG way to flow away from the source of heat. so it would dissipoate very nicely before the return trip.

    unlike a cow…the blood all stays in a relatively much smaller area.

    maybe physics has a role to play given their structure?

  • ChH

    m, larger animals have a large collection of challenges to overcome that are all related to the same phenomenon – as you get bigger, your mass rises to the cube of length, while surface area rises only to the square. This is why large animals have villi in their intestines, alveoli in their lungs, and other methods to increase surface area. This also places an upper limit on the mass of flying animals.

    Very small animals have smooth, straight guts and very simple lung/gill structures, and can fly / become airborne with trivial effort.

    So for heat dissipation … the amount of heat generated is relative to mass, while the amount dissipated is relative to surface area. That is why heat dissipation would be more difficult for a bigger animal.

  • SHJ

    ChH – you are correct about area vs volume. With a background in mechanical engineering, I reviewed the SHAPE of a specific dino…the brachiosaur (i think i spelled it correctly).

    I’m no biologist…and I barely know dinosaurs. But I know mechanics and physics cold.

    M might be onto something. Looking at the skeleton of a brach..i went on the assumption the animal generated its heat like a cow does, and that there was no outside “coolant”. so how could it effeciently disperse excess heat given the restrictions of area vs volume? The answer…as I said was the animal’s shape.

    I put the model through my design program and the answer came back was amazing!

    The neck. The neck would work in essence, like a smokestack. The dispersion of heat would be released during 2 phases…when the animal breathes (apparently it had hollow neck bones…so maybe filled with air?) as well as the journey the blood has to travel from the source of heat and back again (in my model, the blood was simulated by a coolant flowsystem of salt water).

    Assuming a 20 foot neck, blood would have to travel to the brain…being cooled by exposure to the air at the skin barrier as well as internally by the animal’s breathing…then make 20 foot trek back (subjected to the cooling process again) to the source of heat ( I assumed a modest 40 psi on the coolant…though an animal that size probably had higher blood pressure) Assuming the start of the journey of salt water at 40 C, by the time it returned back, the program calculated a significant drop in temperature of about 12%.

    So strictly speaking, from a mechanical point of view, it is plausible that a dinosaur this size could overcome some of the challenges modern mammals face because of the extreme shape of it’s neck. ( for all intense and purposes, i ended up designing a rudimentary air cooled furnace using a salt water heat exchanger)

    I suspect the tail played a factor in cooling the animal as well.

    I think the researchers might be well served to have a look at something like this from a mechanical point of view. It took me less than 2 hours for my models result to come back…but someone with more time (hey! i’m on vacation!!) might be better able to create something more sustainable to scientific review.

    Who knows right?

  • Dirty Harry

    Interesting debate Point Warm vs Cold Blooded…if these Extinct Dino’s are related to Modern day Crocs [1st Cousins Twice removed type of thing…Crocs being as Old in the Family Tree thing] and the Crocs are Cold Blooded…so How Come the earlier version of Dino’s gets to be Warm blooded and the More Modern day Croc’s are now Cold Blooded…and they are still related…Funnily enough I dont see many questions raised on what allowed the Croc’s and other reptiles Tortoises/Turtles to escape the Global Extinction 65 Million Years ago…was it that the Cold Blooded Ones [Crocs etc] somehow survived and other Warm blooded repitilian species went boom bust…Wonder if someone has the Answer…

  • lyllyth

    SHJ, that is BRILLIANT!
    I do hope someone takes note of this.
    What program did you use, and would it reliably calculate at higher PSI calculations?

    p.s. enjoy your vacation…please write a letter to DISCOVER or the study authors when you get back, though? =)

  • YetAnotherBob

    Dirty Harry,

    Dinosaurs were related to crocodiles, but they do have important differences.

    Dinosaurs are much more closely related to modern day birds. Dinosaurs had gizzards, as birds do. Dinosaurs (at least some) had feathers, and young ones had down. Scaley feet on both dinosaurs and birds are similarly formed.Dinosaur eggs were shelled.

    Plus, predator/prey ratios were more similar to modern day warm blooded species than to modern day cold blooded species.

    Crocodiles dominated in the time before the rise of dinosaurs. Hip structure is very different. That is the time of the first mammals too. As the dinosaurs got bigger, mammals larger than a big rat, or a small rabbit disappeared.


Discover's Newsletter

Sign up to get the latest science news delivered weekly right to your inbox!


80beats is DISCOVER's news aggregator, weaving together the choicest tidbits from the best articles covering the day's most compelling topics.

See More

Collapse bottom bar