Planet Earth

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

80beatsBy Veronique GreenwoodJun 24, 2011 8:21 PM

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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

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