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Were dinosaurs warm-blooded?

Scientists don't know yet whether large dinosaurs like Apatasaurus were endotherms or ectotherms. © AMNH
Scientists don't know yet whether large dinosaurs like Apatasaurus were endotherms or ectotherms. © AMNH
Some chemical reactions in the body, such as the burning of sugar to produce energy while releasing carbon dioxide and water, are referred to as metabolism. These reactions run most efficiently at a particular optimum temperature. In mammals and birds, the optimum temperature is higher than the normal outside temperature and is regulated internally. So these animals maintain generally higher body temperatures and are called "warm-blooded" or endothermic, for their internal temperature control.
Other animals, such as turtles, crocodiles, and lizards, have more variable body temperatures based on their level of activity and regulate body temperature through external sources, such as warming up in the sun or cooling off in the shade. Thus, they are often called "cold-blooded," or more appropriately, ectothermic, for their external temperature control.

Ectothermic or endothermic?

Were dinosaurs ectothermic or endothermic? Since birds are a group of living dinosaurs, we know that at least some dinosaurs are endothermic. But the question of whether all dinosaurs were endothermic is more difficult to answer. One approach to investigate this question is to look at the microscopic structure of bone. In many ectothermic animals, bone grows in dense, concentric rings, somewhat like tree rings. In endothermic animals, a complex system of closely spaced cavities, called the Haversian system, permeates the bone. By cutting bones of extinct, non-avian dinosaurs into thin slices and examining them under the microscope, we can look for these characteristics.
However, many complications exist, such as the need to compare animals of similar size, and no living dinosaurs as large as Tyrannosaurus and Apatosaurus exist today for us to observe. In most non-avian dinosaurs, the microstructure of the bone looks more like that of ectotherms, but the evidence is not conclusive. Because birds are endothermic, it's clear that "warm-bloodedness" evolved somewhere along the evolutionary tree of dinosaurs. But it is not yet possible to identify with certainty which groups of non-avian dinosaurs were "warm-blooded."

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  • blobby green style avatar for user Richard Collier
    Perhaps, it was the ectothermic dinosaurs that died off 65 million years ago because conditions were too extreme and they just "shut down", but at least some of the endothermic dinosaurs survived, which went on to become birds. Just a thought. Have you heard of any theories on this idea?
    (3 votes)
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    • leafers tree style avatar for user Derek LeMarr
      However after the meteor impact that caused the mass extinction of the dinosaurs the world in a darkness for months which would have killed off many of the producers in the environment which would have caused the consumers, herbivores, to start to die off in large numbers due to starvation. This in turn would have had the carnivores to starvation. The largest of the dinosaurs, cold or warm blooded, would have found it nearly impossible to maintain the energy needed to survive, let alone thrive. This could explain why smaller dinosaurs may have remained around and evolved into the birds of today. While the up and down temperatures following the meteor strike mixed with the acid rain could have been too much for ectotherms to would have proven difficult for larger endotherms as well.
      (3 votes)
  • duskpin ultimate style avatar for user Eck's dee
    if the theory of the meteor crashing in the ocean causing steam to cut off the sun is true, then wouldn't the majority of dinosuars be coldblooded?
    (1 vote)
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    • blobby green style avatar for user cosimpsonco
      When the asteroid hit the Earth and blocked out the Sun, the cold it educed wasn't really the problem. It was that without Sun-light, plants began to die, eventually leading to the large plant eating Dinosaurs starving. Once all of the prey Dinosaurs were gone, the predators died off too.
      (2 votes)
  • winston baby style avatar for user NickDeeter
    were dinosaurs warm-blooded? I thank they were warm-blooded but were dinosaurs smart.
    (1 vote)
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  • piceratops ultimate style avatar for user mather999
    Dinosaurs are important because they ruled the 65 million years. Paleontologist study fossils of dinosaurs to learn amazing facts and learn from the prehistoric tyrants.
    (1 vote)
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  • blobby green style avatar for user johnwshaw971
    Would the warm-blooded be more suceptiable to the transmission of disease and infections
    (1 vote)
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