A new study helps answer a longstanding dinosaur mystery by revealing that the largest dinosaurs could likely maintain warm body temperatures while their smaller cousins were probably similar to modern cold-blooded reptiles.
While warm-blooded creatures can regulate their body temperature, ectotherms can't and have body temperatures roughly equivalent to their surrounding environment.
A third hypothesis is that similar to modern-day alligators, Galapagos tortoises and Komodo dragons, large dinosaurs relied on a process called thermal inertia to maintain a body temperature several degrees warmer than the environment.
Thermal inertia is a body's ability to conduct and store heat that is generated either through metabolism or moving around.
Large animals are typically well equipped for this mechanism because of their low surface-to-body-volume ratio. For example, an elephant loses heat at a slower rate than does a mouse.
Researchers entered dinosaur growth trajectories — taken from recently published studies estimating the maximum growth rates and masses of eight dinosaur species — into a computer model to provide estimates of body temperature.
They tested the validity of the model by successfully predicting the body temperatures of differently sized living crocodiles.
As suspected, the model revealed that body temperature increased with body size for seven species, and that the largest dinosaurs had relatively constant body temperatures — similar to those of modern warm-blooded creatures — even though that temperature was maintained by thermal inertia.
The model shows that a small, 26-pound dinosau would have a body temperature of roughly 77 degrees Fahrenheit — about the same as environmental temperatures at the time, indicating that the animal would have acquired heat from external sources, much like a small, modern reptile.
A 14-ton beast, however, would have ran a temperature around 105.8 degrees Fahrenheit.
The largest dinosaur in the study, Sauroposeidon proteles, weighed in at about 60 tons and had a body temperature, the study suggests, of about 118 degrees Fahrenheit.
That's just past the upper temperature limit for most animals, leading the researchers to suggest that extremely high body temperatures might have been the only thing preventing dinosaurs from growing even larger.
Dinosaurs likely got warmer as they became adults.
A 661-pound adult dinosaur probably ran a temperature 37 degrees Fahrenheit warmer than it did as a juvenile, the scientists conclude.
The difference was even greater for a 27-ton Apatosaurus, which would have been 68 degrees Fahrenheit warmer as an adult.
The study is detailed in the August issue of the journal PLoS Biology.
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