Doug's Dynamic Drivel

If you had asked me this morning if I thought dinosaurs were warm blooded or cold blooded I would most certainly have responded cold. That’s what I was taught 5 decades ago in school and it has been reinforced over and over again by comparing dinosaurs to modern day lizards. If you were to ask me this afternoon I would unhesitatingly say many, if not most or all, were warm blooded. That’s after hearing this fascinating discussion between CBC Quirks & Quarks host Bob MacDonald and Dr. Herman Pontzer, a professor of Anthropology at Washington University in St. Louis.

From Futurity.org

Studies of present-day animals have shown that endothermic animals are able to sustain much higher rates of energy use than ectothermic animals can. Following this observation, the researchers reasoned that if the energy cost of walking and running could be estimated in dinosaurs, the results might show whether these extinct species were warm- or cold-blooded. If walking and running burned more energy than a cold-blooded physiology can supply, these dinosaurs were probably warm-blooded.

But metabolism and energy use are complex biological processes, and all that remains of extinct dinosaurs are their bones. So, the authors made use of a recent work by Pontzer showing that the energy cost of walking and running is strongly associated with leg length—so much so that hip height (the distance from the hip joint to the ground) can predict the observed cost of locomotion with 98 percent accuracy for a wide variety of land animals. As hip height can be simply estimated from the length of fossilized leg bones, Pontzer and colleagues were able to use this to obtain simple but reliable estimates of locomotor cost for dinosaurs.

To back up these estimates, the authors used a more complex method based on estimating the actual volume of leg muscle dinosaurs would have had to activate in order to move, using methods Hutchinson and Pontzer had previously developed. Activating more muscle leads to greater energy demands, which may in turn require an endothermic metabolism to fuel.

Estimating active muscle volume in an extinct animal is a great deal more complicated than measuring the length of the legs, however, and so the authors went back to basic principles of locomotion.

First, how large would the forces required from the legs have to be to move the animal? In present-day animals, this is mainly determined by how much the animal weighs and what sort of leg posture it uses—straight-legged like a human or bent-legged like a bird, for example.

Second, how much muscle would be needed to supply these forces? Experiments in biological mechanics have shown that this depends mainly on the limb muscles’ mechanical advantage, which in turn depends strongly on the size of the bony levers they are attached to.

To apply these principles to extinct dinosaurs, Pontzer and colleagues examined recent anatomical models of 13 extinct dinosaur species, using detailed measurements of the fossilized bony levers that limb muscles attached to. From this, the authors were able to reconstruct the mechanical advantage of the limb muscles and calculate the active muscle volume required for each dinosaur to walk or run at different speeds. The cost of activating this muscle was then compared to similar costs in present-day endothermic and ectothermic animals.

The results of both the simple and complex method were in very close agreement: based on the energy they consumed when moving, many dinosaurs were probably endothermic, athletic animals because their energy requirements during walking and running were too high for cold-blooded animals to produce.

Just as interesting though is that, if correct, it pushes the dawn of warm bloodedness a lot further back in time.

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