Dinosaurs were warm-blooded, scientific paper reports January 29, 2013

Another scientific paper offers convincing evidence that (at least some) dinosaurs were warm-blooded, such as this Allosaurs, but what of the Apatosaurus whose tail is also visible in this picture? Photo by the author, taken at the Carnegie Museum of Natural History in Pittsburgh.

The dinosaurs were warm-blooded, so reports a recently-published scientific paper.  To that, those of us who have paid any serious attention to dinosaurs over the past 25+ years, we reply in one big voice, “well, duh!”

But believe it or not, there has been a four-decade debate as to whether or not dinosaurs were ectothermic (i.e., cold-blooded) like all reptiles today, or endothermic (i.e., warm-blooded) like birds and mammals.  It was not always that way; even most of the earliest dinosaur fossils discovered roughly 190 years ago gave scientists clues that the dinosaurs were indeed reptiles.  Once complete skulls were discovered in the subsequent decades — particularly the 1840s onward — it because quite clear that not only were they reptiles, but they were diapsids like most reptiles today, save for turtles and tortoises, which are anapsids.  The explanation to differentiate those anatomically cladistic terms is for a different article at a different time.

Given that the earliest evidence was that dinos were indeed reptiles, people therefore accepted it as a given that they were ectotherms.  After all, every species of reptile today is cold-blooded, why therefore not the dinosaurs from roughly 225 to 65 million years ago?  All that thinking changed with John Ostrom‘s discovery of Deinonychus in Montana in 1964.  All of a sudden, the bird-like characteristics of some of the feet and parts of the skeleton caused scientists to totally re-think dino metabolism, and eventually kicked off the great debate of warm-blooded — if not outright hot-blooded — vs. cold-blooded schools of thought.

The paper referenced in the linked article announcing its publication will, in all likelihood, not settle the debate, and for a valid reason.  It is easy to see the Carnosaurs, or meat-eaters, to be warm-blooded, as well as the less-vicious but very-much bipedal Coelurosaurs, what with their bird-like characteristics — albeit to varying extents — but what about the plant-eaters?  If, say, the Sauropods were warm-blooded, can one imagine how much energy it would require — in other words, how much plant matter they would have to eat — in order to sustain themselves?  It remains an intriguing question.

This time around, in the latest study, published in the scientific journal Nature, the scientists cite the bone growth rates of dinosaurs, and how they match up to all sorts of different species of modern mammals.  In the abstract, it affirms what has stood to reason within part of the paleontological community for roughly forty years.  What is left out in the piece, though, is what specific dino species’ bones were examined, and whether or not plant-eaters’ bones were part of this microscopic examination.  If they can demonstrate that, say, Sauropods had similar bone growth patterns as the established warm-blooded Theropods, then it shall open up the floodgates for all sorts of speculation about the sustenance behaviors of the vegetarian dinos, if nothing else!  Let the fascinating discoveries continue!