When Warm-Blooded Dinosaurs Roamed the Earth

I have always been fascinated by dinosaurs, ever since I was knee-high to a Pteranodon:  Dinosaur exhibits in museums, dinosaur illustrations, dinosaurs in the movies, dinosaurs on television.  When I was a tyke, my favorite Christmas present was a set of twelve plastic dinosaurs and an accompanying picture book packed with artists' renderings of the creatures.  In those days - and this was in the late-1950's, you understand - our knowledge of the prehistoric beasts was sketchy at best.  Dinosaurs were commonly depicted as plodding, dull-colored reptiles, with tails dragging uselessly behind them. 

Of course we now know that dinosaurs were actually streamlined and bird-like, long tails balancing their gargantuan bodies, with air pockets inside many of their bones.  Some sported furculas and feathers.

Paleontologists have for many years been discussing whether or not dinosaurs were cold-blooded, the conventional wisdom for almost half a century - but recent evidence leads scientists to suspect that these so-called "terrible lizards" (neither terrible nor lizards) were in fact as warm-blooded as the family dog.  Jason Palmer reports for the BBC:  Prior studies of dinosaur bones uncovered what are known as "lines of arrested growth."  The creatures were presumed to be cold-blooded because modern cold-blooded animals show these same lines.  But scientists reporting in Nature have studied the bones of 41 modern mammal species from around the world, finding every one had these lines as well.  A number of discoveries in recent years have challenged the 40-year-old notion that dinosaurs were cold-blooded.  But because soft tissues such as organs and skin are not preserved, much of what is known about dinosaurs must be inferred from their bones, and comparisons made with modern animals that can be studied in greater detail...  David Weishampel, a palaeontologist at the Center for Functional Anatomy and Evolution at Johns Hopkins University School of Medicine in Maryland called the new work "a wonderful paper" and said it was a welcome addition to the debate.  "I think most (palaeontologists) regard dinosaurs as being warm-blooded but there's a lot of waffling in the data that appeared before that wasn't conclusive," he told BBC News.  "It's about time we have a connection between the modern bone histology and fossil bone histology, through a very nice ecological and metabolic comparison."

Jennifer Welsh writes on CS Monitor:  The growth lines they found on the ruminants were similar to those seen in previous studies of dinosaur bones — indicating that both ruminants and dinosaurs have periods of high growth punctuated by "unfavorable" seasons with limited resources and little growth. This means that dinosaurs were likely warm-blooded like the ruminants.  "The argument we are giving in our paper, rather in favor of endothermy in dinosaurs, is that between the growth and rest lines, there's always a big region of highly vascularized [infiltrated with blood vessels] tissue that indicates very high growth rates," study researcher Meike Köhler, of the Autonomous University of Barcelona in Spain, told LiveScience. "This is typical in dinosaurs and very different from reptiles, which have slow growth between the rest lines." 

This is exciting news.  Now if we can just convince fundamentalist Christians that velociraptors weren't playfully nibbling on fig leaves in the Garden of Eden, or that Noah and his sons didn't go rounding up baby T-Rexes and stuffing them inside the ark...  but perhaps that's too much to hope for.  (The cartoon below is by  TTTP.)

Comments

[Seth]

Hey, love your blog. I'm something of an amateur paleontologist (in that I do paleontology work without actually getting paid for it) and it was funny to see this getting posted as something "new". Honestly the idea of dinosaurs being warm-blooded has pretty much been the scientific consensus for the last twenty years. I honestly haven't heard of anyone in the field even float the idea of cold blooded dinosaurs since I graduated. Any doubt should have been definitively put to rest as soon as feather impressions started showing up on dinosaur skeletons. The first feathers couldn't have been used for flight, so they could have only been used for insulation. Insulation only works if the animal in question is generating it's own heat, i.e. is warm blooded. Feathers or fur on a cold blooded creature would only make it more difficult to absorb heat from the sun and much easier to die. So dinosaurs had to evolve warm-bloodedness first, then feathers to keep the heat in, then adapt them for flight.