Is it possible to prove from fossil evidence that Dinosaurs were either warm or cold blooded? If not what kind of evidence would you need to conclusively prove it either way? Or is it not possible?
Beside a live dinosaur ? According to Robert Bakker in his book The Dinosaur Heresies, micro-osteology seems to indicate that at least some of them were warm blooded. The bones studied were laced with blood vessel channels, more than for a cold-blooded animal, an indication, according to him, of being warm-blooded.
There are several forms of indirect evidence that dinosaurs were at least partly homoeothermic.
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The bone structure mentioned by detop is one (most but not all warm-blooded animals and few but not no cold-blooded animals have intraossial blood vessels in a particular style of array; most but not all dinosaur bones with sufficient fine-structure preservation have that array.
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Predator-prey ratios are consistently different between populations of warm-blooded and cold-blooded predators. Where we have sufficient fossils to suggest an ecosystem, carnivorous dinosaurs tend toward the lower ratio characteristic of warm-bloodedness.
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Turtles and squamates (lizards and snakes) have a three-chambered heart in which oxygenated and unoxygenated blood is mixed in the ventricle. Mammals and birds have a four-chambered heart that keeps oxygenated blood separate. The only surviving non-avian archosaurs, the crocodilians, have an adaptation on a four-chambered heart that permits the separated double-cycle when on land/breathing air, and allows the two to mix while operating submerged. Apparently crocodilians have a real but poor ability to heat themselves above ambient temperature – the origins/essence of warm-bloodedenss without the full talent.
I have personally had the opportunity to observe repeatedly the sole dinosaur fossil that might have some bearing on this: the heterodontosaur dubbed “Willo” in the North Carolina State Museum of Natural Science. There is an iron-oxide concretion in approximately the right size and shape for a heart. There is no clear proof one way or another, but the mass appears to have a similar configuration to the heart of a large bird, as opposed to the different shape of a lepidosaur heart.
There are a number of other evidences much more indirect. For example, ornithomimids show every evidence of having been built for speed. But why would a dinosaur evolve to do something its body power source would not equip it to do? Poikilotherms are built for at most bursts of speed, sprints, but ornithomimids show every evidence of being distance runners, like horses or ostriches. For which they’d need a homoeothermic metabolism.
I thought homeothermy only refered to a reasonably stable body tempeture, that which either endo/ectotherms can maintain.
The real clincher woudl be finding solid evidence of some sort of full body covering: fur, feathers or similar. Such coverings are only of use to animals generating internal heat, since for cold blooded critters they only serve to block incoming heat from sunlight, rocks etc.
The problem is that what evidence we do have is dubious and patchy. It is quite possible for isolated tufts and patches of fur or feathers to serve as displays or even for flight, so we realy need to find an obviously terrestrial animnal with a more-or-less full body covering.
Yeah like I said, what evidence we do have is dubious and patchy. There is much dispute about whether the structure on Sinosauropteryx were even feathers, much less the extent of the covering and the possible role they may have played.
This is a long way from being convincing evidence that the creature was warm blooded. The “feathers” may not even have been external structures. What we need is an animal with an unambiguous full covering of some sort.
Is insulation for the Sinosauropteryx enough to prove endothermy? Wouldn’t a high metabolic rate also be needed.
Blake thank you for the link
Dispute that they are feathers in the sense of “feathers like birds have” or in the sense of “a coating of some sort”? I couldn’t find a link to actual scientific papers describing it-- do you have any? The best I could come up with was National Geographic, which I wouldn’t trust on something this new.
I hadn’t heard that some scientists think they might have been internal. What are the thoughts on what type of an internal structure they could possibly be?
At any rate, I think this specimen and afew others like it are the best candidate we have so far for a dino that had feathers over most of its body. I’m not sure we’ll get fossils any better than that.
Sorry, somehow I left out the link to that article: http://www.dinosauria.com/jdp/archie/sinonews.htm
Basically whether these are fathers of any sort remains in dispute. They may be “a support structure for some sort of a crest” or an “internal… collagen structure used to maintain body shape”.
Unfortunately they are, and we can’t even agree whether r hey are external, much les whether they are feathers or whether they covered the entire body.
There is no reason why we shouldn’t get much, much better specimens if dinos had feather covering. We have many very good, very unambiguous fossils of birds with feathers, and birds are far more fragile creatures than dinos. We also have many fossils of dino skins showing fine details of scale patterns that lack any trace of feathers.
The fact that we know that feathers are fairly frequently preserved where they exist, and we know that dino fossils fairly frequently forme din locations that preserved fine skin structures is one of the biggest arguments against the vast majority of dinos having feathers.
Of course we know that at least one dino must have had feathers, but we don’t know to what extent or even whether those proto-birds were warm blooded or whether that evolved afterwards.
In the realm of speculation… “warm bloodedness” probably evolved in a small-ish therapod covered with feathers. Smaller animals lose heat faster, and it makes a lot more sense as a pre-adaptation to flight than something that evolved afterwards. These small animals tend to fossilize leaving a largely two-dimensional imprint, so it might be quite difficult to see whether or not it was covered in feathers.
As for the OP, we could, of course, invoke the fact that birds are dinosaurs. Therefore some dinos are “warm-blooded”. Q.E.D. 
Doesn’t the absence of turbinate bones in early birds nasal cavities suggest that endothermy evolved after flight. Without them water conservation would’ve been made more difficult.
Interesting post, Polycarp, but you left out respiratory turbinates. Turbinates are structures in the sinus cavities that enable all present-day warm-blooded (but not cold-blooded) animals to recycle exhaled moisture back into the body. A few years ago, a paleontologist decided to get serious and examine dinosaur skulls for turbinates. Having found them to be lacking, he concluded dinosaurs were cold-blooded.
Interesting-- I didn’t know that. Which early birds are you referring to that lacked these structures?
I’m at work right now, but real quick off the top of my head (so forgive any misspelling)
Caudipteryx
Ichthyornis
Sinornis
Archaeopteryx
Caudipteryx isn’t a bird. Or at least it isn’t generally classified as one.
As for the others, do you have cites that they lack turbinate bones? If they do, that would seem to be more indicative of the hypothesis that turbinate bones are not necessary for “warm-bloodedness”. Isn’t it generally assumed that archaeopteryx, being a bird, was “warm-blooded”?
Regarding respiratory turbinates:
As to when “warm-bloodedness” evolved, it would almost certainly have happened before flight evolved, as flight is itself metabolicly expensive. The general consensus (speculation, of course, albeit based on what meager evidence we do have) is that feathers evolved as a metabolic covering which was then later adapted for flight. If warm-bloodedness evolved before flight, then it’s a matter of being able to track down exactly when it did evolve, and whether it was pervasive through the Dinosauria, or only existed within certain lineages (e.g., Theropoda or Aves). Regardless, though, it could be said that there were (and, indeed, are) warm-blooded dinosaurs. We just don’t know how many or how common the trait was as yet.
Predator/prey ratios based on fossil records are suspect for any number of reasons, not the least of which include sampling errors and biases of the fossil record itself. That, and few, if any, studies have been done with regards to extant avian predator/prey ratios; birds, of course, being direct descendents of theropods would provide much better analogs in this regard than mammals, but we really lack sufficient data to really say anything one way or another as far as if / to what degree fossil dinosaur ratios correlate to endothermy.
Keep in mind, though, that that book is about 20 years old, and Bakker himself is a bit of a kook. He took the idea that John Ostrom put forth upon his discovery of Deinonychus that that animal was likely endothermic, and extrapolated it to all dinosaurs, based on limited evidence.
Also, keep in mind that however hazy the evidence might be for endothermy in dinosaurs, the evidence is equaly hazy for ectothermy. As yet, there really hasn’t been any hard and fast rule based on skeletal morphology which allows us to determine metabolic rates. For the most part, inferences regarding metabolism to date have been based more on relationships than any fossil evidence. We don’t even know for certain when endothermy evolved along the mammal lineage.
And that is why I started my answer with “According to…”
Any opinions on the findings presented in this article?