That’s what I was thinking. But what about pterosaurs? Were they mostly gliders? Or, were they potentially “warm-blooded” as well?
A handwritten note from Jesus.
One thing we can almost guarantee is that this is not the case. Any animal covered with feathers will be severely limited in its ability to absorb heat from direct sunlight or warm surfaces because the feathers act as insulators. Warm bloodedness had to evolve before any protective covering.
There are many who argue exactly the opposite. But more on that later.
But as I noted, we have numerous small bird fossils of all ages showing what are indisputably feathers, so apparently seeing feathers isn’t difficult when they exist. The fact that we so far have no dinosaurs with indisputable feathers despite a great many fossils is indicative that feathers were either rare in the group or rare on individuals.
I was wondering when someone would say that. I was biting my tongue.
I’ve seen several authors argue exactly the opposite.
Flight requires large, rapidly moving muscles. While a cold animal can walk or swim sluggishly a cold animal simply can not fly at all. What we commonly see in ectothermic flyers such as insects is the use of the flight muscles to generate the internal heat needed to fly in cold conditions. At the extreme several insect species in at least two distinct groups have evolved body coverings of “scales” or “hair” and a kind of primitive endothermy.
So the argument runs that birds evolved flight when they were still cold blooded, and having done so they then needed to adopted a technique to warm the flight muscles. Having adopted a solution of using large amounts of energy to warm the flight muscles by shivering in cold conditions it then made perfect sense to trap that internal heat using feathers. After all as John Mace points out small animals lose heat fast. And since the heat was being internally generated their was little impediment to the coverings. From there it was a very small step to full-blown endothermy.
I think that pterosaurs are firmly established as having been warm blooded and covered in hair. That was certainly accepted by the vast majority of authors when I studied the subject some 15 years ago. Nothing has changed since then except the discovery of even more and better fossils of hairy pterosaurs so I can’t imagine consensus has changed.
Some pterosaurs (smaller ones, of course) appear to have been the equal of modern birds as far as flying agilty. Others, such as the larger Pterandon or Quetzalcoatlus were likely soarers (not gliders). As near as we can tell, they (as a group) performed about as well as equivalent-sized birds, really. There is some evidence of a hair-like body covering for some pterosaurs, implying endothermy, but, as with dinosaurs, there is scant direct evidence. The evolutionary lineage of pterosaurs is substantially less clear than, say, dinosaurs’, so we can only make guesses as to their partilcular metabolism.
Nothing in paleontology is “indisputable”. But there are numerous specimens, many out of assorted formations in Liaoning, China, which show something very like feathers. For example, a a juvenile tyrannosaurid, Microraptor, and this fellow (which I think was later christened Bambiraptor), just to name a few. For the most part, though, the only folks who deny the existence of feathered dinosaurs are the dwindling crowd who deny that birds evolved from dinosaurs.
So have I. I don’t particularly agree with them, though.
Personally, I find the prospect of insect-like physiology and metabolism to be far more unlikely than the observed endothermy in both extant birds and bats.
Besides which, the sequence of events you list makes little sense, as feathers (since we’re talking about birds) are needed before flight. And the sequence of downy feathers -> flight feathers makes more sense than the reverse, considering how feather development works.
Well let’s just say that nobody does dispute it.
No doubt about that, but not one of them is universally accepted as having feathers.
I’m well behind the current research on this topic, but that isn’t the impression I get. My impression is that a great many people who happily accept that birds descended form dinos are dubious that we have yet found any fossils of dinos with feathers.
That really misrepresents the hypothesis quite grieviously. Nobody is assuming anything remotely insect like, rather the physiology would be more akin to the crocodilians, the only other archosaur group we have access to.
Similarly the contention that all extant birds and bats are endotherms is quite irrelevant since the hypothesis requires that the birds also became endothermic almost as soon as they could truly fly, but not homeothermic. A great many birds and bats today are endothermic without being homeothermic so the condition appears to be a common solution amongst flying animals to the extent that it has re-evolved numerous times.
I fail to see your point here. In bats and pterosaurs skin membranes are needed before flight. That doesn’t justify a claim that their ancestors must have been covered from head to foot in rolls of membranous skin like a mutant hellbender.
Once again, I fail to see your point. It seems like you are saying that since pangolin scales are a development of spines the evolutionary sequence of hair must have been spines >>> bristle hair >>> fur and therefore the therapsids must have looked like porcupines and mammal hair devloped from those spines.
I just can’t see the sense in it. Structures get co-opted all the time from localised to general usage and it’s quite possible for birds to have possessed isolated display feathers eons before they developed either flight or a general body covering.
Surely Noah would be a more likely witness.