That used to be the thinking, but not so much anymore; feathers look to be an evolutionary novelty. See, for example, here (.pdf).
The thing to understand about this evolution stuff…
When the BIG ONE hit it destroyed pretty much everything. General theory is that a huge meteor hit somewhere near the Yucatan about 65 million years ago. The destruction was catstrophic. Not only did the first wave destroy pretty much everything with blast effects, but subsequent fallout and smoke destroyed most ecologies and ruined the climate (smoke blocking sunlight). As a result, food sources were destroyed and it may have been years before they rebounded and decades or centuries before things setttled down. One theory I saw was that anything over 20 pounds did not survive, and other that it was 5 pounds. Basically, almost all the species and ecologies “rebooted”. Some seas boiled, many fertile areas buried under soot and mud and volcanic ash.
As a result, the small things survived- baby alligators turtles, small things like proto-mice that happened to live in a sheltered areas. As things cleared up, they suddenly found food sources bursting out all over, and evolution happened at a break-neck pace. (The “punctuated equilibria” model of evolution - this happens when niches are disturbed or open up.)
Odds are, the first species of tiny fluffy lizard to turn those fluffs into extremely lightweight gliding aids dominated the search for food and had nowhere to go but up. Like Darwin’s finches, some groups evolved to be predators on others. Animal size is a function of environment; there’s an optimal size, too big and you starve in tough times or overheat chasing dinner, too small and your bigger brothers steal your lunch or it gets away or you freeze. Evolution determines a good compromise to all the issues.
So from one of these survivors, likely, all birds evolved. From another, most mammals. A few species like turtles and crocodiles continued in their choice niches once they recovered, with minimal change.
Sometimes people don’t seem to realize how destructive the Chicxulub meteor impact actually was. I have seen estimates that it set the atmosphere on fire; most sources agree that it set plant matter on fire all around the world. Tektites (small bits of molten glass thrown out by impactors) believed to be from Chicxulub have been found on the opposite side of the earth – it threw molten glass completely around the world!
One estimate I saw (Science channel, iirc) was that the fires reached 1,500 degrees F. But, in a test conducted in a combustion chamber, temperatures were tolerable only a few inches below the soil surface. The implication was that it was mostly burrowing animals who survived.
Okay, here you deviate from my understanding of what happened – birds and mammals had already evolved long before the impactor struck 65 million years ago.
Also, there were several bird lineages which survived the K-Pg extinction event, not just one.
There were already flying birds long before the end of the Cretaceous. It may be that only one species of bird survived the impact, and all modern birds are descended from that one species of bird. Or it might be that several bird species survived, and so the common ancestor of all birds lived before the impact. But for mammals, we know at least that monotremes and marsupials were established before the end of the Cretaceous, so there were at the very least three mammal species that survived, but probably more.
During the Mesozoic there were all sorts of closely related dinosaurs with feathers, some of which could fly. So if you use the word “bird” to describe a feathered creature that can fly, it’s likely that Mesozoic birds were polyphyletic, several different species of feathered dinosaurs evolved flight independently. But modern birds are not polyphyletic, because all those other lineages of flying feathered theropods went extinct.
That’s basically the OP question and the whole evolutionary debate.
-To what extent had feathers changed from fluffy (pillow stuffing type) to gliding aids (Village People Indian headdress stiff) before the Big One?
-How many different and varied species survived the Big One with such feathers to become bird species? How related were they before then, and how much flying did they do before then?
There were mammals before the impact. Presumably, only a few species survived.
The common charcteristics suggest that somewhere back before the impact, mammals had a common anscestor or birds had a common ancestor. The structure of fur, lactating sweat glands, calcium-shelled eggs, and especially flight-capable feathers, suggests they are unique “inventions” of evolution that conferred a definite advantage.
I haven’t seen a serious discussion of hot-blooded biology that gets into whether it was simultaneous evolution in mammals and birds, inherited from a comon ancestor, or most likely, parallel refinement of a semi-hot-blooded characteristic present in some dinousaurs that produced the first mammals and birds.
At this point it’s all guess work, refined with each important discovery.
however, when we look at all birds - or all mammals - one group has so much in common, it’s difficult to believe that evolution took two or more different species of naked or fluffy dinosaurs like T. Rex and Velociraptor, and offspring from both developed the same feather patters, toothless beaks, similarly clawed feet, etc. from two different paths. Most likely, when you consider any group - birds, mammals, or subgroups like the cats, the bears, the split-hoof ruminants - it seems logical, absent evidence to the contrary, that they are each the offspring of one most successful species at one point - which then spread and diversified into other niches, evolved into different species.
We are pretty certain that all modern birds evolved from one species of bird. But back when the most recent common ancestor of all modern birds lived, there were lots of other creatures out there with feathers that could fly, that looked a lot like birds but were not ancestral to any modern birds because they went extinct without leaving any descendents.
Same thing with mammals. Back in the Permian era, before the age of dinosaurs, there were all sorts of reptiles with some mammal like features. Scientists call them “mammal-like reptiles”. One lineage of the mammal-like reptiles evolved into modern mammals, all the others went extinct. But if you went back in time to the Permian, you’d find lots of creatures very similar to the ancestors of modern mammals, but there are no modern descendents of those animals. We don’t know exactly when mammals evolved mammary glands or hair, the earliest known fossil with unambigous preserved hair impressions is from the Jurassic. And of course, some modern mammals lay eggs, so live birth isn’t a characteristic that distinguishes mammals from non-mammals.
Same thing with toothlessness in birds. Plenty of birds in the Mesozoic had teeth, but only toothless species survived into the Tertiary. Toothlessness isn’t a good diagnostic to differentiate between bird and non-bird.
Good lord, I didn’t know they were Christians.
Thanks, ignorance fought.
The earliest known feathers suitable for gliding show up in the dinosaurs Anchiornis and Xiaotingia dated to about 160 million years ago.
Bird fossils are usually very incomplete, making identification difficult, but it looks like at least a few bird lineages crossed the line. There are ducks (Vegavis), loons (Polarornis), chickens (Austinornis), and a few types of modern-style shorebirds (Cimolopteryx and friends) known from shortly before the Big One, so these must have survived (otherwise we would have no chickens alive today).
Anatomical evidence suggests that numerous groups of birds that lived alongside traditional fliers were just as competent at flying as your basic modern bird. Keep in mind there are entire subclasses of birds that perished in the Big one (Enantiornithes etc.) and not only were they adept fliers, they have very werid flight anatomy (shoulder articulation, breastbone shape, etc.) that shows not only were these probably good fliers (hard to tell exactly how good since we have no living examples with similar anatomy), they were flying in a way not seen in any modern birds.
Huh, ducks and loons were already distinguished from each other back at the K-T event? I thought they were more closely related than that.
And it’s my understanding that the feature paleontologists use to define “mammals” is not the milk or fur, but the three-bone structure of the inner ear. Mostly, of course, this is because fur and mammary glands don’t fossilize well.
Think of the marsupial wolf, which is more closely related to kangaroos and koalas that to modern wolves. A similar ecological niche in a different place and time often gives rise to outwardly similar species. So a top predator in one era can look a lot like an extinct predecessor, even if they have very different ancestry.
This sort of ties back to the OP, where a fairly superficial characteristic was thought to have been preserved along its own lineage rather than re-created as needed later.
Form follows function… Perhaps no surprise an “attack dog” type of animal has basically a running thin body shape and a long snout whether a marsupial or canine. What’s surprising is that there are not long-snout cats. I presume the longer caninoid snout is for “nipping at the heels” of larger prey, typically in packs - something cats tend not to do.
Also surprising is that multiple families of the same “bird” anscestor survived the impact and its aftermath, unless we can point to one characteristic that made the difference… Size? Warm-blooded? Better feather insulation too? Or do we have evidence that other quasi-bird families persistent well past the KT extinction and then all died for other reasons.
We see only neornithine bird fossils after the K-Pg boundary; right up to the extinction event, however, we see enantiornithes, ichthyornithes, and hesperornithes - all very much birds, but none of which survived into the Cenozoic. All modern birds are descended from neornithine ancestors.
The longer snout is the norm in mammals. It’s not something specifically designed for nipping, it’s an all purpose tool found in grazers, browsers, insectivores, predators and almost any other niche.
Cats are an oddity in having somewhat foreshortened muzzles, but as you note, that’s a specific design that enables to them to apply maximal force with the canines at the expense of mobility and speed, which isn’t needed because they use their claws to hold the prey.
I’m not quite sure what you mean by this. Multiple families of all sorts of groups survived the impact. There wasn’t just one bird that gave rise to all birds, one mammal that gave rise to all mammals, one lizard that gave rise to all lizards etc. Multiple families of almost all groups survived. And most of the families within those groups subsequently died out. The groups that were survived by only one family seem to have been in the minority. In general it seems to have been the case that if one family survived, many other families within the order was likely to survive. The extinction wiped out some entire classes and orders but doesn;t seem to have been near so complete within orders, presumably because whatever traits allowed one species within an order to survive also tended to permit most close relatives to survive.
Well, there was one bird that gave rise to all modern birds, since all modern birds share a common ancestor that was also a bird (the hypothetical “first bird”). The point is that that ancestor lived before the impact, not after, because there were already several lineages of modern birds running around under the feet of T. rex.
Why some types of animal survived and others didn’t (or more specifically to this discussion, why some types of bird survived and other didn’t) is one of the big mysteries of paleontology right now. Lots of hypotheses, no clear consensus.
One I tend to think has some legs is relative ecology. The common ancestor of all modern birds (that is those alive today, excluding totally extinct bird groups) seems based on current evidence to have been a shorebird. All of the “true” modern-style birds alive before the Big Impact were water birds (ducks, loons, gull-like things). Even those members of modern groups today considered terrestrial appear to have been shorebirds at the time (Austinornis, an early member of the chicken family, was found in marine deposits, and the earliest possible members of the ostrich/kiwi/tinamou etc. group also appear to have been seabirds e.g. Limenavis and Lithornis). If I had to pick one type of bird that I’d bet on surviving a similar extinction today, it would be gulls and other shorebirds–those guys will eat anything. It’s better to be a generalist under ecological stress than a specialist. For comparison, almost all of the totally extinct bird subclass Enantiornithes (“opposite birds”) seem to have been tree-dwelling forest birds, many with highly specialized teeth and snouts very adapted to eating one particular kind of food.
So right now, it looks like mainly water-associated birds survived the extinction. Afterwords, those couple species of waterbird that survived diversified into all the birds alive today. This compares well with other notable survivals, which tend to be small aquatic or semi-aquatic types (crocs, turtles, frogs, monotreme mammals etc.) and burrowing types (placental and marsupial mammals, lizards, snakes). Why did mostly small semi-aquatic species survive? Who knows?
Another interesting thing to note is that several of the ‘definitive’ modern birds that lived before the impact are known from shoreline environments…in Antarctica. It’s possible that Antarctica acted as a sort of refuge for some modern groups, but obviously we’d need a few more expeditions there to see how many species there might have crossed the boundary.
ETA here’s a handy diagram of bird evolution that might clear up some questions:
I find it odd that “right up to the extinction event, however, we see enantiornithes, ichthyornithes, and hesperornithes” yet after 'We see only neornithine bird fossils", even though that latter family had fragmented into multiple species. What special situation let all those differnt variations on neornithines survive, but none of the others?
We can speculate wildly - warmblooded? Bottom feeders? (The swamp bottom would survive, the surface plant life not?) insectivores? (more resilient food source?) I was wondering if someone who knew the subjct knew of some better theories.
it’s as if there were a major event, and all the canines and ursines died out but several different species of felines survived. Curious.
Possibly they just lived far away from the impact zone. They might also have been better adapted to cold environments, where the areas free of damage were, or a condition to follow. The insulating property of feathers may have allowed them to thrive in areas too cold for pterosaurs before the extinction, and those birds already driven into a niche could have been the survivors. That’s all speculation, but protected niches were probably what saved a lot of animals. And notably mammals and birds were the survivors best adapted or adaptable to cold weather.
Stephen Jay Gould wrote a lot about contingence as a poorly-understood factor in evolution. Contingence in this context means something akin to luck – not really randomness, but the fact that events (which cannot have been predicted) have consequences that affect the outcome.
Suppose an animal is born with high resistance to meteor strikes (humor me) which can be passed on to offspring. But two days before the Chicxulub impact, that animal is eaten by a Tyrannosaur, or a drought kills the animal, or something. The “meteor resistance” is never passed on, and the fact that it is never passed on has nothing to do with the animal’s fitness for the new meteor-dense environment. The fittest, at least for this event in this imaginary case, did not survive.
it’s entirely possible that some, or even most, of the animals surviving the Chicxulub impact did so for contingent reasons – even something as simple as having been sleeping on the other side of a hill from the blast that morning or whatnot.
Another possible factor favoring coastal animals is that water can act as a moderator to ease rapid changes. It’s got a high specific heat, so it’ll stay near a comfortable temperature for longer. And even something as simple as taking a month longer to cool off might have been just the edge a handful of species needed.
When considering a world-wide event, luck as a statistical anomoly is usually evened out by sheer numbers. If basically all plants fried, but some regrew from deep roots ( more than a few inches down) something that could survive the waiting period would have the edge. Swamp bottom-feeders might not even notice a lot of their ecology disappeared, since the food-mud would still be there for a few months. In fact, partly fried leaves would add to the available food. Insects would rebound faster, if their eggs survived, so insectivores would also survive. One big question is the effect on climate. Obviously, many species- reptiles and amphibians - survived despite being cold-blooded.
I was just wondering, if we can speculae like this - does anyone with a deeper knowledge of the situation have any more interesting theories?
Of course, IIRC there’s still even some professional disagreement over whether the impact did the degree of damage we are saying. Some think it was simply part of a change that accelerated a long-term decline in dinosaurs; although the evidence of severe destruction is pretty convincing, debris layer around the world.