OK, I am quite aware that most scientists consider birds a form of Dinosaurs, but for this thread, instead of using the term “non-avian dinosaurs” we will shorten that to dinosaurs. And call the dinoaurs that are avian= birds.
But many of the small dinosaurs were warm blooded and feathered. Crocodiles made it also.
So, why couldn’t a small feathered dinosaur species survive the event? Sure, maybe later they might be pushed out by mammals or birds, but any survival of species seems to be unknown or controversial.
This of course leads to the question of how impossible some small feather dino might be aaive today, thought of as just another bird by the natives and unknown to science.
Well, as you noted a chicken IS basically a dinosaur without the tail or teeth (though the genes are still in there, and I understand some work has been done to turn those back on and see them expressed…sort of reactivating latent traits), so not sure how to answer. I don’t think any large dinosaurs survived because the conditions were so bad that only smaller species made it through, but certainly not ALL the dinos went extinct.
What you’re asking is “Other than the ones which did survive, why didn’t any of the others survive?”. The answer to which is tautological: If a different set had survived, then those would instead be the ones that you were excluding from the question.
Well, to some extent. But Birds are a special type of dinosaurs, Dinosaurs were many and varied and the birds were a tiny part of that. Why did the tiny part survive and the rest didnt?
Because pretty much all land animals larger than a cat died out. It might have been possible for a few small dinosaurs to have survived, but by the luck of the draw they didn’t. And remember that almost all birds died out as well. The enantiornithes or “opposite birds” were the dominant group in the Cretaceous but became extinct at the KT event, leaving just the modern birds.
Because marine food webs collapsed. Much of the plankton was killed in the KT event, which killed off the ammonites, which were food for many mosasaurs. Larger fish would also have died out.
Crocodilians probably survived because they were capable of becoming dormant and remaining submerged for an extended period, an option that wasn’t available to marine reptiles.
Modern crocs are reputed to go up to 3 years without food. A smaller ancestor could have easily survived on the other small water creatures, fish, worms, small amphibians, etc.
When a habitat undergoes a drastic change. Some of the species find that to their advantage. Predators and competitors can be wiped out. So some now have a far better habitat. They thrive. Whatever is left of their predators also thrive. As well as those who are somewhat symbiotic with them all.
It is a choke point. But some can squeeze through, or even take great advantage of it.
That huge change selected for a narrow band of traits. The big dinosaurs were not terribly efficient creatures. They required a large amount of large vegetation. Which became scarce. Smaller creatures fed on smaller flora and fauna. Which seems to recover and flourish faster after competition is eliminated. Large predators usually hunt larger prey. Which quickly starved out. So predators starved. T Rex would not be good at catching small fast prey.
It’s probably worth noting that, at the time of the famous ‘dinosaur killer’ extinction event at the end of the Cretaceous, a lot of species we are familiar with from fossils, were already extinct for other reasons. - Stegasaurus, Iguanadon, Brachiosaurus, Icthyosaurus etc were already gone.
It’s a little too easy to just imagine the world looked like one of those 1950s ‘age of the dinosaurs’ posters - with all of the different known species visible in a single vista - starting from that notion, it might be very perplexing that they were all wiped out simultaneously with no exceptions.
Another point is that even those species which survive a mass extinction are likely to have their numbers significantly reduced. If your dominance of your niche is weakened, then it’s going to be easier for some other fast-adapting creature to move in and outcompete you. So even after the Big Event, there are going to be more extinctions as the ramifications of the Big Event shake out ecologically.
The Chicxulub impactor set the entire surface of the earth on fire. There’s a worldwide layer of ash at the boundary. Tektites (cooled droplets of molten glass) believed to be from the impact have been found in the ocean on the other side of the world – it threw molten glass completely around the planet.
In tests, burning vegetation cover presumed comparable to typical Cretaceous flora produced temperatures of 1,500 degrees F at ground level. That would kill every land animal on the surface of the earth.
But not those under the earth. A few inches below the soil, the temperature under the test fires was normal. So it has been proposed that, among land animals, ONLY burrowing animals survived.
As a generalization, large animals do not burrow – it’s too much work and there’s not enough need driving them to do so. So it’s likely that small, burrowed birds and mammals made it through the impact and every large dinosaur perished in a single day.
The famous “impact winter” which followed would have increased the stress on plants, plankton, and the whole food chain. This is probably what did in most of the sea fauna. And it would have been hard on the small surviving land animals. But it was probably a moot point for the giant dinosaurs, who were almost certainly killed before the cold and darkness mattered.
Good point. While your second paragraph corrects a common misconception, I’d like to expand upon your first: in many cases the “other reasons” for extinctions mentioned in your first paragraph were more “mind-boggling amounts of time” than some kind of unfitness. By the time Tyrannosaurus came along, Stegosaurus had been gone for 85 million years. Tyrannosaurus has been gone “only” 65-66 million years now, so the gap between us and T-Rex is 20 million years larger than the gap between those two dinosaurs.
While the large dinosaurs only had to compete with each other there was competition among the smallest creatures. The smallest non-avian dinos were competing with their avian cousins, the little mammals that survived in caves and underground, and all the reptiles and amphibians that survived underwater. So yes, no surprise that all the smaller animals did not survive, and that those best able to cope with the post-apocalyptic world did.
Indeed - ‘other reasons’ covers quite a lot -
[ul]
[li]Time - i.e. they just fizzled out due to loss of habitat or competition from something else, or their line continued evolving into something recognisably different[/li][li]Local extinction events - populations with a limited geographic spread being wiped out by something non-global such as floods, volcanoes, tsunamis[/li][li]Other major extinction events[/li][li]Etc[/li][/ul]
Genetic information indicates that several different lineages of modern birds survived the impact, not all of which made or lived in burrows. So there must have been at least a few places where not everything was incinerated. For birds, the ability to fly long distances in search of food may have been critical.
But yes, the land animals that survived were either small and capable of hiding in burrows or small and capable of flight. A few large freshwater animals like crocodilians survived. The dinosaurs living at the time of the KT event were non-flying (per the definition in the OP) and did not burrow.
Small pterosaurs might feasibly have survived the extinction, but could have lost out in the luck of the draw like enantiornithine birds.
