Chicxulub misses Earth. What does Earth look like today?

In My Humble Opinion
41

The notion that dinosaurs would still be the apex (collective) species on Earth today if the Chicxulub Impact didn’t occur just doesn’t seem as obvious to me as it seems to others, for a number of reasons.

First and foremost is the fact that before impact, non-avian dinosaurs were on the decline, while mammals were on the incline. Sure, dinosaurs dominated Earth for ~165 million years prior to impact, but their environment was dino-lifestyle-favorable and mostly homeostatic during that 165-million year reign. They adapted and evolved, but they did so slowly and steadily.

It’s also important to note that the bolide impact didn’t just affect dinosaurs, it also wiped out ~75% of the avian dinosaurs (birds) and ~90% of the mammals. Had those 75% / 90% lived, they too would have continued to evolve, and further compete against the non-avian dinosaurs. Had the pre-impact dinosaur-decline trend continued (mainly due to cooling climate and other environmental changes), I believe the dinosaurs would not dominate Earth today. Mammals (or possibly birds) would dominate, it just would have taken a bit longer than it did with the Chicxulub Impact.

I think it’s fair to say that warm-blooded animals adapt and evolve more quickly and effectively than cold-blooded animals. For example, cold blooded (ectothermic) crocodiles existed on Earth virtually unchanged for 200 million years. That’s fine because their habitat didn’t really change all that much for 200 million years. If it did change significantly, they would probably have gone extinct—because they’re stupid and slow-to-change.

Mammals and birds are warm-blooded (endotherms). Warm-blooded animals adapt and evolve quickly. Reptiles and amphibians are cold-blooded (ectotherms). Cold-blooded animals adapt and evolve slowly. Non-avian dinosaurs are now believed to be mesotherms (in between cold- and warm-blooded). They can adapt and evolve more quickly than cold-blooded critters, but less quickly than warm-blooded critters.

My bet is on mammals for the world domination win, with a side-bet on birds. Betting on dinosaurs for the win is like betting on a sway-back nag…IMHO.

42

This is hardly a “fact”. While some papers coming out in recent years HAVE suggested that non avian dinosaur biodiversity was declining for millions of years before the KT boundry, other studies looking at the very same data disagree. The “dinosaurs were dumb, slow, and doomed” narrative is by no means uncontroversial anymore, and stating it as fact is IMHO misleading.

This on the other hand could not be more wrong. The Mesozoic was not some calm, gentle, warm period. There were huge shifts in ecology and climate as Pangea split up and ocean currents changed. Dinosaurs adapted to every terrestrial habitat on Earth. They didn’t just luck in to that; dinosaurs were incredibly well adapted to their environment, and were capable of adapting to change.

43

[Citation needed]

Actually, crocodialians belong to an incredivly diverse tree of life. Superficially, some crocodiles were ambush hunters or fish specialists 200 MYA and some still are today, but to say this means that crocodilians were “virtually unchanged” is pretty ignorant. Between then and now, crocodiles adapted into thousands of forms and niches, from active sprinting terrestrial hunters to fully aquatic marine species to herbivores to everything in between.

44

There are a lot of assumptions here, but little evidence.

Calling the group that dominated Earth for practically half the time that life has been on land a sway-back nag seems like a big stretch.

45

Betting on birds is betting on dinosaurs.

46

A little earlier, but…

47

Who I might note are still extremely common today, dominate the air, and have adapted to the roles of marine predator, megafaunal terrestrial grazer, and even social intelligent generalist (corvids). And they’d already adapted to many of these roles before the other dinosaurs died out - see Hesperornis (marine) and Patagopteryx (terrestrial grazer, though small).

48

Yes, birds are dinosaurs and I noted that they are avian dinosaurs. In this discussion, I’m making a distinction between them and non-avian dinosaurs. Mea culpa for not clarifying that better.

Ok, it’s not a “fact” (I would not use that term if this was Great Debates, or General Questions), but it’s a premise with compelling evidence that I believe is correct.

If it is correct that non-avian dinosaurs were declining before the K/Pg event, then I don’t think it’s a stretch to conclude that they couldn’t adapt well to all the changes that were occurring, climate cooling in particular. These changes probably wouldn’t have wiped out all the non-avian dinos, but it wouldn’t need to for mammals to exploit the vacated niches and evolve similarly to the way did. They just need opportunity and more time. Maybe the real showdown would be avian dinos vs. mammals (warm-blooded vs warm-blooded). I’d root for the mammals. I don’t want giant birds pooping on my car.

Crocs held onto their particular niches for a long long time. I think it’s fair to say they are kings of African mudholes. They have also ventured into other environments, including marine. But, against mammalian predators of similar or larger size, they don’t fair well.

Jaguars, with bone-crushing bite force pick off large caimans with ease. Hippos have no problem against African crocs. If marine crocs tried to encroach on orca or bottle-nose dolphin territory in open ocean, they wouldn’t stand a chance. IOW, crocs do well in their specific niches, so long as large predator mammals don’t want in on the action.

I’d like to see a battle between T-rex and a 15,000 lb house cat. I think Kitty would end up dragging Rex home to feed her kittens.

It’s not unlike dogs vs. cats. Sure, dogs kill small cats with ease. But one-on-one, I don’t believe any canine (including wolves) can beat any cat of similar size and health, without a lot of luck…or a gun. If you want to include pack wolves vs. cats, then pit the wolves against a hunting pride of similar sized lions. They’d be yelping away with their tails between their legs. Cat’s are a better model for one-on-one combat, or pack vs. pride combat over dogs. And mammals are a better model in general (more intelligent; more adaptable) over non-avian dinosaurs. That’s my opinion.

The question is, would mammals have had the opportunity to evolve into larger species and exploit additional niches without the bolide impact? I believe the answer is yes. They would find a way.

49

Hippos would like a word…
https://roaring.earth/hippos-eat-meat/

(I know you expanded later on hippos vs crocs, but this was too good to pass up)

50

There are studies that have found that dinosaur diversity was in decline in the later cretaceous; other studies disagree:

https://royalsocietypublishing.org/doi/10.1098/rsos.201195

I think it’s far too early to declare that one side or the other is correct on this issue. Regardless -

But over the 166 million years or so that dinosaurs were dominant, they deeply declined in diversity MANY TIMES. If the asteroid had hit just after the l end of the Jurassic, you might be saying “most dinosaur genrea were in decline anyways, even without the asteroid it is highly unlikely that any dinosaurs would have made it to the present day”.

51

Sorry, but I don’t see the connection between warm-bloodedness and adaptive speed. Can you give a cite?

52

Endotherms can remain active in cold climates; ectotherms can’t. One disadvantage I see with this is that a cold-blooded species would have trouble expanding into a niche dominated by warm-blooded predators (i.e. they would be easy to catch). They would also have trouble mating in very cold climates and below a certain temperature their metabolism would stop entirely. It’s easier for warm blooded animals to survive anywhere (i.e. they can adapt to a broader range of environments).

Endotherms can evolve more intelligence than ectotherms due to the metabolic demands of larger brains. I believe increased intelligence gives a species a competitive edge and is more adaptable. Midway down this article explains the brain situation.

Avian dinosaurs are warm blooded, but non-avian dinosaurs weren’t (they were most likely mesotherms).

53

Or were they? This is an ongoing area of research, but it looks like the divide was more ornithischians vs saurischians rather than avian vs non-avian.

And of course I know better than to go running down the street shouting “Give me a towel!” based on just one study.

54

Well, that was certainly poor timing for that study to come out, potentially knocking a hole in my argument. :frowning_face:

They couldn’t have waited a few more days to publish?!?

But, as they say, it ain’t over till the fat lady sings—or till the T-rex hibernates.

55

“These human kabobs taste like Archaeopteryx”

56

Perhaps the world would look much like it does today, and this thread would be speculating on what if the Deccan Traps had been a much slower phenomenon?