How'd the little herps survive the comet?

GeoffP

GeoffP

Caput gerat lupinum
Valued Senior Member
I don't usually post threads in B&G, basically because what I read I'm usually working on, and I've already had a few ideas lifted off me. But here's one I'm definitely not doing: how did small reptiles make it past the K-T extinction event? Large reptiles - and not just dinos, either: aerials and aquatics also - didn't. So how'd turtles and crocs pull it off? Three hypotheses, based generally off presumed fundamental physiological differentiation between small reptiles and dinos/aquatic reptiles/pterosaurs:

i) surviving reptiles had lower energetic demands - either relative to size or overall, being heterotherms.

ii) estivation: related to above. Did they estivate for a lot of it? Must have been cold with the dirt in the air. But these are environmentally-sex-determinate (ESD) species: wouldn't they have produced all-male or all-female sex ratios during the dirt-cover period after impact? Surely that would wipe out most of the short-generation time species, like lizards and snakes? Most amphibians too. Or maybe it wasn't so cold after all, or not for long?

iii) Higher population density? They just "powered through" massive demographic losses?

iv) Other?
 
Perhaps their ability to adapt by having a better mental ability could have helped them along. :shrug:
 
Small and low-lying animals made it through in larger fractions, from every kind. Mammals, reptiles, and even dinos (we see them as birds, now), of modest size or ecological needs, of high reproductive capability or long endurance of privation or great flexibility in location, food, etc, made it through in fair diversity and number.

That is, a lot of reasons - but it was easier to be lucky if you needed less luck. An herd living animal the size of a bus, with a breeding population requirement of 500 or more and a food requirement of several square miles of undisturbed wet marshland in both its winter and summer ranges, needs a lot more luck than a dispersed population of insectivorous lizards living under rocks in sheltered ravines. And so do its predators, carrion eaters, etc.
 
So your position is predicated on the collapse of the food chain? I suppose: but then again, the small dinos went out too. There were a vast array of those, smaller than crocodilians. Combination of energetic demand per gram and size, possibly?
 
geoff said:
So your position is predicated on the collapse of the food chain? I suppose: but then again, the small dinos went out too. There were a vast array of those, smaller than crocodilian
Click to expand...
Not just food source, but habitat - exposed, above water and above ground, high metabolism living needed more luck.

The initial size range of the surviving crocodilians is unknown - they are essentially independent from the moment of hatching, comparatively slow growing, and numerous - at any given time there are many small crocodilians that need no parental care hiding out along various shores.

Small dinos - smaller than yearling crocs - were probably under parental care, and unlikely to be either living in well-sheltered circumstances or able to survive on a diet of dead stuff, buried stuff, and remnant arthropods. And they needed more food - crocs can starve for weeks, larger ones for months.

A croc needs less food in cold weather, the ancestors of the modern birds would have needed more.
 
iceaura said:
Not just food source, but habitat - exposed, above water and above ground, high metabolism living needed more luck.
Click to expand...

Interesting: but small aquatic reptiles outside the crocodilia and testudines also got whacked. I think if we drew the line at high metabolism that would make sense.

I agree with some of the rest, but about this:

A croc needs less food in cold weather, the ancestors of the modern birds would have needed more.
Click to expand...

So how did birds get through?
 
geoff said:
A croc needs less food in cold weather, the ancestors of the modern birds would have needed more.
”
So how did birds get through?
Click to expand...
No mystery if a very lucky, small, apparently well-feathered and very mobile, selection of dinos got through. As you observe, a larger fraction of other kinds of critters made it.
 
Yes, but it meets the criteria for not surviving: very high metabolism for its size being the key.
 
geoff said:
Yes, but it meets the criteria for not surviving: very high metabolism for its size being the key.
Click to expand...
And a lower proportion survived, concentrated in the mobile and well-insulated and individual and small enough to survive in pocket-sized refuges category.
 
I dunno. I've thought about the isolated pockets thing...but statistically speaking, shouldn't some small dinosaurs have been in such pockets as well?

Here's a possibility: flight. Birds could flutter around over wide distances to forage on whatever ephemeral resources became available: they're not all that rigid in their feeding preferences (i.e. the cream-eating rooks of England) and might range widely. Land-based therapods and sauropods should have less relative ability to move around. So birds could move from location to location to forage, maybe even as mixed-flocks, like you see in the fall sometimes.

Actually, you did mention mobile.

This still doesn't quite explain the persistence of smaller reptiles and even amphibians. Presumably, it must be a similar process to the previous extinction events. Ecological delay in the interruption of energetic transfer to aquatic ecosystems? Takes a while to move calories around.
 
So larger r should be preventative of allele loss. Agreed, naturally. Although I still think there'd be lots of small dinos.
 
An Ockham thingy

GeoffP said:

i) surviving reptiles had lower energetic demands - either relative to size or overall, being heterotherms.
Click to expand...

This would be my primary theory. Like my friend's turtle: I'm quite certain the light bulb that keeps Toby warm in the winter would not suffice for even a six-foot dinosaur. I know that's not a whole lot to go on, but maybe it's one of those Ockham things.
 
This might be of use:
K-T Extinction Event

I had an... Extended discussion with Walter. L. Wagner on this very topic.

Essentially, as I understand it, it goes along these lines:

Asteroid hits earth, blots out sun for an extended period of time.
Food Chain Collapses.
Most Dinosaurs were dependent on the food chain for survival, there's a name for it, primary something or other I think, pretty sure I mention it in that thread. Essentially, they ate the plants, or they ate the flesh of those that ate the plants.
Those that survived were able to live on detritus or carrion, and lived in environments where there was a 'store' of detritus or carrion, or were insectivorous (even in various aquatic habitats).
AFAIK most dinosaur nests have been found in open environments, but those that survived - including those dinosaurs that evolved into birds (people always seem to forget that) were capable of seeking shelter and raring their young in shelter (under ground, trees, swamps etc.

As a specific example, some traits that Crocodillians have that might have enabled them to survive include the ability to store food(?), and their habitat suggests they would have been able to continue preying off insectivorous species, or carrion or detritus eating species.

There's other factors involved as well, which I think are delved into, but I hope it helps.
 
Energy efficiency of crocodile:

Naturally hidden, floating and stalking in high-probability strike zones.

Energy efficiency of an elephant:

You get the point.

I think it is best stated that the crocodile's energy efficient design contributed to a higher than average likelihood of success.

In business, higher management often prioritize simplicity to mitigate unpredictable risk inherent in complexity. In a world based on energy consumption, the crocodile wins.
 
Tiassa said:
This would be my primary theory. Like my friend's turtle: I'm quite certain the light bulb that keeps Toby warm in the winter would not suffice for even a six-foot dinosaur. I know that's not a whole lot to go on, but maybe it's one of those Ockham things.
Click to expand...

well said
 
"He said the research showed that currents could carry crocodiles _ which can survive for months without food or fresh water _ across vast tracks of ocean."

http://www.newser.com/article/d9g7ev800/australian-study-finds-crocodiles-surf-the-seas.html

Large crocodiles are powerful, but tire quickly. A 20-minute struggle in a trap can kill a crocodile, because exertion causes a rapid buildup of lactic acid in their blood, Webb said.
Click to expand...

Sounds like mother nature really punishes the crocs for using energy.
 
Search & Destroy said:
I think it is best stated that the crocodile's energy efficient design contributed to a higher than average likelihood of success.
Click to expand...

I think this statement oversimplifies the issue, because energy efficiency isn't neccessarily the only way to survive the collapse of the food chain.
 
Search & Destroy said:
"He said the research showed that currents could carry crocodiles _ which can survive for months without food or fresh water _ across vast tracks of ocean."
Click to expand...

Thanks, I was going to raise this as another reason why Crocodillians might have survived, but for reasons that escape me (most likely haste or uncertainty) I didn't.
 
You must log in or register to reply here.
Back
Top