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I'm picturing a world say a 100 years after a devastating nuclear war with a decades long nuclear winter where DNA damage due to war related radiation as well as subsequent ozone depletion have destabilized genetic lines. Some mutations have helped certain species. So not only I'm asking which species would fare better but also what would say a certain species may end up looking like. For example, we may see smaller cats with short limbs that can burrow deep underground, hence are half-blind with large mole-like claws, etc..

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    $\begingroup$ ALL HAIL OUR TARDIGRADE OVERLORDS!!! $\endgroup$ – Joe Bloggs Feb 16 '17 at 20:20
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Mesothermics.
Contrary to believe, cocroaches would not survive a nuclear winter, but not because of the radiation, but because of the cold. A global nuclear winter would see the appearance of endothermic characteristics in animal that use to be exothermic. Sadly this would mean that lizards and insects would be much more voracious.
But the ability to lower the metabolism when there is little food or a creature finds itself in a warmer place could also be crucial. So many creatures could appear with the capacity to generate just enough internal heat to survive eficiently.

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  • $\begingroup$ I like it. Sort of an ad-hock hibernation capability. $\endgroup$ – KalleMP Feb 16 '17 at 20:47
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Well, for one thing, a decades-long nuclear winter is probably not a real thing (at least not with any quantity and size of nuclear weapons humans have made so far). The idea of apocalyptic nuclear winter in the first place is quite questionable.

However, assuming it was, we're basically talking about something like the end-Cretaceous extinction event, but maybe worse, and with radiation.

So good adaptations:

cryptobiosis: survive through the nuclear winter in an inert state. Tardigrades are famous for this, but other small invertebrates can do it too - some rotifers, some nematodes, at least one insect. https://en.wikipedia.org/wiki/Polypedilum_vanderplanki - "In the dehydrated state the larvae become impervious to many extreme environmental conditions, and can survive temperatures from 3 K to up to 375 K, very high (7000 gray) levels of gamma-rays, and exposure to vacuum."

This is pretty much the perfect adaptation for surviving something like this, but it doesn't seem to be available to vertebrates. (Well, the wood frog can freeze solid and recover, but it's only known to do this over winter IIRC, not for multiple years.)

feed on something not dependent on sunlight: deep-sea tube worms etc. whose food chain is based on chemosynthesis rather than photosynthesis. Again, this is only available to a very limited set of animals.

eat pretty much anything, including dead stuff: small omnivores that can scavenge probably have the best chance among vertebrates of getting through a mass extinction. While I can't remember where I read this, IIRC freshwater streams were less badly hit by the end-Cretaceous extinction since the ecosystems are largely detritus based.

Radiation probably won't be terribly determinative of what survives and what goes extinct, since most of the most vulnerable things will probably go extinct anyway from the food crunch. Many invertebrates are really resistant, and even among the more vulnerable mammals etc., there will probably be pockets where the radiation levels are lower.

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  • $\begingroup$ Thanks. Very informative. I'm writing a story and can tweak the time span a bit. I need some non-human threats to a small community of humans that have survived. So let's imagine then a shorter nuclear winter, ozone depletion, massive changes in weather patterns, killer frosts and food crunch have all contributed to the extinction of many species. There is also considerable DNA damage to genetic lines. What types of animals could have moved a top the food change, roaming the land for any available scraps of food? $\endgroup$ – Pirpir Feb 18 '17 at 2:20
  • $\begingroup$ something that can survive long winters, near desert landscape with clear positive mutations that have helped them to adapt. Would love to hear what's genetically possible or at least enough to be believable? $\endgroup$ – Pirpir Feb 18 '17 at 2:20
  • $\begingroup$ Depends on what part of the world. Coyotes are really adaptable, highly omnivorous, and live in semi-desert landscapes already. Plus, canids tend to be pretty liable to hybridize. In fact over the last century coyotes have moved into the eastern US and hybridized with the last few Eastern US wolves as well as domestic dogs - so eastern coyotes are larger than the western ones now. After such a major disaster, coyote-dog hybrids might move into the vacant large predator niches & pose a threat to humans. The variety of traits available in dog breeds could lead to some interesting mixes - maybe $\endgroup$ – cometaryorbit Feb 21 '17 at 0:37
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    $\begingroup$ , if we're talking about a "cold desert" (or semi-desert) landscape rather than a hot desert, traits from Huskies and other wolf-like breeds deriving from northern climates would become fixed in the new hybrid population. This could also drive up the size as those breeds tend to be, while not the largest dogs, more wolf-size than coyote-size. Outside the Americas, you could get a similar result with feral dogs interbreeding with the last few wolves. As a weirder possibility, what about feral hogs? They're already omnivorous - an extreme event like this could make them more aggressive. $\endgroup$ – cometaryorbit Feb 21 '17 at 0:39
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If radiation is an issue, I believe cockroaches are more resistant to it because their cells divide less frequently than other organisms, so a lower cell division rate might help.

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