[Junior]

You obviously haven't read much on the effects of the impact. It would have thrown millions of tons of dust into the atmosphere, increasing the albedo of the planet and dropping the temperature worldwide. Plants died off -- but not all plants. Plant matter would still be available for smaller animals to subsist upon, and other animals feasted upon those. The situation lasted about two years. Small, quick, warm-blooded animals had the best chance of survival and survive they did. Cold-blooded reptiles and amphibians already had slower metabolisms and are known to hibernate in cold times, so they survived, too. Your simplistic scenario would have the entire biosphere wiped out, instead of the 75 percent that was (a similar event 150 million years earlier had wiped out 90 percent).

[ican'tbelieveit]

instead of the 75 percent that was

You know for a fact it was 75%? You know for a fact that it just threw a million tons of dust into the air? Oh, wait, these are ALL THEORIES ON WHAT HAPPENED and as such, are open to question and debate.