Comet wiped out the wooly mammoth and mastodon?

Could the last cataclsym (and the next one) be due to a comet? Traces of iridium suggest that the wiping out of large mammals in North America was:

A theory put forth by a group of 25 geo-scientists suggests that a massive comet exploded over Canada, possibly wiping out both beast and man around 12,900 years ago, and pushing the earth into another ice age.