Actually if you read further you will find that evolution can make (relatively) quick leaps when cataclysms occur.

If the astroid kills off all large land animals the toads and lizards that were buried in mud come out after thirty years when the climate allows them to survive and they have an exlplosion of growth (as a group) and fill "niches" which may have previously been filled by mammals (or visa versa).

Hence we have different forms of animals filling the same "niche" in different locals.

For example there is a marsupial animal in south america which is so similar to a squirrell that you would swear it is one until you find its little pouch. It eats nuts and everty thing.

White tail deer and Kangaroos are very similar in many ways too. (even color). Developed in separate continents but filling essentially the same niche.

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.