They tried to simulate the pattern. 1st birds, radiations by marine fish and terr. Mass Extinctions versus Background Extinctions Raup and Sepkoski 1982 mass extinctions. Within a taxonomic group the number of species declines linearly with time. Therefore, older taxa are no more likely to survive than younger taxa.
Species have to continually evolve just to keep up in the race.
Impact site has been identified in the Yucatan peninisula. K previously det.