Hasta el 60% "GeoKansas--Geotopics--Mass Extinctions" http://www.kgs.ku.edu/Extension/fossils/massExtinct.html "GeoKansas--Geotopics--Mass Extinctions" Hasta el 60% http://www.kgs.ku.edu/Extension/fossils/massExtinct.html "GeoKansas--Geotopics--Mass Extinctions" "GeoKansas--Geotopics--Mass Extinctions" "GeoKansas--Geotopics--Mass Extinctions"