found: Work cat.: Mass extinctions : processes and evidence, 1989.
found: New world encyclopedia, Dec. 9, 2009, via WWW(A mass extinction or extinction event is the phenomenon in which a large number of species of life on Earth become extinct in a relatively short period of time; "mass extinction" refers to an extinction affecting a great many different groups of organisms occupying diverse and wide-spread environments)
found: Encyclopedia of evolution (Oxford), online, Dec. 9, 2009(Mass Extinctions: A mass extinction is an extinction of a significant proportion of the world's biota in a geologically brief period of time)
found: Dict. of biology, (Oxford), online, Dec. 9, 2009(mass extinction: The extinction of a large number of species within a relatively short interval of the geological time scale)
found: Wikipedia, Dec. 9, 2009"Extinction event" entry (Mass extinctions affect most major taxonomic groups present at the time - - birds, mammals, reptiles, ... )