Extinction periodicity or episodicity

Mention has already been made (in Chapter 3) of Jack Sep-koski's huge compendium of Phanerozoic marine families, which was the basis for the recognition with his colleague Dave Raup of the 'big five' mass-extinction events. Later on, using a combination of methods involving Fourier analysis and Monte Carlo simulation, they discovered to their great excitement a statistically highly significant 26 million-year periodicity in extinction events during the past 250 million years. This was a most...

In search of possible causes of mass extinctions

When the subject of extinctions in the geological past comes up, nearly everyone's thoughts turn to dinosaurs. It may well be true that these long-extinct beasts mean more to most children than the vast majority of living creatures. One could even go so far as to paraphrase Voltaire and maintain that if dinosaurs had never existed it would have been necessary to invent them, if only as a metaphor for obsolescence. To refer to a particular machine as a dinosaur would certainly do nothing for its...

How catastrophic were massextinction events

Butler Tourism Model

Determining whether a given extinction event was catastrophic or merely gradual is not a straightforward matter, Table 3.1 The five biggest mass extinction events of the Phanerozoic The graptolites underwent the worst crisis in their history, and the conodonts were also severely affected. The dominant benthic (bottom-living) trilobites and brachiopods suffered major extinctions. (2) Late Devonian event (Frasnian-Famennian boundary) (22) Reef ecosystems, comprising rugose and tabulate corals and...

The role of competition as perceived from the stratigraphic record

The type of competition that Darwin had in mind might be termed displacive competition, implying dynamic behaviour on the part of the newly arrived species or higher taxon in the wedge. How could this be recognized in the stratigraphic record One reasonable inference is that after the new taxon first appeared, it might progressively expand its abundance and diversity concomitant with the progressive reduction of its biologically most closely related or potentially competitive rival, known as...

The evolutionary significance of mass extinctions

Darwin was firmly of the opinion that biotic interactions, such as competition for food and space - the 'struggle for existence' - were of considerably greater importance in promoting evolution and extinction than changes in the physical environment. This is clearly brought out by this quotation from The Origin of Species Species are produced and exterminated by slowly acting causes . . . and the most important of all causes of organic change is one that is almost independent of altered . . ....