Page 175 - Introduction to Paleobiology and The Fossil Record

Chapter 7

Mass extinctions and biodiversity loss

Key points

• During mass extinctions, 20–90% of species were wiped out; these include a broad
range of organisms, and the events appear to have happened rapidly.
• It is diffi cult to study mass extinctions in the Precambrian, but there seems to have been
a Neoproterozoic event between the Ediacaran and Early Cambrian faunas.
• The “big fi ve” Phanerozoic mass extinctions occurred in the end-Ordovician, the Late
Devonian, the end of the Permian, the end of the Triassic and the end of the Cretaceous.
Of these, the Late Devonian and end-Triassic events seem to have lasted some time and
involved depressed origination as much as heightened extinction.
• The end-Permian mass extinction was the largest of all time, and probably caused by a
series of Earth-bound causes that began with massive volcanic eruptions, leading to acid
rain and global anoxia.
• The end-Cretaceous mass extinction has been most studied, and it was probably caused
by a major impact on the Earth.
• Smaller-scale extinction events include the loss of mammals at the end of the Pleistocene,
perhaps the result of climate change and human hunting.
• Recovery from mass extinctions can take a long time; first on the scene may be some

unusual disaster taxa that cope well in harsh conditions; they give way to the longer-
lived taxa that rebuild normal ecosystems.
• Extinction is a major concern today, with calculated species loss as high as during any
mass extinction of the past. The severity of the current extinction episode is still
debated.

The Dodo never had a chance. He seems to have been invented for the sole purpose
of becoming extinct and that was all he was good for.
Will Cuppy (1941) How to Become Extinct