Horniman Museum

Permian period: The Time Before Dinosaurs

The Five Mass Extinctions:

1) Ordovician Mass Extinction

• occurred 444 million years ago
• majority of losses were within the marine ecosystem (life on land was still embryonic at the time)
• reef building animals died out (as many families within the brachiopods (lamp shells), echinoderms (such as starfish and sea urchins), and trilobites)
• In total, 85% of marine species were lost

2) Devonian Mass Extinction (also referred to as ‘Late Devonian Biodiversity Crisis’)

• occurred several millions of years (between 374 and 360 million years ago)
• was caused as much by lower speciation rates as higher extinction rates
• Free-swimming cephalopods (ammonites, etc) were decimated, as were other marine invertebrates such as corals, brachiopods, and trilobites.
• As the Devonian mass extinction occurred over such a long time period, no one single cause can be pinpointed.
• There is evidence for a major cooling phase related to an anoxic event (oxygen depletion), and potentially also for an asteroid strike as both would be a cause for environmental changes but there is no certain answer for now.

3) Permo-Triassic Mass Extinction

• The biggest mass extinction
• Occurred around 252 million years ago, two major pulses of extinction occurred – The first pulse wiped out 57 % of species, whilst the second wiped out 71 % of those that had survived the first.
• It is estimated that 90% of life (including plants) was lost in the Permo-Triasic extinction.
• Evidence for the cause points towards massive volcanic eruptions in Siberia. Volcanic activity on this scale would cause ocean stagnation, acid rain, and global warming.

4) Triassic Mass Extinction

• Occurred 201 million years ago – was the cause of a major turnover of species in the ammonite, brachiopod, and bivalve (a type of mollusc) groups.
• Marine reptiles were hit the hardest in this period as they lost 2 whole species.
• The cause is thought to be linked to eruptions of the Central Atlantic Magmatic Province, which increased in intensity in the Late Triassic, leading to acid rain and oxygen depletion in marine environments.

5) Cretaceous Mass Extinction

• Occurred 66 million years ago
• the mass extinction made famous by the demise of non-avian dinosaurs (while dinobirds, and subsequently birds, survived)
• Large reptilian vertebrates were completely wiped out
• This event was caused by a meteor striking the earth, combined with massive volcanic activity, changing the climate and environmental conditions on both a local and global scale.