The Permian Extinction was the major event which creates a meaningful boundary between the Permian and Triassic period, and the Paleozoic and Mesozoic eras. It represents a significant loss of biodiversity, and is interesting to study as it relates to the way that a mass extinction impacts the planet. In order to fully understand the topic, however, it is first important to define what mass extinction is.
Mass extinction is actually a mathematical construct, based upon an established ratio. More specifically, when up to 75 % of the existing species fail, globally, in a relatively compact geological time frame, it is defined as a mass extinction (Barnosky et al., 2011). The total species lost as a result of extinction can then be determined from the fossil record from that time period.
The Permian extinction, in particular is of marked interest because it is bar far the most profound mass extinction that the world has ever suffered (Sahney & Benton, 2008). More specifically, roughly 251 million years ago, a worldwide ecological decimation occurred, leaving only a small fraction of the previously occurring species left alive, and even these organisms suffering from significantly reduced total populations (Sahney & Benton, 2008). This resulted in an extreme loss of diversity including the loss of an estimated 96% of all marine species, 70% of all terrestrial vertebrates, up to 83% of some insect genera, not including plant life and other significant biological organisms (Benton, 2005). These losses are believed to have occurred because of a catastrophic event. While the even remains unknown ,the researchers indicate that it was likely caused by an asteroid impact, mass volcanism, and global heating and cooling (Benton & Twitchett, 2003). This loss can be more fully understood if the Taxonomic groups which were in existence before the Permian extinction.
Known taxa, or taxonomic groups which were present before the Permian extinction were dominated by marine life. Marine organisms included both marine invertebrates and vertebrates, terrestrial vertebrates and invertebrates, and terrestrial plants. Though the exact number of genus are unknown, researchers have worked to estimate what larger taxonomies were lost as a direct result of the mass extinction. In order to understand the fossil records that help define what was lost, and what survived the extinction however, it is important to understand how the continents were arranged, and what areas of the globe likely shared taxonomy during the Permian period. This can be illustrated in Figure 1 below.
Source: http://www.discoveringfossils.co.uk/how_britain_formed.htm
The Permian extinction resulted in the loss of a number of taxonomies. Marine life was reduced by 90%, and terrestrial life by 70% leaving very few life forms to repopulate the globe and generate the diversity experienced during the following period.
More specifically, for example the fossil records for fish life during the Triassic period are exceedingly uniform, which indicates that very few fish varieties survived the mass extinction. However the fossil records indicate that certain life forms found the space and opportunity to flourish as a result of the decreased competition from other life forms (Benton, 2005). Notable life forms that survive include: mammal like reptiles, including Lystrosaurus, early pseudo mammals like cynodonts, semi-aquatic reptiles, similar to crocodilian species, thereocephalians, amphibians known as temnospondyls, and a variety of water life including some sharks, crinoids, ammonites, and crabs. Anthropods like spiders, scorpions and cockroaches also survived. As did a number of lizard or lizard like creatures.
Recovery was slow, and opportunistic species were allowed to take a foothold, and greatly impact the current biodoveresity of the planet. However, what is perhaps more significant is the relevance that the findings related to this mass extinction have on the mass extinction we are experiencing today. Experts suggest that we are currently experiencing the globes 6th major mass extinction, and many of the principles which are witnessed in the Permian extinction can be used as a basis for understanding todays loss of diversity. Those species that survive, and which thrive will be those that are least susceptible to the underlying causes and most well equipped to live according to the planets new normal. For example one of the theories for the previous mass extinction holds that animals which require a large amount of oxygen suffocated as the result of ash in the air. As such, those smaller species which had a lower oxygen requirement survived, and flourished in the days after the mass extinction. The same is true today, with our current global loss of diversity.
References:
Barnosky, A. D., Matzke, N., Tomiya, S., Wogan, G. O., Swartz, B., Quental, T. B., . . . Ferrer, E. A. (2011). Has the Earth’s sixth mass extinction already arrived? Nature, 471(7336), 51-57.
Benton M. J. (2005). When life nearly died: the greatest mass extinction of all time. London: Thames & Hudson.
Benton, M. J., & Twitchett, R. J. (2003). How to kill (almost) all life: The end-Permian extinction event.Trends in Ecology & Evolution, 18(7), 358-365.
Sahney, S., & Benton, M. J. (2008). Recovery from the most profound mass extinction of all time.Proceedings of the Royal Society B: Biological Sciences, 275(1636), 759-765.
