Saturday, 29 October 2011

New Insight Into Terrestrial Life And Its Recovery Just After The Great Dying

Lystrosaurus in a scrubland forest composed of
the meter high, spore bearing tree Pleuromaia
The Great Dying wiped out around 78% of terrestrial fauna 250 million years ago. Life recovered around 8 million years later. However the period between extinction and recovery is very sketchy. As there were few creatures, the fossil record during this time is scant and therefore we cannot build up a very good picture of ecosystems during the the Permo-Triassic boundary. However a recent and exhaustive study has given us new insight into this mysterious time in evolutionary history.

A team composed of researchers from Brown University and the University of Utah used their exhaustive data-pile to investigate how the terrestrial biota recovered over 8 million years. The creatures that survived the catastrophe, known as disaster taxa, were free to roam around and occupy new ecological niches without any competition from other species or threats from predators. The team found that this caused a cycle of events called 'boom and bust' in the Permo-Triassic ecosystems.

A creature is left in an ecosystem with an abundance of food. With no predators, it breeds and multiplies at an exponential rate. This places a strain upon their habitat. Eventually there is no food and the consumptive species dies out. Hence the label 'boom and bust.' One of the best examples of this cycle, out of the 8,600 species with an age range of 260 to 242 million years old, sampled from the Karoo Basin, South Africa and the Ural Mountains, Russia, was the dicynodont, Lystrosaurus.

The German shepherd-sized reptile, was not very common or diverse during the Permian period, when it evolved. However it became a very common and diverse species just after the extinction, dominating the scrubland and desert due to its ability to consume most available forms of vegetation. The 'bust' came during the early Triassic, when there was not enough vegetation left to sustain the species. It became less diverse, less common and was extinct by 248 million years ago.

It seems that the species that survived the extinction and died out during the 'boom and bust' era were the species that could consume the most types of food. The team's hypothesis is that the terrestrial recovery was not due to external factors such as climate change, but was internal within ecosystems and food webs, via re-population and diversification caused by the boom side of the cycle.

'These results are consistent with the idea that the fluctuating carbon cycle reflects the unstable ecosystems in the aftermath of the extinction event,' said Jessica Whiteside, co-author of the paper and head of geology at Brown University. 'It really is the same pattern with land-based ecosystems as marine environments. The same seems to hold true for plants,' she added. Studies like these are very useful to palaeontologists. It is all very well knowing the causes of an extinction. Yet interest lies in how the biota recovers after.