Survival is when having survived the extinction event, organisms must be able to adapt to an environment which may have been changed by whatever caused the extinction. This may mean a change in environmental variables such as temperature, salinity and atmospheric gas proportions. With so many organisms having been killed there will also be a drop in the number of breeding pairs within a taxa, if this slows down reproduction to a rate where it is exceeded by the death rate within an order then it will eventually lead to extinction.
There are examples of orders of organism which managed to scrape across the Permo-Triassic boundary, only to become extinct early in the Triassic. These incude the Orthocerids and the Conodonts.
By some of these species becoming extinct it would have a knock-on effect to those organisms that predated on them higher in the food chain. This causes a phenomena known as the "Lilliput effect", where it is often only the smaller species which are lower down the food chain which survive through extinctions.
Diversification occurs after the survival phase is complete. With so many organisms having become extinct it leaves a massive ecological vacuum, this creates new opportunities for the surviving lineages to diversify into niches left vacated by the now extinct predecessors. While this radiation is rapid for all surviving taxa, some orders can diversify faster than others. This means that by undergoing a mass extinction some orders which diversify the fastest eventually benefit, from being able to fill the empty niches and becoming the dominant order. At the Permo-Triassic boundary this is especially the case with the Ammonoids.
Stabilisation is when the rapid diversification has filled the empty niches left by the mass extinction. This can be defined when increased competition and selection reduces the rate of evolution (Benton 1987, 1991) and a new, not simply reconstituted ecosystem is created, (Erwin 1996).
This point is most easily spotted within the fossil record by the reappearance of Lazarus taxa (see below) and by when reefs, one of the most sensitive ecological indicators, have reappeared.
Having a very widespread geographical distribution was probably the most important factor for species escaping extinction, with the increased number of organisms having a greater chance of adapting to survive or finding a safe refuge in which to survive. Once a genera had survived through the initial survival phase, diversification and recovery was rapid. All the sea-urchins which are seen throughout the world today are derived from only 2 genera of Echinoidea which passed through the Permo-Triassic filter.
Lazarus taxa is a term referring to some taxa living around the Permo-Triassic extinction which seemingly disappear from the fossil record as if having become extinct, only to reappear millions of years later with near identical morphology. Systematic of preservational bias this effect is thought to be likely to be caused by a reduction in numbers within the taxa to a point that the species lived within a localised area which has yet to be discovered, such as an off-shore refugia.
Sediments from these regions which may contain these "missing" fossils may still be in off-shore locations where they cannot be found, or may have been lost forever having been subducted by plate tectonics. It has also been suggested that the taxa were from nearshore habitats and have been poorly sampled from the rare boundary sections found, or that it may simply reflect poor preservation.
Which ever reason it is as to why these fossils are absent it does show that the fossil record from this time is far from complete. This means that rates of extinction during the Permian derived from looking at the fossil record are only as accurate as the completeness of the fossil record. For a page on analysis of extinction rate, and how carbon isotope study may give a more accurate extinction rate, click here.
When Lazarus taxa do reappear after having been "missing" for millions of years they are nearly always of almost identical morphology to when they were last seen. This asks many questions about traditional views on evolution as they seem to have defied processes of change. Natural selection and mutations have affected them very little.