Recovery from the Permo-Triassic filter

Following mass extinctions there are three phases to the recovery that follows. These are

• survival
• diversification
• stabilisation.

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 include the Orthocerids and the Conodonts. When some of these species became extinct there would have been a knock-on effect to those organisms that preyed on them higher in the food chain. This becomes a phenomenon known as the "Lilliput effect", where often only the smaller species (which are lower down the food chain) survive through extinctions.

Diversification occurs after the survival phase is complete. Surviving lineages have new opportunities 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. After a mass extinction the 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 Ammonoidea.