252 Million B.C.T. - Marine Life Was Decimated

During the Permian-Triassic extinction event that began around 252 million years ago, it is estimated that as much as 96 percent of all marine species were exterminated.

Marine invertebrates suffered the greatest losses during the Permian-Triassic extinction. In the intensively-sampled south China sections at the Permian-Triassic boundary, for instance, 286 out of 329 marine invertebrate genera disappear within the final 2 sedimentary zones containing conodonts (eel-like creatures) from the Permian.

Statistical analysis of marine losses at the end of the Permian suggests that the decrease in diversity was caused by a sharp increase in extinctions instead of a decrease in speciation. The extinction primarily affected organisms with calcium carbonate skeletons, especially those reliant on ambient CO₂ levels to produce their skeletons.


Among benthic organisms, the extinction event multiplied background extinction rates, and therefore caused most damage to taxa that had a high background extinction rate (by implication, taxa with a high turnover). The extinction rate of marine organisms was catastrophic.


Surviving marine invertebrate groups include: articulate brachiopods (those with a hinge), which have suffered a slow decline in numbers since the Permian-Triassic extinction.  The Ceratitida order of ammonites; and crinoids ("sea lilies"), which very nearly became extinct but later became abundant and diverse.

The groups with the highest survival rates generally had active control of circulation, elaborate gas exchange mechanisms, and light calcification; more heavily calcified organisms with simpler breathing apparatus were the worst hit.  In the case of the brachiopods at least, surviving taxa were generally small, rare members of a diverse community.


The ammonoids, which had been in a long-term decline for the 30 million years since the Roadian (middle Permian), suffered a selective end-Guadalupian extinction pulse. This extinction greatly reduced disparity, and suggests that environmental factors were responsible for this extinction. Diversity and disparity fell further until the Permian-Triassic boundary.  The extinction here was non-selective, consistent with a catastrophic initiator. During the Triassic, diversity rose rapidly, but disparity remained low.