<P> Among benthic organisms the extinction event multiplied background extinction rates, and therefore caused maximum species loss to taxa that had a high background extinction rate (by implication, taxa with a high turnover). The extinction rate of marine organisms was catastrophic . </P> <P> Surviving marine invertebrate groups include: articulate brachiopods (those with a hinge), which have undergone a slow decline in numbers since the P--Tr extinction; the Ceratitida order of ammonites; and crinoids ("sea lilies"), which very nearly became extinct but later became abundant and diverse . </P> <P> 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 apparatuses suffered the greatest loss of species diversity . In the case of the brachiopods, at least, surviving taxa were generally small, rare members of a formerly diverse community . </P> <P> The ammonoids, which had been in a long - term decline for the 30 million years since the Roadian (middle Permian), suffered a selective extinction pulse 10 million years before the main event, at the end of the Capitanian stage . In this preliminary extinction, which greatly reduced disparity, or the range of different ecological guilds, environmental factors were apparently responsible . Diversity and disparity fell further until the P--Tr boundary; the extinction here (P--Tr) was non-selective, consistent with a catastrophic initiator . During the Triassic, diversity rose rapidly, but disparity remained low . </P>

When did over 96 of marine and 70 of land species on earth become extinct