Survival strategies of brachiopod faunas from the end-Permian mass extinction

Global reviews reveal that 102 brachiopod species (including 40 indeterminate species) belonging to 43 genera within 27 families survived the end-Permian mass extinction in South China, the Himalayan regions (southern Tibet, Nepal, Salt Range and Kashmir), southern Alps (Italy), Arctic Canada, western USA and Western Australia. Of these, the surviving brachiopods are most abundant and widespread in South China where they occur in 32 of the 42 Permian-Triassic (P/T) boundary sections around the world. Brachiopod faunas are the most abundant and diverse post-extinction survivors, and their appearance above the end-Permian mass extinction horizon somewhat masks recognition of the end-Permian extinction. These surviving brachiopods occur in three stratal intervals corresponding to the “Mixed Fauna Beds” (MFB hereafter) 1-3 of the P/T boundary beds. A sharp drop in diversity of the brachiopod faunas coincides with the widely accepted end-Permian mass extinction horizon. The post-extinction brachiopods were also affected by a subsequent crisis corresponding to the boundary between MFB 2 and MFB 3 so that most survivors were extinct approximately 0.7 Ma after the end-Permian mass extinction. The surviving brachiopods were mainly Productida, followed by Spiriferida. In particular, small chonetids, chonetid-like productellids and smooth, thin-shelled ambocollid spiriferids are most abundant. Lingula is extraordinarily abundant and widespread approximately 0.7 Ma after the greatest extinction when many regions became devoid of articulate brachiopods. Widespread, broadly adapted and small-sized taxa preferentially survived. Frequent intrageneric speciation of widespread, widely adapted generalist genera enabled survival brachiopods to occupy rapidly and efficiently vacant ecospace in the aftermath of the end-Permian extinction. The ecological habitats of the post-extinction brachiopods are subdivided into nearshore, epeiric sea, restricted carbonate platform, open carbonate platform, ramp and outer shelf environments. Of these, the survival brachiopods are most diverse in the open platform environments. The nearshore zone provided ideal habitats for the nonarticulated brachiopods to occupy; whereas the survivors in the outer shelf are predominantly chonetids and chonetid-like productellids. The most successful survivors, the productid brachiopods, are widely distributed in six types of ecological habitats and thus have no apparent preference for specific environments. The end-Permian extinction resulted in the movement of biogeographical provinces towards the palaeo-equator. The brachiopods survived mostly in the palaeo-equatorial provinces and along the southern margins of the Palaeo-Tethys Ocean.