ASIAN-WESTERN PACIFIC PERMIAN BRACHIOPODA IN SPACE AND TIME: BIOGEOGRAPHY AND EXTINCTION PATTERNS

Abstract

A database of 86 Permian brachiopod families, 411 genera and 1931 species of the Asian-western Pacific region was analysed using a range of statistical measures to unravel the changing patterns of diversity, origination and extinction rates through six Permian intervals. Prior to the quantitative analysis, the evolutionary pattern of the Permian marine provincialism of the region was reviewed to provide a framework for investigating possible palaeogeographical patterns of the Permian brachiopod extinctions and the likelihood of biogeographical control on the extinctions. It was revealed that the Permian brachiopod diversity variation and extinction patterns are broadly compatible among the Gondwanan, Palaeo-equatorial and Boreal Realms as well as with the overall diversity and extinction pattern of the Asian-western Pacific region. Two major extinctions are recognised regardless of taxonomic ranks (species, genera, or families): one occurring during the Kazanian-Midian (end-Guadalupian) and the other at the Changhsingian. The end-Guadalupian extinction is most pronounced in the Gondwanan and Boreal Realms and less well expressed in the Palaeo-equatorial Realm. On a regional scale, the end-Guadalupian extinction appears to have lasted through the whole Kazanian-Midian interval. The Changhsingian extinction is recorded only in the Palaeo-equatorial and Gondwanan Realms. This event appears to be much more severe than the end-Guadalupian extinction and also lasted a much shorter duration than the latter event. The two major extinction episodes were coupled with low originations. Comparatively high originations occurred in the Sterlitamakian-Aktastinian (middle Early Permian) and Wuchiapingian (early Late Permian). It was also revealed that there appears to be a positive correlation between provinciality and species and generic diversity, but not direct, consistent correlation between Permian palaeolatitude and brachiopod species diversity in the Asian-western Pacific region. Discussion on the causes of Permian extinctions was not intended. However, we found that there is a good correlation in timing between the end-Guadalupian extinction and at least a regional (Asian-western Pacific wise) regression. The relationship between eustatic motion and the Changhsingian extinction is far less clear. Although an end-Changhsingian transgression appears evident in view of our field observations of several sections in South China, the exact timing of this event in relation to the timing of the Changhsingian extinction requires further study.