Global brachiopod palaeobiogeographical evolution from Changhsingian (Late Permian) to Rhaetian (Late Triassic)

Recognized as the mother of mass extinctions in earth history, the end-Permian mass extinction is said to have wiped out > 90% marine species and permanently altered the trajectory of macroevolution of the marine evolutionary fauna (Sepkoski, 1984, Erwin, 1994). Brachiopods were among the most affected marine invertebrate groups by this event and consequently lost their long-held dominance role in the Palaeozoic marine ecosystems to mollusks in the ensuing Mesozoic and Cenozoic eras (Sepkoski, 1984, Payne et al., 2014). Many papers have been published on the regional and global diversity patterns of brachiopods across the Palaeozoic–Mesozoic transition and during the subsequent survival, recovery and radiation (Shen and Shi, 1996, Shen and Shi, 2002, Rong and Shen, 2002, Chen et al., 2005, Chen et al., 2006, Chen et al., 2015, Shen et al., 2006a, Shen et al., 2006b, Powers and Bottjer, 2009, Ruban, 2010, Ruban, 2012). From these researches, it has been well documented that four major brachiopod orders (Productida, Spiriferida, Orthida, Orthotetida) became extinct near the Permian–Triassic boundary; while four other orders (Terebratulida, Rhynchonellida, Athyridida, Spiriferinida) as well as some Linguliformea survived the extinction (Shen and Shi, 1996, Chen et al., 2005, Shen et al., 2006a, Shen et al., 2006b). Following this mass extinction, not only brachiopod species diversity remained low (Rong and Shen, 2002, Shen et al., 2006a, Shen et al., 2006b), their average body size was also significantly reduced (Peng et al., 2007, He et al., 2014a).

The Permian Period is well known for its pronounced global marine provincialism in general, as well as for its dynamic changes through the Permian. Among the key factors that contributed to this high level of global provincialism, both geographic barriers and a strong latitude-related thermal gradient are known to have played a crucial role (Waterhouse and Bonham-Carter, 1975, Shi and Grunt, 2000). In general, three Permian marine biogeographical realms (Boreal, Palaeoequatorial/Tethyan and Gondwanan realms) are recognized and these three realms in turn have been subdivided into provinces (Waterhouse and Bonham-Carter, 1975, Shi et al., 1995, Shen and Shi, 2000, Shen and Shi, 2004, Shen et al., 2000a, Shen et al., 2009, Shen et al., 2013b, Shi and Grunt, 2000, Shi and Shen, 2000, Angiolini, 2001, Angiolini et al., 2013, Wang et al., 2014) leading to a general perception of a high γ diversity for the Permian global marine ecosystem.

By comparison with the Permian, data and knowledge on Triassic global marine biogeography are still very scanty, notwithstanding some excellent earlier papers published (Valentine and Moores, 1973, Stevens, 1980, Ager and Sun, 1988, Dagys, 1993, Ehiro, 1997). To the best of our knowledge, detailed Triassic stage-by-stage brachiopod biogeography is lacking. In particular, relatively less research has been undertaken to examine the secular variation of global brachiopod biogeography across the Permian–Triassic transition. To this end, for example, we do not know if (and how) the high level γ diversity observed for the Permian might have been impacted upon by the end-Permian extinction, and how the global brachiopod provincialism evolved in the Triassic. Though Shen et al. (2000a) carried out a study of Changhsingian global brachiopod biogeography, they did not comment on patterns and features of brachiopod provincialism beyond the Permian. Also, the primary data used in their study now requires updating as numerous significant new taxonomic data have been published since 2000 (e.g., the monographic work by Shen et al., 2000b, Shen et al., 2001, Shen et al., 2003, Shen and Shi, 2007, He et al., 2014b, Angiolini and Carabelli, 2010, Angiolini et al., 2015, Gaetani and Mantovani, 2015). As for the Triassic, the most significant recent analyses of brachiopod biogeography were works by Chen et al. (2005) and Chen et al. (2015), but they were most concerned on the aspects of Early and Middle Triassic brachiopod faunas especially aspects in relation to their survival strategies and recovery processes. Additionally, much of the discussion in these two papers was focused on regional datasets and qualitative comparisons. Different to any previous work, the present paper is designed to undertake a systematic, stage-by-stage quantitative analysis of the global brachiopod biogeography from the latest Permian Changhsingian to the latest Triassic Rhaetian, thus covering not only the end-Permian mass extinction interval, but also its ensuing episodes of survival, recovery and radiation. As such, this study should provide some useful insights into the dynamic processes between brachiopod mass extinction, survival and recovery, and their global provincialism.