Quantitative Review of the Systematic Taxonomy, Distribution and Palaeoenvironmental Preferences of Cathaysia and Paryphella(Brachiopoda, Productida)

The Permian brachiopods Paryphella and Cathaysia are very similar in morphology. This brings both the validity of Paryphella, and the taxonomic and evolutionary relationship between Paryphella and Cathaysia, into question. A principal components analysis conducted on Cathaysia and Paryphella showed that they are different genera and that Cathaysia can be distinguished from Paryphella by its more abundant, finer and commonly bifurcated and/or intercalated costellae. Both genera originated in the Roadian, and then Cathaysia diversified steadily from the Wordian into the Changhsingian before it went extinct, whereas Paryphella had a lower species richness than Cathaysia until the Changhsingian, when it diversified quickly. The two genera were commonly found in shallow-water settings in the Permian; however, Paryphella was also widely distributed in deep-water basins in the Changhsingian. The small size and coarse and simple costellae of Paryphella reduced its requirements for oxygen and lowered its metabolism, thereby favouring adaption to harsh environments. Consequently, Paryphella was able to live in varied settings, including oxygen-deficient deep water. It even temporarily survived the Permian–Triassic mass extinction as a dead clade walking, with the Lilliput effect observed. Furthermore, marine deoxygenation and high temperatures played a principal role in driving the biotic crisis of Cathaysia and Paryphella. All species of Cathaysia and Paryphella revised in the present study are discussed, and four new species, Cathaysia plana, C. striata, C. xiaojiangensis and Paryphella yangshanensis, are proposed.