Late Ordovician and early Silurian Trimerellide brachiopods from Kazakhstan

Abstract

All previously known late Ordovician and Silurian trimerellides of Kazakhstan are reviewed and reillustrated, together with some recently discovered taxa, including the late Caradoc-Ashgill Palaeotrimerella medojevi new species from the Chu-Ili Range, the late middle Ashgill Gasconsia cf. worsleyi Hanken and Harper, and Silurian Dinobolus cf. hubeiensis Rong and Yang, both from Central Kazakhstan. Kazakhstanian terranes appear to contain the oldest-known trimerellide faunas from late Llandeilo to early Caradoc. The observed geographic distribution of Ordovician trimerellides may be explained as the result of two major migrations from the Kazakhstanian terranes: 1) during the early Caradoc, to Gondwana and North America; 2) during the late Caradoc, to Baltica and Angaria. All local trimerellide lineages in Kazakhstan became extinct just before the Hirnantian, and were replaced in the Llandovery by new forms, probably of Chinese origin.