Original paper

Frequentispirifer, a new spiriferid genus and its phylogenetic position within the Delthyridoidea (Brachiopoda, Lower Devonian)

Schemm-Gregory, Mena

Abstract

Frequentispirifer gen. nov. (Spiriferida, Brachiopoda) from the Upper Emsian of the Rudny Altai (southwestern Siberia, Russia) is erected. Representatives of Frequentispirifer have hitherto been considered as taxa of Undispirifer or Acrospirifer from which they differ in various characters, e.g., from Undispirifer in a larger width of hinge line and from Acrospirifer in the lack of a median plication in the sulcus. Biometric analyses show a linear growth of length and width both of the shell and of the ventral muscle field during its ontogeny. Morphological comparisons with other Acrospirifer-like genera proof the identification of the new genus and its relations to the South Chinese Rostrospirifer group. The present study suggests a phylogenetic position of the new genus close to Intermedites and Otospirifer. An attempt at a new phylogeny for the South Chinese delthyridoid spiriferids is made including the European/North African genus Intermedites that is now regarded as a descendant of South Chinese brachiopods, the Rostrospirifer group, with which it shares the lack of a notothyrial shelf, the development of crural plates, and pronounced deltidial lamellae and that differ markedly from the Rhenish European/North African delthyridoid spiriferids to which it has hitherto been assigned. It is concluded that ancestors of Intermedites migrated during Late Emsian and Early Eifelian times from South China to Europe and North Africa. The occurrence of Xenospirifer in South China and Siberia, as well as the close phylogenetic relationship between Intermedites and Frequentispirifer, show the beginnings of the global faunal exchange of marine organisms in the Late Emsian that follows the provincialism that characterises Early Devonian time.

Keywords

frequentispiriferspiriferidabrachiopodaphylogenypalaeobiogeographysiberiasouth chinadevonian