Species of Inversiulidae Vigneaux, 1949 (Bryozoa: Cheilostomatida) in the early Miocene of Patagonia (Argentina), with a phylogenetic and palaeobiogeographical analysis of the family

Abstract

The family Inversiulidae, and its only genus Inversiula, are unique among cheilostome bryozoans owing to the reverse orientation of the operculum, which hinges distally instead of proximally. Inversiula currently includes four extant and one fossil species almost exclusively distributed in the Southern Hemisphere. A phylogenetic analysis of the Inversiulidae based on morphological characters was performed, showing the existence of two clades with contrasting development of the frontal shield. As a result of this analysis, Parainversiula gen. nov. is erected to contain inversiulid species with an umbonuloid frontal shield structure and fewer than 30 central spoked pores. Two poorly known fossil species from the early Miocene of Patagonia (Argentina), originally assigned to the genus Microporella, are here redescribed as Parainversiula sp. and P. chubutiana (Canu) comb. nov. The historical, time-calibrated biogeography of Inversiulidae was estimated using an event-based, multi-model quantitative analysis. The analyses estimated that Australasia was the ancestral area of Parainversiula and a dispersion of the genus into South America occurred between the late Eocene and Oligocene (c. 23–42 Ma), an event that could have been helped by the origin of the AntarcticCircumpolar Current.