Taphonomic aspects and the Lilliput Effect on Devonian discinoids of the Paraná Basin, Apucarana Sub-basin, Brazil

Abstract

Discinoids are exclusively marine, epibenthic, inarticulate brachiopods, which use their pedicle to attach to the substrate. The global stratigraphic range of the genera range from the ?Ordovician to Holocene, but the Devonian period was the climax of this group. They have a broad geographical distribution and, in Brazil, are found in the Paraná, Amazonas, Parnaíba and Parecis basins. The discinoids from the Paraná Basin are found in the Ponta Grossa and São Domingos formations. Three genera of discinoids are recorded in the Brazilian Devonian strata, Orbiculoidea, Gigadiscina and Rugadiscina. Five species are recognized in the Paraná basin (Orbiculoidea baini, Orbiculoidea bodenbenderi, Orbiculoidea excentrica, Gigadiscina collis and Rugadiscina sp.). As far the taphonomy is concerned, the discinoids can be found isolated or in clusters, as complete and articulated valves, or as complete and disarticulated valves and/or fragmented valves, and constitute assemblages of shoreface and offshore settings. The analysis presented herein establishes the stratigraphic range of the Discinidae family between the late Pragian and the early Givetian. Orbiculoidea baini and Orbiculoidea excentrica showed phenotypes with reduced size attributed to the Lilliput Effect. This effect resulted of a biotic crisis recorded shortly before the collapse of Malvinokaffric fauna that caused a global extinction, the Ka?ák Event, in the Eifelian-Givetian transition.

Keywords: Discinoids, Lilliput Effect, Devonian, Ka?ák Event, Taphonomy.