Eco-taphonomy of mass-aggregated giant balanids Concavus (Concavus) concavus (DARWIN, 1854) from the Lower Pliocene (Zanclean) of Rafina near Pikermi (Attica, Greece)

Abstract

The large- to giant-sized balanids, mass-aggregated in a tempestite of the Lower Pliocene (Zanclean) section at Rafina near Pikermi,Greece, represent a single species, Concavus (Concavus) concavus (DARWIN, 1854) [non BRONN, 1831], the taxonomy of which is revised. The peculiarly shaped forms ‘raphanoides’ and ‘scutorum’ are ecophenotypes of this species; the same applies to the ‘tulipiformis’ specimens reported previously fromthis section.Discussed are dynamic events controlling the life and death conditions in the nearshore (offshore) environment of Rafina, where the giant specimens of Concavus (Concavus) concavus (DARWIN, 1854) flourished through several successive generations. As opportunistic species they adopted the r-selection reproduction strategy in order to dominate over other biota. The intermittent action of high-energy agents was responsible for the production of balanid-shell hash that involved taphonomic feedback. This enabled further colonization of the biotope and the growth of multiphased (bouquet-like and pyramidal) clusters. The demise of the monospecific balanid communities is ascribed to a heavy storm which stirred-up the whole balanid-bearing sequence, to produce a proximal tempestite. This final burial and subsequent depositional lull in the Rafina environment was favoured by a temporary deepening of the whole Lower Pliocene (Zanclean) basin beyond the bathymetric range in which the balanid population could survive.