A farewell to Świniary sequence of mass-aggregated, spine-coated echinoids Psammechinus and their associates (Middle Miocene; Holy Cross Mountains, Central Poland)

Abstract

The Świniary sand-pit (Middle Miocene; southern slopes of the Holy Cross Mountains, Central Poland), which has yielded innumerable fossils of various kinds over the last fifty years, is revisited. Most significant there were mass accumulation of a single echinoid species, Psammechinus dubius (L. AGASSIZ, 1840), tests of which preserved spine canopies and Aristotle's lanterns in position. Other echinoids represented were rare, e.g. Spatangus austriacus LAUBE, 1871, 'Giant Psammechinus sp.', Echinocardium peroni COTTEAU, 1877, and Echinocyamus pusillus (O.F. M LLER, 1776). The pit has since been abandoned and recultivated entirely; in view of this an updated review of, and supplement to, previous data on the Świniary biotic assemblages, and their environmental living conditions, is here presented. The mass accumulations of Psammechinus dubius are interpreted to have been of storm origin, i.e. mass transportation and burial of live, or freshly dead, specimens.Hinted at is a predatory activity of the starfish Astropecten forbesi HELLER, 1858, upon juveniles of Psammechinus dubius absent from the storm-related thanatocoenoses. Associated with echinoderms are, amongst other groups, verrucid barnacles Verruca sp. and inarticulate brachiopods Discinisca leopolitana (FRIEDBERG, 1921) derived from eulittoral habitats, as well as pieces of terrestrial amber swept out of the shore. A general shallowing-up trend in the Świniary sequence is recognised, as indicated by environmental conditions changing from deeper offshore to proximal sublittoral, possibly shallow subtidal.