Encrustation patterns on Late Cretaceous (Turonian) echinoids from southern Poland

Abstract

This study focuses on sclerobionts from a large collection of epibenthic echinoids ([2,000 specimens) of the genera Conulus and Camerogalerus. Samples were collected from five localities in southern Poland (Polish Jura and Miecho´w Trough), where Turonian carbonates with terrigenous input are exposed. Low intensity (mean ca. 5 %, maximum ca. 10 %) and slight encrustation (‘‘loosening effect’’) exclusively by episkeletozoans probably resulted from low productivity of encrusters while the importance of other factors cannot be excluded unambiguously. Echinoids served as a main substratum and after death formed shellgrounds (‘echinoid carpet’) offering abundant benthic islands for encrusters in an otherwise soft-bottom environment. The moderate abundance but low-diversity assemblage is represented by bivalves, sedentary polychaetes, foraminifera, bryozoans, corals, and sponges. This assemblage is similar to a nearly contemporaneous assemblage from the Bohemian Basin. The presence of numerous spirorbins offers insights into their early evolution and may indicate that their first peak in abundance after origination was not prior to the earliest Turonian. This is regarded as one of the important ecological steps towards the rise of modern sclerobiont communities. Encruster diversities are independent of their abundance and, as shown in our novel planar projections, lateral parts of tests were preferentially encrusted. This pattern is explained by the combination of largest flat area and stable orientation. Encrusting bivalves and serpulids dominated hard substrate environments in the Turonian of Poland.