Evidence of Predation on Early Pleistocene Freshwater Ostracods (Umbria, Central Italy)

Angela Baldanza,Francesco Posati,Manuel Ravoni,Roberto Bizzarri

doi:10.3390/geosciences10100416

Abstract

Although drillholes in modern and ancient ostracods are known, the record is relatively scarce when compared to other taxa, and mainly exist with reference to the marine environment. Moreover, less is known about perforated ostracods, and more generally, about bioerosion in freshwater environments. Traces of predation on freshwater ostracods are reported for the first time in deep-lake deposits belonging to the early Pleistocene Fosso Bianco Unit, and outcropping in the Cava Nuova section (Umbria, central Italy). Deposits are mainly clay to silty clay and sand; the fossil record is sparse, and is mainly comprised of very rare gastropods and bivalves, ostracods and plant remains (leaves, seeds and wood’s fragments). The association of ostracods consists of Candona (Neglecandona) neglecta, Caspiocypris basilicii, Caspiocypris tiberina, Caspiocypris perusia, Caspiocypris tuderis, Caspiocypris posteroacuta, and Cyprideis torosa. The Caspiocypris group, considered to be endemic to the grey clays of the Fosso Bianco Unit, present the majority of specimens affected by predation, with a prevalence of predated female valves and a comparable number of right and left predated valves, while only a few of Candona(N.) neglecta (adult and juvenile) valves are perforated. Traces of predation for nourishment, represented by microborings of different types, were abscribed to the ichnospecies Oichnus paraboloides Bromley 1981, Oichnus simplex Bromley 1981, Oichnus gradatus Nielsen and Nielsen 2001, Oichnus ovalis Bromley 1993, and Dipatulichnus rotundus Nielsen and Nielsen 2001. Microboring affected both adult and juvenile specimens, evidencing prey–predator coexistence in the same environment over a long period of time. This report makes a fundamental contribution to the knowledge of predation in this peculiar confined environment, also suggesting prey–predator relations over a relatively short time interval (80–160 ka).

Highlights

The term “bioerosion” was coined by Neumann [1] as an abbreviation of “biological erosion” and describes every form of biologic penetration into hard substrates, i.e., lithic and woody
The new data about valve bioerosion have allowed broadening the knowledge of the microboring phenomenon in freshwater ostracods, and in particular to define: (1) the frequency of predated valves and the palaeoenvironmental conditions under which predators developed, (2) the type of valves predated and in some cases the sex of the specimens, (3) the types of predation, (4) attribution to ichnospecies, and (5) the dimensional difference with microboring ichnotaxa known from the literature
The ostracods affected by predation and intense microboring represent a very interesting population of confined taxa that carried out their whole life cycle on a relatively deep lake floor with low availability of CaCO3 and low environmental energy

Summary

Introduction

The term “bioerosion” was coined by Neumann [1] as an abbreviation of “biological erosion” and describes every form of biologic penetration into hard substrates, i.e., lithic (including skeletal) and woody. An extremely wide range of organisms cause bioerosion, and the work of these organisms produces trace fossils at all scales, from microscopic to gigantic [2]. Reconsidered this definition, adding “the process by which animals, plants and microbes sculpt or penetrate surfaces of hard substrate”. The term “microboring” refers to a trace left by another body or a mechanical abrasion trace, generally acting on mineralized shells. “perforation” indicates a phenomenon of interaction between organisms, or between organism and substrate. The most common drilling structures or anchors found in fossils or recent skeletal remains are “small depressions or holes of variable shape

Methods

Results

Discussion

Conclusion