Gniazdowe akumulacje szczątków fauny w środkowojurajskich iłach rudonooenych Wyżyny Krakowsko-Częstochowskiej—wnioski paleobiologiczne
Abstract
Nest-like accumulations of faunal remains in the Middle Jurassic ore-bearing clays of the Kraków-Częstochowa Upland and their palaeobiological implications.
S u m m a r y . Distinct faunal accumulations in the uppermost Bajocian/lowermost Bathonian, lowermost and Middle Bathonian of the Polish Jura (south-central Poland) have been detected. The fossils are densely packed in the centre of the accumulations and more or less dispersed in their margins. The accumulations vary in size, but all are rich in various groups of organisms, of which the molluscs (mainly bivalves) and echinoderms predominate. The echinoderms are all disarticulated, and shelly fauna occur as angular fragments with sharp edges, of random sizes and without any signs of abrasion. The different sizes of the fossil remains, from tiny echinoderm ossicles or juvenile shelly fauna to medium-sized shell fragments or belemnite rostra, exclude any transportation and thus sorting. Worth of noting is the occurrence of similar faunal groups in each accumulation. The general shape and composition of the accumulations, as well as their taphonomical features, especially the angularity of shell fragments, point to durophagous (shell-crushing) predation rather than physical processes. The various organisms may indicate that the potential predator (most probably fish) fed on various invertebrates. The indigestible particles were later regurgitated forming the accumulations discussed. The presence of various epibionts on the fossil fragments indicate,that
they rested upon the sea-floor for some time-span after they had been regurgitated. Then the scavengers, as well as current action or water movements, have been responsible for dispersion of some of the fossils, as is well-visible at the margins of the investigated accumulations..
S u m m a r y . Distinct faunal accumulations in the uppermost Bajocian/lowermost Bathonian, lowermost and Middle Bathonian of the Polish Jura (south-central Poland) have been detected. The fossils are densely packed in the centre of the accumulations and more or less dispersed in their margins. The accumulations vary in size, but all are rich in various groups of organisms, of which the molluscs (mainly bivalves) and echinoderms predominate. The echinoderms are all disarticulated, and shelly fauna occur as angular fragments with sharp edges, of random sizes and without any signs of abrasion. The different sizes of the fossil remains, from tiny echinoderm ossicles or juvenile shelly fauna to medium-sized shell fragments or belemnite rostra, exclude any transportation and thus sorting. Worth of noting is the occurrence of similar faunal groups in each accumulation. The general shape and composition of the accumulations, as well as their taphonomical features, especially the angularity of shell fragments, point to durophagous (shell-crushing) predation rather than physical processes. The various organisms may indicate that the potential predator (most probably fish) fed on various invertebrates. The indigestible particles were later regurgitated forming the accumulations discussed. The presence of various epibionts on the fossil fragments indicate,that
they rested upon the sea-floor for some time-span after they had been regurgitated. Then the scavengers, as well as current action or water movements, have been responsible for dispersion of some of the fossils, as is well-visible at the margins of the investigated accumulations..