Ecophenotypic variations of Encrinus liliiformis (Echinodermata: Crinoidea) from the middle Triassic Muschelkalk of Southwest Germany

Abstract

Encrinus liliiformis is a well known crinoid from the middle Triassic Muschelkalk of Europe. A statistical analysis of crown shape was conducted in order to quantify possible differences in crown morphology of E.liliiformis originating from three localities in Southwest Germany (Upper Muschelkalk). These differences basically refer to the length of the brachia and ornamentation patterns on the aboral surfaces of the brachials. The populations originate from different environments: Crailsheim, reflecting a shallow water habitat on a carbonate ramp; Neckarwestheim and Mistlau, originating from a deeper basinal environment. The analysis led to a distinction of two ecophenotypes adapted to the varying habitats: (1) an ecophenotype originating in shallow water showing shorter brachia with less ornamented surfaces of brachials; this type is represented by the Crailsheim population; (2) an ecophenotype originating in a deeper water environment showing longer brachia and a higher degree of ornamentation on brachial surfaces, as represented by the Neckarwestheim population. The crinoids from the Mistlau locality take up an intermediate position in morphology, but the low number of specimens does not allow for statistically significant comparisons. Interpretations of these differences in crown morphology are made with respect to reactions to predatory pressure as well as to variations in water flow energy which is of prime importance for obtaining food resources for these filter feeding animals.