Life habit, feeding mechanism and population structure of the Cretaceous brachiopod genus Aemula

Abstract

Comparison with close Recent relatives, studies of functional morphology and the discovery of specimens preserved in life position indicate with a high degree of certainty the mode of life of the Cretaceous brachiopod genus Aemula. This genus is an important member of the brachiopod communities of the north European Maastrichtian. In resting position Aemula lived with its dorsal valve pressed against the substrate. When feeding the shell was somewhat elevated anteriorly and the two valves gaped at an angle of about 45°. Preserved calcitic mesodermal spicular skeletons show that the adult lophophore was a schizolophe. During the younger stages only one inhalant feeding current flowed into the bell-shaped trocholophe and early schizolophe, whereas the exhalant current flowed out in all directions between the filaments. In the later stages when the schizolophe was fully developed the current system was divided into two lateral inhalant and one median exhalant current. The species Aemula inusitata has been investigated with regard to size frequency and survivorship revealing an initially very high, but slightly decreasing mortality rate corresponding to the dangerous life on small substrates close to the sediment—water interface of the muddy-chalk sea bottom. The species of Aemula never dominate the brachiopod assemblages of the Maastrichtian chalk but is found in almost all samples in small but rather constant numbers.