Exceptionally preserved nauplius larvae from the Devonian Windyfield chert, Rhynie, Aberdeenshire, Scotland

Abstract

We examined a large number of exceptionally preserved nauplius larvae from the Early Devonian Windyfield chert, Rhynie, NE Scotland, situated 600 m from the famous Rhynie chert lagerstätte locality. Two of the specimens have already been mentioned briefly in an earlier description of Windyfield material, presumed to belong to anostracan crustaceans. From the 79 specimens at hand image stacks were recorded with up to 302 single images of each specimen using a transmitted light microscope. Subsequently, the stacks were projected to obtain stereo images of each specimen. Morphometric analysis made in order to detect possible growth stages revealed three different clusters. These may represent size classes, but we could not recognize any differences in the number of appendage elements, setae, or similar structures between representatives of the different size classes. The eucrustacean nature of the larvae is confirmed, but the new data do not hint at anostracan affinities. In light of their special appendage morphology, particularly the possession of biramous mandibles, the larvae do not even appear to be eubranchiopods, which have a mandible lacking the outer ramus, the exopod. Possibly the larvae belong to a species, which was derived from below the evolutionary level of Eubranchiopoda, but maxillopod affinities are also possible and equally supported from the morphological data. More precisely the species might be a representative of the thecostracan lineage, but the ephemeral freshwater depositional environment and continental palaeogeography do not support this interpretation given that all living representatives of Thecostraca are marine. © Palaeontological Association August 2012.