Morphologically diverse vase-shaped microfossils from the Russøya Member, Elbobreen Formation, in Spitsbergen

Abstract

Vase-shaped microfossils (VSMs) constitute a distinct group of fossils characteristic of late Tonian marine rocks. They often occur in high densities and in relatively diverse assemblages that include several morphotypes. All VSMs may have shared a test wall of similar structure and composition, as inferred from common patterns of preservation. However, little is known about the detailed morphology and structure of this wall. Here we examine the diversity, preservation, and wall morphology of a diverse assemblage of VSMs from the Russøya Member of the Elbobreen Formation in northeastern Spitsbergen. SEM imaging of exceptionally preserved specimens with their wall replicated in iron oxide reveals that these VSMs shared a well-defined, smooth, micrometre-thick wall ornamented with complex structures including facets, closed “pores”, and intricate relief patterns on the internal surface of the aperture. The observed similarities among different morphotypes suggest VSMs assemblages reflect the diversification of a single clade, likely related to the Arcellinida (Amoebozoa), an extant order to which they have been phylogenetically linked.