A whole-plant specimen of the marine macroalga Pterigophycos from the Eocene of Bolca (Veneto, N-Italy)

Abstract

Uncalcified macroalgae are generally rare as fossils, and hence their past diversity and evolutionary history remain poorly resolved. The Bolca area in northern Italy has yielded abundant adpression fossils of Eocene macroalgae. However, the vast majority of specimens are detached blades and blade portions. Here, we present an almost complete thallus of the macroalga Pterigophycos from Bolca that consists of a squat holdfast from which leaf-like blades up to 30 cm long extend. Each blade has a midrib extending over its entire length. Proximally the lamina forms a narrow rim on each side of the midrib, but becomes wider and lobed in the lower mid-portion. In the upper three quarters of the blade the lamina consists of spathulate or wedge-shaped segments. Pterigophycos blades have certain features in common with the present-day Phycodrys rubens, Delesseria sanguinea (both Ceramiales, Rhodophyta), Undaria pinnatifida, and Egregia menziesii (both Laminariales, Phaeophyceae); however, the systematic affinity of the fossil remains unresolved. The fossil is suggestive of intraspecific variability in blade morphology, and thus contests the historic view that there are several different species of Pterigophycos in the Bolca flora.