Mallomonas elephantus sp. nov. (Synurophyceae), an Extinct Fossil Lineage Bearing Unique Scales from the Eocene
Siver, Peter A.; Wolfe, Alexander P.
A new fossil species of Mallomonas, M. elephantus sp. nov., is described from an Eocene maar lake situated near the Arctic Circle in northern Canada. The new species has three distinctly different types of scales, craspedodont bristles, and is believed to represent a stem taxon of the section Planae. Body scales are large, oval to square-shaped, with a shallow U-shaped transverse rib centrally positioned on the base plate, large rimmed pores at the base of the posterior rim, and large widely-spaced papillae. The anterior margin of a second, and smaller, scale type bends sharply 90° to the right forming a unique type of extension and resulting in a highly asymmetrical shape. The size of the asymmetric scales is highly variable, and this scale type likely covered the posterior end of the cell. The third scale type has a triangular-shape caused by a short projecting spine. The variation in size of the triangular scales is small and these scales are believed to have formed a ring around the flagellar pore. Bristles are long with smooth, rolled shafts, and a broad flat foot. The surface area of body scales is about three times the size of the mean for modern species, supporting the hypothesis that many extinct synurophyte species had gigantic scales. Based on a model relating scale length to cell length, the size of M. elephantus cells is estimated to have been twice as large as the mean for modern species.