Mallomonas skogstadii sp. nov. and M. bakeri sp. nov.: Two New Fossil Species from the Middle Eocene Representing Extinct Members of the Section Heterospinae?

Abstract Two new fossil species of the synurophyte genus Mallomonas, M. skogstadii and M. bakeri, are described from Giraffe Pipe, an Eocene locality situated near the Arctic Circle in northern Canada. Scales of both new species share a suite of characters, including an oval-shaped rib encircling approximately half of the base plate and most of the dome, a series of thick ribs on the posterior flange, but lacking on the shield, a thin posterior rim, and a flat and shallow dome. In addition, both species possess two types of scales, body scales and apical scales. Apical scales of M. bakeri form a unique forward–projecting dome, and those of M. skogstadii are significantly different in shape than the body scales. Scales of M. skogstadii are significantly larger and have a different base plate pore pattern than those of M. bakeri, and remains of both taxa were uncovered in strata deposited hundreds of years apart. Based on comparison made with modern species, M. bakeri, and to a lesser extent M. skogstadii, are placed into, and likely represent basal representatives of section Heterospinae. The floras associated with each species reflect acidic environments, probably high in dissolved humic content.