Morphology and paleoecology of Ricciopsis speirsae sp.nov. (Ricciaceae), a fossil liverwort from the Paleocene Joffre Bridge locality, Alberta, Canada

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Abstract
More than 60 specimens of a fossil liverwort gametophyte have been recovered from the Paleocene Paskapoo Formation at the Joffre Bridge locality near Red Deer, Alta. They closely resemble thalli of extant Riccia and have been assigned to the genus Ricciopsis Lundblad. Thalli are linear and prostrate, with smooth margins and a distinct dorsal sulcus. Dichotomous branching occurs in a single plane. Ribbonlike segments reach lengths as great as 55.0 mm, with up to seven dichotomies. Width is typically 1.5–2.0 mm, but abrupt constrictions and dilations are sometimes present proximal to dichotomies. The latter feature distinguishes this fossil from known fossil and living Ricciaceae, and thus it is referred to a new species, Ricciopsis speirsae sp.nov. Liverworts are not common in the fossil record. Ricciopsis speirsae is the first ricciaceous fossil to be described from North America and the first of Paleocene age worldwide. The specimens are found in a layer of lacustrine claystone, scattered among remains of a free-floating lemnaceous plant. Both the geologic setting and the associated fossils indicate that the environment of deposition was a shallow oxbow lake. Key words: Ricciaceae, Riccia, Ricciopsis, liverwort, Paleocene, fossil.