A new anatomically-preserved plant from the lower Devonian of Quebec (Canada): implications for Euphyllophyte phylogeny and early evolution of structural complexity
An abrupt transition in the fossil record between Early Devonian plants with simple structure and structurally-complex later Devonian plants, has frustrated efforts to understand patterns of phylogeny across the Early/Middle Devonian boundary and the evolution of complex forms. Both these aspects have important implications for lignophyte and seed plant evolution. In the first chapter, I evaluate phylogenetic relationships between the earliest seed plants, Aneurophytales, and Stenokoleales, using comprehensive taxon sampling (28 species, including all relevant permineralized species) and a set of 40 discrete and nine continuous morpho-anatomical characters. Analysis of this dataset supports the three traditional taxonomic groups (seed plants, Aneurophytales, and Stenokoleales) and place Stenokoleales among the lignophytes. In the second chapter, I characterize a new fossil plant from the Lower Devonian of Gaspé (Canada), Kenricrana bivena gen. et sp. nov., and I integrate it in the phylogenetic matrix developed in the first chapter. Kenricrana shares features with the progymnosperms, Stenokoleales, and early seed plants. Inclusion of Kenricrana introduces stability in the phylogenetic relationships among these groups. Kenricrana is recovered as sister to the rest of the ingroup and Stenokoleales as paraphyletic to a lignophyte clade wherein aneurophytes and seed plants fall into sister clades. These results shed light on early euphyllophyte relationships and evolution, indicating early exploration of structural complexity by multiple euphyllophyte lineages and raising the possibility of a single origin of secondary growth in euphyllophytes
