Correa, Julian Eduardo (2015-08). Morphological Cladistic Analysis of the Cordaitean Cones and Implications for Plant Lineages. Master's Thesis.
Thesis
The cordaiteans were a group of Carboniferous and Permian woody plants, which thrived in wetlands and thrived in wetlands and terra firma habitats. Cordaitean cones from wetland habitats are exquisitely well preserved and contain a suit of characters that make their fossils prime candidates for cladistic analysis; historically, there are more male cones than female cone. Cordaitean morphological characteristics make this clade a possible precursor lineage of modern conifer and gnetalean lineages. However, the exact relation between fossil seed-plant clades and modern gymnosperm groups remains enigmatic. The resent discovery of a bisexual cordaitean cone calls into question the relationship between cordaiteans, gnetaleans and angiosperms. This study performs three cladistics analyses in order to find the relations of taxa within the cordaitean clade and other early plant lineages using primarily PAUP* and TNT. An analysis of male only cones provides a phylogram for the relations between the corditean taxa; the results also suggest a bisexual ancestry for the clade. A second analysis attempted to introduce the morphologically distinct female cones; the results produce a similar strict consensus tree. However, many of the female cones do not pair with their associated male cones indentified in 'whole-plant' reconstructions of cordaitean lineages. Instead, female cones formed separate linages. A final analysis incorporated other plant lineages and assigned traits associated with seeds and pollen to both male and female cones. The results support an early bisexual ancestry to the cordaiteans, and suggests that the cordaiteans are a polyphylecit clade, which gave rise to the voltzialean-conifer lineage. Including more fossil taxa lineages may prove useful, as well as establishing other criteria to compare characters to taxa in cladistics analysis.
