New perspectives on the structure and evolution of the early Mesozoic conifers

A relatively poor understanding of the early Mesozoic conifers has limited our overall knowledge of conifer evolution, because the group was undergoing a major radiation at that time. This dissertation attempts to fill some of the gaps in the early Mesozoic fossil record based on reconsiderations of several key taxa and descriptions of new forms. It is determined that Fraxinopsis is an anthophyte of uncertain affinities rather than a conifer as previously described. A reconsideration of the Triassic conifer Glyptolepis, which has played a prominent role in concepts of conifer phylogeny, indicates that previous interpretations of this genus were based on inaccurate reconstructions of unrelated conifers. A conifer from the Triassic of Pennsylvania is described as a new species of the otherwise Permian family Majonicaceae. Based on this material, a revised concept of conifer cone scale morphology is presented. Another new species (Conewagia longiloba) from the same locality fills a morphological gap in the conifer record by demonstrating that some early Mesozoic forms possessed a greater number of fertile dwarf-shoot foliar components than previously realized. Anatomically preserved leaves of the podocarp Notophytum krauselii are described from the Triassic of Antarctica, and are shown to be similar to the common Gondwanan leaf compression fossil Heidiphyllum elongatum. New association and cuticular evidence are presented in support of the hypothesis that Heidiphyllum leaves and Telemachus ovulate cones were produced by the same plant. These findings also indicate a close phylogenetic relationship between Telemachus and other Mesozoic conifers with multiveined leaves, including Aethophyllum, Cycadocarpidium, and Swedenborgia. A new species of the family Cheirolepidiaceae is described from the Jurassic of Connecticut based on specimens of branching systems with attached ovuliferous cones, and associated male cones with in situ Classopollis pollen. The cone scale morphology is primitive and supports the hypothesis of a close phylogenetic relationship between the Cheirolepidiaceae and Majonicaceae. Finally, a phylogenetic analysis of the conifers based on morphological features of the ovulate cones, pollen cones, and leaves is presented in support of the hypotheses of relationship and homology presented here.