Ovulate Cones of Schizolepidopsis ediae sp. nov. Provide Insights into the Evolution of Pinaceae

Abstract

Premise of research. The extinct conifer genus Schizolepidopsis is characterized by deeply bilobed ovuliferous scales bearing two adaxial seeds. Although it is frequently placed in Pinaceae, the evidence for a close relationship with the family is mixed. Resolving the affinities of Schizolepidopsis has important implications for the age of Pinaceae because putative reports of the genus extend into the Late Permian. We describe a new species, Schizolepidopsis ediae sp. nov., based on specimens from the Lower Cretaceous of Mongolia and Inner Mongolia, China, that represent the first anatomically preserved occurrences of Schizolepidopsis. Methodology. Specimens were studied using light microscopy, cellulose acetate peels, and X-ray micro–computed tomography. To test relationships between Schizolepidopsis and Pinaceae, we performed conifer-wide phylogenetic analyses that included 10 previously described fossil conifers using DNA sequence data and a new morphological matrix of ovulate reproductive characters. Analyses were performed using Bayesian total evidence and parsimony backbone approaches. Pivotal results. Schizolepidopsis ediae possesses key characters of Pinaceae, including those related to pollination biology. Most analyses placed S. ediae in crown group Pinaceae (abietoid clade), with all other Schizolepidopsis species forming a grade along the Pinaceae stem. Uncertainty in the data indicates that stem group affinities of S. ediae are also possible. Conclusions. Schizolepidopsis ediae provides the first conclusive evidence linking Schizolepidopsis with extant Pinaceae. The phylogenetic relationships between extant Pinaceae and Schizolepidopsis suggest that seed wings evolved along the Pinaceae stem and not with the crown group and that, in combination with developmental genetic evidence, the simple ovuliferous scales of Pinaceae likely evolved from bilobed ovuliferous scales like those of Schizolepidopsis. More broadly, this study provides evidence of a Mesozoic Pinaceae stem group that might extend into the Paleozoic, helping to reconcile the ancient stem divergence of Pinaceae with its relatively recent crown age.