The Permian peltasperm radiation: evidence from the southwestem United States

Abstract—The Peltaspermales are a group of pteridosperms or "seed ferns, " plants with fern-Uke, compound leaves (fronds) that also bear seeds. Historically thought to be one of several groups of exclusively Mesozoic seed-ferns, the peltasperms have proven more recently to be widespread and abundant in the Permian tropics, appearing at least as early as latest Carboniferous. The group includes a number of genera, most of which occur in the southwestern United States, which is the focus of this report. The ancestral subgroup appears to be the callipterids, represented by the genera Autunia and Rhachiphyllum. Derived foliage taxa include the comioids (Comia and an undescribed genus), the supaioids (Supaia, Glenopteris, cf. Brongniartities, and perhaps several undescribed genera; this group is taxonomically "difficult"). Several genera of North American gigantopterids also most likely are assignable to the Peltaspermales (Gigantopteridium, Lonesomia, Evolsonia, Delnortea, and three genera equated with Chinese taxa on the basis of venation but that, in fact, may be distinct, Cathaysiopteris, Zeilleropteris, and Gigantonoclea, and at least one new genus certainly occurring in China where it was described as "Gigantopteridium " marginervum). All of these foliage forms are associated with the reproductive organs Autunia ( = Sandrewia) or Peltaspermum. The abundance and diversity of this group in southwestern North America indicates an extensive and early radiation of the peltasperms, during which they became ecological dominants in the Permian lowland tropics. 6