Abstract Detail

Paleobotany

Raymond, Anne [1], Costanza, Suzanne [2].

One Cone, Two Genders: A bisexual cordaitean from the Late Pennsylvanian of Iowa.

Extinct cordaitean gymnosperms produced compound cones in which the primary axis bore secondary fertile shoots. Like their sister group, conifers, most cordaiteans had unisexual cones. However, a new cordaitean cone from the Late Pennsylvanian of Iowa has bisexual secondary fertile shoots organized like angiosperm flowers, with basal sterile scales, intermediate male scales bearing pollen sacs, and an upper female scale bearing a single, basally attached seed. Unlike angiosperm flowers, the new bisexual cordaitean cone has an extra set of sterile scales, inserted between the male scales and the apical female scale. The new cone comes from the Kalo Formation (Pennsylvanian) of Iowa. Five specimens have attached seeds, identified as Nucellangium based on features of the integument. Like angiosperm flowers, the new cone matured from base to tip (pollen first, seed last), so that specimens with mature seeds generally lack intact, filled pollen sacs. We interpret cones with attached seeds as bisexual due to the extraordinary amount of cordaitean pollen between the intermediate cone scales, the presence of male scales with developing pollen sacs, and male scales bearing fragmented pollen sacs that contain cordaitean pollen. In developing cones, the upper sterile scales have abundant trichomes and closely surround the developing seed; these scales may have protected immature ovules from self-pollination. The discovery of a cordaitean with bisexual secondary fertile shoots supports molecular phylogenies linking gnetaleans and conifers, and suggests that the common ancestor of gnetaleans and cordaiteans may have had compound cones with bisexual secondary fertile shoots. The basal sterile, intermediate male, apical female organization of the new bisexual cordaitean cone echoes the organization of angiosperm flowers, controlled by interactions of A-, B-, C- and E-family genes. No angiosperm flowers have a set of ‘upper’ sterile scales inserted between stamens and carpel; and in angiosperms, sterile organs do not form after down-regulation of A-family genes caused by the expression of C-family genes. However, the gnetalean genus, Gnetum, has basal sterile scales that express orthologues of C- and D-family genes (GGM-3), suggesting that these are not like angiosperm petals or sepals, which we would expect to express B- or A-family genes. Perhaps orthologues of C-family genes also controlled the development of the upper sterile scales in the new bisexual cordaitean cone. If so, this cone provides direct evidence of A-, B-, C- and E-family genes and of ABCE reproductive patterning in the Late Pennsylvanian.

1 - Texas A & M University, Dept. of Geology and Geophysics, College Station, Texas, 77843, United States
2 - Harvard Botanical Museum, 26 Oxford Ave, Cambridge, MA, 02138, United States

Keywords:
bisexual Cordaitean cone
Late Pennsylvanian
gnetalean
phylogeny
evolution.

Presentation Type: Oral Paper
Session: 17, Paleozoic and Mesozoic paleobotany
Location: Sundance 3/Omni Hotel
Date: Tuesday, June 27th, 2017
Time: 8:15 AM
Number: 17002
Abstract ID:202
Candidate for Awards:None