| Abstract Detail
Paleobotany Manchester, Steven [1], Doyle, James [2], Hotton, Carol [3], Zhang, Xiaoqing [4], Wing, Scott [5]. New gymnosperm reproductive organs of possible gnetalean affinity from the Upper Jurassic of the Morrison Formation in southern Utah. Calcitic casts and partially permineralized reproductive organs from the Late Jurassic Brushy Basin Member of the Morrison Formation in the Henry Mountains of southern Utah include various cones and seeds yet to be described. Abundant among these remains are unisexual pollen and ovule-bearing organs of possible gnetalean affinity. Despite lack of preserved pollen and limited cellular details, micro-CT scanning has been useful in documenting details of internal and external morphology. The pollen organs, 10-11 mm long, 5.1-8 mm wide, are square in cross section and obovate in lateral view, with a 0.5 mm thick, continuous lateral wall that opens apically exposing eight elongate structures, presumed to be microsporangia or synangia, which are four-lobed in cross section and arise directly from a cup-like “receptacle” in two parallel rows. Associated ovulate organs bear a pair of ovules in a heart shaped envelope 3.5 mm long, 2.6 mm wide, and 2.0 mm thick, arising from a short, thick, quadrangular stalk with four symmetrically placed vascular strands. The ovules are smooth and ellipsoidal with their long axes diverging at ca. 30 degrees. The envelope is composed of two opposite pairs of laterally fused bracts, with 6-8 prominent longitudinal ribs, a subapical flange, and a micropylar channel emerging distally, aligned with each ovule. A pair of longitudinal fissures promotes dehiscence by separation of two valves, leaving the central portion attached to the stalk. These structures bear similarities in symmetry and organization to the axillary ovulate units in cones of extant Ephedra and Welwitschia, but living Gnetales have only one terminal ovule per unit. They also show similarities to Early Cretaceous ephedroid mesofossils with an envelope of four valves but one ovule rather than two. If they are related of Gnetales, the biovulate condition could represent a hypothesized earlier evolutionary stage with axillary fertile short shoots bearing two pairs of bracts and two lateral ovules, as also argued for Protoephedrites from the Early Cretaceous of British Columbia, consistent with molecular and morphological evidence for a coniferophytic origin of Gnetales. This interpretation may remain speculative until information is found on how the structures were borne and what kind of pollen they produced. However, these remains, and the presence of dispersed but rare ephedralean pollen (Ephedripites or Equisetosporites), which occurs throughout the the Morrison Formation, raise the prospect that these sediments may provide clues to the origin and early diversification of Gnetales.
1 - Florida Museum of Natural History, Dickinson Hall, Museum Rd & Newell Dr. Gainesville, Gainesville, FL, 32611, USA
2 - University Of California Davis, DEPT OF EVOL & ECOLOGY, One Shields Avenue, Davis, CA, 95616, United States
3 - National Museum of Natural History, Smithsonian Institution, 10th St. & Constitution Ave. NW, Washington, DC, 20560, USA
4 - , Jiangsu, , China, State Key Laboratory of Palaeobiology and Stratigraphy, Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, Nanjing, Jiangsu, 210008, China
5 - Smithsonian Institution, Dept. Of Paleobiology NHB 121, PO Box 37012, Washington, DC, 20013, United States
Keywords:
Gnetales
reproductive organs
Jurassic
Utah.
Presentation Type: Oral Paper
Session: PAL3, Paleobotany I: Paleozoic and Mesozoic Paleobotany
Location: Virtual/Virtual
Date: Tuesday, July 28th, 2020
Time: 11:00 AM
Number: PAL3005
Abstract ID:750
Candidate for Awards:None |
