Abstract Detail

Paleobotany

Rothwell, Gar W [1], Stockey, Ruth A [1].

Will the real Corystospermales please stand up.

The Corystospermales is a distinctive order of Mesozoic seed ferns that is well represented by both compressed fossils and anatomically preserved remains. Based upon widely distributed ovulate fructificatons (Umkomasia spp.), pollen producing fructifications (Pteruchus spp.), and leaf fossils (Dicroidium spp.), as well as an organismal concept of the “Dicroidium” plant from Antarctica, the order is well characterized and considered to typify many Triassic floras of Gondwana. Wider stratigraphic distribution of the clade in both Northern and Southern Hemisphere biotas also has been proposed on the basis of less diagnostic evidence, including two recent reports of Early Cretaceous ovulate structures from the Northern Hemisphere. These are the anatomically preserved uni-ovulate cupules from Vancouver Island, Canada described as Doylea tetrahedrasperma Stockey & Rothwell and the lignified ovulate bract/scale complexes described as Umkomasia mongolica Shi, Leslie, Herendeen, Herrera, Ichinnorov, Takahashi, Knopf & Crane from Mongolia. The discovery of D. tetrahedrasperma ovules attached to a compact seed cone of compound structure provides evidence that these two Northern Hemisphere taxa are extremely similar to one another, and reveals diagnostic details of the ovulate organs, pollination biology, cupule homologies, post-pollination cupule development, and dispersal biology for the plants they represent. A distinctive combination of concordant characters demonstrates that these two Early Cretaceous, Northern Hemisphere taxa are unlike fossils assignable to the Corystospermales or any other well-known clade of spermatophytes, and that they represent a previously unrecognized order of seed plants. Results of phylogenetic analyses using morphological characters place this clade on the stem of the seed plant tree between the levels where cordaites/conifers and gnetophytes are attached. Careful reevaluations of other Permian-Cretaceous corystosperm fossils are required to determine whether the order is restricted to the Triassic of Gondwana, or if it has much broader stratigraphic and geographic distributions. The latter data also will help clarify possible sister group relationships of Corystospermales to flowering plants.

1 - Oregon State University, Botany and Plant Pathology, 2082 Cordley Hall , Corvallis, OR, 97331, USA

Keywords:
Corystospermales
Cretaceous
Seed cone
pollination biology
Cupule
Seed fern.

Presentation Type: Oral Paper
Session: 23, Paleozoic and Mesozoic Paleobotany
Location: 102/Savannah International Trade and Convention Center
Date: Tuesday, August 2nd, 2016
Time: 11:15 AM
Number: 23012
Abstract ID:365
Candidate for Awards:None