Abstract Detail

Paleobotany

Rothwell, Gar W. [1], Klymiuk, Ashley [2], Stockey, Ruth A. [3].

Mesozoic “cupulate” gymnosperms: how to distinguish Doyleales from Umkomasiales.

Several gymnospermous clades that bear seeds within "cupulate" structures are preserved in Triassic through Cretaceous deposits.   However, a wide variety of seed cupule morphologies and anatomies, the structure of ovulate fructifications, and differing homologies among these plant parts reveal that a majority of such fructifications are of parallel origins.   Many of the most well-known representatives of such plants are easily distinguished from one another, but relationships between the primarily Triassic Umkomasiales and Early Cretaceous Doyleales have been repeatedly confused.   To address this uncertainty we have conducted an in depth analysis of the structure and homologies of the seed enclosing cupules and cupulate fructifications produced by Mesozoic gymnosperms, with particular emphasis on Umkomasiales and Doyleales.   We also have critically reevaluated the known stratigraphic ranges of each.   Whereas, assemblages of unequivocal umkomasialean stems, fronds, pollen organs, and cupulate fructifications are commonly preserved in Triassic Gondwana sediments, in post-Triassic deposits each of the organs is rare or absent; and there are no examples of multiple-organ umkomasialean assemblages.   No unequivocal umkomasialean stems, fronds, or pollen organs are present in post-Triassic strata, and reports of umkomasialean cupulate structures are equivocal.   Most obvious is the absence of plants with Dicroidium-like fronds (i.e., basally forked with modified basal foliar elements). There is general agreement about the structural equivalence of ovulate fructifications of Doylea tetrahedrasperma from western North America and the three Doylea-like species from Mongolia.   "Cupules" of Doyleales, including the specimens described as three species of Umkomasia from the Lower Cretaceous of Mongolia, consist of a pair of meristematic lobes that grow toward the apex of an inverted seed plus the cupule axis, and are borne in the axil of a bract as part of a compound cone. It is the equivocal structure of the originally described Triassic Umkomasia fructifications that has caused the confusion. Although apparently misinterpreted by Thomas and many subsequent authors as being borne in the axil of a bract, the cupulate organ of Umkomasiales typically consists of an abaxially inverted and enrolled, laterally flattened apex that is borne on the structural equivalent of a frond.   By comparing the variety of Triassic Umkomasia spp. morphologies interpreted from compression specimens with the morphology and anatomy of the permineralized U. resinosa from Antarctica, the structural dissimilarities between Umkomasia and Doylea become obvious.

1 - Ohio University and Oregon State University, Environ. & Plant Biol./Botany & Plant Path., Cordley Hall, Crovallis, OR, 97331, USA
2 - Field Museum, Gantz Family Collections Center, 400 Lake Shore Drive, Chicago, IL, 60605, United States
3 - Oregon State University, Botany and Plant Pathology, Cordley Hall, Corvallis, United States, 97331, USA

Keywords:
Cupulate Gymnosperms
Doylea
mesozoic
homology
Seed Ferns
Umkomasia.

Presentation Type: Oral Paper
Session: PL6, Paleobotany: Paleozoic/Mesozoic Paleobotany
Location: /
Date: Thursday, July 22nd, 2021
Time: 10:15 AM(EDT)
Number: PL6002
Abstract ID:297
Candidate for Awards:None