Sharon D. Klavins

Fungi from the Rhynie chert: a view from the dark side

The exquisite preservation of organisms in the Early Devonian Rhynie chert ecosystem has permitted the documentation of the morphology and life history biology of fungi belonging to several major taxonomic groups (e.g., Chytridiomycota, Ascomycota, Glomeromycota). The Rhynie chert also provides the first unequivocal evidence in the fossil record of fungal interactions that can in turn be compared with those in modern ecosystems. These interactions in the Rhynie chert involve both green algae and macroplants, with examples of saprophytism, parasitism, and mutualism, including the earliest mycorrhizal associations and lichen symbiosis known to date in the fossil record. Especially significant are several types of specific host responses to fungal infection that indicate that these plants had already evolved methods of defence similar and perhaps analogous to those of extant plants. This suggests that mechanisms underlying the establishment and sustenance of associations of fungi with land plants were well in place prior to the Early Devonian. In addition, a more complete understanding of the microbial organisms involved in this complex ecosystem can also provide calibration points for phylogenies based on molecular data analysis. The richness of the microbial community in the Rhynie chert holds tremendous potential for documenting additional fungal groups, which permits speculation about further interactions with abiotic and biotic components of the environment.

Anatomy of Umkomasia (Corystospermales) from the Triassic of Antarctica

The permineralized, corystosperm, cupulate, ovule-bearing organ Umkomasia resinosa is described from the early Middle Triassic of Antarctica. This is the first description of anatomically preserved Umkomasia, which consists of a determinate cupulate branch with helically arranged, recurved, pedicellate megasporophylls, each of which bears one or two abaxially attached unitegmic ovules. Cupules are ovoid, bilobed with elongate ventral and dorsal openings or unlobed with a single ventral opening, and have a two-zoned parenchymatous cortex and abundant secretory cavities. Ovules are small, orthotropous, and possess a thin integument that contains numerous secretory cavities. The ovules are broadly attached at the base, with a bifid integumentary apex that extends past the cupule lobes. The cupulate branch displays stem-like anatomy, producing paired traces into each cupule stalk. These structurally preserved ovulate organs can be related to other corystosperm organs from Antarctica, particularly the pollen-organ Pteruchus fremouwensis. Both anatomical and morphological features support interpretation of corystosperm reproductive structures as branching systems rather than as compound sporophylls. As a result of an increased understanding of the organization of Umkomasia, it appears doubtful that any direct relationship exists between the corystosperm and angiosperm lineages.

Gymnosperms from the Middle Triassic of Antarctica: The First Structurally Preserved Cycad Pollen Cone

The first permineralized cycad pollen cone is described from the lower Middle Triassic of Antarctica. The cone is characterized by helically arranged, wedge‐shaped microsporophylls, each with five or more spinelike projections extending from the rhomboid distal face. The vascular cylinder is dissected and produces paired traces to each microsporophyll. Three vascular bundles enter the base of the microsporophyll and divide to produce at least five vascular strands in the sporophyll lamina. Pollen sacs occur in two radial clusters near the lateral margins on the abaxial surface of the microsporophyll. Each cluster bears up to eight elongate pollen sacs that are fused for approximately half their length and display longitudinal dehiscence. Pollen sacs are sessile and attached to a vascularized, receptacle‐like pad of tissue that is raised from the surface of the microsporophyll. Pollen is ovoid, psilate, and monosulcate. Although the affinities of this cone with the Cycadales are obvious, the complement of characters in the fossil is unique and thus does not permit assignment to an extant family. Features of the cone are evaluated against reproductive aspects of living cycads.

An unusual, structurally preserved ovule from the Permian of Antarctica.

Anatomically preserved ovules are described from silicified peat of Late Permian age collected from Skaar Ridge in the central Transantarctic Mountains, Antarctica. The small ovules are significant in possessing fleshy apical appendages and a funnel-shaped micropylar extension formed by the sarcotestal layer of the integument, by which they differ from all other Permian ovules described to date. The apical modifications may have functioned in pollination and/or seed dispersal. Similarity with the apical organization of earlier Paleozoic ovules is shown to be superficial, since the analogous structures are developmentally derived from different tissues. Although the ovules occur in rocks in which glossopterids are the only gymnosperms represented, there is insufficient evidence to assign them to a taxonomic group. These ovules are of particular importance because there are so few anatomically preserved gymnosperm reproductive structures known from the Permian and thus provide new data on the diversity of late Paleozoic gymnosperms.

MATONIACEOUS FERNS (GLEICHENIALES) FROM THE MIDDLE TRIASSIC OF ANTARCTICA

Abstract The Matoniaceae is one of the most ancient lineages of extant ferns, with a fossil record that extends from the early Mesozoic. Currently they are considered to be a systematically isolated group that occupies a basal position in the phylogeny of leptosporangiate ferns. Although the extant taxa of Matoniaceae are today restricted to the Malaysian archipelago, a diverse assemblage of matoniaceous ferns occurred on every continent, including Antarctica, during the Mesozoic. Here we describe anatomically preserved, detached fern sori and sporangia from the Fremouw Formation with a combination of characters that affiliates them with the Matoniaceae. Sori are peltate with more than 25 crowded sporangia that display simple maturation. The indusium is multiseriate and centrally attached to a massive, vascularized receptacle. Sporangia are globose to ovoid with vertical, meandering, incomplete annuli, and are helically attached to the receptacle in three to four gyres. This report places this fern as the earliest known occurrence of the Matoniaceae in the fossil record. Characters observed in the sori offer insights regarding organizational patterns of reproductive structures in the family. Additionally, the presence of a peltate indusium in the earliest known representative of the family contradicts the hypothesized evolutionary sequence in development of this structure in the family.