Skaar Ridge Research Articles

A Permian nurse log and evidence for facilitation in high-latitudeGlossopterisforests

The biology of trees that grew in high‐latitude forests during warmer geological periods is of major interest in understanding past and future ecosystem dynamics. As we study the different plants that composed these forests, it becomes possible to make comparisons with ecosystem processes that occur today. Here we describe a silicified late Permian (Lopingian) glossopterid (seed fern) trunk from Skaar Ridge, central Transantarctic Mountains, Antarctica, with evidence of glossopterid rootlets growing into its wood. The specimen is interpreted as a nurse log similar to those seen in some extant forests. Together with evidence of glossopterid roots growing within the lacunae of older roots, this new specimen suggests the existence of facilitative interactions among the glossopterid trees that dominated the high‐latitude forests of Gondwana during the late Permian. More generally, the existence of self‐facilitation might have favoured the expansion of glossopterids within various environments, especially those at high palaeolatitudes, during the Permian icehouse to greenhouse transition.

Fungal sporulation in a Permian plant fragment from Antarctica

Documented evidence of fungi from the Permian of Antarctica mostly consists of dispersed remains that do not provide the whole complement of diagnostic features necessary to determine even broad systematic affinities. A dense cluster of > 250 fungal spores occurs within a degraded vascular plant (probably glossopteridalean) fragment in Permian permineralized peat from Skaar Ridge, central Transantarctic Mountains, Antarctica. Spores are spheroidal to ovoid, similar to 50 pm in diameter, and possess a massive wall composed of three wall components (wcl-3);one or two canals extend from the spore lumen to the outside. The spores are embedded in a confluent meshwork of tenuous hyphae. Structural similarities exist between the fossil spores and spores produced by certain present-day Mucoromycota, Ascomycota, and Basidiomycota;however, the precise systematic affinities of the fossils cannot be determined. The relationship between the spore producer and its also host plant remains unresolved. Nevertheless, the spatial arrangement of the spores within the plant structure suggests that the fungus required the host for sporulation, and perhaps even influenced plant development for this purpose. This discovery adds to the inventory of distinctive fungal fossils from the Permian of Antarctica and presents a new type of association/interaction between a Permian fungus and a vascular plant.

Growth habit indicators from Permian Antarctic glossopterids

Glossopteridales dominated the Gondwanan landscape during the Permian with Glossopteris leaves in mats suggesting a deciduous nature. While a great deal of anatomical and morphological information is known about the glossopterids, growth habit indicators have been limited to wood anatomical analyses and the presence of leaf mats. In this study the relative and absolute abundances were calculated on impression specimens collected from the Skaar Ridge locality in the Transantarctic Mountains, Antarctica. Results indicate that material is parautochthonous with layers dominated by either Glossopteris leaves or scale leaves. Three morphologies of scale leaves are present, two of which are associated with reproductive structures and one probably representing bud scales. Only pollen organ-bearing leaves have been observed on the specimens indicating that glossopterids may have been dioecious since ovulate material is not observed in any layer. A second hypothesis is that the glossopterids are monecious, but shed pollen structures early in the season and ovulate structures in the fall with Glossopteris leaves and just have not been observed in the leaf mats. The results from this study will help fill in gaps currently present for the glossopterids in phylogenetic analyses to help resolve their true position in a phylogenetic context.

Fungal decay in Permian Glossopteridalean stem and root wood from Antarctica

Evidence of fungal decay is frequently encountered in silicified wood. However, studies focusing on fossil fungal wood degradation remain rare. A characteristic pattern of degradation and decay symptoms congruent with present-day white pocket rot occur in Late Permian silicified glossopteridalean stem and root wood (Australoxylon sp.) from Skaar Ridge, Antarctica. Co-occurring with the decay symptoms are fungal hyphae with clamp connections. Hyphae usually progress through the pit apertures, but some may also penetrate tracheid walls. The individual wall layers in some of the infected tracheids are separated from each other, apparently forming appositions. Small, opaque bodies (? arthropod coprolites) occur in some of the decay pockets. The abundance of infected specimens among the silicified woods from Skaar Ridge suggests that white pocket rot fungi were important decomposers in late Paleozoic high-latitude forest ecosystems.

BARK ANATOMY OF LATE PERMIAN GLOSSOPTERID TREES FROM ANTARCTICA

The Glossopteridales are an extinct group of seed plants that dominated Gondwanan floras during the Permian. Their remains are found across a wide range of habitats and paleolatitudes, and it is particularly interesting to understand the anatomical characteristics that might have enabled such an extensive distribution. Here, we document for the first time the bark anatomy of high-latitude glossopteridalean trees using peels and thin sections made from a Late Permian trunk from Skaar Ridge, Antarctica. The bark is 3 cm thick. The secondary phloem is composed of sieve cells, axial and ray parenchyma, and fibers arranged in discontinuous unicellular tangential layers. The outer bark is a rhytidome, with numerous alternating layers of periderm and non-conducting secondary phloem showing some proliferation of the axial parenchyma. Successive periderms mostly run parallel to the cambium, with some longitudinal undulation and rare connections between two periderms. A similar anatomy was observed in bark fragments found isolated in the matrix or closely associated with large glossopterid stems or roots. The anatomy of the Skaar Ridge specimens shows that Antarctic Glossopteridales had a relatively thick, probably stringy bark. The retention of a significant amount of insulating dead bark tissue on the trunk likely provided protection of the cambium, conducting secondary phloem, and potential latent buds against biotic and abiotic environmental hazards (fire, frost, scalding, insects, etc.) and may have contributed to the extensive paleolatitudinal distribution of the Glossopteridales during the Permian.

Lonchiphyllum aplospermum gen. et sp. nov.: An Anatomically Preserved Glossopterid Megasporophyll from the Upper Permian of Skaar Ridge, Transantarctic Mountains, Antarctica

A new anatomically preserved megasporophyll, Lonchiphyllum aplospermum, is described from permineralized peat collected on Skaar Ridge in the central Transantarctic Mountains. This new genus contains vascular features similar to those of the leaf genus Glossopteris schopfii, which is the exclusive leaf genus in the specimens in which the sporophylls were found. The vasculature of the sporophyll consists of a central vascular region with bordered pitting and anastomosing lateral bundles with helical-scalariform thickenings. Ovules are attached oppositely to suboppositely to lateral veins on the adaxial surface of the sporophyll. There is an abundance of bisaccate pollen of the Protohaploxypinus type at the base of the ovules. The ovules of Lonchiphyllum are small (1.1 mm × 0.97 mm) and ovate and have an unornamented integument. Comparison with anatomically known ovules from Skaar Ridge, i.e., Plectilospermum elliotii, Choanostoma verruculosum, and Lakkosia kerasata and Homevaleia gouldii from the Bowen Basin of Australia, supports the classification of Lonchiphyllum as a glossopterid. The differences in the sarcotesta and sclerotesta of all the Skaar Ridge ovules may indicate specialization for pollination or dispersal.

Permineralized lycopsid from the Permian of Antarctica

Compression–impression fossils from the central Transantarctic Mountains suggest a somewhat diverse Permian flora, but permineralized peat of the same age does not exhibit this diversity. Permineralized fossils from Skaar Ridge in the central Transantarctic Mountains contain helically arranged sporophylls, each bearing a single reniform-shaped adaxial sporangium that contains trilete spores. Although the fossils are fragmentary, they are important as the first record of lycopsids with cellular detail from the Late Permian of Antarctica. The only Permian record to date of this group from the Transantarctic Mountains is Collinsonites schopfii Schwendemann et al., which consists of only impressions of vegetative parts.

Lakkosia kerasata gen. et sp. nov., a Permineralized Megasporangiate Glossopterid Structure from the Central Transantarctic Mountains, Antarctica

Permineralized reproductive structures have been known from Antarctica for the past four decades. No formal descriptions have been available for this material, however, leaving a gap in our knowledge of the glossopterid clade. Lakkosia kerasata gen. et sp. nov. is a multiovulate, megasporangiate structure found in silicified peat from the Upper Permian Skaar Ridge locality in the central Transantarctic Mountains. Ovules are borne in depressions on the adaxial surface of the megasporophyll and enclosed in thin strips of tissue that arise from the sporophyll. Transfusion tissue with scalariform wall thickenings is present in the sporophyll and may have acted as storage or conducting tissue. In longitudinal sections of the ovules, the sclerotesta forms two appressed, hemispherical masses of lignified parenchyma cells, which create the micropyle. Tissue of the sarcotesta overarches these parenchymatous masses, creating a chamber above the micropyle. Lakkosia is compared to previously described permineralized ...

A Glomalean Fungus from the Permian of Antarctica

A new genus and species of fossil fungus, Glomorphites intercalaris, is described from silicified peat of Late Permian age from Skaar Ridge in the central Transantarctic Mountains, Antarctica. The fungus consists of compact clusters of terminal and intercalary chlamydospores occurring in decaying silicified tissue, possibly roots. The chlamydospores have a wide size and shape range, a multilayered wall, porelike attachment scars at the ends of the body, and subtending hyphae of different shapes. The overall morphology of G. intercalaris resembles that of fossil and extant endomycorrhizal fungi, especially species producing Glomus‐type chlamydospores. This is the first report of an endomycorrhizal‐like fungus from the Permian.

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.

Anatomically Preserved Glossopteris Stems with Attached Leaves from the Central Transantarctic Mountains, Antarctica

Stems and buds of Glossopteris skaarensis Pigg and buds of G. schopfii Pigg from the Permian Skaar Ridge locality in the central Transantarctic Mountains, Antarctica demonstrate the first anatomically preserved glossopterids known with stem/leaf attachment. Stems of G. skaarensis are 1–12 mm in diameter ( = 3.1 mm) with a broad pith, poorly defined primary xylem, and a zone of secondary xylem up to 6 mm thick. Pycnoxylic wood conforming to Araucarioxylon Kraus is composed of tracheids with uni- to biseriate oval to hexagonal bordered pits on radial walls, uniseriate rays one to a few cells high, and cupressoid to taxodioid cross-field pitting. Stems have a narrow zone of secondary phloem, aerenchymatous cortex with scattered sclereids, and sometimes a narrow periderm. Two wedge-shaped leaf traces each bifurcate to form four strands in the base of each petiole. Small axillary branches are vascularized by double branch traces that fuse at the margin of the main axis. Buds of G. skaarensis have leaves with narrow lateral laminae and a thickened midrib containing a wide lacuna, delicate vascular strands, and a prominent hypodermis. In contrast, buds of G. schopfii have uniformly thick leaves with prominent, circular vascular bundle sheaths. These anatomical details are used to reconstruct individual types of glossopterid plants, providing new information toward understanding the ecology and evolution of this important group of Permian seed plants.

ANATOMICALLY PRESERVED GLOSSOPTERIS STEMS WITH ATTACHED LEAVES FROM THE CENTRAL TRANSANTARCTIC MOUNTAINS, ANTARCTICA.

Stems and buds of Glossopteris skaarensis Pigg and buds of G. schopfii Pigg from the Permian Skaar Ridge locality in the central Transantarctic Mountains, Antarctica demonstrate the first anatomically preserved glossopterids known with stem/leaf attachment. Stems of G. skaarensis are 1-12 mm in diameter ( = 3.1 mm) with a broad pith, poorly defined primary xylem, and a zone of secondary xylem up to 6 mm thick. Pycnoxylic wood conforming to Araucarioxylon Kraus is composed of tracheids with uni- to biseriate oval to hexagonal bordered pits on radial walls, uniseriate rays one to a few cells high, and cupressoid to taxodioid cross-field pitting. Stems have a narrow zone of secondary phloem, aerenchymatous cortex with scattered sclereids, and sometimes a narrow periderm. Two wedge-shaped leaf traces each bifurcate to form four strands in the base of each petiole. Small axillary branches are vascularized by double branch traces that fuse at the margin of the main axis. Buds of G. skaarensis have leaves with narrow lateral laminae and a thickened midrib containing a wide lacuna, delicate vascular strands, and a prominent hypodermis. In contrast, buds of G. schopfii have uniformly thick leaves with prominent, circular vascular bundle sheaths. These anatomical details are used to reconstruct individual types of glossopterid plants, providing new information toward understanding the ecology and evolution of this important group of Permian seed plants.

Depositional setting and paleobotany of Permian and Triassic permineralized peat from the central Transantarctic Mountains, Antarctica

Silicified peat is known from two sites in the central Transantarctic Mountains. Both are within a 2-km-thick Permo-Triassic sandstone-shale sequence that was deposited by braided streams in a rapidly subsiding foreland basin along the paleo-Pacific margin of Antarctica. Upper Permian permineralized peat occurs as scattered boulders just above a channel-form sandstone in the upper part of the Buckley Formation on Skaar Ridge overlooking the Beardmore Glacier. These boulders are erosional remnants of fine-grained deposits that accumulated in shallow lakes or swamps on a flood plain. At Fremouw Peak, the peat occurs near the top of the Fremouw Formation in strata that are probably Middle to Late Triassic in age. The peat consists of large blocks that were rafted into a sandy braided stream channel during a flood and then stranded and buried as flood waters receded. Both sites are characterized by exceptionally well-preserved plant material, although the composition and diversity of the two floras are very different. Permineralization apparently took place rapidly and was enhanced by the dissolution of siliceous volcanic detritus that is abundant in both formations.