The Beartooth Butte Formation hosts the most extensive Early Devonian macroflora of western North America. The age of the flora at Cottonwood Canyon (Wyoming) has been constrained to the Lochkovian–Pragian interval, based on fish biostratigraphy and unpublished palynological data. We present a detailed palynological analysis of the plant‐bearing layers at Cottonwood Canyon. The palynomorphs consist of 32 spore, five cryptospore, two prasinophycean algae and an acritarch species. The stratigraphic ranges of these palynomorphs indicate a late Lochkovian or Pragian age, confirming previous age assignments. Analysis of samples from three different depositional environments of the plant‐bearing sequence (layers with
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Abstract in situ lycophyte populations, flood layers that buried those populations and an organic matter accumulation zone within a flood layer) demonstrate distinct palynofacies. Comparisons between palynomorph and plant macrofossil diversity reveal some discrepancies. Whereas zosterophylls and lycophytes, most diverse and abundant among the macrofossils, have only one known corresponding spore type (assignable to zosterophylls) in the palynomorph assemblage, the trimerophytes, rare in the macrofossil assemblage, are represented by three spore types. Some of these discrepancies reflect taphonomic differences between the macrofossils and palynomorphs, while others could be due to the fact that the parent plants of most palynomorph types in the Cottonwood Canyon assemblage are unknown. These observations emphasize the need for concerted efforts to bring together the knowledge of macro‐ and microfloras within Early Devonian localities. Nevertheless, given the palaeophytogeographic significance of the Beartooth Butte Formation flora, its palynofossil and macrofossil assemblages, taken together, provide new data relevant to future discussions of Early Devonian biogeography. -
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PREMISE Mosses are a major component of Arctic vegetation today, with >500 species known to date. However, the origins of the Arctic moss flora are poorly documented in the fossil record, especially prior to the Pliocene. Here, we present the first anatomically preserved pre‐Cenozoic Arctic moss and discuss how the unique biology of bryophytes has facilitated their success in polar environments over geologic time.
METHODS A permineralized fossil moss gametophyte within a block of Late Cretaceous terrestrial limestone, collected along the Colville River on the North Slope of Alaska, was studied in serial sections prepared using the cellulose acetate peel technique.
RESULTS The moss gametophyte is branched and has leaves with a broad base, narrow blade, and excurrent costa. We describe this fossil as
Cynodontium luthii sp. nov., an extinct species of a genus that is known from the High Arctic today.Cynodontium luthii is the oldest evidence of the family Rhabdoweisiaceae (by ≥18 Ma) and reveals that genera of haplolepideous mosses known in the extant Arctic flora also lived in high‐latitude temperate deciduous forests during the Late Cretaceous.CONCLUSIONS The occurrence of
C. luthii in Cretaceous sediments, together with a rich Pliocene‐to‐Holocene fossil record of extant moss genera in the High Arctic, suggests that some moss lineages have exploited their poikilohydric, cold‐ and desiccation‐tolerant physiology to live in the region when it experienced both temperate and freezing climates. -
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Background In extant ecosystems, complex networks of ecological interactions between organisms can be readily studied. In contrast, understanding of such interactions in ecosystems of the geologic past is incomplete. Specifically, in past terrestrial ecosystems we know comparatively little about plant biotic interactions besides saprotrophy, herbivory, mycorrhizal associations, and oviposition. Due to taphonomic biases, epiphyte communities are particularly rare in the plant-fossil record, despite their prominence in modern ecosystems. Accordingly, little is known about how terrestrial epiphyte communities have changed across geologic time. Here, we describe a tiny
in situ fossil epiphyte community that sheds light on plant-animal and plant-plant interactions more than 50 million years ago.Methods A single silicified
Todea (Osmundaceae) rhizome from a new locality of the early Eocene (ca. 52 Ma) Tufolitas Laguna del Hunco (Patagonia, Argentina) was studied in serial thin sections using light microscopy. The community of organisms colonizing the tissues of the rhizome was characterized by identifying the organisms and mapping and quantifying their distribution. A 200 × 200 µm grid was superimposed onto the rhizome cross section, and the colonizers present at each node of the grid were tallied.Results Preserved
in situ , this community offers a rare window onto aspects of ancient ecosystems usually lost to time and taphonomic processes. The community is surprisingly diverse and includes the first fossilized leafy liverworts in South America, also marking the only fossil record of leafy bryophyte epiphytes outside of amber deposits; as well as several types of fungal hyphae and spores; microsclerotia with possible affinities in several ascomycete families; and evidence for oribatid mites.Discussion The community associated with the Patagonian rhizome enriches our understanding of terrestrial epiphyte communities in the distant past and adds to a growing body of literature on osmundaceous rhizomes as important hosts for component communities in ancient ecosystems, just as they are today. Because osmundaceous rhizomes represent an ecological niche that has remained virtually unchanged over time and space and are abundant in the fossil record, they provide a paleoecological model system that could be used to explore epiphyte community structure through time.
