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Premise of research. Ten anatomically preserved conifer seed cone specimens are preserved on the surfaces of, and within, three interlocking rock fragments of terrestrial limestone discovered as float along the Colville River on the North Slope of Alaska, providing additional evidence for the diversification of taiwanioid Cupressaceae during the Upper Cretaceous–Cenozoic interval. Methodology. Specimens on rock surfaces were measured and photographed, and then serial anatomical thin sections were prepared by the cellulose acetate peel technique. Three-dimensional images of selected specimens were also captured using micro–computed tomography (micro-CT). Pivotal results. The structure of these seed cones is similar to that of living Taiwania cryptomerioides in cone shape, the presence of subtending scalelike leaves, helically arranged and imbricating foliate ovuliferous complexes (OCs), the absence of a separate ovuliferous scale tip, variation in numbers of OCs, and by having two adaxially positioned winged seeds per complex. However, abruptly upturned OC, details of OC vasculature, and distinctive histological features reveal that these seed cones represent a new species of the extinct genus Mukawastrobus. Conclusions. When added to the existing record of fossil seed cones, the new species Mukawastrobus arnoldii highlights the recent discovery that among early-diverging lineages of Cupressaceae, there has been considerable Cretaceous, Paleogene, and Neogene evolution that is reflected by variations among subtle characters that are not recognizable in any but the most completely preserved specimens. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]