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An anatomically preserved moss gametophyte has been discovered in a marine carbonate concretion from the Baculites Hill locality, James Ross Island, Antarctica. The concretion is derived from the Late Cretaceous Beta Member of the Santa Marta Formation, dated as early to middle Campanian (ca. 80 Ma). The moss has actinomorphic stems with alternate branching, spiral, patent leaf arrangement and large numbers of attached rhizoids. The largest stem is 210 mm in diameter with the largest branch measuring up to 3.7 mm long and 90–100 mm wide. Most stems appear to contain a distinct conducting strand. Cross sections show that the leaves are strongly plicate with a simple D-shaped costal anatomy and unistratose laminae typically with bistratose margins. Leaves range from 650–700 mm wide and at least 700 mm long. The costa appears percurrent, 90 mm wide and 55 mm thick. Laminar cells are elongate, rhomboidal, L/W ¼ 5:1. No ornamentation or papillae have been observed on the upper medial cells of the leaf. These fossils show leaf morphology and costal anatomy similar to several orders of acrocarpous mosses, in the Dicranidae including species of the family Rhabdoweisiaceae. While the combination of characters does not fit into any known genus, it suggests that this moss represents a fossil member of the Dicranales s.l. To date, this represents the most completely preserved moss gametophyte from Gondwana. 

Abstract PremiseMechanistic models using stomatal traits and leaf carbon isotope ratios to reconstruct atmospheric carbon dioxide (CO₂) concentrations (c_a) are important to understand the Phanerozoic paleoclimate. However, methods for preparing leaf cuticles to measure stomatal traits have not been standardized. MethodsThree people measured the stomatal density and index, guard cell length, guard cell pair width, and pore length of leaves from the sameGinkgo biloba,Quercus alba, andZingiber miogaleaves growing at known CO₂levels using four preparation methods: fluorescence on cleared leaves, nail polish, dental putty on fresh leaves, and dental putty on dried leaves. ResultsThere are significant differences between trait measurements from each method. Modeledc_acalculations are less sensitive to method than individual traits; however, the choice of assumed carbon isotope fractionation also impacted the accuracy of the results. DiscussionWe show that there is not a significant difference betweenc_aestimates made using any of the four methods. Further study is needed on the fractionation due to carboxylation of ribulose bisphosphate (RuBP) in individual plant species before use as a paleo‐CO₂barometer and to refine estimates based upon widely applied taxa (e.g.,Ginkgo). Finally, we recommend that morphological measurements be made by multiple observers to reduce the effect of individual observational biases. 

Abstract PremiseThe ecological conditions that constrain plants to an environmental niche are assumed to be constant through time. While the fossil record has been used previously to test for niche conservatism of woody flowering plants, additional studies are needed in other plant groups especially since they can provide insight with paleoclimatic reconstructions, high biodiversity in modern terrestrial ecosystems, and significant contributions to agriculture. MethodsWe tested climatic niche conservatism across time by characterizing the climatic niches of living herbaceous ginger plants (Zingiberaceae) and woody dawn redwood (Metasequoia) against paleoniches reconstructed based on fossil distribution data and paleoclimatic models. ResultsDespite few fossil Zingiberaceae occurrences in the latitudinal tropics, unlike living Zingiberaceae, extinct Zingiberaceae likely experienced paratropical conditions in the higher latitudes, especially in the Cretaceous and Paleogene. The living and fossil distributions ofMetasequoialargely remain in the upper latitudes of the northern hemisphere. The Zingiberaceae shifted from an initial subtropical climatic paleoniche in the Cretaceous, toward a temperate regime in the late Cenozoic;Metasequoiaoccupied a more consistent climatic niche over the same time intervals. ConclusionsBecause of the inconsistent climatic niches of Zingiberaceae over geologic time, we are less confident of using them for taxonomic‐based paleoclimatic reconstruction methods like nearest living relative, which assume a consistent climatic niche between extant and extinct relatives; we argue that the consistent climatic niche ofMetasequoiais more appropriate for these reconstructions. Niche conservatism cannot be assumed between extant and extinct plants and should be tested further in groups used for paleoclimatic reconstructions. 

More than 20,000 siderite concretions from the Mazon Creek area of northern Illinois, United States are housed in the paleobotanical collections of the Field Museum. A large proportion contain fossil plants of Middle Pennsylvanian age that often have excellent three-dimensional morphology and sometimes anatomical detail. Approximately eighty plant taxa have been recognized from the Mazon Creek Lagerstätte, but few have been studied in detail, and in some cases the systematic affinities of these fossils need reevaluation. The three-dimensional (3D) preservation of Mazon Creek fossil plants makes them ideal candidates for study using x-ray micro-computed tomography (μCT), and here we apply these techniques to more accurately reconstruct the morphology of specimens of Tetraphyllostrobus Gao et Zodrow and Crossotheca Zeiller. The mineralogical composition of the fossil plant preservation was studied using elemental maps and Raman spectroscopy. In-situ spores were studied with differential interference contrast, Airyscan confocal super-resolution microscopy, and scanning electron microscopy, which reveal different features of the spores with different degrees of clarity. Our analyses show that μCT can provide excellent detail on the three-dimensional structure of Mazon Creek plant fossils, with the nature of associated mineralization sometimes enhancing and sometimes obscuring critical information. Results provide guidance for selecting and prioritizing fossil plant specimens preserved in siderite concretions for future research. 

The genus Surangea Chitaley et Sheikh, based on permineralized specimens from the Deccan Intertrappean Beds of central India, was originally considered to represent a fern megasporangium. Reexamination of original material and new specimens has revealed that the structures are capsular fruits with well-defined seeds, rather than megasporangia. We describe Surangea fruits in detail, based on peels and micro-CT scanning, and document its distribution among multiple localities of the Deccan Intertrappean Beds. The fruits are pentacarpellate septicidal capsules with ~8–12 seeds per locule. The seeds are prominently ornamented with parallel ridges and have a curved embryo/endosperm cavity and a prominent aril. This set of features indicates eudicotyledonous affinities for Surangea. In particular, the combination of septicidal capsules, axile placentation and arillate campylotropus seeds suggests affinity with the order Myrtales, but it does not fit cleanly within an extant family. Surangea fruits add to the diversity of angiosperms known from this late Maastrichtian flora. It joins several other fruit types known from the Deccan flora that do not fall neatly into extant families, possibly representing parts of an endemic community that succumbed to environmental stress associated K-Pg boundary events and/or subsequent northward rafting of the Indian subcontinent. 

Summary Cunoniaceae are important elements of rainforests across the Southern Hemisphere. Many of these flowering plants are considered Paleo‐Antarctic Rainforest Lineages that had a Gondwanan distribution since the Paleocene. Fossils of several modern genera within the family, such asCeratopetalum, have indicated biogeographical connections between South America and Australia in the Cenozoic.Here, we report a dramatic geographical range extension forCeratopetalum, and Cunoniaceae as a whole, based on two exceptionally preserved fossil winged fruits from Campanian (c. 82–80 Ma old) deposits on Sucia Island, Washington, USA. The fossils were studied using physical sectioning, light microscopy, micro‐computed tomography scanning and multiple phylogenetic analyses.The fossil fruits share diagnostic characters withCeratopetalumsuch as the presence of four to five persistent calyx lobes, a prominent nectary disk, persistent stamens, a semi‐inferior ovary and two persistent styles. Based on morphological comparisons with fruits of extant species and support from phylogenetic analyses, the fossils are assigned to a new speciesCeratopetalum suciensis.These fossils are the first unequivocal evidence of crown Cunoniaceae from the Cretaceous of North America, indicating a more complicated biogeographical history for this important Gondwanan family.