James F. Basinger

Early Tertiary Vegetation of Arctic Canada and Its Relevance to Paleoclimatic Interpretation

Early Tertiary fossil plants representing polar Arcto-Tertiary vegetation are found on Ellesmere and Axel Heiberg islands, northernmost of the Canadian Arctic Archipelago. Growing at a paleolatitude of 75–80 °N, these forests experienced prolonged periods of continuous daylight in the summer and continuous darkness in winter. The primarily deciduous vegetation, including members of the Taxodiaceae, Cupressaceae, Pinaceae, Ginkgoaceae, Platanaceae, Juglandaceae, Betulaceae, Menispermaceae, Cercidiphyllaceae, Ulmaceae, Fagaceae, and Magnoliaceae, clearly indicates that summer growing conditions were mild and moist, a conclusion supported by breadth and uniformity of annual growth increments of wood and by estimates of structure and productivity of forests. More significantly, probable frost-sensitive members of, for example, the Taxodiaceae, as well as fossil crocodilians and other frost-sensitive animals indicate that severe frost never occurred, even during the long, dark winter. Cold month mean temperatures of 0–4 °C, warm month mean of >25 °C, and mean annual temperature of 12–15 °C are estimated. These estimates are higher than those derived from physiognomic analogy, probably because dark polar winters in the high paleolatitudes and cold winter temperatures in the modern mid-latitudes similarly effect vegetation and enforce deciduousness. The transition from ‘greenhouse’ to icehouse’ began during the mid-Tertiary. The onset of climatic decline may be apparent in the appearance of diverse evergreen Pinaceae in the Eocene Axel Heiberg Island assemblages and other contemporaneous floras of the Eocene mid- to high latitudes. Neogene floras of northern Canada indicate that mixed evergreen coniferous/deciduous broad-leaved vegetation typical of modern boreal ecosystems persisted throughout the Arctic Archipelago until the onset of Pleistocene glaciation.

Evolutionary History of the Genus Pseudolarix Gordon (Pinaceae)

The fossil record of Pseudolarix (Pinaceae) reveals wide distribution in North America and Eurasia from at least the Early Cretaceous (Berriasian) and possibly the Late Jurassic (Portlandian) to the Plio-Pleistocene. Several hundred reproductive and vegetative remains, representing two species of Pseudolarix, were recovered from sediments of Eocene age on Axel Heiberg and Ellesmere Islands, Canadian Arctic Archipelago. These specimens form the basis for reassessment of the fossil record of the genus and evaluation of morphology and variability of seed-cone scales, winged seeds, leaves, and brachioblasts. Unfortunately, most reports of Pseudolarix lack sufficient details of the character traits of the cone scales, particularly those of the bracts, that are required for identification at the species level. Following review of the known fossil record, only two species are recognized, discrimination being based on differences in length and morphology of the bract subtending the cone scale. One species, the short-bracted form, possesses anatomical and morphological features that conform entirely to the living species P. amabilis (Nelson) Rehder. On the basis of the now considerable data available for both living and fossil material, segregation of the fossil as a distinct species cannot be justified. As interpreted, P. amabilis is an extraordinary example of evolutionary stasis. The second species, P wehrii Gooch, a long-bracted form, appears to represent an extinct lineage of limited range. The spatial and temporal distribution pattern of fossil Pseudolarix indicates that displacement between Eurasia and North America from the Late Jurassic/Early Cretaceous to the Plio-Pleistocene occurred through Beringia and the newly defined Spitsbergen Corridor; the North Atlantic routes were apparently not used by Pseudolarix. Displacement into Europe from eastern Asia was delayed until regression of the Turgai Strait and late Tertiary, after significant global climatic deterioration.

How wet was the Arctic Eocene rain forest? Estimates of precipitation from Paleogene Arctic macrofloras

The Eocene was the warmest part of the Cenozoic, when warm climates extended into the Arctic, and substantive paleobotanical evidence indicates broadleaf and coniferous polar forests. Paleontological temperature proxies provide a basis for understanding Arctic early Paleogene climates; however, there is a lack of corresponding proxy data on precipitation. Both leaf physiognomic analysis and quantitative analysis of nearest living relatives of an Arctic macroflora indicate upper microthermal to lower mesothermal moist climates (mean annual temperature ∼13–15 °C; cold month mean temperature ∼4 °C; mean annual precipitation >120 cm/yr) for Axel Heiberg Island in the middle Eocene. Leaf-size analysis of Paleocene and Eocene Arctic floras demonstrates high precipitation for the Paleogene western and eastern Arctic. The predicted enormous volume of freshwater entering the Arctic Ocean as a result of northward drainage of a significant region of the Northern Hemisphere under a high-precipitation regime would have strongly affected Arctic Ocean salinity, potentially supporting Arctic Ocean Azolla blooms. High Paleogene precipitation around the Arctic Basin is consistent with high atmospheric humidity, which would have contributed significantly to polar, and global, Eocene warming.

Morphologically complex plant macrofossils from the Late Silurian of Arctic Canada

In addition to vegetative remains, fertile remains from ten plants, representing seven distinct taxa whose size and complexity are much greater than most contemporaneous fossils, are reported from late Ludlow (Ludfordian) sediments of Bathurst Island in Nunavut, Canada. Evidence for the age of these beds is gathered from stratigraphic relationships and index fossils including conodonts, graptolites, and brachiopods. Zosterophylls dominate the collection, some of which constitute the earliest record of fertile structures arranged in dense clusters and longitudinal rows along axes. Representatives include a plant that resembles Bathurstia, one species of Zosterophyllum, and two specimens that bear affinity to this genus. Distichophytum is also represented, as is a new zosterophyll named Macivera gracilis. The prevalence of sporangial clustering and reduced sporangial stalks in this flora leads to a discussion of the origins and significance of these morphological features. Following a review of some of the other Silurian floras, particularly the Baragwanathia-bearing Lower Plant Assemblage of Victoria, Australia, which also shows morphological advancement over the rhyniophytoid-dominated floras common to Laurussia, it is concluded that the Bathurst Island flora presents the best evidence to date of substantial morphological diversity, complexity, and stature of vascular land plants in this period.

Fossil Cathaya (Pinaceae) Pollen from the Canadian High Arctic

Palynological studies of the Eocene Buchanan Lake Formation, Axel Heiberg Island, Canadian High Arctic, have yielded pollen grains closely comparable to those of extant Cathaya Chun et Kuang, a paleoendemic conifer of southwestern China. These palynomorphs are assigned to Cathaya gaussenii Sivak, which is here interpreted as the only species to which known fossil pollen of this genus can be assigned. Unless scanning electron microscopy is used, generic affinity cannot be determined with certainty. On the basis of light microscopy alone, Cathaya‐like pollen fossils may be grouped into one form‐taxon, Pityosporites microalatus (Potonié) Thomson et Pflug. The Eocene record from Canada provides convincing evidence for the occurrence of Cathaya in North America and is consistent with interpretations for warm climatic conditions in the Canadian Arctic in the Middle to Late Eocene. An appraisal of the available literature on fossil Cathaya and Cathaya‐like pollen of Cretaceous to Recent age has been undertaken. The pre‐Cretaceous record is difficult to evaluate. The genus Cathaya was apparently restricted to North America and East Asia during the Cretaceous but had dispersed to Europe, possibly via a North Atlantic land bridge, by the Early Tertiary. In the Neogene, Cathaya became widespread in North America, East Asia, and Europe. Late Tertiary climatic deterioration and Quaternary glaciation appears to have been responsible for extirpation of Cathaya from North America first (latest record Late Miocene), and then from Europe (Pleistocene). Therefore, the endemic distribution of extant Cathaya in China represents a remnant of a formerly widespread Asiatic population.

The paleoecology of high-latitude Eocene swamp forests from Axel Heiberg Island, Canadian High Arctic

Abstract A record of high-latitude (79°55′N) Eocene polar vegetation is preserved on Axel Heiberg Island, Canadian High Arctic, in megafloras in an alternating sequence of swamp-coal, fluvio-lacustrine shale and channel-sand lithofacies of the upper coal member of the Buchanan Lake Formation. Some exposures of the swamp facies contain significant fossil forests represented by autochthonous assemblages of mummified in-situ tree stumps and forest-floor leaf-litter mats. Exposed trunks within a single coal layer represent multiple stands of trees killed and buried at the different times over 500–2000 yr. Stratigraphic examination of peat and coal megafossil floristics of the “level N” fossil forest at the centimetre-scale demonstrates small-scale changes in forest composition and swamp hydrology horizontally, and temporal variation vertically within this layer. A mosaic of taxodiaceous swamp (Metasequoia dominant with or without Glyptostrobus), a mixed coniferous community, and Alnus/fern bog appears to have produced both the leaf mats and the in-situ stumps, with the taxodiaceous swamp the dominant peat-accumulating phase. Taxodiaceous layers are interpreted as areas of standing water which may have experienced seasonal water-level fluctuations. Alnus/fern (with or without other broadleaved angiosperms) communities reflect areas of slightly higher peat and hence locally lower water tables, but may also reflect successional processes. The areal extent and position of these different hydrologically-controlled plant communities appears to have changed throughout the interval of accumulation of the peat layer examined.

A new species of Larix (Pinaceae) from the early tertiary of Axel Heiberg Island, Arctic Canada

Abstract Fertile and vegetative remains of Larix altoborealis sp. nov. have been recovered from sediments of the Eocene Buchanan Lake Formation of Axel Heiberg Island, Canadian High Arctic. Palynological and megafossil diversity and abundance data indicate that Larix was a subordinate member within a regionally diverse, mixed forest of broad-leaved and needle-leaved deciduous and needle-leaved evergreen taxa. Vegetative remains include leafy-leading shoots as well as branches with attached brachioblasts and needle fascicles. Cuticular analyses reveal that epidermal cells have distinctive undulatory anticlinal wall patterns bearing small projections. Seed cones are 14–30 mm long, 10–15 mm wide and are elliptical to ovoid, with 35 to 70 scales per cone. Ovuliferous scales are rounded to emarginate, each cone scale bearing two adaxial, winged seeds. Subtending each cone scale is a bract possessing a distinct apical tooth which does not exceed the length of the cone scale. The cuticular patterns of L. altoborealis needles are at present unique among Larix, but cone morphology indicates a relationship to the short-bracted taxa that are currently widely distributed in the boreal forests of North America and Eurasia, including L. laricina, L. sibirica, L. gmelini. Examination of bracts from L. altoborealis sp. nov. and all extant Larix indicates that bract morphology is distinctive for each species and is useful in identification. A phylogenetic scheme is developed for Larix based upon the seed-cone morphology, including features of the bract, and distribution patterns of extant and extinct species of Larix. Larix altoborealis sp. nov. is the first unequivocal report of pre-Oligocene Larix and provides insight into the early evolution and distribution of the genus.

Growth-ring analysis of Early Tertiary conifer woods from the Canadian High Arctic and its paleoclimatic interpretation

Abstract Fossil forests, where petrified stumps were preserved in growth position, have been found within Early Tertiary sediments near Strathcona Fiord, Ellesmere Island, Canadian Arctic Archipelago. These fossil forests are obvious evidence for Early Tertiary climate much warmer than that of today. We analyzed the growth rings of petrified woods from two fossil forest sites (one in middle Paleocene, and the other in late Early Eocene) to extract information on climate change. The woods consist most abundantly of Metasequoia and cf. Glyptostrobus, suggesting that these forests grew in similar environments of warm to cool temperate climates. Mean ring width, mean sensitivity and power spectrum were calculated for ring-width sequences. Although significant difference in the mean ring width between the two forests was found, a comparison with living trees suggests that the difference can be attributed to the specific difference between the forests, so that a significant climate change may not necessarily be invoked. We found little significant difference in the mean sensitivity and power spectrum between the forests, neither did we find any strong indication of periodicities. Consideration of all features suggests that there was no significant difference in climate of middle Paleocene and late Early Eocene time in the High Arctic. However, the mean ring-widths of these forests were significantly smaller than that reported for mid-Cretaceous High Arctic fossil forest.

Sixty-five-million-year-old flowers bearing pollen of the extinct triprojectate complex—a Cretaceous-Tertiary boundary survivor

Abstract Fossil flowers bearing pollen of Kurtzipites trispissatus Anderson have been recovered from the Paleocene Ravenscrag Formation, southwestern Saskatchewan, Canada. The flowers occur in clays about 7.0 m above the coal-zone associated with the Cretaceous-Tertiary boundary and represent a lineage that survived the Cretaceous-Tertiary boundary extinction event. Flowers are globular in shape, about 6.0 mm in diameter, and without an obvious perianth. All flowers are staminate and unisexual with numerous stamens inserted on a disk-shaped receptable. The stamens are long, narrow and basifixed; the filaments are short, the anthers are long ans slender and filled with K. trispissatus pollen. Pollen grains are tricolporate, about 20 μm in diameter, the exine tectate and scabrate, the endexine apparently restricted to the apertural region. This putatively anemophilous palynomorph is one of the few members of the mainly zoophilous triprojectate complex to survive the Cretaceous-Tertiary boundary event. Flower morphology supports the anemophilous reproductive strategy previously inferred for the plants producing Kurtzipites , suggesting that an anemophilous habit may have had selective advantage in the triprojectate complex, and perhaps other groups, at the Cretaceous-Tertiary boundary. The fossil flowers, hereassigned to Kurtziflora antherosa gen. et sp. nov., belong to a taxon that apparently became extinct during the Paleocene leaving no modern relatives.

Early Eocene plant diversity and dynamics in the Falkland flora, Okanagan Highlands, British Columbia, Canada

The early Eocene fossil localities of the Okanagan Highlands in British Columbia, Canada, and Washington State, USA, span the Early Eocene Climatic Optimum, the warmest period of the Cenozoic, and reflect mild but equable upland climates (mean annual temperature <15°C, cold month mean temperature >0°C). The Okanagan Highlands region has been identified as a centre of temperate plant family diversification in the northern hemisphere during the early Eocene. Here, we test the hypothesis of mid-latitude high diversity through rarefaction analysis of unbiased census collections from the Okanagan Highlands Falkland fossil locality, demonstrating levels of diversity similar to those documented at hyperdiverse Eocene sites in South America when adjusted for sample size. An explanation for this diversity may lie in the upland character of the Falkland site, as altitudinal gradients provide a mosaic of microhabitats through interacting effects of topography and climate. Fine-scale trends are also examined within the Falkland site, demonstrating a shift in plant community composition over time to a more diverse flora, although the dominant taxa persist through the section in varying levels of abundance. Intra-site patterns in plant community structure and composition are attributed to a combination of environmental factors, including disturbance and microhabitat diversity.