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Dating the subsidence history of the North Atlantic Land Bridge (NALB) is crucial for understanding intercontinental disjunctions of northern temperate trees. Traditionally, the NALB has been assumed to have functioned as a corridor for plant migration only during the early Cenozoic, but recent findings of plant fossils and inferences from molecular studies are challenging this view. Here, we report dispersed pollen of Quercus from Late Miocene sediments in Iceland that shows affinities with extant northern hemispheric white oaks and North American red oaks. Older (15 to 10 Ma) sediments do not contain pollen of Quercus suggesting it arrived after that time. Pollen from the 9-8 Ma Hrátagil locality is indistinguishable from morphotypes common among white and red oaks. In contrast, pollen from the 5.5 Ma Selárgil locality has a tectum that is at present confined to North American white and red oaks, indicating a second episode of migration to Iceland. These findings suggest that transatlantic migration of temperate plant taxa may not have been limited by vast areas of sea or by cold climates during the Miocene. Furthermore, our results offer a plausible explanation for the remarkably low degree of genetic differentiation between modern disjunct European and North American oaks. [ABSTRACT FROM AUTHOR]

Aim This study aims to document the floristic changes that occurred in Iceland between 15 and 6 Ma and to establish the dispersal mechanisms for the plant taxa encountered. Using changing patterns of dispersal, two factors controlling floristic changes are tested. Possible factors are (1) climate change, and (2) the changing biogeography of Iceland over the time interval studied; that is, the presence or absence of a Miocene North Atlantic Land Bridge. Location The North Atlantic. Methods Species lists of fossil plants from Iceland in the time period 15 to 6 Ma were compiled using published data and new data. Closest living analogues were used to establish dispersal properties for the fossil taxa. Dispersal mechanisms of fossil plants were then used to reconstruct how Iceland was colonized during various periods. Results Miocene floras of Iceland (15–6 Ma) show relatively high floristic turnover from the oldest floras towards the youngest; and few taxa from the oldest floras persist in the younger floras. The frequencies of the various dispersal mechanisms seen in the 15-Ma floras are quite different from those recorded in the 6-Ma floras, and there is a gradual change in the prevailing mode of dispersal from short-distance anemochory and dyschory to long-distance anemochory. Two mechanisms can be used to explain changing floral composition: (1) climate change, and (2) the interaction between the dispersal mechanisms of plants and the increasing isolation of proto-Iceland during the Miocene. Main conclusions Dispersal mechanisms can be used to extract palaeogeographic signals from fossil floras. The composition of floras and dispersal mechanisms indicate that Iceland was connected both to Greenland and to Europe in the early Middle Miocene, allowing transcontinental migration. The change in prevalence of dispersal modes from 15 to 6 Ma appears to reflect the break-up of a land bridge and the increasing isolation of Iceland after 12 Ma. Concurrent gradual cooling and isolation caused changes in species composition. Specifically, the widening of the North Atlantic Ocean prevented taxa with limited dispersal capability from colonizing Iceland, while climate cooling led to the extinction of thermophilous taxa. [ABSTRACT FROM AUTHOR]

Abstract: Two macrofloras, 15 and 13.5 Ma old, are described from the oldest exposed plant bearing sediments on Iceland. Many of the taxa are mentioned for the first time and a lime tree, Tilia selardalense, is described as a new species. In case of the older flora, differences in the environment are reflected in plants derived from volcanic sediments from high elevations (Selárdalur, 15 Ma) and from lowland alluvial plains (Botn, 15 Ma). The former are characterized by zonal elements and dominated by Fagus. The latter is dominated by conifers inhabiting swamps and hummocks. The younger Ketilseyri flora (13.5 Ma) is poorer and more similar to the Selárdalur flora. Both floras suggest a humid warm temperate climate (mostly Cfa climate sensu Köppen) with a number of exotic elements (Glyptostrobus, Sequoia, Magnolia, Cercidiphyllum). Evaluating the dispersal mechanisms of all the taxa shows that at least some (Aesculus, Fagus) could not have possibly colonized Iceland crossing large ocean barriers. Furthermore, most anemochorous taxa recorded have a very limited dispersal radius. This suggests that when “proto-Iceland” was colonized, it was connected to the mainland or accessible via a chain of islands. This land could have been part of the Greenland–Scotland Transverse Ridge that is believed to have persisted from the early Cenozoic to Late Oligocene and partly into the Middle Miocene. [Copyright &y& Elsevier]

A large number of plant macrofossils from several Middle to Upper Miocene localities from Iceland have been studied. The fossil material includes four ferns and fern allies, seven conifers, and about 40 species of flowering plants. Betula islandica and Salix gruberi are described as new species. Coniferous twigs previously ascribed to the genus Sequoia are shown to belong to Cryptomeria based on macro-morphological and epidermal features. Fossil plants from Iceland are compared with coeval fossil taxa from Europe and North America and with living plants. The main finding is that the Miocene flora of Iceland belongs to a widespread Neogene northern hemispheric floral type including plants whose representatives are restricted to East Asia, North America and to western Eurasia at the present time. Previously inferred conspicuous similarities to North American modern equivalents appear to be misleading. The type of vegetation in four plant-bearing sedimentary formations from the late Mid Miocene to Late Miocene, the 12 Ma Brjánslækur-Seljá Formation, the 10 Ma Tröllatunga-Gautshamar Formation, the 9–8 Ma Skarðsströnd-Mókollsdalur Formation, and the 7–6 Ma Hreðavatn-Stafholt Formation, corresponds to a humid temperate broadleaved (deciduous)–coniferous mixed forest dominated by Betulaceae, Fagaceae and Acer. Changes in species composition in the sedimentary formations reflect a shift from warm temperate (Cfa climate) to cool temperate (Cfb climate) conditions from the late Mid Miocene to the latest Miocene. This shift was connected to repeated phases of extinction and colonization. Specifically, one set of thermophilic taxa including Magnolia, Liriodendron, Sassafras and Comptonia went extinct between 12 and 10 Ma, and appears to have been replaced by another set of thermophilic taxa in the 10 Ma formation (Juglandaceae aff. Pterocarya/Cyclocarya, Rhododendron ponticum type). The 9–8 and 7–6 Ma formations are characterized by taxa that migrated to Iceland from Europe, such as Fagus gussonii, Betula cristata and Pterocarya fraxinifolia type. Although there is convincing evidence that plants colonized Iceland both from North America and Europe until 12 Ma, migration in the younger formations (9–8, 7–6 Ma) is suggested to have occurred mainly from Europe. © 2005 The Linnean Society of London, Botanical Journal of the Linnean Society, 2005, 149, 369–417. [ABSTRACT FROM AUTHOR]

Abstract: Leaf and cupule/nut remains belonging to Fagus (beech) have previously been reported from three plant-bearing formations on Iceland, the 15 Ma Selárdalur–Botn Formation, the 13.5 Ma Dufansdalur–Ketilseyri Formation, and the ca. 9–8 Ma Skarðströnd–Mókollsdalur Formation, and have traditionally been assigned to various species. In this paper, we study Fagus leaves and cupules from the Miocene of Iceland based on unpublished and newly collected material and assess their taxonomic position. Leaves from Selárdalur (15 Ma) and Tafla (13.5 Ma) are described as a new species, Fagus friedrichii, on grounds of unique combinations of morphological features such as the large elliptical leaves with densely spaced secondary veins, the attenuate leaf apex, and the consistently craspedodromous venation. Specimens from the middle Miocene Seldovian flora of Alaska that have previously been suggested to belong to Fagus antipofii Heer are included within F. friedrichii. Coeval and slightly older Fagus species from Eurasia are compared to the new species from Iceland. For F. friedrichii, a migration to Iceland from North America via Greenland is assumed. The leaf remains from the younger Mókollsdalur exposure (ca. 9–8 Ma) are clearly distinct from F. friedrichii and are identical to Fagus gussonii Massalongo emend. Knobloch and Velitzelos from the upper Miocene of Europe. This is also indicated by the relatively large cupules associated with the Icelandic leaves that are identical to cupules cooccurring with leaves of F. gussonii in Greece and Spain. The large geographical gap between Icelandic and coeval southern European populations of F. gussonii may be related to the general distribution of F. gussonii at the margin of the western Eurasian range of Fagus during the Neogene and perhaps to markedly oceanic climatic conditions under which it grew. For F. gussonii, a migration to Iceland from Europe is suggested. [Copyright &y& Elsevier]