Early–middle Eocene (ca. 53–38 Ma) sediments of the Eureka Sound Group in Canada’s Arctic Archipelago preserve evidence of lush mixed conifer-broadleaf rain forests, inhabited at times by alligators, turtles, and diverse mammals, including primates, tapirs, brontotheres, and hippo-like Coryphodon. This biota reflects a greenhouse world, offering a climatic and ecologic deep time analog of a mild ice-free Arctic that may be our best means to predict what is in store for the future Arctic if current climate change goes unchecked. In our review of the early–middle Eocene Arctic flora and vertebrate fauna, we place the Arctic fossil localities in historic, geographic, and stratigraphic context, and we provide an integrated synthesis and discussion of the paleobiology and paleoecology of these Eocene Arctic forests and their vertebrate inhabitants. The abundance and diversity of tapirs and plagiomenids (both rare elements in midlatitude faunas), and the absence of artiodactyls, early horses, and the hyopsodontid “condylarth” Hyopsodus (well represented at midlatitude localities) are peculiar to the Eocene Arctic. The Eocene Arctic macrofloras reveal a forested landscape analogous to the swamp-cypress and broadleaf floodplain forests of the modern southeastern United States. Multiple climate proxies indicate a mild temperate early–middle Eocene Arctic with winter temperatures at or just above freezing and summer temperatures of 20 °C (or higher), and high precipitation. At times, this high precipitation resulted in freshwater discharge into a nearly enclosed Arctic Ocean basin, sufficient to cause surface freshening of the Arctic Ocean, supporting mats of the floating fern Azolla . Fluctuating Arctic Ocean sea level due to freshwater inputs as well as tectonics produced temporary land bridges, allowing land plants and animals to disperse between North America and both Europe and Asia.

Life at the top of the greenhouse Eocene world--A review of the Eocene flora and vertebrate fauna from Canada's High Arctic

The origin and spread of grass-dominated ecosystems in the late Tertiary of North America: preliminary results concerning the evolution of hypsodonty

Baltic amber constitutes the largest known deposit of fossil plant resin and the richest repository of fossil insects of any age. Despite a remarkable legacy of archaeological, geochemical and palaeobiological investigation, the botanical origin of this exceptional resource remains controversial. Here, we use taxonomically explicit applications of solid-state Fourier-transform infrared (FTIR) microspectroscopy, coupled with multivariate clustering and palaeobotanical observations, to propose that conifers of the family Sciadopityaceae, closely allied to the sole extant representative, Sciadopitys verticillata, were involved in the genesis of Baltic amber. The fidelity of FTIR-based chemotaxonomic inferences is upheld by modern-fossil comparisons of resins from additional conifer families and genera (Cupressaceae: Metasequoia; Pinaceae: Pinus and Pseudolarix). Our conclusions challenge hypotheses advocating members of either of the families Araucariaceae or Pinaceae as the primary amber-producing trees and correlate favourably with the progressive demise of subtropical forest biomes from northern Europe as palaeotemperatures cooled following the Eocene climate optimum.

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A new proposal concerning the botanical origin of Baltic amber

Phylogenetic relationships among 108 oak species (genus Quercus L.) were inferred using DNA sequences of six nuclear genes selected from the existing genomic resources of the genus. Previous phylogenetic reconstructions based on traditional molecular markers are inconclusive at the deeper nodes. Overall, weak phylogenetic signals were obtained for each individual gene analysis, but stronger signals were obtained when gene sequences were concatenated. Our data support the recognition of six major intrageneric groups Cyclobalanopsis, Cerris, Ilex, Quercus, Lobatae and Protobalanus. Our analyses provide resolution at deeper nodes but with moderate support and a more robust infrageneric classification within the two major clades, the ‘Old World Oaks’ (Cyclobalanopsis, Cerris, Ilex) and ‘New World Oaks’ (Quercus, Lobatae, Protobalanus). However, depending on outgroup choice, our analysis yielded two alternative placements of the Cyclobalanopsis clade within the genus Quercus. When Castanea Mill. was chosen as ...

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Multiple nuclear genes stabilize the phylogenetic backbone of the genus Quercus

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.

R L Christie

Papers

Tertiary fossil forests of the Geodetic Hills, Axel Heiberg Island, Arctic Archipelago