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 Hrútagil 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.
• Premise of the study: The early Cenozoic was a key period of evolutionary radiation in Fagaceae. The common notion is that species thriving in the modern summer-dry climate of California originated ...in climates with ample summer rain during the Paleogene.• Methods: We investigated in situ and dispersed pollen of Fagaceae from the uppermost Eocene Florissant fossil beds, Colorado, United States, using a combined light and scanning electron microscopy approach.• Key results: Pollen types of Castaneoideae with affinities to modern Castanea, Lithocarpus, and Castanopsis were recognized. Pollen of the extinct genus Fagopsis represents a derived type of Castaneoideae pollen. Infrageneric groups of Quercus were well represented, including pollen of Group Protobalanus. The taxonomic diversity of Fagaceae and of the total plant assemblage indicates a mosaic of microclimates, that range from pronounced to weakly seasonal climates and depend on slope aspect and elevation. Continental climatic conditions may have triggered the evolution of sclerophyllous leaves and adaptive radiation in Quercus and other taxa thriving today under distinctly summer-dry and winter-dry climates.• Conclusions: Vegetation types similar to modern vegetation belts of the Coastal Ranges (chaparral, nemoral conifer forest) were established in the Front Range in the late Eocene. Coeval plant assemblages from the Coastal Ranges of California indicate distinctly subtropical, moist climates. Hence, characteristic elements found today in the summer-dry and winter-dry climates of Pacific North America (Quercus Group Protobalanus, Notholithocarpus) may opportunistically have dispersed into their modern ranges later in the Cenozoic. This scenario is in contrast to the evolution and migration patterns of their western Eurasian Mediterranean counterparts (Quercus Group Ilex).
Modern lineages of the beech family, Fagaceae, one of the most important north-temperate families of woody flowering plants, have been traced back to the early Eocene. In contrast, molecular ...differentiation patterns indicate that the Fagus lineage, Fagoideae, with a single modern genus, evolved much earlier than the remaining lineages within Fagaceae (Trigonobalanoideae, Castaneoideae, Quercoideae). The minimum age for this primary split in the Fagaceae has been estimated as 80 ± 20 Ma (i.e. Late Cretaceous) in recently published, time-calibrated phylogenetic trees including all Fagales. Here, we report fagaceous fossils from the Campanian of Wyoming (82-81 Ma; Eagle Formation Fm), the Danian of western Greenland (64-62 Ma; Agatdal Fm), and the middle Eocene of British Columbia (ca 48 Ma; Princeton Chert), and compare them to the Fagaceae diversity of the recently studied middle Eocene Hareøen Fm of western Greenland (42-40 Ma). The studied assemblages confirm that the Fagus lineage (= Fagoideae) and the remainder of modern Fagaceae were diverged by the middle Late Cretaceous, together with the extinct Fagaceae lineage(s) of Eotrigonobalanus and the newly recognised genus Paraquercus, a unique pollen morph with similarities to both Eotrigonobalanus and Quercus. The new records push back the origin of (modern) Fagus by 10 Ma and that of the earliest Fagoideae by 30 Ma. The earliest Fagoideae pollen from the Campanian of North America differs from its single modern genus Fagus by its markedly thicker pollen wall, a feature also seen in fossil and extant Castaneoideae. This suggests that a thick type 1 foot layer is also the plesiomorphic feature in Fagoideae although not seen in any of its living representatives. The Danian Fagus pollen of Greenland differs in size from those of modern species but is highly similar to that of the western North American early Eocene F. langevinii, the oldest known beech so far. Together with the Quercus pollen record, absent in the Campanian and Danian formations but represented by several types by the middle Eocene, this confirms recent dating estimates focussing on the genera Fagus and Quercus, while rejecting estimates from all-Fagales-dated trees as too young. The basic Castaneoideae pollen type, still found in species of all five extant genera of this putatively paraphyletic subfamily, represents the ancestral pollen type of most (modern) Fagaceae (Trigonobalanoideae, Castaneoideae, Quercoideae).
Middle Miocene deposits belonging to the Eskihisar Formation exposed at the Tınaz lignite mine, Yatağan Basin, Muğla, southwestern Turkey, were investigated palynologically. Nine spores, ...aplanospores/zygospores and cysts of fungi and algae, seven moss and fern spores, 12 gymnosperm pollen types, and more than 80 angiosperm pollen taxa were recovered from the Tınaz lignite mine section. Three informal pollen zones were recognized: pollen zone 1 corresponds to the main lignite seam and reflects changes from fluviatile to lacustrine depositional settings; pollen zones 2 and 3 and a transitional zone 2–3 reflect different stages of lake development and a shift from forested (pollen zones 1 and 2) to possibly more open (transitional zone, zone 3) local vegetation. Interpreting changes in regional vegetation from pollen zones 1 to 3 is not straightforward because changes in the pollen spectra may be affected by changing contributions of airborne and water-transported pollen and spores to the depositional site. In addition, changes of the water table may have promoted temporary dominance of herbaceous plants (Amaranthaceae, Nitraria). Palaeobiogeographic relationships of the palynofloras are generally northern hemispheric, with many northern temperate tree taxa having modern disjunctions between East Asia and North America (Tsuga, Carya), East Asia and western Eurasia (Zelkova), East Asia, North America and western Eurasia (Liquidambar), or restricted to East Asia (Cathaya, Eucommia) or North America (Decodon). A few taxa belong to extinct lineages that have complex biogeographic patterns (Engelhardioideae, Cedrelospermum). The presence of Picrasma (Simaroubaceae) in the lower lignite layers of pollen zone 1 is remarkable, as the botanical affinities of the enigmatic flower Chaneya, present in lower to middle Miocene deposits of Turkey and Central Europe, have recently been shown to be with Picrasma.
•Middle Miocene palynofloras of the Tınaz lignite mine, Yatağan Basin, SW Anatolia, are investigated.•High taxonomic resolution is achieved by a combined LM and SEM approach.•Mammals co-occurring with palynofloras provide age constraints.•Palaeogeographic relationships of the pollen floras are mainly northern hemispheric.
The palynoflora from the Lavanttal Basin is characterised by a diverse spectrum of conifers. Their pollen is mostly well preserved allowing for high taxonomic resolution. Most coniferous taxa belong ...to the Pinaceae (Abies, Cathaya, Cedrus, Keteleeria, Larix, Picea, Pinus and Tsuga) and the Cupressaceae (Cryptomeria, Glyptostrobus and Sequoia), but pollen of Sciadopityaceae (Sciadopitys) is also occuring. The presence of these conifer taxa supports previous suggestions based on sedimentological and palynological observations that the sediments of the Lavanttal Basin accumulated in a lowland/wetland environment. Many of the taxa described in this paper had a wide, mostly Northern Hemispheric distribution, occupying swamps, river plains, deltas, hummocks and also better drained habitats located near to the main areas of sedimentation during most of the Cenozoic. Modern relatives of most of the fossil taxa prefer ample precipitation, suggesting that during the Middle Miocene (Sarmatian), the Lavanttal area received plenty of rainfall; there is no indication of a seasonal climate with a drought period. In general, the conifer taxa identified here are suggestive of a warm-temperate climate.
Premise of the study: To fully understand the evolution of today's angiosperms, the fossil record of plant families and genera must be used to determine their time of origin and phytogeographic ...history. As within many angiosperm families, the interrelationships of extant Lythraceae are hard to resolve without sufficient data from the geological past. Here we establish the earliest fossil occurrences of Lythraceae and start resolving the interrelationships and evolution of two of its genera, Lythrum and Peplis. Methods: We studied several Cretaceous and Cenozoic palynofloras from the northern and southern hemispheres. Using the single-grain technique, we screened the treated samples for Lythrum-and Peplis-type pollen. The same individual pollen grains were observed under both the light-and scanning electron microscope, allowing a high taxonomic resolution to be achieved. Key results: Fossil Lythraceae pollen grains are rare in palynological samples. Nevertheless, we were able to identify Lythrum and Peplis pollen from Late Cretaceous sediments and thereby extend the fossil record of the two genera by ca 70 million years. Conclusions: The appearance of Lythrum and Peplis in North America and Peplis in Asia at approximately the same interval in the mid Late Cretaceous points to an already wide geographical distribution by then. These findings add vital information for the time of origin of the Lythraceae and suggest a higher diversity within the family. They also indicate that the distribution of particular genera during the Cretaceous was wider than previously thought.
An ongoing investigation of the middle Miocene (Sarmatian) palynoflora from the Lavanttal Basin continues to show that it contains an extremely rich assemblage of angiosperm taxa. The Fagales to ...Rosales pollen record documented here contains 34 different taxa belonging to the Betulaceae (Alnus, Betula, Carpinus, Corylus, Ostrya), Fagaceae (Castanea, Fagus, Quercus Groups Cerris, Ilex, Cyclobalanopsis, Quercus/Lobatae), Juglandaceae (Engelhardioideae, Carya, Juglans, Pterocarya), Myricaceae (Morrella vel Myrica), Cannabaceae (Celtis), Elaeagnaceae (Elaeagnus), Rhamnaceae, Rosaceae (Prunus) and Ulmaceae (Cedrelospermum, Ulmus, Zelkova). Two of the pollen types represent extinct genera, Trigonobalanopsis and Cedrelospermum, and are also reported for the first time from the Lavanttal Basin along with pollen of Rhamnaceae and Prunus. The different types of Quercus pollen are now affiliated with Groups Cerris, Cyclobalanopsis, Ilex and Quercus/Lobatae based on sculpturing elements observed using scanning electron microscopy (SEM). Köppen signatures of potential modern analogues of the fossil Fagales and Rosales suggest a subtropical (Cfa, Cwa) climate at lower elevation and subsequent subtropical to temperate climate with altitudinal succession (Cfa → Cfb/Dfa→ Dfb; Cwa → Cwb → Dwb) in the Lavanttal area during accumulation of the palynoflora. Most of the fossil taxa have potential modern analogues that can be grouped as nemoral and/or merido-nemoral vegetation elements, and the diversity of Fagales indicates a varying landscape with a high variety of niches.
Iceland is the only known terrestrial place in the subarctic North Atlantic providing a fairly continuous sedimentary and plant fossil record over the past 15millionyears. While the basic ...palaeobotanical framework of this pattern has been well established during the last decade, less attention has been paid to the abundant insect traces on fossil leaves/leaflets. Here, we assess the diversity and frequency of insect herbivory on 4349 fossil angiosperm leaves/leaflets from six plant-bearing sedimentary formations exposed at 18 localities. By combining analyses of environmental factors, species interactions, ecology, biogeography, and the geological history, our results demonstrate how patterns of herbivory have changed over time in relation to temperature fluctuations that profoundly influenced levels of insect-mediated damage diversity and frequency. In addition, higher structural complexity, particularly the establishment of species-rich herb layer communities seems to have positively influenced the structure of insect communities in early late Miocene palaeoforests of Iceland.
•Iceland provides a continuous plant fossil record over the past 15Ma.•We assess diversity and frequency herbivory on 4349 fossil leaves/leaflets.•Herbivory have changed over time in relation to temperature fluctuations.•Higher complexity of herb layer communities influenced insect communities.
Previous studies on the palynoflora from the Lavanttal Basin show that it contains a rich assemblage of spores and gymnosperm pollen. Present and ongoing investigations of dispersed angiosperm pollen ...suggest a high diversity within this group, and due to the excellent preservation of the material, some rare pollen types are recognised. The Magnoliales to Fabales pollen record documented here contains 30 different taxa. Only a few pollen types are assigned to Magnoliids (four taxa); these are rare in the pollen record. Similarly, the Commelinids comprise five taxa and are also rare. Most of the angiosperm pollen originates from Eudicots (21 taxa). Of the angiosperm taxa documented here, Magnolia, Carex , Ranunculaceae, Platanus , Trochodendron, Buxus , Cercidiphyllum, Daphniphyllum , Distylium , Fortunearia , Parrotia, Parthenocissus , Vitis, Euphorbia , Salix and Papilionoideae are recorded for the first time from the Lavanttal Basin. This also includes the first fossil pollen record of Trochodendron worldwide and the first reliable pollen record of Daphniphyllum . Several of the taxa described here had a wide Northern Hemispheric distribution from the Eocene until the end of the Miocene. Also, key relatives of the fossil taxa are presently confined to humid warm-temperate environments, suggesting a very mild climate during the middle Miocene (Sarmatian) of the Lavanttal area. Some of the taxa encountered also support previous observations that the sediments of the Lavanttal Basin accumulated in a lowland wetland environment. This is based on pollen from aquatic taxa thriving in lakes, streams and swamps, and pollen from terrestrial plant taxa occupying margins of lakes and streams, backswamps, floodplains, river plains and hummocks. Other angiosperm pollen clearly originates from plants thriving on drier substrates, reflecting various vegetation units of the mixed evergreen/deciduous broad-leaved/conifer forests surrounding the wetland basin.
An advanced protocol to prepare single extant and fossil pollen grains for transmission electron microscopy (TEM) analysis allows for the fast recovery of data on the ultrastructure of pollen/spores. ...The protocol is easy to apply and less time consuming than previous methods. The 'loss' of pollen grains and pollen that is 'difficult to locate' within the embedding material is avoided, and each single pollen grain can be prepared successfully for TEM analysis. This preparation method is meant as an addition to the single-grain method using combined light and scanning electron microscopy to investigate dispersed fossil pollen grains developed by Dr Reinhard Zetter in the late 1980s.
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