Figure 1 - uploaded by Thomas Denk
Content may be subject to copyright.
2.1 Bathymetric map of the northern North Atlantic showing the Greenland-Scotland Transverse Ridge (Picture courtesy NOAA, National Geophysical Data Centre)

2.1 Bathymetric map of the northern North Atlantic showing the Greenland-Scotland Transverse Ridge (Picture courtesy NOAA, National Geophysical Data Centre)

Source publication
Chapter
Full-text available
Plants lacking long distance dispersal mechanisms required a functioning land bridge to colonize Iceland, a route provided by the North Atlantic Land Bridge (NALB). During the Cainozoic, the NALB, also referred to as the Thulean route, came into existence in the latest Paleocene and Early Eocene, but there has been considerable debate about the tim...

Citations

... Transatlantic phylogenetic links of species have been reported for some deciduous trees (e.g., Denk et al., 2010). Forest species assemblages could have spread across the Atlantic via the "North Atlantic Land Bridge" (NALB) (Denk et al., 2011). This link from Europe via Iceland and Greenland to North America is known from the Miocene, so it could have been a relatively old event in the speciation of Cucujus beetles, which corresponds quite well with the estimated divergence times for the splits of the major phylogenetic lineages and in particular the divergence of eastern North American C. clavipes (95% HPD =4.1-5.9 ...
Article
Recent progress in the taxonomy of flat bark beetles (Cucujidae), specifically, in the genus Cucujus, has revealed great diversity in subtropical Asia, but the seemingly well-known temperate and boreal taxa need further attention because of their conservation status. Here, we used an integrative approach using morphology, DNA, and species distribution modelling to disentangle phylogenetic relations, verify the number of species, and understand the historical biogeography of Palearctic and Nearctic Cucujus beetles, particularly the C. haematodes species group. Species distinctiveness was supported for C. cinnaberinus, but present-day C. haematodes turned out to be a species complex made up of separate lineages in the western, middle and eastern parts of its Palearctic range. Cucujus muelleri was a member of that complex, being sister to Asian C. haematodes. Moreover, C. haematodes caucasicus was found to be phylogenetically closely related to Italian C. tulliae, and both to be sister to European C. haematodes. North American C. clavipes clavipes and C. c. puniceus resulted to be enough divergent to be considered different species. Interestingly, western American C. puniceus turned out to be closely related to the C. haematodes complex (including C. muelleri), whereas eastern American C. clavipes constituted a separate lineage, being distantly related to both C. puniceus and C. cinnaberinus. These patterns suggest former trans-continental connections among the ancestors of extant flat bark beetle species. Moreover, a divergent lineage of C. cinnaberinus was found in Calabria, which should be regarded at the very least as a subspecies. The ancestor of C. hameatodes group originated in mid-Miocene, and next, c. 6.2 Mya, a line leading to C. cinnaberinus had split. Speciation of the American lineages occurred during Pliocene (4.4 Mya for C. clavipes and 3.3 Mya for C. puniceus). Species classified as C. haematodes, C. tulliae and C. muelleri, as well as distinct lineages within C. cinnaberinus split during mid Pleistocene (c. 1.5 Mya). A comparison of species climatic requirements and their present distribution allowed to identify glacial refugia in south-eastern areas of North America (C. clavipes), south-western areas of North America (C. puniceus), and the Mediterranean and Caspian Sea Basins (European Cucujus species), or south-eastern areas of Asia and the foothills of the central Asian mountains (eastern C. haematodes). Subsequent climatic changes in the Holocene forced these beetles to move their ranges northwards along the coasts of the Pacific (C. puniceus) or Atlantic (C. clavipes), north-eastwards to central, northern, and eastern Europe (C. cinnaberinus and European C. haematodes) or Siberia (Asian C. haematodes). The combined use of molecular, morphological and climatic data allows a comprehensive understanding of the phylogenetic relations and past distributions of Cucujus beetles, highlighting the complexity of C. haematodes species group evolution.
... In the case of M. temperata, Asia and North America were likely colonized out of Europe during the Miocene. During the Eocene to Miocene the Northern Hemisphere was characterized by the presence of the North Atlantic Land Bridge (NALB) and Bering Land Bridge (BLB), which connected North America, Europe, and Asia (Denk et al. 2011;Brikiati 2014). In a recent publication, Lee et al. (2020) stressed the importance of these little-considered migration routes for the biogeographic history of epiphytic liverworts, which may have also triggered the current distribution of the four Metzgeria species mentioned above. ...
Article
Among liverworts, the epiphytic lifestyle is not only present in leafy forms but also in thalloid liverworts, which so far has received little attention in evolutionary and biogeographical studies. Metzgeria, with about 107 species worldwide, is the only genus of thalloid liverworts that comprises true epiphytes. In the present study, we provide the first comprehensive molecular phylogeny, including estimated divergence times and ancestral ranges of this genus. Analyses are based on a plastid marker dataset representing about half of the Metzgeria species diversity. We show for the first time with molecular data that Austrometzgeria is indeed a member of Metzgeria and that two morpho-species M. furcata and M. leptoneura are not monophyletic, but rather represent geographically well-defined clades. Our analyses indicate that Metzgeria started to diversify in the Cretaceous in an area encompassing today’s South America and Australasia. Thus, Metzgeria is one of the few known epiphytic liverwort genera whose biogeographic history was directly shaped by Gondwana vicariance. Subsequent dispersal events in the Cenozoic resulted in the colonization of Asia, Africa, North America, and Europe and led to today’s worldwide distribution of its species. We also provide the first reliable stem age estimate for Metzgeria due to the inclusion of its sister taxon Vandiemenia in our dating analyses. Additionally, this stem age estimate of about 240 million years most likely marks the starting point of a transition from a terrestrial to an epiphytic lifestyle in thalloid liverworts of the Metzgeriales. We assume that the Cretaceous Terrestrial Revolution played a key role in the evolution of epiphytic thalloid liverworts similar to that known for leafy liverworts.
... It has been hypothesized that most of the biota colonized Iceland after the last (Weichselian) glacial period (Sadler 1999, Kristinsson 2015. The vegetation history after this period is better known than that of the fauna (Norðdahl et al. 2008;Denk et al. 2011). The extent of glaciation and the size of refugia would have influenced the faunal development. ...
Chapter
This chapter analyses the bird faunas on two Northeast Atlantic island groups, Iceland and the much smaller Faroe Islands. Birds are more mobile than most animal groups. The first Icelandic bird list stems from around 1590 and only mentions about 30 species. The details whereby island communities evolve are subject to general principles of island biogeography; islands generally have fewer species, less competition and greater predation rates. With fossil records hardly existing, the dynamic development of the island bird communities is rather speculative. The history of the immigration and colonization is only known during the last centuries and although the islands have been ice-free for thousands of years new bird species are immigrating. Birds that competed with economic interests were previously violently pursued and slaughtered. Many of the variations in colonization and population sizes are believed to be due to climate change.
... The dispersal of Ulmus from East Asia to North America may have occurred through the BLB, which allowed the migration of terrestrial organisms from at least the early Paleogene until the late Neogene ( Fig. 5; . Then, a dispersal event of Ulmus from North America to Europe from the middle Eocene to the middle Miocene may have occurred via the NALB, acting as a corridor for migration until the latest Miocene via island hopping (Fig. 5;Denk et al., 2010Denk et al., , 2011. Our results confirmed that both the BLB and NALB played essential roles in allowing the dispersal of temperate Ulmaceae species. ...
Article
Full-text available
Ulmaceae are a woody family widespread in northern temperate forests. Despite the ecological importance of this family, its phylogeny and biogeographic history are poorly understood. In this study, we reconstruct phylogenetic relationships within the family and infer spatio‐temporal diversification patterns based on chloroplast genome (complete cpDNA) and nuclear ribosomal DNA sequences (nrDNA). The seven Ulmaceae genera comprising the family are resolved in two main clades (temperate vs. tropical) by both cpDNA and nrDNA sequences. The temperate clade includes four genera, Hemiptelea, Zelkova, Planera, and Ulmus. The relationships among Planera and other genera are controversial because of inconsistent topologies between plastid and nuclear data. The tropical clade includes three genera, ((Ampelocera, Phyllostylon), Holoptelea). Molecular dating and diversification analyses shows that Ulmaceae originated in the Early Cretaceous (ca. 110–125 Ma) with the main lineages establishing from the Late Cretaceous to the early Eocene. The diversification rate slowed during the middle to the late Paleogene (ca. 23–45 Ma), followed by a rapid diversification of the East Asian temperate group in the Neogene, congruent with a global cooling event. The ancestral state optimization analysis suggests an East Asian origin of the temperate Ulmaceae clade during the Paleocene, which is consistent with the fossil record. Both phylogenomic and fossil evidence support East Asia as a center of origin and diversification for the temperate woody lineages. This article is protected by copyright. All rights reserved.
... This dispersal event likely occurred across the North Atlantic land bridge (NALB) due to the water barrier of the Turgai Strait that separated Asia and Europe and the moisture and mountain barriers separating western and eastern North America during this time period (Tiffney & Manchester, 2001). The dispersal across the NALB was likely via "island hopping" (Denk et al., 2011), due to the degradation of the NALB after the early Eocene (Tiffney & Manchester, 2001); island hopping was possible in bird-dispersed genera such as Cornus that produce fleshy, nutritious fruits with a stony endocarp. The fleshy fruits of both C. alternifolia and C. controversa of disjunct 1 were known to attract birds (Coladonato, 1994;Masaki et al., 1994), supporting the hypothesis of "island hopping" as a mode of dispersal for disjunct 1 ancestor. ...
Article
Full-text available
The eastern Asian (EA) ‐ eastern North American (ENA) floristic disjunction represents a major pattern of phytogeography of the Northern Hemisphere. Despite 20 years of studies dedicated to identifying taxa that display this disjunct pattern, its origin and evolution remain an open question, especially regarding post‐isolation evolution. The blue‐ or white‐fruited dogwoods (BW) are the most species‐rich among the four major clades of Cornus L., consisting of ~35 species divided into three subgenera (subg. Yinquania, subg. Mesomora, and subg. Kraniopsis). The BW group provides an excellent example of the EA‐ENA floristic disjunction for biogeographic study due to its diversity distribution centered in eastern Asia and eastern North America, yet its species relationships and delineation have remained poorly understood. In this study, we combined genome‐wide markers from RAD‐seq, morphology, fossils, and climate data to understand species relationships, biogeographic history, and ecological niche and morphological evolution. Our phylogenomic analyses with RAxML and MrBayes recovered a strongly supported and well‐resolved phylogeny of the BW group with three intercontinental disjunct clades in EA and ENA or Eurasia and North America; two of which are newly identified within subg. Kraniopsis. These analyses also recovered a potential new species but failed to resolve relationships within the C. hemsleyi ‐ C. schindleri complex. In an effort to develop an approach to reduce computation time, analysis of different nodal age settings in treePL suggest setting a node's minimum age constraint to the lower bound of a fossil's age range to obtain similar ages to that of BEAST. Divergence time analyses with BEAST and treePL dated the BW stem back to the very Late Cretaceous and the divergence of the three subgenera in the Paleogene. By integrating fossil ages and morphology, a total evidence‐based dating approach was used in conjunction with time‐slice probabilities of dispersal under a DEC model to resolve ancestral ranges of each disjunct in the Miocene: Eurasia and ENA (disjunct 1), EA and western North America (disjunct 2), and EA (disjunct 3). The dated biogeographic history supports dispersal via the North Atlantic Land Bridge in the late Paleogene in disjunct 1 and dispersal via the Bering Land Bridge in the Miocene for disjuncts 2 and 3. Character mapping with a stochastic model in phytools and comparison of ecological niche, morphospace, and rate of evolution indicated differential divergence patterns in morphology, ecological niche, and molecules between disjunct sisters. Although morphological stasis was observed in most of the characters, evolutionary changes in growth habit and some features of leaf, flower and fruit morphology occurred in one or both sister clades. Significant differentiation of ecological habitats in temperature, precipitation, and elevation between disjunct sisters were observed, suggesting a role of niche divergence in morphological evolution post‐isolation. The patterns of evolutionary rate between morphology and molecules varied among disjunct clades and were not always congruent between morphology and molecules, suggesting cases of non‐neutral morphological evolution driven by ecological selection. Our phylogenetic evidence and comparisons of evolutionary rate among disjunct lineages lends new insights into the formation of the diversity anomaly between EA and ENA, with particular support of an early diversification in EA. These findings, in conjunction with previous studies, again suggest the EA‐ENA disjunct floras are an assembly of lineages descended from the Mesophytic Forests that evolved from the early Paleogene “boreotropical flora” through varied evolutionary pathways across lineages. This article is protected by copyright. All rights reserved.
... For example, the range of estimates for the subsidence of the GSR (including the Faroe-Shetland Channel) spans almost 30 Myrs from the Mid Eocene to the Mid-Late Miocene (e.g. Clift and Turner, 1995;Davies et al., 2001;Denk et al., 2011;Hohbein et al., 2012;Poore et al., 2006;Wold, 1995); the time for the closure of the Tethys Seaway varies by ~ 30 Myrs from Early Eocene to Mid Miocene (e.g. Allen and Armstrong, 2008;Harzhauser et al., 2007;Oberhänsli, 1992;Rögl, 1999), and the CAS timing approximations spans ~ 20 Myrs from Early Miocene to Pleistocene (e.g. ...
... From Late Eocene to Early Oligocene, this configuration changed as the Southern Ocean gateways Ehlers and Jokat, 2013;Jakobsson et al., 2007;Jokat et al., 2016;Knies and Gaina, 2008;Myhre et al., 1995b), for the GSR (i.e. Davies et al., 2001;Denk et al., 2011;Ellis and Stoker, 2014;Poore et al., 2006;Wold, 1995), for the Tethys Seaway (i.e. Allen and Armstrong, 2008;Dercourt et al., 1986;Oberhänsli, 1992;Okay et al., 2010;Rögl, 1999), for the CAS (i.e. ...
... Evidence of a submerged Greenland -Scotland Ridge, modified fromDenk et al. (2011). ...
Article
Full-text available
The evolution of the Northern Hemisphere oceanic gateways has facilitated ocean circulation changes and may have influenced climatic variations in the Cenozoic time (66 Ma–0 Ma). However, the timing of these oceanic gateway events is poorly constrained and is often neglected in global paleobathymetric reconstructions. We have therefore re-evaluated the evolution of the Northern hemisphere oceanic gateways (i.e. the Fram Strait, Greenland–Scotland Ridge, the Central American Seaway, and the Tethys Seaway) and embedded their tectonic histories in a new global paleobathymetry and topography model for the Cenozoic time. Our new paleobathymetry model incorporates Northeast Atlantic paleobathymetric variations due to Iceland mantle plume activity, updated regional plate kinematics, and models for the oceanic lithospheric age, sediment thickness, and reconstructed oceanic plateaus and microcontinents. We also provide a global paleotopography model based on new and previously published regional models. In particular, the new model documents important bathymetric changes in the Northeast Atlantic and in the Tethys Seaway at Eocene–Oligocene transition (~34 Ma), the time of the first glaciations of Antarctica, believed to be triggered by the opening of the Southern Ocean gateways (i.e. the Drake Passage and the Tasman Gateway) and subsequent Antarctic Circumpolar Current initiation. Our new model can be used to test whether the Northern Hemisphere gateways could have also played an important role modulating ocean circulation and climate at that time. In addition, we provide a set of realistic global bathymetric and topographic reconstructions for the Cenozoic time at one million-year interval for further use in paleo-ocean circulation and climate models.
... The presence of fossil leaves from Ellesmere Island referred to Tetracentron supports previous suggestions of a dispersal route for this genus across the Bering Land Bridge from Asia (e.g., Grímsson & Denk 2007;Grímsson et al. 2008;Denk et al. 2011); and provides evidence for the idea that Tetracentron would have migrated northward through Ellesmere Island to eventually colonize Iceland in the Miocene, as suggested by Grímsson et al. (2008). ...
The late Paleocene to early Eocene sediments of Ellesmere and Axel Heiberg islands, Nunavut, of the Canadian High Arctic contain a rich fossil flora and fauna. Although the megafloral fossils have been known for more than a century, limited descriptions of the fossil flora have been presented. Here, we provide a comprehensive morphotype catalogue of fossil plants from multiple localities from Ellesmere and Axel Heiberg islands that form a systematic framework for establishing an early Paleogene polar flora from High Arctic latitudes in Canada. Described are 62 ‘dicot’ angiosperm morphotypes, three monocotyledonous angiosperms, 13 gymnosperms, and five pteridophyte morphotypes. This work presents a significant contribution to the understanding of north-polar diversity and environments during the warm greenhouse climate of the early Paleogene.
... The presence of fossil leaves from Ellesmere Island referred to Tetracentron supports previous suggestions of a dispersal route for this genus across the Bering Land Bridge from Asia (e.g., Grímsson & Denk 2007;Grímsson et al. 2008;Denk et al. 2011); and provides evidence for the idea that Tetracentron would have migrated northward through Ellesmere Island to eventually colonize Iceland in the Miocene, as suggested by Grímsson et al. (2008). ...
Presentation
Understanding the causal mechanisms of the modern latitudinal diversity gradient (LDG) is a long-established problem in ecology. Temperature has been proposed as the primary driver of the modern LDG, although other hypotheses (e.g. precipitation, insolation, seasonality, biogeographical history, and biological interactions), have been suggested as constraints or drivers of diversity in the extra-tropics (i.e. the mid- and high-latitudes). The modern Arctic is characterized by very low floral diversity and a cold dry climate; however, the early Eocene Arctic was much warmer and wetter, as evidenced from paleobotanical climate reconstructions (e.g. MAT ≈ 8.5–12.7 ºC and MAP >150 cm/yr), and the presence of thermophilic flora and fauna (e.g. palm or palm-like palynomorphs and alligators). Nevertheless, forest diversity for Arctic Eocene ecosystems remains relatively untested and is typically described as low and homogenous. Reported here are the first quantitative megafloral diversity estimates from Stenkul Fiord, Ellesmere Island, Canada, utilizing two purpose-made census-sampled fossil leaf collections coupled with horizon-specific palynological analyses. Recent U-Pb zircon geochronology, and new geological mapping at Stenkul Fiord, place the fossil sites stratigraphically near the PETM and ETM2 hyperthermal events of the early Eocene, a time when warm equable climates allowed temperate and tropical plant taxa to survive at high northern latitudes. Diversity was assessed using coverage-based interpolation- and extrapolation-based rarefaction, a method that reconstructs richness with high accuracy. The results show that the early Eocene paleoarctic forests supported diverse forest ecosystems with floral diversity similar to modern mid-latitude mesic-mesothermal broadleaf forests from North America, but overall floral diversity may have been restricted as a result of photic seasonality. Furthermore, these ecosystems experienced floristic change probably related to the transient hyperthermal events.
... Biogeographical evidence for plant and animal dispersal [Denk et al., 2011] and dating of the onset of the overflow of intermediate-and deep waters between the Norway and Iceland basins [Ellis & Stoker, 2014;Stoker et al., 2005b] suggest that the GIFR formed a largely intact, trans-Atlantic landbridge (the Thulean landbridge) until ~ 15-10 Ma and that much survived above sea level longer than this. This leads to the surprising conclusion that the Thulean landbridge presented a major topographic barrier to inter-basin connectivity until the NE Atlantic Ocean had attained a width of ~ 1000 km. ...
Article
The breakup of Laurasia to form the Northeast Atlantic Realm disintegrated an inhomogeneous collage of cratons sutured by cross-cutting orogens. Volcanic rifted margins formed that are underlain by magma-inflated, extended continental crust. North of the Greenland-Iceland-Faroe Ridge a new rift–the Aegir Ridge–propagated south along the Caledonian suture. South of the Greenland-Iceland-Faroe Ridge the proto-Reykjanes Ridge propagated north through the North Atlantic Craton along an axis displaced ~150 km to the west of the rift to the north. Both propagators stalled where the confluence of the Nagssugtoqidian and Caledonian orogens formed an ~300-km-wide transverse barrier. Thereafter, the ~150 × 300-km block of continental crust between the rift tips–the Iceland Microcontinent–extended in a distributed, unstable manner along multiple axes of extension. These axes repeatedly migrated or jumped laterally with shearing occurring between them in diffuse transfer zones. This style of deformation continues to the present day in Iceland. It is the surface expression of underlying magma-assisted stretching of ductile continental crust that has flowed from the Iceland Microplate and flanking continental areas to form the lower crust of the Greenland-Iceland-Faroe Ridge. Icelandic-type crust which underlies the Greenland-Iceland-Faroe Ridge is thus not anomalously thick oceanic crust as is often assumed. Upper Icelandic-type crust comprises magma flows and dykes. Lower Icelandic-type crust comprises magma-inflated continental mid- and lower crust. Contemporary magma production in Iceland, equivalent to oceanic layers 2–3, corresponds to Icelandic-type upper crust plus intrusions in the lower crust, and has a total thickness of only 10–15 km. This is much less than the total maximum thickness of 42 km for Icelandic-type crust measured seismically in Iceland. The feasibility of the structure we propose is confirmed by numerical modeling that shows extension of the continental crust can continue for many tens of millions of years by lower-crustal ductile flow. A composition of Icelandic-type lower crust that is largely continental can account for multiple seismic observations along with gravity, bathymetric, topographic, petrological and geochemical data that are inconsistent with a gabbroic composition for Icelandic-type lower crust. It also offers a solution to difficulties in numerical models for melt-production by downward-revising the amount of melt needed. Unstable tectonics on the Greenland-Iceland-Faroe Ridge can account for long-term tectonic disequilibrium on the adjacent rifted margins, the southerly migrating rift propagators that build diachronous chevron ridges of thick crust about the Reykjanes Ridge, and the tectonic decoupling of the oceans to the north and south. A model of complex, discontinuous continental breakup influenced by crustal inhomogeneity that distributes continental material in growing oceans fits other regions including the Davis Strait, the South Atlantic and the West Indian Ocean.
... This relationship is not supported elsewhere, but other studies have shown A. macrophyllum as sister to other Eurasian lineages (Tian et al. 2001, Grimm et al. 2006, Renner et al. 2008. Clearly, a better resolved phylogeny and denser taxonomic sampling is needed to test specific biogeographic hypotheses, such as the roles of dispersal and the Bering and North Atlantic land bridges in explaining the modern disjunctions in Acereae (Budantsev 1983, Tiffney 1985, Kropf et al. 2006, Ree & Sanmartín 2009, Denk et al. 2011. ...
Article
We sought to test the utility of two single-copy nuclear genes for resolving phylogenetic relationships within the woody plant tribe, Acereae (Sapindaceae). Acereae comprises Acer (125+ spp.) and Dipteronia (2 spp.), two genera that possess schizocarpic fruits, which split into two winged mericarps. In Acer, the mericarps are elongated with a basally arranged locule and a dorsal or distal wing. In Dipteronia, the mericarp is obovate, and the locule is located centrally and surrounded by the wing. We analyzed 35 species of Acer representing 12 of 16 taxonomic sections plus Dipteronia sinensis to elucidate the phylogeny of Acereae using the single-copy nuclear genes AT103 and SQD1. Both genes exhibited limited variation in Acereae and, therefore, provided limited support for phylogenetic relationships. The phylogeny of concatenated AT103 and SQD1 showed Dipteronia sinensis within Acer with negligible support (0.14 posterior probability, < 50% maximum parsimony bootstrap, MP-BS), a position that is congruent with results from prior studies using chloroplast DNA and internal transcribed spacer (ITS). Based on our results and results from prior studies, we discuss implications for leaf and fruit evolution in Acereae.