Aim I re-evaluate the specific biogeographical significance of each of the land bridges (Beringia, Thulean and De Geer) in the Northern Hemisphere during the latest Cretaceous-early Cenozoic, showing that the Thulean and De Geer routes did not operate contemporaneously.Location Northern Hemisphere landmasses.Methods I review the recent climatic, sea-level, geotectonic, palaeofloristic, and marine and terrestrial faunal data that have emerged since the establishment in the 1980s of the biogeographical concepts of the early Cenozoic Northern Hemisphere land bridges and present a synthesis supporting a revised scenario for early Cenozoic biogeographical development.Results Palaeogeographical and geotectonic data, supported by strong floral and faunal evidence, suggest that the palaeogeographical and chronological frames for the formation of all three land bridges are different from those originally proposed. Dispersal events via the causeways seem to have taken place during specific time intervals resulting from fluctuations in sea level and climate.

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Genetic isolation due to geographic separation (vicariance) is the best understood cause of vertebrate speciation. nevertheless, it has never been demonstrated in the fossil record across a wide range of taxa. Here, by reviewing in-depth the available data of the Late Palaeozoic (~ 350-250 million years ago), i reconstructed an early pangaean junction-disjunction palaeogeographic model and showed that it coincides strongly with time-calibrated cladograms of the Late palaeozoic synapsids (the primitive ancestors of modern mammals). the temporal development of the vicariant topology seems to fit closely with the emergence rhythm of the recovered synapsid taxa, suggesting vicariance due to pangaean separation as the cause of early amniote evolution. the inferred vicariant topology also accounts for the observed pattern in the north American marine biostratigraphic units. Accordingly, the model demonstrates the link between the evolution of life on earth and palaeogeographic evolution and strongly supports allopatric speciation through vicariance as the prominent mode of amniote evolution. furthermore, correlations between state-of-the-art biochronostratigraphic charts and this palaeogeographic model suggest that the arido-eustasy model can explain the mid-permian biotic extinction event and depositional cycles, such as the pre-Zechstein of the central european Basin. Vicariance is the geographical separation of previously sympatric populations due to the development of geographical and/or ecological barriers to gene flow 1. Through vicariance, conspecific populations become genetically isolated and subsequently accumulate different mutations that render them reproductively incompatible resulting in the creation of new species 2. One common way for temporally heterogeneous geographic barriers to form is via eustatic sea-level changes that produce seaways on low profile intercontinental land bridges 3. Accordingly, transgressive stages, which occur when sea-levels are high, are expected to coincide with vicariance of the terrestrial biota, whereas regressive stages, which occur when sea-levels are low, are expected to coincide with geodispersals, and the opposite pattern is expected for marine biota 4. To verify a vicariance pattern, a junction-disjunction palaeogeographic model must correlate with phylogenetic topologies of multiple taxa 5. Although vicariance is the best understood mode of speciation 1,2 , due to the absence of detailed scenarios of palaeogeographic changes and sufficiently resolved and representative phylogenetic trees, allopatric speciation has not been confirmed for a wide range of taxa in the vertebrate fossil record. Based on the most apparent episodes of sea-level change that affected the southern connections between the Uralian Seaway (URS) and the Palaeotethys, an early Pangaean junction-disjunction palaeogeographic model was reconstructed and compared to time-calibrated consensus cladograms ("clado-stratigraphic patterns") of Late Palaeozoic vertebrates to determine whether a vicariance pat...

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The exact age of the final formation of the Isthmus of Panama is a critical reference point for oceanographic, climatic, biogeographic, and evolutionary hypotheses. Geotectonic evidence suggests that the isthmus was completed between 12 Mya and 3 Mya, and an age of 3–4 Mya has been used as a benchmark in hundreds of studies over the past 30 years. Phylogeographic data indicate the existence of marine connections across the isthmus much more recently, however. I reconsider the available geotectonic, biostratigraphic, oceanographic, and paleoclimatic data and show that multiple lines of indirect evidence suggest that four transisthmian seaways may have persisted until as recently as the onset of the Middle Pleistocene (~ 0.6 Mya). Subduction of the Cocos Plate beneath one transisthmian seaway (the only seaway featuring a deep sill) caused rapid tectonic shoaling and reorganisation of oceanic currents, which coincided with a major glacioeustatic sea level fall ~ 950–917 Mya that led to a temporary closing of the Bering Strait. This resulted in unusual and contrasting climate phenomena, including the “900-Kyr (cold) event” and the “greening” of South Greenland during the MIS 22 glacial maximum. The concurrence of the final formation of the Isthmus of Panama with the mid-Pleistocene Transition of glacial/interglacial periodicity suggests a tight relationship between these events.