model was presented. Today, paleomagnetism, Plate tectonics in radiometric dating, stratigraphy, and spatial biogeography information allow detailed interpretation and paleogeographic reconstruction. One type of evidence presented in support Steve Trewick of continental drift by Wegener and others was Massey University, New Zealand (paleo)biogeographic: the widespread distribu- tion of certain fossil animals and plants across Plate tectonics deals with the motions of the landscapes that are now disconnected (Figure 1). Earth’s rocky shell, or lithosphere, which cause However, although widely reiterated even today, the gradual shift of continents and are also the occurrence of fossils did not in truth inform responsible for mountain building, volcanic on the process of continental isolation. An alter- islands, and thermal vents. These geological native idea (land bridging) resolves the spatial processes have influenced the distribution of discontinuity of biota problem equally well and biodiversity. Prior to the identification of a makes the same biological assumptions. As with geophysical mechanism that could drive move- continental drift, land bridging assumes that the ment at the Earth’s surface, its effects had been organisms of interest were unlikely to disperse predicted. The concept of “continental drift” between patches of suitable habitat. Thus both is usually attributed to Alfred Wegener, who hypotheses require habitat continuity if species presented his ideas on the origin of continents (or their lineages) are to be shared among areas. and oceans in 1915. However, in the 1500s the In biogeography, distribution patterns are often Belgian mapmaker Abraham Ortelius had noted taken as evidence of past processes but they that the coincidence of the coastal outlines of the provide only the basis for formulating alterna- Americas, Africa, and Europe implied former tive hypotheses about the processes that might juxtaposition. In the 1800s, the “father of bio- explain them. This is a subtle but vital distinction geography,” Alfred Russell Wallace, developed that underpins scientific method; a proposition his ideas with the benefit of geographer Charles cannot be simultaneously proposed and tested Lyell’s Principles of Geography. Lyell had noted using the same observations. that “Continents … shift their positions entirely In later editions of his book, Wegener recog- in the course of ages.” Nevertheless, in the nized that his continental drift hypothesis was 1900s continental drift was strongly opposed by not to be tested with fossils, or for that matter a many, and the rejection of this hypothesis, which coincidence of continental crust outline. Rather, was built on extensive evidence, represents a the best approach to testing the hypothesis was notable failure of twentieth-century scientific geodetics (Earth measurement), because the method. The claim that consideration of the hypothesis that continents had moved in the past theory required demonstration of a geophysical generated the prediction that continents would mechanism was unjustified, but was nevertheless still be moving. Wegener died in his tent during assuaged in the 1950s and 1960s when a tectonic a trip to Greenland to confirm longitudinal drift, The International Encyclopedia of Geography. Edited by Douglas Richardson, Noel Castree, Michael F. Goodchild, Audrey Kobayashi, Weidong Liu, and Richard A. Marston. © 2017 John Wiley & Sons, Ltd. Published 2017 by John Wiley & Sons, Ltd. DOI: 10.1002/9781118786352.wbieg0638 PLATE TECTONICS IN BIOGEOGRAPHY Lystrosaurus Glossopteris Cynognathus Mesosaurus Africa Lystrosaurus India South America Australia Antartica Cynognathus Glossopteris Mesosaurus Figure 1 Distribution of four Permian and Triassic fossil groups used as biogeographic evidence for continental drift, and land bridging. Mesosaurus included a small number of meter-long marine reptile species recorded in early Permian time (299–280 Ma). It is said that Mesosaurus could not have crossed the Atlantic but this is speculative, and at least one popular web resource incorrectly states that these were freshwater reptiles. Lystrosaurus included a debated number of species of pig-like land reptiles less than 1 m long. The genus is unusual in being present on either side of the Permian-Triassic extinction boundary (255–241 Ma). Cynognathus (C. crateronotus) was a meter-long predatory mammal-like reptile usually treated as one species that existed in early to mid-Triassic time (247–237 Ma). Glossopteris was a group of woody gymnosperm plants with wide but mostly southern (i.e., Gondwanan) distribution in the Permian (290–252 Ma). The identification of Glossopteris from northern areas has been questioned, and estimates of diversity vary. Fossil sites were mapped using the database and tools of the Fossilworks Paleobiology Database, Macquarie University ( John Alroy). Paleogeographic reconstruction is for Permian-Triassic time (250 mya). The inset on left is a version of a popular iconographic but misleading depiction of the fossil distributions (The Snider-Pellegrini Wegener fossil map; WikiCommons). Permian Map by C.R. Scotese, PALEOMAP Project. Reproduced by permission of C.R. Scotese. but geodetic data have since demonstrated the the distribution and evolution of biological fact that continents move. Plate tectonics explains diversity, in many different ways. how. Geological (rather than biogeographic) data informs paleogeographic reconstruction, and in Continental drift vicariance doing so provides the context for biogeography. Plate tectonics is not, however, only about drifting continents; it generates short- and Recognition of the potential for continental-scale long-term environmental changes that influence effects of plate tectonics on biology developed 2 PLATE TECTONICS IN BIOGEOGRAPHY side by side with plate tectonic theory. The understood (e.g., colonization and speciation on founding concept of continental drift was that oceanic islands such as the Galapagos). In studies most of the Earth’s land had formerly been con- of living biota, evidence for plate tectonic vicari- nected in a single supercontinent (Pangea). Fossils ance can come from dated phylogenetic analysis of Permian age indicate that Pangea existed more (see Phylogeography and landscape genetics). than 250 mya, and modern evidence supports Appropriate sampling and fossil calibration (see this (see Figure 1). In fact the key fossils occur Figure 2) allow the timing of evolutionary events primarily across the southern part of this conti- and continental drift to be compared. A match nent, a region usually referred to as Gondwana between the estimated time of origins of regional (or Gondwanaland), and it is noteworthy that biota and the time of continental separation is this term was also used by land-bridgers who also consistent with, but not proof of, vicariance. envisaged a former extensive continent, parts of which subsequently disappeared. Although the geophysical evidence for a supercontinent Land bridges and sea barriers is very clear, we now know that it did not include all continental areas at any one time. Plate tectonics can result in the connection of The idea that past breakup of a supercontinent formerly disjunct land areas and simultaneously (up to 200 million years later) could result in the sundering of marine environments, through the establishment of biotas that are visible today volcanics, accretion, orogenics, and deformation. makes many assumptions, among them that Although land bridging has been largely rejected a supercontinent would have a homogeneous from consideration of ancient biological history environment with continuous distributions of of Earth, younger examples show its influence. plants and animals, that other global events did The Central American (or Panama) isthmus not cause local changes in biotic assemblages, between North America and South America is a and that dispersal between continents had little narrow strip of land (60–177 m wide) that finally influence on biological assemblages. In fact, shut off the equatorial link between Atlantic and paleoecological evidence indicates diverse and Pacific oceans (the Central American seaway) sometimes extreme environmental conditions in the late Pliocene (about 3 million years ago). existed across Pangea. Continental drift itself Several tectonic plates intersect in the region resulted in changes in climatic conditions so that (Figure 3) and their interaction appears to have natural selection on the biota would change, an led to the formation of numerous volcanic islands extreme case being the wholesale extinction of starting at about 5.5 mya. Sediment accumu- Antarctic biota due to the drift of the continent lation between these islands is one mechanism over the South Pole. Mass extinctions across proposed for the land bridge. the globe radically altered biotas and dispersal Closure forced the Gulf Stream to carry warm between continents influenced regional biotic equatorial water into the northern Atlantic composition through time. Ocean, where it influences the composition Intriguingly, although vicariance biogeogra- and ecology of regional marine biota. Separa- phy associated with continental drift is a highly tion was accompanied by other environmental attractive and popular idea, contrary evidence change; upwelling on the Pacific side see ms of the power of biota to disperse and colonize to have increased while salinity has increased across habitat discontinuities is abundant and well in the Caribbean.