How do you choose between dispersalist and vicariance models?1. Acceptance of plate tectonicsUp until the 1960s, most persons considered theearth's crust to be fixed. Finally, in the 1960s thegeological evidence was at hand that madecontinental drift irrefutable.Two important scientific advances – in the study of earth history andorganismal history - revolutionized historical biogeography2. Development of new phylogenetic methodsWilli Hennig (1950) introduced the modernconcepts of phylogenetic theory (first published in1956). Using this methodology, hypotheses ofhistorical lineages of species could bereconstructed.Species and Areas: History of IdeasEarth History: Plate TectonicsAbraham Ortellius’ 1587 map with exaggerated fit of SouthAmerican and African coastlinesEarth History: Plate TectonicsDuring the great world explorations of the 15th - 16th centuries, cartographers firstbegan to entertain ideas of earth’s mutability based on continental outlinesRichard Owen’s 1857Tetrahedral TheoryEarth History: Plate TectonicsWith no known process to account for these patterns, a variety of imaginativemechanisms were proposed in the 19th and early 20th centuries:Continents were superimposedon each other (e.g., SouthAmerica on Africa, Australiaon Arabia) prior to theirseparation“This approximation, althoughinvolving great doubt, is givenbecause it may facilitate theworking of the problem whichall desire to solve, regardingthe earth’s development”Key to the Geology of GlobeAntonio Snider’s map of “before” and “after” the separation from 1858.Many of the mid 19th century models (like Owens’ and Snider’s) invokedcatastrophism with indirect reference to a world-wide flood.Earth History: Plate TectonicsBefore AfterWith no known process to account for these patterns, a variety of imaginativemechanisms were proposed in the 19th and early 20th centuries:Charles Lyell’stheory of cycles ofglobal climaticchangeEarth History: Plate TectonicsWith no known process to account for these patterns, a variety of imaginativemechanisms were proposed in the 19th and early 20th centuries:Based on his observations oftropical fossils in Europe, Lyellrealized that climate had changedand invoked repeated andconcerted continental movementsduring times of heat and cold(in Principles of Geology, 1830)American geologist F. B. Taylor’s idea of crustal movements in 1910. Continentswere hypothesized to move, distorting crustal material to form mountains andleave oceans behind. His directions of movement are clearly wrong.Earth History: Plate TectonicsWith no known process to account for these patterns, a variety of imaginativemechanisms were proposed in the 19th and early 20th centuries:Earth History: Plate TectonicsAlfred Wegener (with Rasmus Villumsen) -prior to their disappearance in the ArcticAlfred Wegener (1880 - 1930)The basic tenets of continental drift theory tracesback to the German meteorologist, Wegener.His views became widely known with the Englishpublication of The Origins of Continents andOceans in 1922 (first in German in 1915).Earth History: Plate TectonicsWegener used a variety of geological and biologicalevidence to refute the prevailing views that theearth’s crust was fixed and thus the need to invokeland bridges and then to support his contention thatcontinents drifted over time.• land bridges defy the principle of isostasy• elevations of earth’s crust not random• contiguous shape of continental shelves• directions of ancient glacial striations• geological strata continuous between continents• fossil distributions between continentsEarth History: Plate Tectonics• directions of ancient glacial striationsEarth History: Plate Tectonics• geological strata continuous between continents• fossil distributions between continentsEarth History: Plate Tectonics• geological strata continuous between continents• fossil distributions between continentsWegener described both plant andanimal fossil examples supportinghis theory — he believed that thisbiogeographic data was thestrongest evidence for his theoryGlossopteris - Permian “fern”Mesosaurus - Permian freshwater reptile Cynognathus - Triassic land reptileLystrosaurus - Triassic land reptileEarth History: Plate TectonicsHowever, Wegener’s criticsargued that the amphi-Atlanticdistribution of the freshwater(estuary) Permian reptileMesosaurus was due to longdistance swimmingMesosaurus - Permian freshwater reptile • geological strata continuous between continents• fossil distributions between continentsEarth History: Plate TectonicsHarry Hess, Professor at YaleHarry Hess, Professor at Yale, put the plate tectonic theory together using newevidence obtained starting during WWII. Between 1960 and 1970 the academiccommunity finally accepted continental drift and the tectonic forces causing it.Despite this evidence, Wegener and a fewsouthern hemisphere scientists were unable topersuade the scientific community that the fixedcontinent hypothesis was incorrect.This bias against continental drift theorycoalesced at a symposium of the AmericanAssociation of Petroleum Geologists in 1928.Due in part to the inability of Wegener and othersto identify or explain the forces that caused themovements of continents.Earth History: Plate TectonicsThe first line of evidence involved thedocumentation that magnetic anomaliesexisted in the earth. Orientation of ironparticles in solidifying lava rock appeared toreverse in an irregular basis back in time,indicating that the earth’s magnetic polarityhad switched from one pole to the other.Earth History: Plate TectonicsThese reversals of magnetic polarity appearedas mirror images from the center ridge of theAtlantic Ocean going both west and east. Rockdating indicated that the youngest rocks werein the middle and got progressively oldergoing both west and eastyoungest oldestEarth History: Plate TectonicsThese lines of evidence allowed Harry Hess to propose the modern tectonictheory of sea-floor spreading. The theory proposes that when new magmafrom the mantle is added at the middle of the ocean ridge, the sea floor spreadsapart and moves existing lithosphere away from the ridge.Earth History: Plate TectonicsAs new material is formed at the ridges, oldest material eventually getssubducted at trenches. Thus, despite the fact the ocean floor makes up morethan 2/3rds of the earth’s surface, no part of it is older than the Jurassic (200Mya).Earth History: Plate