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The Great American Biotic Interchange: Patterns and Processes Author(s): S. David Webb Source: Annals of the Missouri Botanical Garden, Vol. 93, No. 2 (Aug., 2006), pp. 245-257 Published by: Missouri Botanical Garden Press Stable URL: http://www.jstor.org/stable/40035724 . Accessed: 08/04/2014 23:14 Your use of the JSTOR archive indicates your acceptance of the Terms & Conditions of Use, available at . http://www.jstor.org/page/info/about/policies/terms.jsp . JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact [email protected]. Missouri Botanical Garden Press is collaborating with JSTOR to digitize, preserve and extend access to Annals of the Missouri Botanical Garden. http://www.jstor.org This content downloaded from 137.111.226.20 on Tue, 8 Apr 2014 23:14:05 PM All use subject to JSTOR Terms and Conditions THE GREAT AMERICAN BIOTIC S. David Webb2 INTERCHANGE: PATTERNS AND PROCESSES1 Abstract Whenthe Panamanianland bridgewas emplacedabout 2.7 Ma, it triggeredthe GreatAmerican Biotic Interchange(GABI), a major mingling of land mammal faunas between North and South America. Four families of northern immigrants (Procyonidae,Felidae, Tayassuidae,and Camelidae)diversified at moderaterates, while four others, Canidae, Mustelidae, Cervidae, and especially Muridae, evolved explosively. As a consequence, half of living South American genera are descendantsof northernimmigrants. The other major consequence of the interchangewas the conquest of tropical North Americaby immigrantsfrom Amazonia, an episode that justifies the term NeotropicalRealm. Key words: biostratigraphy,evolutionary rates, isthmianland bridge, mammals,Neotropical Realm. Resumen Cuandoel corredorterrestre panameno se ubico hace cerca de 2.7 Ma, desencadenoel GranIntercambio Biotico Americano (GABI),una mezcla importantede las faunas de mamiferosterrestres entre Americadel Norte y del Sur. Cuatrofamilias de inmigrantesdel norte (Procyonidae,Felidae, Tayassuidae,and Camelidae)se diversificarona un ritmomoderado, mientras que otras cuatro, Canidae, Mustelidae, Cervidae y especialmente Muridae, evolucionaron en forma explosiva. Por consiguiente, la mitad de generos suramericanosactuales son descendientes de inmigrantesdel norte. La otra principal consecuenciadel intercambiofue la conquistade Norteamericatropical por inmigrantesamazonicos, un episodioque justifica el terminode Reino Neotropical. The rootsof the LatinAmerican biota can be traced living faunas, along with their fossil predecessors, down throughthe epochs of earth history to several recordboth the rapidlychanging distributions and the formativechapters. During most of the MesozoicEra, dynamic evolutionarydiversifications that illuminate the South Americanbiota was an integral part of the the origins of the Latin Americanbiota. Gondwananbiota. Throughmost of the CenozoicEra, My own introductionto the nature of the GABI the terrestrialand freshwaterbiotas of SouthAmerica began in the 1960s when the Florida Museum of were isolated from those of North America and all NaturalHistory was actively filling chronologicalgaps other continents by deep ocean troughs. The most in that state's rich late Cenozoic record of land recent chapterbegins with the GreatAmerican Biotic vertebrates. One fossil site in particular opened Interchange (GABI). This occurred approximately a critical window into the late Pliocene, which is three million years ago during the late Pliocene, knownin the system of NorthAmerican land mammal when the powerfulforces of plate tectonics raised the ages as the Blancan. Unlike any precedingstage, that isthmianland bridge in a final phase of upliftingthe intervalintroduced to NorthAmerica a large cohortof northernand southerncordilleras to connect them as land mammalspreviously restricted to SouthAmerica. the backboneof the Americas.Such dramaticphysical Our site, Inglis 1A (Fig. 1), yielded the richest changes inevitably triggered major new biological sample of late Pliocene vertebratesin eastern North interactions between the two previously separate America. Our team excavated and screenwashed Americancontinental biotas, and that is the focus of about 100 tons of fossiliferous sediment, which this paper. yielded about 120 species of land and freshwater In the following pages, I consider the major animals. Early in our studies, I realized that ten evolutionaryfeatures of the GABI as registered by genera of new immigranttaxa from South America land mammals.The mammalsoffer the richest, most accounted for about 20% of the entire rich fauna nearly coherent record of faunal changes in both (Webb, 1976). There were three families of ground American continents during the late Cenozoic. The sloths; three families of shelled edentates, ranging 1 1 thank Peter Raven and Alan Grahamfor inviting me to participatein the 51st Annual SystematicsSymposium at the MissouriBotanical Garden. I am also gratefulto manycolleagues who have expandedmy perspectivesin both biologicaland geological sciences, in particularR. H. Tedford, M. C. McKenna,B. J. MacFadden,the late J. F. Eisenberg, and the participantsin our symposium.This paper is ContributionNo. 575 fromthe FloridaMuseum of NaturalHistory. 2 FloridaMuseum of NaturalHistory, University of Florida,Gainesville, Florida 32611, U.S.A. [email protected] Ann. Missouri Bot. Gard. 93: 245-257. Published on 23 August 2006. This content downloaded from 137.111.226.20 on Tue, 8 Apr 2014 23:14:05 PM All use subject to JSTOR Terms and Conditions 246 Annals of the Missouri Botanical Garden Figure 1. Paleontologicalexcavations by the FloridaMuseum of NaturalHistory at Inglis 1A (late Pliocene)at cross-state barge canal, west-centralFlorida. Photo by author. fromtiny Dasypusto gigantic "\Glyptotherium3;as well esis on an intercontinentalscale. We may ask how the as two families of rodents,namely Erethizontidaeand modern South American fauna differ from the pre- Hydrochoeridae.The truly surprising forms were ceding fauna living in isolation.Likewise, we may ask a vampire bat, Desmodus Wied, and a giant pre- how the present CentralAmerican fauna differ from daceous bird named "\TitanisBrodkorb. Additionally, the preceding fauna that had lived in the southern nearly 40% of the fauna at Inglis 1A represented portion of North America. Clearly, the land bridge NorthAmerican genera, representativesof which had catalyzed a rapid remodelingof the Latin American dispersedto South Americaduring roughlythe same fauna. Such geological changes represented the time in the late Pliocene. Therewere relativesof such underlying cause that triggered major biological living Neotropicaltaxa as llamas, peccaries, tapirs, effects. jaguars, raccoons, foxes, and spectacled bears (cf. We begin by indicating some preliminary land Table 1 for taxa).Thus, a majorityof the land mammal mammaldispersals that precededthe GABI.I referto faunarecovered from Inglis 1A, and living in Florida these as herald taxa. Thereafter,we will consider the nearly three million years ago, were participants,in much larger cohorts that burst across a fully acces- one direction or the other, of the GABI. I was also sible Panamanianland bridge, which I refer to as astonished to realize how similar the mingled legions taxa. We also briefly review current geo- elements of the Inglis 1A local fauna were to chronological evidence regardingthe timing of the contemporaneousinterchange faunas through the GABI. Finally, we will consider evolutionary and Americantropics and all the way into Argentinaand ecological factors that influenced the origin of the the "southerncone" of the continent.Thus, in Florida South and CentralAmerican land mammalfaunas. we had stumbled fortuitouslyinto the acme of the GABI(Webb, 1976). Herald Taxa The interamerican evolution of land mammals representsa dramaticexperiment in rapid cladogen- A very small number of interamerican land mammaldispersals have been recorded earlier than 3 f representsextinct taxa. the latest Pliocene in Northand SouthAmerica. These This content downloaded from 137.111.226.20 on Tue, 8 Apr 2014 23:14:05 PM All use subject to JSTOR Terms and Conditions Volume 93, Number 2 Webb 247 2006 Great American Biotic Interchange Table 1. Families of land mammalsin the GABI. the Miocene of Mesoamerica "show strict North Americanaffinities." Family Commonname According to present records, the herald taxa Northernlegion taxa (17 families) consist of only two distinct genera of ground sloths Soricidae shrews in North America and one genus of large raccoon in Leporidae rabbits SouthAmerica. As indicatedby Tedfordet al. (2004), Heteromyidae pocket mice "\ThinobadistesHay, a mylodontidsloth, and "fPlio- Geomyidae pocket gophers metanastesHirshfeld & Webb, a megalonychidsloth, Sciuridae squirrels arrived in the early Hemphilllian about 9 million Muridae field mice years ago (Ma). One record of "fPliometanastesfrom Felidae cats Californiayields the best age estimatefor these early skunks and otters Mustelidae sloth Thereit occursin sediments4 Canidae foxes and wolves immigrant genera. meters below the MehrtenTuff, which is radiometri- Procyonidae raccoons Ursidae bears cally dated at 8.2 Ma (Hirschfeld& Webb, 1968). Gomphotheriidae elephantoids "\ArctonasuaBaskin is a large procyonid, well Tapiridae tapirs knownin NorthAmerica