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ECOL 182h: The Great American Interchange Thylacosmilus , a South American borhyaenid, died out after the arrival of true sabertooths from the north. Also shown are a Glyptodont (Xenarthra) and toxodonts (Notoungulata). 1 Mammalian Evolution. Simplified amniote (reptiles, birds and mammals) phylogeny. Mammals arise in the Triassic and subsequently (late Jurassic) differentiate into pr o- therians (platypus, echidna) and therians. The latter split into metatherians (marsupials) and eutherians (placentals) early in the Cretaceous. 2 Mammalian Evolution – II. A more detailed view of mammalian evolution. Of the various Mes- ozoic mammals, only multituberculates survived the end- Cretaceous mass extinction. 3 Marsupial Dispersal. Marsupials are believed to have evolved in Asia from whence they dispersed into the Americas, Antarctica and Australia prior to the separation of North and South America. 4 History of South Amrica. • Connected to NA (directly or by islands) during most of the Mesozoic. • An island continent thereafter until late Tertiary. • During this period, a unique mammalian fauna evolved. 1. Marsupials including borhyaenid carnivores. 2. Placental herbivores including a. Xenarthrans (armadillos, sloths, anteaters) b. Indigenous ungulates (condylarths, litopterns, etc .) 3. Some spectacular examples of convergent evolution. • Following reconnection with SA, 1. Many northern species went south. 2. A smaller number (opossums, amadillos, sloths) went north. 3. Many indigenous pecies died out. 5 SA Old Timers (Marsupials & Xenarthrans). 6 SA Old Timers (Ungulates). 7 Litoptern Relations. Whereas Darwin imagined Macrauchenia , to be closely related to then living Guanaco (Camelidae), Litopterna and Artiodactyla (along with Perissodactyla and Cetacea, turn out to be sister texa. 8 Mammalian Dentition. Dentition of Juramaia sinensis, a late Jurassic eutherian. Note the differentiation of teeth into in- cisors, canines, premolars and molars. From Luo et al . (2011). 9 Carnivore Evolution and Convergence. Top. Evolution of eutherian Carnivora. Dental formulas refer to shearing teeth (carnassials). Bottom. Thylacosmilus (left ) and Smilodon (right ). 10 Thoatherium : A Horse-like Litoptern. Equus (left) and Thoatherium (right) compared. Note the absence of splints (vestigial 2 nd and 4 th toes) in the latter. 11 Terror Birds (Phorusrhacids). • Dominant South American predators during most of the Cenozoic. 1. 1-3 m in height. 2. One species, Titanis walleri, migrated north to FLA / TX during the Pleistocene. After the interchange. Terror birds drive Smilodon from a kill. Video at http://www.youtube.com/watch?v=-o5OvDJxM78. 12 After the Interchange. 13 After the Interchange – II. Results of the great American faunal exchange. Not all southe rners making it north are shown; some that did, e.g. , sloths, subsequently died out north of the filter. 14 .

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The Great American Biotic Interchange: Patterns and Processes Author(S): S
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.
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108 ©2017 by the Society of Vertebrate Paleontology
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