Transcript Geology
Geological History of Panama and the Great American Biotic Exchange Isthmus of Panama The Isthmus of Panama, in the past has been known as the Isthmus of Darien, it is the narrow strip of land that lies between the Caribbean Sea and the Pacific Ocean, linking Central and South America. MYA Geological Ages Pangea ~200 mya Pangea splits 135 mya Laurasia Gondwana Gondwana splits 100 mya Quaternary ~2-3 mya Formation of Isthmus 5 mya Early Pliocene 7 mya Miocene 3mya LateLate Pliocene 15 mya Middle Miocene Geological History of Panama Before ~4 mya Panama represented by island archipelago Islands arose by tectonic uplift Sea level changes modified the character of the “stepping stone” link Glaciations late Cretaceous: 300 m higher Pleistocene minimum: 92 m lower Today, melt all polar ice: 60 m higher Darien lowlands: 84 m Costa Rica/Nicaragua lowlands: 34 m Geological History of Panama Before ~4 mya Oceanic barrier to migration between NA & SA Flora & fauna of SA were more like Africa/Australia than NA E.g. marsupials were restricted mostly to SA/Australia Flora & fauna of NA were more like Europe Marsupial fossils in NA (extinct since the Miocene) probably originated in Europe Geological History of Panama Before ~4 mya Some N <=> S migration occurred Early tertiary 5 amphibians to NA Late Tertiary 1 salamander to SA Late Tertiary 8 reptile families to NA, 4 to SA By Early Tertiary few mammals migrated Few marsupials & placentals to NA Notoungulates to NA Late Miocene raccoon & kin to SA, 2 ground sloths to NA Geological History of Panama Before ~4 mya How these pre-Panamanian migrations occurred is debated a proto-Antillean land bridge? Island hopping? Geological History of Panama Before ~4 mya Panama’s biodiversity was low Limited land area Limited altitudinal zonation Limited highland areas Paleocommunities Fringing mangrove forests Floating or submerged freshwater communities Moderate altitude cloud forest Geological History of Panama Before ~4 mya SA hosted 29 land mammal families NA hosted 27 land mammal families 58 total families Geological History of Panama ~ 3 mya 4 tectonic plates collided Sea level dropped significantly Panama arose to provide a dry land bridge between SA and NA Panama originated from tectonic rather than volcanic events Geological History of Panama ~ 3 mya Late Pliocene, Early Pleistocene migrations 10 bird families to SA, 2 to NA 15 mammalian families to SA, 7 to NA 3 survived N of Mexico opossum, armadillo, porcupine 23 families of other vertebrates to NA, 18 to SA Biogeoraphic History of Panama The Great American Interchange Gradual migrations N => S during periods of cooling Stadial periods and Glaciations S => N during periods of warming Interglacial and interstadial Biogeoraphic History of Panama Between 3 & 2 mya Pleistocene - soon after the migrations began Extinction of several SA groups Notoungulates Biogeoraphic History of Panama Between 3 & 2 mya Pleistocene - soon after the migrations began Extinction of several SA groups Notoungulates Litopterns Biogeoraphic History of Panama Between 3 & 2 mya Pleistocene - soon after the migrations began Extinction of several SA groups Notoungulates Litopterns Marsupial carnivores Biogeoraphic History of Panama Between 3 & 2 mya Pleistocene - soon after the migrations began Extinction of several SA groups Notoungulates Litopterns Marsupial carnivores Flightless birds Phorusrhacids : Terror Bird Biogeoraphic History of Panama Between 3 & 2 mya Pleistocene - soon after the migrations began Extinction of several SA groups Notoungulates Litopterns Marsupial carnivores Sloths extended far into NA before extinction Biogeoraphic History of Panama Before ~4 mya SA hosted 29 land mammal families NA hosted 27 land mammal families 58 total families Soon after the opening of the land bridge 22 shared families 7 from NA, 14 from SA, 1 doubtful SA: 17 native families confined, NA: 9 Biogeography of Panama Before ~4 mya SA hosted 29 land mammal families NA hosted 27 land mammal families 58 total families Soon after the opening of the land bridge 22 shared families 7 from NA, 14 from SA, 1 unsure SA: 17 native families confined, NA: 9 Recently 15-20ish shared, 11-15 confined to SA, 9 confined to NA CA and SA Mammal Families Bull-dog Bats, Fish-eating Bats Noctilionidae Anteaters Myrmecophagidae Hutias, Nutria Pacas Agoutis, Disc-winged Bats New World Monkeys Marmosets, Tamarins West Indian Sloth &Two-toed Tree Sloth Funnel-eared Bats Capromyidae*4 Agoutidae Dasyproctidae Thyropteridae Cebidae Callitrichidae Megalonychidae Natalidae CA & SA SA Only Shrew or Rat Opossums Smokey Bats Three-toed Tree Sloths Guinea Pigs, etc Capybara Pacarana Chinchilla Rats Spiny Rats Octodonts, Degu Tuco Tucos Coypu Caenolestidae Furipteridae Bradypodidae Caviidae Hydrochaeridae Dinomyidae Abrocomidae Echimyidae Octodontidae Ctenomyidae Myocastoridae*3 Pan-American Mammal Families Pocket Mice, Kangaroo Rats Pocket Gophers New World Porcupines Peccaries, Javelinas Racoons, etc Opossums Armadillos Shrews Common Bats Dogs, Wolves, Foxes Free-tailed Bats Weasels, Otters, Skunks, Badgers Bears Cats Squirrels, Chipmonks, Marmots, Prarie Dogs etc Eared Seals, Sea Lions Rats, Mice, Voles, Gerbils, Hamsters, etc Cattle, Sheep, Goats, Antelopes, etc*** Deer, etc Heteromyidae Geomyidae Erethizontidae Tayassuidae Procyonidae Didelphidae Dasypodidae Soricidae Vespertilionidae Canidae Molossidae Mustelidae Ursidae Felidae Sciuridae Otariidae Muridae Bovidae Cervidae Hares and Rabbits Leporidae Biogeography of Panama Biodiversity today SA is about as species rich as before, but different NA is less rich, but more similar in composition Both achieved maximum density soon after opening of the bridge and then declined Biogeography of Panama Marsupial Migrations Biogeography of Panama Before ~4 mya Panama’s biodiversity was low Limited land area Limited altitudinal zonation Limited highland areas Paleocommunities Fringing mangrove forests Floating or submerged freshwater communities Moderate altitude cloud forest Biogeography of Panama ~3-2 mya Isthmus land bridge used by species displaced by climatic changes Biogeography of Panama Names Inter/Glacial N. American Period (kya) S. American interglacial glacial period present – 12 12 – 110 Sangamonian Illinoian Santa María Yarmouth Kansan Río Llico Aftonian Nebraskan Caracol interglacial glacial period interglacial(s) glacial period(s) interglacial(s) glacial period 110 – 130 130 – 200 200 – 300/380 300/380 – 455 455 – 620 620 – 680 Pastonian Stage Pre-Pastonian Stage Bramertonian Stage interglacial glacial period interglacial 600 – 800 800 – 1300 1300 – 1550 Wisconsin Epoch Llanquihue Holocene Pleistocene Biogeography of Panama Today As Panama’s geographic character became more complex - biodiversity increased Each migrant species passed through Panama Some stayed Some passed through Some stayed and sent representatives on Immigrant species occupied newly developing niches Biogeography of Panama Panama’s biodiversity today 960 bird species 220 mammal species 240 reptile species 160 amphibian species >10,000 vascular plants All species arrived since Panama arose All “native” or “endemic” species arrived from NA or SA