and the

1. Geological History of Panama andthe Great American Biotic Exchange

2. 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.

3. MYA Geological Ages

5. Pangea • ~200 mya

6. Pangea splits • 135 mya • Laurasia • Gondwana

7. Gondwana splits • 100 mya

10. Quaternary • ~2-3 mya

13. Formation of Isthmus 7 mya Late Miocene 15 mya Middle Miocene 3mya Late Pliocene 5 mya Early Pliocene

14. 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

15. 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

16. 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

17. Geological History of Panama • Before ~4 mya • How these pre-Panamanian migrations occurred is debated • a proto-Antillean land bridge? • Island hopping?

18. 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

19. Geological History of Panama • Before ~4 mya • SA hosted 29 land mammal families • NA hosted 27 land mammal families • 58 total families

20. 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

21. Panama originated from tectonic rather than volcanic events

22. 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

23. 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

24. Biogeoraphic History of Panama • Between 3 & 2 mya • Pleistocene - soon after the migrations began • Extinction of several SA groups • Notoungulates

26. Biogeoraphic History of Panama • Between 3 & 2 mya • Pleistocene - soon after the migrations began • Extinction of several SA groups • Notoungulates • Litopterns

28. Biogeoraphic History of Panama • Between 3 & 2 mya • Pleistocene - soon after the migrations began • Extinction of several SA groups • Notoungulates • Litopterns • Marsupial carnivores

30. 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

31. Phorusrhacids : Terror Bird

32. 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

34. 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

36. 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

37. CA and SA Mammal Families SA Only CA & SA

38. Pan-American Mammal Families

39. 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

40. Biogeography of Panama • Marsupial Migrations

41. 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

42. Biogeography of Panama • ~3-2 mya • Isthmus land bridge used by species displaced by climatic changes

43. Biogeography of Panama

44. 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

45. 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