Formation of the Isthmus of Panama (original) (raw)
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Testing geological models of evolution of the Isthmus of Panama in a phylogenetic framework
Botanical Journal of the Linnean Society, 2013
The emergence and closure of the Isthmus of Panama had regional and global impacts that were rivalled by few other Cenozoic geological events. The closure of the Central American Seaway and the rise of the Isthmus had dramatic affects on climate and air and oceanic currents worldwide. Formation of the Isthmus also drove terrestrial biotic interchange, ending the isolation of South America by permitting the mixing of its biota with that of North and Central America. A dated phylogenetic tree of a well-sampled clade of palms in the tribe Trachycarpeae (Copernicia, Pritchardia and Washingtonia) was used to conduct biogeographical analyses. Examination of the timing of lineage dispersal from North into South America was performed and two contrasting temporal hypotheses of the Isthmus formation were tested: occurrence in the Pliocene (c. 5 Mya to the present) or in the Miocene (prior to c. 5 Mya). Copernicia is inferred to have dispersed through the Isthmus of Panama region into South America and subsequently into the Caribbean, where it underwent a rapid radiation. Consistent with a geologically older age for the Isthmus than previously understood, our results support recent geological and palaeobiological data that suggest an early Oligocene to early Miocene model of evolution of the Isthmus of Panama.
Biological evidence supports an early and complex emergence of the Isthmus of Panama
The linking of North and South America by the Isthmus of Panama had major impacts on global climate, oceanic and atmospheric currents, and biodiversity, yet the timing of this critical event remains contentious. The Isthmus is traditionally understood to have fully closed by ca. 3.5 million years ago (Ma), and this date has been used as a benchmark for oceanographic, climatic, and evolutionary research, but recent evidence suggests a more complex geological formation. Here, we analyze both molecular and fossil data to evaluate the tempo of biotic exchange across the Americas in light of geological evidence. We demonstrate significant waves of dispersal of terrestrial organisms at approximately ca. 20 and 6 Ma and corresponding events separating marine organisms in the Atlantic and Pacific oceans at ca. 23 and 7 Ma. The direction of dispersal and their rates were symmetrical until the last ca. 6 Ma, when northern migration of South American lineages increased significantly. Variability among taxa in their timing of dispersal or vicariance across the Isthmus is not explained by the ecological factors tested in these analyses, including biome type, dispersal ability, and elevation preference. Migration was therefore not generally regulated by intrinsic traits but more likely reflects the presence of emergent terrain several millions of years earlier than commonly assumed. These results indicate that the dramatic biotic turnover associated with the Great American Biotic Interchange was a long and complex process that began as early as the Oligocene-Miocene transition. biogeography | evolution | neotropics | fossil | migration
Data to Accompany: PALYNOLOGICAL RECORD OF THE LAST 20 MILLION YEARS IN PANAMA
Data to Accompany: PALYNOLOGICAL RECORD OF THE LAST 20 MILLION YEARS IN PANAMA
The Isthmus of Panama illustrates how the vegetation of a newly created landscape in a tropical setting evolves over time. It also allows us to investigate biological invasions, because the landscape was first connected to temperate North America, and later connected to tropical South America. Using a large number of outcrops newly exposed during the recent expansion of the Panama Canal, we were able to complement the extensive palynological research that Alan Graham conducted in Panama over the past 25 years. We analyzed the palynological record of the interval 19.5-1.2 Ma, represented by 282 samples containing 27,910 grains (pollen/spores) with 496 morphotypes. Further, a revision of the plant macrofossil literature of Panama and analysis of the carbon isotope content of 14 samples were carried out. Our results indicate that since the Early Miocene, Panamanian forests have been dominated by Gondwana-Amazonian taxa, suggesting that plants were able to cross the Central American Seaway much earlier than mammals. The landscape was dominated by tropical rainforest and lower montane to montane forest, contrary to the dry and open habitats that some previous studies have proposed. Plant diversity seems to have increased over the past 10 My, but it is unclear if this increase is due to a taphonomic bias. Further studies are needed to understand the relationships of the Early Miocene Panamanian mammals derived from North American temperate forest lineages as they faced new habitats in Panama dominated by South American-derived tropical rainforest.
Middle Miocene global change and paleogeography of Panama
Palaios, 2007
Fossil leaves in the middle Miocene Cucaracha Formation along the Panama Canal are 10-15 cm long, thick, and entire-margined; fossil pollen is also dicot dominated, as expected for wet tropical forests. Fossil woods include palms and ring-porous dicots, with smooth bark as is found in weakly seasonal tropical climates. In contrast, late Hemingfordian to early Barstovian mammals of the Cucaracha Formation are the same as those found in Nebraska, Kansas, and Florida, where climate was drier and cooler and vegetation more open. Cucaracha paleosols reconcile these differences as evidence of a mosaic of swamps to mangal (mangrove forests) preserving plants and dry uplands preserving mammals. A dozen pedotypes represent as many vegetation types, including mangrove, fresh-water and marineinfluenced swamp, early successional riparian woodland, colonizing forest, dry tropical forest, and woodland. Many paleosols have calcareous nodules, and some have pedogenic barite nodules. Depth to carbonate and paleosol thickness with carbonate indicate mean annual precipitation of 573-916 ؎ 147 mm and mean annual range of precipitation of 27-65 ؎ 22 mm. Chemical analyses of paleosol Bt horizons confirm mean annual precipitation of 296-1142 mm and mean annual temperature of 15-16 ؎ 4.4؇C. Low precipitation and temperature estimates imply a rain shadow from a high (1400-4000 m) volcanic mountain range to the west, with continuous land connection to allow immigration of mammals from North America. Partial enclosure of the Caribbean Sea by a mountainous Panama peninsula, as well as by Antillean arcs, initiated high Caribbean marine temperature and salinity well before Pliocene isthmian closure.
PALYNOLOGICAL RECORD OF THE LAST 20 MILLION YEARS IN PANAMA
The Isthmus of Panama illustrates how the vegetation of a newly created landscape in a tropical setting evolves over time. It also allows us to investigate biological invasions, because the landscape was first connected to temperate North America, and later connected to tropical South America. Using a large number of outcrops newly exposed during the recent expansion of the Panama Canal, we were able to complement the extensive palynological research that Alan Graham conductedn in Panama over the past 25 years. We analyzed the palynological record of the interval 19.5–1.2 Ma, represented by 282 samples containing 27,910 grains (pollen/spores) with 496 morphotypes. Further, a revision of the plant macrofossil literature of Panama and analysis of the carbon isotope content of 14 samples were carried out. Our results indicate that since the Early Miocene, Panamanian forests have been dominated by Gondwana Amazonian taxa, suggesting that plants were able to cross the Central American Seaway much earlier than mammals. The landscape was dominated by tropical rainforest and lower montane to montane forest, contrary to the dry and open habitats that some previous studies have proposed. Plant diversity seems to have increased over the past 10 My, but it is unclear if this increase is due to a taphonomic bias. Further studies are needed to understand the relationships of the Early Miocene Panamanian mammals derived from North American temperate forest lineages as they faced new habitats in Panama dominated by South American–derived tropical rainforest.
Early Neogene history of the Central American arc from Bocas del Toro, western Panama
Geological Society of America Bulletin, 2003
A newly discovered sequence of lower to middle Miocene rocks from the eastern Bocas del Toro archipelago, western Panama, reveals the timing and environment of the earliest stages in the rise of the Isthmus of Panama in this region. Two new formations, the Punta Alegre Formation (lower Miocene, Aquitanian to Burdigalian) and the Valiente Formation (middle Miocene, Langhian to Serravallian), are here named and formally described. The Punta Alegre Formation contains a diagnostic microfauna of benthic and planktic foraminifera and calcareous nannofossils that indicate deposition in a 2000-m-deep pre-isthmian neotropical ocean from as old as 21.5-18.3 Ma. Its lithology varies from silty mudstone to muddy foraminiferal ooze with rare thin microturbidite layers near the top. The Valiente Formation, which ranges in age from 16.4 to ca. 12.0 Ma, lies with slight angular unconformity on the Punta Alegre Formation and consists of five lithofacies: (1) columnar basalt and flow breccia, (2) pyroclastic deposits, (3) coarse-grained volcaniclastic deposits, (4) coral-reef limestone with diverse large coral colonies, and
New dates and new rates for divergence across the Isthmus of Panama
Proceedings of the Royal Society B: Biological Sciences, 1998
Sister species separated by the Isthmus of Panama have been widely used to estimate rates of molecular evolution. These estimates are based on the assumption that geographic isolation occurred nearly simultaneously for most taxa, when connections between the Caribbean and eastern Paci¢c closed approximately three million years ago. Here we show that this assumption is invalid for the only genus for which many taxa and multiple genetic markers have been analysed. Patterns of divergence exhibited by allozymes and the mitochondrial COI gene are highly concordant for 15 pairs of snapping shrimp in the genus Alpheus, indicating that they provide a reasonable basis for estimating time since cessation of gene £ow. The extent of genetic divergence between pairs of sister species varied over fourfold. Sister species from mangrove environments showed the least divergence, as would be expected if these were among the last habitats to be divided. Using this pair yields a rate of sequence divergence of 1.4% per one million years, with implied times of separation for the 15 pairs of 3^18 million years ago. Many past studies may have overestimated rates of molecular evolution because they sampled pairs that were separated well before ¢nal closure of the Isthmus.
Palynologycal recor of the last 20 million years in Panama
The Isthmus of Panama illustrates how the vegetation of a newly created landscape in a tropical setting evolves over time. It also allows us to investigate biological invasions, because the landscape was first connected to temperate North America, and later connected to tropical South America. Using a large number of outcrops newly exposed during the recent expansion of the Panama Canal, we were able to complement the extensive palynological research that Alan Graham conducted in Panama over the past 25 years. We analyzed the palynological record of the interval 19.5–1.2 Ma, represented by 282 samples containing 27,910 grains (pollen/spores) with 496 morphotypes. Further, a revision of the plant macrofossil literature of Panama and analysis of the carbon isotope content of 14 samples were carried out. Our results indicate that since the Early Miocene, Panamanian forests have been dominated by Gondwana-Amazonian taxa, suggesting that plants were able to cross the Central American Seaway much earlier than mammals. The landscape was dominated by tropical rainforest and lower montane to montane forest, contrary to the dry and open habitats that some previous studies have proposed. Plant diversity seems to have increased over the past 10 My, but it is unclear if this increase is due to a taphonomic bias. Further studies are needed to understand the relationships of the Early Miocene Panamanian mammals derived from North American temperate forest lineages as they faced new habitats in Panama dominated by South American–derived tropical rainforest. Key words: biogeography, GABI, Neogene, paleobotany, palynology.
—Two megafaunal deposits were discovered next to the villages of La Trinidaíta and Llano Hato during an archaeological survey on the Azuero Peninsula of Panama. The fossil sites were found near other localities first reported in 1957 by Smithsonian paleontologist Lewis Gazin. Bones at La Trinidaíta and Llano Hato rested in tight horizontal clusters at the bottom of ancient creeks and ponds. The remains appear to have been buried rapidly by thick deposits of fine clay when environmental conditions were wetter and cooler than today. Animals identified at La Trinidaíta and Llano Hato include Cuvieronius tropicus, Eremo-therium sp., and some turtles. Radiocarbon-dated charcoal fragments associated with the bones gave con-temporaneous dates of 44,840 ± 700 and 47,040 ± 900 14 C yr B.P. These dates indicate that carcasses accumulated during the Marine Isotope Stage 3 (MIS3) interstadial. Because other fossils were not found above or below these principal deposits, it is argued that the MIS3 environment was especially favorable for supporting large browsers and mixed-feeders and preserving their bones on the landscape. These environmental and taphonomical characteristics likely disappeared as the climate of the lowland Neotropics became drier in response to the following arid glacial advance. During this time, C 4 plants dominated the landscape and may have forced gomphotheres and giant ground sloths to abandon the dry Pacific lowlands and follow the rising tree-lines. Such large-scale range reorganization may have caused animals to abandon some regions of lower Central America during the Last Glacial Maximum.