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Studies in Neotropical Paleobotany. I. The Oligocene Communities of Puerto Rico

Alan Graham and David M. Jarzen
Annals of the Missouri Botanical Garden
Vol. 56, No. 3 (1969), pp. 308-357
DOI: 10.2307/2394849
Stable URL: http://www.jstor.org/stable/2394849
Page Count: 50
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Studies in Neotropical Paleobotany. I. The Oligocene Communities of Puerto Rico
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Abstract

Studies are being made of plant microfossils from seven Tertiary formations in Mexico, Panama, and Puerto Rico. The Puerto Rican samples from the Oligocene San Sebastian Formation have yielded 165 morphological forms; 44 have been identified, and 15 of these have no previously known fossil record. Community types include a coastal, brackish-water assemblage of Rhizophora and Pelliciera, an upland tropical to subtropical community, and an arboreal cool-temperate community of Fagus, Liquidambar, and Nyssa. Of the 44 genera identified, 31 presently grow in Puerto Rico, three grow on other islands of the Antilles, seven are found in ecologically comparable habitats elsewhere in Latin America, and only the three temperate trees require habitats not presently available on the island. The temperate element suggests altitudes greater than those of today, and recently available geological data reveal the presence of Oligocene highlands of 13,000 to 15,000 feet elevation. These would be sufficient to provide cool-temperate conditions in an insular environment at 18 degrees north. Ancestral Puerto Rico (Hispaniola, Puerto Rico, and the Virgin Islands) provided an effective landbridge between northern South America, the West Indies, and Mexico (Yucatan). However, the Oligocene seas extended across at least part of peninsula Florida and up to 120 miles inland along the Texas Gulf Coast; thus the barrier to migration from the Antilles into southeastern North America was probably greater than at present. Of the 44 genera identified all have affinities with northern South America, eastern Mexico, and the Antilles; and none have exclusive affinities with the vegetation of southeastern North America. Studies from Panama and Veracruz, Mexico, suggest tropical elements in the modern and fossil floras of southeastern North America were introduced along an Isthmian-coastal Mexico route during the early Tertiary or subsequently through long-distant dispersal into tropical outliers (southern peninsula Florida).

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