studies in neotropical paleobotany. xii. a palynoflora from ... - CiteSeerX

American Journal of Botany 85(10): 1426–1438. 1998.

STUDIES A

IN

NEOTROPICAL

PALEOBOTANY.

XII. BANANO

PLIOCENE RIO FORMATION OF COSTA RICA AND THE NEOGENE VEGETATION OF MESOAMERICA1 PALYNOFLORA FROM THE

ALAN GRAHAM2

AND

DAVID L. DILCHER

Department of Biological Sciences, Kent State University, Kent, Ohio 44242; and Florida Museum of Natural History, Gainesville, Florida 32611 An assemblage of 17 identified and four unknown pollen and spore types is reported from the Pliocene Rio Banano Formation of southeastern Costa Rica. The most abundant are monolete fern spores, Palmae, cf. Antrophyum, Symphonia, Pelliceria, Lacmella (previously unreported in the fossil record), Alchornea, and Sabicea. These arrange into two paleocommunities—mangroves and lowland tropical rain forest. Annual precipitation is estimated at near the present ;3500 mm, but less seasonal, and the MAT (mean annual temperature) at ;278C. No pollen taxa representing distinctly arid or high-altitude vegetation was being blown or washed into the coastal depositional basin, and no pollen grains were recovered of northern temperate elements that are present in Neogene floras to the north in Guatemala and southeastern Mexico. These data are consistent with those from 12 other Miocene and Pliocene palynofloras from northern Latin America, indicating the late appearance of dry habitats and moderate paleoelevations and a progressive southward introduction of northern temperate elements with late Cenozoic cooling. Key words:

Costa Rica; palynoflora; Pliocene.

The Neogene vegetation and terrestrial paleoenvironments of Mesoamerica are becoming better understood through study of palynofloras ranging in age from early Miocene through middle Pliocene, and extending from Veracruz, Mexico, to the Canal region of central Panama. One of these fossil floras is an assemblage of spores and pollen from the Pliocene Rio Banano Formation of southeastern Costa Rica. In combination with 12 other floras of Neogene age and with context information from marine and terrestrial faunas, tectonics, snow-line depressions, noble gases, oxygen isotope paleotemperature data, sea-level curves, and an array of other approaches, a broad picture is emerging of the biotic and environmental history of the region during the Cenozoic.

safranin and mounted in Protexx. This mounting medium tends to shrink or preserve the specimens without swelling (particularly thin-walled types), in contrast to glycerine jelly, used in other studies in this series, which tends to expand the specimens. Thus, size measurements for some of these pollen grains and spores are smaller than for comparable ones described and illustrated from previously studied floras. The specimens were examined and photographed at 4003 magnification with a Leitz Orthoplan Photomicroscope using Panotomic X black and white film. Identifications were made by comparisons to a spore and pollen reference collection of ;24 000 slides, and from illustrations and descriptions in the literature. Slides, residues, unprocessed samples, negatives, and duplicate prints are in the palynological collections at Kent State University.

MATERIALS AND METHODS

The collection locality is an experimental open pit operated by RECOPE for mining lignite. It is near Zent (108 029N, 838179W), adjacent to the Talamanca Indian Reservation, in southeastern Costa Rica, ;30 km west southwest of Limo´n in the province of Limo´n. Samples were collected from the hillside exposure shown in Figs. 1 and 2. Maximum thickness of the lignite is ;50 cm, and it is underlain by a gray organic-rich sandstone and overlain by the weathered surface. The samples bearing the most well-preserved and diverse palynomorphs are number 8, ;30.5 cm from the base of the exposure, and especially number 4, ;91 cm from the base. There was no significant difference in composition between the two samples, but the most abundant and well-preserved specimens were from sample 4. The Rio Banano Formation was earlier considered to be late Miocene to Recent in age, but mostly Plio-Pleistocene (Taylor, 1975). Escalante (1990, fig. 6) places it in the Plio-Pleistocene and, most recently, Coates et al. (1992) assign it to the middle Pliocene with an age between 3.6 and 2.5 Ma.

The method used for recovering the plant microfossils from the sediments follows standard techniques described in a number of publications (Gray, 1965; Traverse, 1988), and recently outlined for Neogene sediments from Guatemala by Graham (in press a). Briefly, the sediments were processed through HCl, HF, and HNO3 to remove mineral matter and organic debris, then acetolyzed (nine parts acetic anhydride to one part of concentrated H2SO4), with acetolysis preceded and followed by washes in glacial acetic acid. The residues were stained with 1 Manuscript received 16 September 1997; revision accepted 9 February 1998. The authors (AG) thank Ricardo Granados and G. A. Lezana F. (Instituto Costaricense Electricidad), Luis Obando (Escuela Centroamericana de Geologı´a), and Rogelio Samuels (RECOPE) for information on the localities and for field assistance in collections made during 1981, 1983, and 1992. Luis D. Gomez P. provided valuable cooperation throughout the study. DLD thanks Eduardo Libby (Universidad de Costa Rica), Ferrnado Alvarado Villalo´n (RECOPE) for information and field assistance during 1991. Research supported by NSF grants DEB8007312 and DEB-9206743 (AG). 2 Author for correspondence.

LOCALITY, AGE, AND STRATIGRAPHY

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Figs. 1–2. Collection locality at RECOPE experimental open pit near Zent, southeastern Costa Rica. 1. Overview of the locality with figures at the collecting horizon. 2. Close-up of the collecting horizon. Photographs by Shirley A. Graham.

COMPOSITION TABLE 1. Approximate age, location, and references to previous records for Neogene palynofloras of northern Latin America. Flora/age

Location

References

Neogene Pliocene Paraje Solo Herrerı´a Rio Banano

SE Veracruz, Mex- Graham, 1976, 1993a ico SE Guatemala Graham, in press a SE Costa Rica this report

Mio-Pliocene Artibonite Gatun (to Miocene) Padre Miguel

Haiti Central Panama SE Guatemala

Graham, 1990 Graham, 1991a, b, c Graham, in press a

Middle Miocene Ixtapa

Chiapas, Mexico

Martı´nez-Herna´ndez, 1992 Palacios Cha´vez and Rzedowski, 1993

Me´ndez Early Miocene Cucaracha Culebra La Boca Uscari La Quinta (Simojovel)

Chiapas, Mexico (not included) Central Panama Central Panama Central Panama SE Costa Rica Chiapas, Mexico

Graham, 1988b Graham, 1988a Graham, 1989 Graham, 1987b Graham and Palacios Cha´vez, 1996; Langenheim, Hackner, and Bartlett, 1967; Graham, in press c

Paleogene Oligocene San Sebastian

Puerto Rico

Graham and Jarzen, 1969

Eocene Gatuncillo Chapelton

Panama Jamaica

Graham, 1985 Graham, 1993b

Seventeen identified and four unknown spores and pollen types are described from the Rio Banano Formation. In the following descriptions the phrase “previous records” refers to other occurrences of the taxa in Tertiary palynofloras from northern Latin America. References to these occurrences are provided in Table 1. The sample and slide numbers are given for each figured specimen, and location of the specimens on the slides is designated by ESF (England Slide Finder) coordinates. A summary of the composition and numerical representations is given in Table 2. Monolete fern spore type 1 (Fig. 3; sample 4, slide 2, ESF N-35,1). This is a laevigate to faintly verrucate spore 54 3 36 mm in size. Type 2 (Fig. 4; sample 4, slide 2, ESF O-41,3; 30 3 24 mm) is a smaller version of type 1; type 3 (Fig. 5; sample 4, slide 1, ESF M-51; 60 3 39 mm) is verrucate; and type 4 (Fig. 6; sample 4, slide 1, ESF Y-51,3; 45 3 33 mm) is coarsely verrucate. These laevigate to verrucate, reniform, monolete fern spores occur in virtually all Cenozoic assemblages from northern Latin America. They are similar to the spores of several genera of the Blechnaceae, Polypodiaceae, and Pteridaceae, and serve only to indicate the presence of moist habitats. Pteris (Pteridaceae; Fig. 7). Triangular, apices rounded; trilete, laesura straight, 15–18 mm long, extending to spore margin, inner margin of laesura lobate, bordered by lip 5–6 mm wide; proximal surface laevigate, distal surface coarsely verrucate (? obscure); flange 7–9 mm wide bordering outer spore margin, smooth, outer margin entire; wall 2–3 mm thick; size 45 mm. Sample 8, slide 4, ESF W-50,4. Previous records: Artibonite, Cucaracha, Culebra, Gatun, Gatuncillo, Ixtapa, La Boca, Uscari formation/group/sequence. Pteris is a tree fern typically growing at low to midelevations in tropical moist and tropical wet forests.

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TABLE 2. Composition and numerical representation of palynomorphs in sample 4-1, Rio Banano Formation, southeastern Costa Rica. Figures are percentages based on a count of 200 and exclude unknown 2, which numerically constitutes .90% of the assemblage. Dashes indicate presence at ,0.5%. Taxon

Monolete fern spore Type 1 Type 2 Type 3 Type 4 cf. Antrophyum Pteris Trilete fern spore Type 1 Palmae Lacmella Ilex Alchornea Symphonia cf. Psittacanthus cf. Struthanthus Pelliceria Polygalaceae Sabicea Unknown 1 Unknown 2 (excluded from pollen sum) Unknown 3 Unknown 4 Others

Percentage

6 — 8 12 4 — 1 37 2 1.5 1 4 — — 3 — 1 — 90 8 — 10

cf. Antrophyum (Vittariaceae; Fig. 8). Oblate to oblatespheroidal, amb oval-triangular; trilete, laesura straight, narrow, 37–41 mm long, extending two-thirds to nearly to spore margin, inner margin entire; laevigate; wall ;2 mm thick; size 67–71 mm. Sample 4, slide 1, ESF P-30,1– 3. Previous records: Artibonite, Cucaracha, Culebra, Gatuncillo, Herrerı´a, La Boca formation/group. Antrophyum is mostly a pendant, epiphytic fern of pantropical distribution. In tropical America it grows from Hidalgo, Mexico, to northern Argentina and southeastern Brazil, usually in deep shade in wet to moist forests at elevations of ;100–1500 m (Tryon and Tryon, 1982, p. 360). Trilete fern spore type 1 (Figs. 9, 10). Oblate, amb triangular, apices rounded; trilete, laesura straight, 8–11 mm long, extending to spore margin, inner margin entire, bordered by faint narrow lip ;2 mm wide; laevigate; wall ;2 mm thick; size 24–32 mm. Sample 4, slide 1, ESF H30,1; Y-44. This spore cannot be identified to genus, and the general type ranges widely both stratigraphically and geographically throughout Cenozoic deposits in northern Latin America. Palmae (Fig. 11). Prolate, with greatest width just above equator; monocolpate, colpus straight to slightly

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sinuous, 16–18 mm long, extending entire length of grain, inner margin of colpus entire to minutely dentate; finely reticulate; tectate-perforate, wall homogeneous to columellae just evident (at 4003 magnification), ;2 mm thick; size 20–22 3 14–16 mm. Sample 4, slide 1, ESF E-48,1–3. Previous record: Gatuncillo Formation. This generalized type of palm pollen is distinguished by its relatively small size, but presently it cannot be identified to genus. Lacmellea (Apocynaceae; Figs. 12, 13). Oblate, amb circular; tri(col)porate, colpi faint, short (;6 mm equator to apex), apices rounded, frequently obscure and grain appearing triporate, pores conspicuous, equatorially arranged, equidistant, situated at midpoint of colpus, circular, 3–4 mm in diameter, inner margin entire to minutely dentate, surrounded by costae pori 2–3 mm wide, surface of costae pori smooth, outer margin slightly diffuse; scabrate; tectate, wall homogeneous to columellae just evident (at 4003 magnification), 2–3 mm thick; size 27–30 mm. Sample 4, slide 1, ESF T-49,2–4. Previous record: none. Lacmella is a genus of 19–20 species of shrubs and trees to 20 m tall found in tropical regions mostly in South America, but with two species extending into Central America (Nowicke, 1970). The principal Central American species is L. panamensis distributed from Belize through Panama and growing primarily in the lowland tropical wet forest. Lacmella has not been reported previously in the fossil record. Ilex (Aquifoliaceae; Fig. 14). Prolate-spheroidal, amb oval to nearly circular; tricolporoidate, colpi equatorially arranged, meridionally elongated, equidistant, straight, 20–22 mm long, inner margin entire, pore poorly defined, frequently obscure, situated at midpoint of colpus; intectate, clavate, wall ;3 mm thick; size 26–28 3 19–21 mm. Sample 4, slide 1, ESF W-51,1–2. Previous records: Cucaracha, Culebra, Gatun, Ixtapa, La Boca, Gatuncillo, Paraje Solo, San Sebastian formations. Ilex is a shrub to small tree widespread in tropical America and occurs primarily in mesic to slightly drier habitats at midelevations. Alchornea (Euphorbiaceae; Fig. 15). Oblate, amb circular; tricolpate, colpi equatorially arranged, meridionally elongated, equidistant, straight, 5–6 mm long, inner margin entire, distinct operculum; psilate; tectate, wall homogeneous (at 400x magnification), 2 mm thick; size 17– 19 mm. Sample 4, slide 1, ESF E-30,2. Previous records: Artibonite, Culebra, Cucaracha, Gatun, La Boca, Paraje Solo, San Sebastian, Uscari formation/ group/ sequence. Alchornea is a small deciduous tree widespread in tropical America. It grows primarily in tropical moist and premontane wet forests at elevations between 300 and 2000 m. Symphonia (Guttiferae; Figs. 19, 20). Oblate, amb polygonal (hexagonal); stephanoporate (pores 6), pores →

Figs. 3–24. Fossil spores and pollen grains from the Pliocene Rio Banano Formation of southeastern Costa Rica. See text for descriptions and measurements, and Table 2 for numerical representations. 3. Monolete fern spore type 1. 4. Monolete fern spore type 2. 5. Monolete fern spore type 3. 6. Monolete fern spore type 4. 7. Pteris. 8. cf. Antrophyum. 9, 10. Trilete fern spore type 1. 11. Palmae. 12–13. Lacmella. 12. Equatorial view. 13. Surface view. 14. Ilex. 15. Alchornea. 16. Pelliceria. 17. Polygalaceae. 18. Sabicea. 19–20. Symphonia. 19. Equatorial view. 20. Polar view. 21. cf. Psittacanthus. 22. cf. Struthanthus. 23. Unknown 1. 24. Unknown 2.

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equatorially arranged, equidistant, circular, 10–12 mm in diameter, surrounded by irregular, granular costae pori; psilate to scabrate; tectate, wall homogeneous (at 400x magnification), conspicuously thick (;6 mm); size 43–47 mm. Sample 4, slide 1, ESF C-46,1; sample 4, slide 2, ESF C-30. Previous records: Paraje Solo. Symphonia is a tree to 27 m tall, which is frequently pollinated by hummingbirds. However, members of the prominent Central American species S. globulifera often occur in stands, and flower and produce pollen throughout the year, increasing the chances of its representation in the pollen record. Individual trees may remain in flower for 2 mo. The species is widespread through tropical America (Belize to South America), and it is a characteristic component of the lowland tropical moist and tropical wet forests. Pollen was recovered in small amounts (,1%) in one sample from the Paraje Solo Formation, but in the Rio Banano assemblage it is more abundant (4%; Table 2). cf. Psittacanthus (Loranthaceae; Fig. 21). Oblate, amb triangular to concave-triangular, apices rounded to nearly blunt; trisyncolpate, colpi equatorially arranged, meridionally elongated, equidistant, straight, margin entire, 20–22 mm long, extending from pole to apices; scabrate to finely verrucate, scabrae diminishing toward apices, interapical margin dentate in median optical section (scabrae evident), margin of apices entire; tectate, columellae just evident (at 400x magnification in inter-apical region), wall ;2 mm thick; size 33–36 mm. Sample 8, slide 4, ESF Y-42, 3–4. Previous record: Gatun (as Loranthaceae type 2; other Loranthaceae types-- Paraje Solo, San Sebastian). Psittacanthus is a genus of ;80 species of tropical shrubs. The specimen is most similar to P. schiedanus in our three collections (Arsene 2900, Mexico, US 1001260; no collector, no collection number, Mexico, US 1494987; Schmalzel 1348, Chiriqui, Panama, STRI). However, in Feuer and Kuijt (1979) pollen grains of that species are shown as deeply concave and P. sonorae appears more similar. cf. Struthanthus (Loranthaceae; Fig. 22). Oblate, amb triangular to oval-triangular; tricolpate, colpi equatorially arranged, merdionally elongated, equidistant, straight, 15–18 mm long, inner margin entire to minutely dentate, syncolpate, colpi apices occasionally branched and forming triangular area at poles; scabrate; tectate, wall homogeneous to columellae just evident (at 4003 magnification), ;2 mm thick; size 29–32 mm. Sample 4, slide 1, ESF X-31,1. Previous record: Paraje Solo. Struthanthus is a scandent shrub to parasitic vine of 40–60 species widely distributed in the American tropics and occurring in a wide variety of habitats (J. Kuijt, University of Victoria; personal communication, 1997). For example, S. orbiculatus grows from Mexico to Peru and western Brazil in tropical moist, premontane dry, premontane moist, premontane wet, premontane rain, and tropical dry forests. The pollen morphology of extant species has been described by Feuer and Kuijt (1985). Pelliceria (Pelliceriaceae; Fig. 16). Oblate, amb circular; tricolporate, colpi equatorially arranged, meridionally elongated, equidistant, 20–24 mm long, tapering to acute apex, inner margin entire to minutely dentate, low margo 8–10 mm wide, pore oval to elongated equatori-

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ally, 3–4 mm in diameter, situated at midpoint of colpus, inner margin of pore entire; sculpture variable, scabrate/ finely verrucate to coarsely verrucate; tectate, columellae evident (at 400x magnification), wall 3–4 mm thick; size variable, 40–60 mm (figured specimen 60 mm). Sample 4, slide 2, ESF R-43,3. Previous records: Chapelton (Guys Hill Member), Gatuncillo, Ixtapa, La Boca, San Sebastian, Simojovel (La Quinta) groups/formations. Pelliceria is a small mangrove tree presently distributed from coastal Costa Rica to northwest Colombia and Ecuador. During the Cenozoic it was widespread in the Gulf/Caribbean region, and it is known from deposits ranging in age from Eocene to Recent and from as far north as Puerto Rico, Jamaica, and southeastern Mexico. The history of Pelliceria and other mangroves in the New World has been summarized by Graham (1977, 1995). Polygalaceae (Fig. 17). Prolate to prolate-spheroidal, amb oval; stephanocolporate, colpi equatorially arranged, meridionally elongated, equidistant (;3 mm apart), straight, extending nearly entire length of grain, 20–22 mm long, ;5 mm wide, inner margin entire, pores faint, situated at midpoint of colpus, circular, 3–4 mm in diameter; psilate; tectate, wall homogeneous (at 4003 magnification), ;2 mm thick; size 23–25 mm. Sample 4, slide 1, ESF B-39,4. Previous record: Paraje Solo (pores more distinct). This pollen type is similar to several types in the Polygalaceae and cannot be referred to genus. Polygala paniculata is a widespread weedy annual herb often growing in clearings, and Securidaca diversifolia is a shrub or liana growing in tropical dry to premontane wet forests in Central America. Sabicea (Rubiaceae; Fig. 18). Oblate, amb oval-triangular to nearly circular; tricol(por)pate, colpi equatorially arranged, meridionally elongated, equidistant, inner margin minutely dentate, short (4–6 mm), faint(?) costae colpi, pores faint, equatorially elongated, slit-like (;1 3 3 mm), situated at midpoint of colpus; finely reticulate, muri smooth, width approximately equal to diameter of lumen (;0.5 mm); tectate-perforate, columellae evident (at 4003 magnification), wall 2–3 mm thick; size 24–26 mm. Sample 4, slide 2, ESF K-36,3–4. Previous record: Culebra (larger specimen, 32–36 mm). Sabicea pollen grains from the Culebra Formation also have been described and illustrated separately (Graham, 1987a). The pollen is similar among the extant Neotropical species, including the widespread S. villosa (cf. Roubik and Moreno P., 1991, fig. 1081). The genus includes ;125 species of climbing shrubs and vines, and in Central America it grows primarily in tropical moist and tropical wet forests. Unknown 1 (Fig. 23). Oblate, amb triangular to ovaltriangular; triporate, pores equatorially arranged, equidistant, ;3 mm in diameter, inner pore margin 6 entire, surrounded by faint annulus 3–4 mm wide; verrucate, verrucae irregular, 3–4 mm in diameter, low (1–2 mm); tectate, wall homogeneous (at 400x magnification), ;2 mm thick. Size 28–30 mm. Sample 4, slide 2, ESF M-32,4. Unknown 2 (Fig. 24). Prolate, amb oval; tricolporate, colpi equatorially arranged, meridionally elongated, equidistant, 14–16 mm long, inner margin entire, pores elongated equatorially, oval, ;3 3 5 mm, bordered along top and bottom margin by costae pore ;1 mm wide; finely

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Figs. 25–29. Fossil spores and pollen grains from the Pliocene Rio Banano Formation of southeastern Costa Rica. See text for descriptions and measurements, and Table 2 for numerical representations. Figs. 25–27. Unknown 3. 25. Specimen with narrow, slit-like pores. 26. Specimen showing narrow costae colpi. 27. Specimen with more oval pores. Figs. 28, 29. Unknown 4. 28. Polar view. 29. Equatorial view.

reticulate, muri smooth, approximately equal in width to diameter of lumen (;0.5 mm); tectate-perforate, columellae evident (at 4003 magnification), wall 2–3 mm thick; size 26–28 3 25–27 mm. Sample 4, slide 2, ESF B-29,3–4. Unknown 3 (Figs. 25–27). Prolate; tricolporate, colpi equatorially arranged, meridionally elongated, equidistant, straight, 17–19 mm long, extending nearly entire length of grain, inner margin entire to minutely dentate, narrow costae colpi, pores oval to slit-like, ;0.5 3 3–4 mm, situated at midpoint of colpus; finely striate; tectate, wall homogeneous to columellae just evident (at 4003 magnification), wall ;2 mm thick; size 25–27 3 17–19 mm. Sample 4, slide 1, ESF V-43, Q-50,2–4, F-35,1–2. Although this unknown is only one of 21 types recognized for the flora, it is the prominent pollen type in the Rio Banano assemblage. In abundance, occurrence in a tropical lowland costal environment, association with Pelliceria, and in size, shape, and general aperture features it is similar to Rhizophora. However, it lacks the prominent costae colpi, colpi transversalis, and the finely reticulate sculpture of that genus. The prolate, tricolporate, striate condition suggests Anacardiaceae (e.g., Tapirira), but in that family the grains are usually larger and the striations are more prominent. Based on the relatively recent age and modern aspect of the flora, the parent plant

is probably a tree or shrub, producing large numbers of flowers, either abundant or occurring locally in stands (as opposed to isolated individuals), and is likely a prominent member of the present lowland tropical vegetation along the Caribbean coast of Central America. Unknown 4 (Figs. 28, 29). Oblate, amb circular; tricolpate, colpi equatorially arranged, meridionally elongated, equidistant, 10–12 mm long, margin diffuse; finely reticulate, muri smooth, width (0.5 mm), approximately one-half diameter of lumen (1 mm); intectate, clavate, wall ;3 mm thick; size 28–30 mm. Sample 4, slide 2, ESF V-39,1–3; sample 4, slide 1, ESF M-51,4. These specimens are similar to pollen of Tetrorchidium (Euphorbiaceae), which has been reported (as cf. Tetrorchidium) from the Paraje Solo Formation. However, in that genus some of the mostly clavate columellae taper to near echinae. Another pollen type is occasional in the Rio Banano assemblage. It is a small, thin-walled, finely reticulate form that is probably a monocotyledon. However, the preservation and/or orientation of the relatively few grains made it impossible to determine the nature of the apertures with certainty. DISCUSSION Paleocommunities and environment—The general paleoenvironmental setting for the Rio Banano assemblage

Fig. 30. Index map of palynofloras mentioned in the text. See Table 1 for age and references. 1 5 Paraje Solo, 2 5 Ixtapa, 3 5 La Quinta (Simojovel), 4 5 Padre Miguel, 5 5 Herrerı´a, 6 5 Rio Banano, 7 5 Culebra, Cucaracha, La Boca, Gatun, 8 5 Uscari, 9 5 Artibonite.

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TABLE 3. Summary of Neogene palynofloras from northern Latin America. 1 5 Paraje Solo, 2 5 Herrerı´a, 3 5 Rio Banano, 4 5 Artibonite, 5 5 Gatun, 6 5 Padre Miguel, 7 5 Ixtapa, 8 5 Cucaracha, 9 5 Culebra, 10 5 La Boca, 11 5 Uscari, 12 5 La Quinta (Simojovel). Specimens not cited as to biological affinities (e.g., Liliacidites) and identifications above the level of family (e.g., monolete fern spores) are not included. See Table 1 for age, localities, and references for the floras. Palynoflora Taxon

Fungi Ascomycete cleistothecium Pyrrophyta Operculodinium Spiniferites Bryophyta Anthocerotaceae Phaeoceros Muscae Psilotaceae Psilotum Lycopodiaceae Lycopodium Selaginellaceae Selaginella Cyatheaceae Alsophila Cyathea Cnemidaria/Hemitelia Sphaeropteris/Trichipteris Dryopteridaceae Ctenitis Lomariopsis Gleicheniaceae Dicranopteris Hymenophyllaceae cf. Hymenophyllum Lophosoriaceae Lophosoria Marattiaceae Danaea Ophioglossaceae Ophioglossum Polypodiaceae Grammitis Pteridaceae cf. Acrostichum Ceratopteris Pityrogramma Pteris Schizaeaceae Lygodium Vittariaceae cf. Antrophyum Cycadaceae Pinaceae Abies Picea Pinus Podocarpaceae Podocarpus Araceae Spathiphyllum Cyperaceae Dioscoreaceae Rajania Gramineae Liliaceae Smilax Palmae cf. Astrocaryum cf. Attalea cf. Brahea cf. Chamaedorea Crysophila-type

1

2

3

4

5

6

7

8

9

10

11

x

x

12

x x

x

x x x x

x x x

x

x x x x

x

x

x

x

x

x

x x x

x

x

x

x

x

x

x

x

x

x

x

x x

x x

x x x x x x x x x

x

x

x

x

x

x

x

x

x

x

x x

x

x x

x

x x

x

x

x

x

x

x

x

x x x x

x x

x x

x

x

x x

x

x

x x

x

x x

x

x

x

x x

x

x

x

x

x

x

x x

x

x

x x x x

x x

x

x

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TABLE 3. Continued. Palynoflora Taxon

Desmoncus-type Manicaria-type cf. Maximiliana type Synechanthus-type Acanthaceae Bravaisia Hygrophila Justicia Amaranthaceae Irisene Amaranthaceae/Chenopodiaceae Anacardiaceae Comocladia Annonaceae Cymbopetalum Apocynaceae Lacmella Aquifoliaceae Ilex Asteraceae Mutisieae type Betulaceae Alnus Bombacaceae cf. Aguiaria Bernoulia Ceiba Pachira-type Pseudobombax Boraginaceae Tournefortia Burseraceae Bursera Protium Cabombaceae Cabomba Chloranthaceae Hedyosmum Combretaceae cf. Bucida Combretum/Terminalia Laguncularia Connaraceae cf. Rourea Cucurbitaceae cf. Cionosicys Dichapetalaceae Dichapetalum Dilleniaceae cf. Doliocarpus Dioscoreaceae Dioscorea/Rajania Ericaceae Euphorbiaceae Alchornea cf. Bernardia cf. Glycydendrum cf. Jatropha cf. Sapium cf. Stillingia cf. Tetrorchidium cf. Tithymalus Fagaceae Quercus

1

2

3

4

5

6

7

8

9

10

x

x x

x

x

x

11

12

x x

x x

x x x x x x

x x

x

x x x x x

x x

x x

x

x x

x x

x

x x x x x x

x

x

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x x x

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x x x x x x x

x

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x x x x x x x

x x

x x x x

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TABLE 3. Continued. Palynoflora Taxon

Flacourtiaceae Casearia Laetia Gentianaceae Lisianthius Guttiferae Symphonia Hamamelidaceae Liquidambar Juglandaceae Alfaroa/Oreomunnea (as Engelhardia) Juglans Lecythidaceae Gustavia Leguminosae Caesalpinioideae Caesalpinia Crudia Mimosoideae Acacia Mimosa Papilinoideae Desmanthus Erythrina Lentibulariaceae Utricularia Loranthaceae Oryctanthus cf. Psittacanthus cf. Struthanthus Lythraceae Cuphea Malpighiaceae cf. Banisteriopsis cf. Hiraea cf. Malpighia cf. Mezia (?) type Malvaceae Hampea/Hibiscus Melastomataceae Meliaceae Cedrela Guarea Myricaceae Myrica Myrtaceae Eugenia/Myrcia Onagraceae Hauya Ludwigia Passifloraceae Passiflora Pelliceriaceae Pelliceria Polygalaceae cf. Bredemeyera cf. Securidaca Polygonaceae Coccoloba Ranunculaceae Thalictrum Rhizophoraceae Rhizophora Rubiaceae

1

2

3

4

5

6

7

8

x x

9

10

11

12

x

x

x

x x

x

x

x

x

x

x

x

x

x

x

x x

x

x x

x x

x x

x

x

x x x

x

x

x x x

x

x x

x

x

x x x

x x x x x

x x

x x

x x

x x

x x

x x

x

x

x

x

x

x x

x

x x x

x

x

x

x x x x x

x

x

x

x

x

x

x x

x

x

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PALYNOFLORA FROM

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TABLE 3. Continued. Palynoflora Taxon

cf. Alibertia Borreria Chomelia type Cosmibuena Faramea Posoqueria Sabicea Terebrania Rutaceae Casimiroa Salicaceae Populus Sapindaceae Allophylus Cupania Matayba Meliosma cf. Paullinia Serjania Sapotaceae cf. Bumelia cf. Pourteria Sterculiaceae Buettneria cf. Guazuma Symplocaceae Symplocos Theaceae Cleyera Thymeliaceae Daphnopsis Tiliaceae Mortoniodendron Ulmaceae Celtis Ulmus Verbenaceae Aegiphila Petrea

1

2

3

4

5

6

7

8

9

10

11

12

x x x x x x

x x

x

x x x x x x x x x

x

x x

x x x

x x x x

x x x x x x x x

x x

is indicated by the composition of the flora and by the sediment type in which the assemblage is preserved. Lignites containing mangroves are deposited under warmtemperate to tropical, coastal, brackish-water conditions. Relative sea-level changes, resulting from a combination of tectonics (movement of the land) and eustatic fluctuations (changes in sea level independent of land movement), produced periodic inundations and regressions that account for the cycles of lignite deposition, and explain the presence of coastal sediments and vegetation at this site presently 20 km inland and 100–200 m above the present coastline. Two paleocommunities are evident in the Rio Banano plant microflora. A fringing community of mangroves was present as indicated by pollen of Pelliceria. Immediately inland there was a lowland tropical rain forest that included Pteris, Palmae, Lacmellea, Alchornea, Symphonia, Psittacanthus, Struthanthus, and Sabicea. In the Rio Banano flora there are no taxa suggesting upland habitats (e.g., Pinus, Podocarpus, Alfaroa/Oreomunnea, Quercus), and there is no evidence for dry to arid vegetation in the immediate vicinity of the depositional basin, although Ilex and Struthanthus can range into these

x x x

habitats. Also, there is no pollen of northern temperate elements as found in the Pliocene Paraje Solo and Padre Miguel floras to the north. The paleovegetation of the Rio Banano Formation is similar to the (potential) extant vegetation of lowland tropical southeastern Costa Rica and, therefore, the present climate gives an approximation of the paleoclimate. The mean annual precipitation at Limo´n is ;3500 mm and seasonal, with the drier part of the year occurring between January and March, although there is no pronounced dry season. The MAT (mean annual temperature) is ;27o C (Portig, 1976). At this value, temperature would not be a limiting factor for mangrove-tropical rain forest vegetation, so the paleobotanically derived approximation is a minimum for the coastal terrestrial habitats in the region. For the interval between 3.6 and 2.5 Ma (million years ago), mean SST (sea-surface temperature) for the Colombia Basin to the south is estimated at warmer than the present 27.9oC based on ostracode evidence (Coates et al., 1992). The Neogene palynofloras of northern Latin America—The Rio Banano palynoflora is one of 13 Neogene assemblages known for the region between southern

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Mexico and central Panama (Table 1; Fig. 30). Each of these floras reveals the paleovegetation and environments within a limited area, but collectively they reveal something of the biotic diversity, climate and climatic change, the biotic responses to these changes, sea-level fluctuations, landscape evolution, lineage histories, and migrations. The Rio Banano flora is the latest Neogene plant microfossil assemblage to be included in the project, Studies in Neotropical Paleobotany, and the results are incorporated into a summary of the Miocene through Pliocene palynofloras reported from northern Latin America (Table 3). In the Rio Banano flora and in the Cucaracha, Culebra, Gatun, and La Boca floras, the tropical rain forest is well represented. This is in contrast to several other Neogene floras in northern Latin America where the rain forest is poorly represented or absent. The Paraje Solo flora of southeastern Veracruz, Mexico is also preserved in coastal lignites and associated sediments. It was deposited in the middle Pliocene (Planktic Foraminiferal Zone 19, 3– 4 Ma) during a period considered by Cronin and Dowsett (1991) to represent the maximum of Pliocene warmth. Yet the flora provides clear evidence of cool climates (presence of Picea, lowering of ecotones, distruption of the rain forest). If the period of warmth was as substantial and widespread as suggested by Cronin and Dowsett (1991), then an alternative explanation must be offered for the cool conditions suggested by the Paraje Solo flora. The likely explanation is upwelling of cool to cold bottom waters that often results along coastal areas with increased rates of ocean circulation. In the Gulf/Caribbean region this increased rate was due to the closing of the Isthmus of Panama that intensifed flow of the Gulf Stream between ;3.5 and 2.5 Ma (Coates et al., 1992; Graham, 1992; Jackson, Budd, and Coates, 1996; Webb and Rancy, 1996; Burnham and Graham, in press). In the Pliocene Herrerı´a flora of coastal southeastern Guatemala (Graham, in press a), mangroves were present (Acrostichum, Rhizophora) but the surrounding vegetation was mostly a fern-sedge-palm marsh or swamp. The more inland Padre Miguel flora of Guatemala is a sedge marsh with grasses and composites, and pine-oak, temperate (Alfaroa-Oreomunnea, Juglans, Ulmus), and possibly cool-temperate (Picea, Pinus, Quercus) forests in the uplands. In the Herrerı´a, Padre Miguel, and Paraje Solo floras the lowland tropical rain forest is absent or poorly represented, but for different reasons. In the Herrerı´a flora high water tables produced swamps and marshes that were priodically innundated by marine waters. The Padre Miguel flora was deposited inland and adjacent to more upland habitats where Picea, Pinus, Alfaroa-Oreomunnea, Juglans, Quercus, and Ulmus were contributing the prominent palynomorphs. In the Paraje Solo flora it was likely a combination of higher mid-Pliocene sea levels that reduced available lowland habitats between the coast and the adjacent mountains, and locally cool climates resulting, in part, from upwelling. Areas of significant physiographic relief existed in the vicinity of the Paraje Solo flora, moderate elevations are suggested by the Padre Miguel flora, and only low elevations are indicated by the Cucaracha, Culebra, Herrerı´a, La Boca, Uscari, and Rio Banano floras (to ;1400 m). By Gatun time, elevations in central Panama increased to

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;1700 m, initiating a differentiation into wet Atlantic and drier Pacific sides, the appearance of slightly drier vegetation (viz. Gramineae, Acacia, Allophylus, Bursera, Cedrela, Ceiba, Combretum, cf. Jatropha, Posoqueria, Pseudobombax, Serjania), and uplands sufficient to support restricted temperate plants (viz. the first appearance of Quercus in southern Central America). However, in none of these Neogene floras is there any evidence for extensive, well-developed dry-habitat vegetation that would suggest an arid corridor connecting the North and South American continents. Disjuncts between the arid regions of North and South America (e.g., Larrea; Hunziker et al., 1972; Orians and Solbrig, 1977; Thrower and Bradbury, 1977; Kalin Arroyo, Zedler, and Fox, 1995) likely orignated, at least in large part, via long-distance transport (Raven, 1963, 1971, 1973; Raven and Axelrod, 1975; Graham, in press b [chapter 9]). The Rio Banano assemblage contains no spore or pollen taxa of northern temperate elements, and this is consistent with the pattern emerging from the study of other floras. Pollen of Pinus, Alnus, Betula, Carya, Castanea, Celtis, Fagus, Quercus, Nyssa, Juglans, Ostrya-Carpinus, Platanus, Tilia, and Ulmus are present in Paleogene deposits in southeastern United States (Gray, 1960; Frederiksen, 1981, 1988, 1991), but none have been found in Paleogene floras from Mexico through Central America. There are few (Picea, Pinus?) in the early Miocene La Quinta (Simojovel) flora, and none in the early Miocene Cucaracha, Culebra, La Boca, or Uscari floras of Panama and Costa Rica. With the exception of Pinus, none were reported from the middle Miocene Ixtapa flora. A surprising mixture of pollen and spore types from plants of present-day temperate and tropical regions of eastern and western North America, eastern Asia, tropical southeastern Asia, and tropical Africa has been reported for Chiapas, Mexico in various abstracts, unpublished theses, and dissertations (Davalia, Nypa, Cedrus, Cupressus, Keteleeria, Pseudotsuga, Sequoia, Tsuga, Baikiaea, Nothofagus, Platycarya). Descriptions and illustrations are not provided, or are inadequate to assess the identifications, and the reports are not included here. The earliest accepted appearance of relatively extensive northern temperate elements in the northern Latin American biota is in the Paraje Solo flora (Abies, Picea, Pinus, Alnus, Celtis, Juglans, Liquidambar, Myrica, Populus, Quercus, Ulmus) and in the Padre Miguel flora (Picea, Pinus, Juglans, Quercus, Ulmus). Quercus (only) is recovered in small quantities in the Gatun flora, and Alnus and Quercus first appear in northern South America in the Quaternary (Hooghiemstra, 1989, 1994; Hooghiemstra and Sarmiento, 1991; Hooghiemstra and Ran, 1994). These records suggest a generally progressive southward migration coinciding with a significant drop in global benthic MAT in the middle Miocene, and continuing into later times as revealed by oxygen isotope data (Miller, Fairbanks, and Mountain, 1987). These 13 Neogene floras, distributed from southeastern Mexico through central Panama and the Antilles, constitute the meager plant microfossil database for reconstructing vegetation, lineages, environments, and migrations through the region for the Miocene through the Pliocene. Some trends are evident, however, and collectively the assemblages are begining to reveal the complex

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mosaic of vegetation that characterized northern Latin America during the Cenozoic and the various factors of climate, upwelling, topography, tectonics, and sea-level changes that influenced its development. LITERATURE CITED BURNHAM, R. J., AND A. GRAHAM. In press. The history of neotropical vegetation: new developments and status. Annals of the Missouri Botanical Garden. COATES, A. G., J. B. C. JACKSON, L. S. COLLINS, T. M. CRONIN, H. J. DOWSETT, L. M. BYBELL, P. JUNG, AND J. A. OBANDO. 1992. Closure of the Isthmus of Panama: the near-shore marine record of Costa Rica and western Panama. Geological Society of America Bulletin 104: 814–828. CRONIN, T. M., AND H. J. DOWSETT [GUEST EDS.]. 1991. Pliocene climates. Quaternary Science Reviews 10: 1–296. ESCALANTE, G. 1990. The geology of southern Central America and western Colombia. In G. Dengo and J. E. Case [eds.], The Caribbean region, 201–230. Geological Society of America, Boulder, CO. FEUER, S., AND J. KUIJT. 1979. Pollen morphology and evolution in Psittacanthus (Loranthaceae). Botanical Notiser 132:295–309. ———, and ———. 1985. Fine structure of mistletoe pollen VI. Small-flowered neotropical Loranthaceae. Annals of the Missouri Botanical Garden 72: 187–212. FREDERIKSEN, N. O. 1981. Middle Eocene to early Oligocene plant communities of the Gulf Coast. In J. Gray, A. J. Boucot, and W. B. Berry [eds.], Communities of the past, 493–549. Dowden, Hutchinson and Ross, Stroudsburg, PA. ———. 1988. Sporomorph biostratigraphy, floral changes, and paleoclimatology, Eocene and earliest Oligocene of the eastern Gulf Coast. United States Geological Survey Professional Paper 1448: 1–68. ———. 1991. Pulses of middle Eocene to earliest Oligocene climatic deterioration in southern California and the Gulf Coast. Palaios 6: 564–571. GRAHAM, A. 1976. Studies in neotropical paleobotany. II. The Miocene communities of Veracruz, Mexico. Annals of the Missouri Botanical Garden 63: 787–842. ———. 1977. New records of Pelliceria (Theaceae/Pelliceriaceae) in the Tertiary of the Caribbean. Biotropica 9: 48–52. ———. 1985. Studies in neotropical paleobotany. IV. The Eocene communities of Panama. Annals of the the Missouri Botanical Garden 72: 504–534. ———. 1987a. Fossil pollen of Sabicea (Rubiaceae) from the lower Miocene Culebra Formation of Panama. Annals of the Missouri Botanical Garden 74: 868–870. ———. 1987b. Miocene communities and paleoenvironments of southern Costa Rica. American Journal of Botany 74: 1501–1518. ———. 1988a. Studies in neotropical paleobotany. V. The lower Miocene communities of Panama-- the Culebra Formation. Annals of the Missouri Botanical Garden 75: 1440–1466. ———. 1988b. Studies in neotropical paleobotany. VI. The lower Miocene communities of Panama-- the Cucaracha Formation. Annals of the Missouri Botanical Garden 75: 1467–1479. ———. 1989. Studies in neotropical paleobotany. VII. The lower Miocene communities of Panama-- the La Boca Formation. Annals of the Missouri Botanical Garden 76: 50–66. ———. 1990. Late Tertiary microfossil flora from the Republic of Haiti. American Journal of Botany 77: 911–926. ———. 1991a. Studies in neotropical paleobotany. VIII. The Pliocene communities of Panama-- introduction and ferns, gymnosperms, angiosperms (monocots). Annals of the Missouri Botanical Garden 78: 190–200. ———. 1991b. Studies in neotropical paleobotany. IX. The Pliocene communities of Panama-- angiosperms (dicots). Annals of the Missouri Botanical Garden 78: 201–223. ———. 1991c. Studies in neotropical paleobotany. X. The Pliocene communities of Panama-- composition, numerical representations, and paleocommunity paleoenvironmental reconstructions. Annals of the Missouri Botanical Garden 78: 465–475.

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———. 1992. Utilization of the isthmian land bridge during the Cenozoic—paleobotanical evidence for timing, and the selective influence of altitudes and climate. Review of Palaeobotany and Palynology 72: 119–128. ———. 1993a. Historical factors and biological diversity in Mexico. In T. P. Ramamoorthy, R. Bye, A. Lot, and J. Fa [eds.], Biological diversity of Mexico, 109–127. Oxford University Press, New York, NY. ———. 1993b. Contribution toward a Tertiary palynostratigraphy for Jamaica: the status of Tertiary paleobotanical studies in northern Latin America and preliminary analysis of the Guys Hill Member (Chapelton Formation, middle Eocene) of Jamaica. In R. M. Wright and E. Robinson [eds.], Biostratigraphy of Jamaica, 443–461. Geological Society of America Memoir 182. Geological Society of America, Boulder, CO. ———. 1995. Diversification of Gulf/Caribbean mangrove communities through Cenozoic time. Biotropica 27: 20–27. ———. In press a. Studies in neotropical paleobotany. XI. Late Tertiary vegetation and environments of southeastern Guatemala: palynofloras from the Mio-Pliocene Padre Miguel Group and the Pliocene Herrerı´a Formation. American Journal of Botany. ———. In press b. Late Cretaceous and Cenozoic history of North American vegetation (north of Mexico). Oxford University Press, Oxford. ———. In press c. Studies in Neotropical paleobotany. XIII. An OligoMiocene palynoflora from Simojovel (Chiapas, Mexico). American Journal of Botany. ———, AND D. M. JARZEN. 1969. Studies in neotropical paleobotany. I. The Oligocene communities of Puerto Rico. Annals of the Missouri Botanical Garden 56: 308–357. ———, AND R. PALACIOS CHA´VEZ. 1996. Additions and preliminary study of an Oligo-Miocene palynoflora from Chiapas, Mexico. Rheedea 6: 1–12. GRAY, J. 1960. Temperate pollen genera in the Eocene (Claiborne) flora, Alabama. Science 132: 808–110. ——— (COORDINATOR). 1965. Techniques in palynology. In B. Kummel and D. Raup [eds.], Handbook of paleontological techniques, 471–706. W. H. Freeman, San Francisco, CA. HOOGHIEMSTRA, H. 1989. Quaternary and upper Pliocene glaciations and forest development in the tropical Andes: evidence from a long high-resolution pollen record from the sedimentary basin of Bogota´. Palaeogeography, Palaeoclimatology, Palaeoecology 72: 11– 26. ———. 1994. Pliocene-Quaternary floral migration, evolution of northern Andean ecosystems and climatic change: implications from the closure of the Panamanian Isthmus. Profile 7: 413–425. ———, AND E. T. H. RAN. 1994. Late and middle Pleistocene climatic change and forest development in Colombia: pollen record Funza II (1–158 m core interval). Palaeogeography, Palaeoclimatology, Palaeoecology 109: 211–246. ———, AND G. SARMIENTO. 1991. New long continental pollen record from a tropical intermontane basin: late Pliocene and Pleistocene history from a 540 m-core. Episodes 14: 107–115. HUNZIKER, J. H., R. A. PALACIOS, A. G. DE VALESI, AND L. POGGIO. 1972. Species disjunctions in Larrea: evidence from morphology, cytogenetics, phenolic compounds, and seed albumins. Annals of the Missouri Botanical Garden 59: 224–233. JACKSON, J. B. C., A. F. BUDD, AND A. G. COATES [EDS.]. 1996. Evolution and environment in tropical America. University of Chicago Press, Chicago, IL. KALIN ARROYO, M. T., P. H. ZEDLER, AND M. D. FOX [EDS.]. 1995. Ecology and biogeography of Mediterranean ecosystems in Chile, California, and Australia. Ecological Studies, vol. 108. SpringerVerlag, Berlin. LANGENHEIM, J. H., B. L. HACKNER, AND A. BARTLETT. 1967. Mangrove pollen at the depositional site of Oligo-Miocene amber from Chiapas, Mexico. Botanical Museum Leaflets Harvard University 21: 289–324. MARTI´NEZ-HERNA´NDEZ, E. 1992. Caracterizacion ambiental del Terciario de la region de Ixtapa, estado de Chiapas-- un enfoque palinoestratigra´fico. Universidad Nacional Autonoma de Mexico, Instituto de Geologia, Revista 10: 54–64. MILLER, K. G., R. G. FAIRBANKS, AND G. S. MOUNTAIN. 1987. Tertiary

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