PALMS IN THE UPPER PALEOCENE OF THE RANCHERÍA RIVER

Transcription

1 PALMS IN THE UPPER PALEOCENE OF THE RANCHERÍA RIVER VALLEY (GUAJIRA DEPARTMENT, COLOMBIA) CAROLINA GÓMEZ NAVARRO Instituto de Biología, Universidad de Antioquia (Medellín, Colombia) Palms are a monophyletic group (APG II 2003) currently confined almost exclusively to the tropics (Henderson et al 1995). However, palm records are mainly from high latitudes (Harley & Morley 1995), while the tropical fossil record has been severely unexplored. The objective of this study is determine the natural affinity of fossil palm fragments (inflorescences, fruits and leaves) collected in the Cerrejón Formation of Upper Paleocene (60 million years ago, Bayona et al 2004). The formation outcrops in the Ranchería river Valley, Guajira department, northeastern Colombia (11 01' N; 72 45' W). To carry out this purpose I described the morphological characters found in the macrofossils and I compared them with those found in herbarium collection specimens. Cuticles were preserved in most specimens because its chemical composition makes them resistant to decay. Cuticles are in intimate association with the epidermal cell walls and preserves much of the characters of the epidermis that are useful taxonomically in some plant groups (Dilcher 1974). I isolated the cuticles from the macrofossils by means of the Schulze method (Kerp & Krings 1999), but almost all fragmented in small pieces that were not useful taxonomically, for this reason, the fossil leaves could not be determined (figure 1). This study document the presence of minimum five palm species in the Upper Paleocene of the Ranchería river Valley. The macrofossil records, are particularly meaningful because represent the first records of the palm family for Colombia. In addition, corresponds to the first records of the Cocoeae tribe (figure 2) for America, to the first fossil record of Euterpeinae subtribe (figure 3), (both of the Arecoid Line of the palm family), and to the second macrofossil records of the Nypa genera (figure 4) of the Nypoideae subfamily for South America.

2 The palm pollen record, also was analyzed for this zone, and evidence the presence of Mauritiidites a fossil pollen genera that has been suggested to be related with the Lepidocaryinae subtribe of the Calamoideae subfamily. However in this study, I suggest to review the identity of this pollen type, because macrofossils were not found neither in the study zone, nor in its distribution area. Literature cited APG II An update of the Angiosperm Phylogeny Group classification for the orders and families of flowering plants: APG II. Botanical Journal of the Linnean Society 141: Bayona, G., C. Jaramillo, M. Rueda, A. Pardo, A. Christie y G. Hernández Important paleotectonic and chronostratigraphic considerations of the Late Paleocene in the northernmost Andes as constrained by Paleocene rocks in the Cerrejón Coal Mine, Guajira, Colombia. III Convención Técnica ACGGP. Dilcher, D. L Approaches to the identification of angiosperm leaf remains. The Botanical Review 40(1): Harley, M. M. & R. J. Morley Ultrastructural studies of some fossil extant palm pollen, and the reconstruction of the biogeographical history of subtribes Iguanurinae and Calaminae. Review of Palaeobotany and Palynology 85: Henderson, A., G. Galeano & R. Bernal Field guide to the palms of the Americas. Princeton University Press, New Jersey, USA, 352 pp. Kerp, H. & M. Krings Light microscopy of cuticles. En: T. P. Jones y N. P. Rowe (eds.), Fossil Plants and Spores: Modern Techniques, pp The Geological Society, London.

3 Figure 1. Undetermined fossil leaf

4 Figure 2. Fossil fruit of Cocoeae tribe

5 Figure 3. Fossil inflorescence of Euterpeinae subtribe

6 Figure 4. Fossil fruit of Nypa

7 STATEMENT OF EXPENSES OF THE FIELD TRIP Item Price (U$) Transportation (Medellín Barranquilla Medellín tickets) 313 Transportation (Barranquilla El Cerrejón coal mine Barranquilla tickets) 32 Transportation of the fossils (El Cerrejón coal mine Medellín) 50 Subsistence (60 days in the Cerrejón coal mine) 720 Supplies 60 Equipment 50 Total 1225