American Journal of Botany 96(7): 1300–1312. 2009. P ALMS (ARECACEAE) FROM A PALEOCENE RAINFOREST OF NORTHERN COLOMBIA 1 C AROLINA GOMEZ-NAVARRO, 2,3 CARLOS JARAMILLO, 2,7 FABIANY HERRERA, 2,4 SCOTT L. WING, 5 AND RICARDO CALLEJAS 6 2 Smithsonian Tropical Research Institute, Unit 0948, APO AA 34002 USA; 3 Department of Plant and Microbial Biology, University of California, Berkeley 94720 USA; 4 Florida Museum of Natural History, University of Florida, Gainesville, Florida 32611-7800 USA; 5 Department of Paleobiology, Smithsonian Museum of Natural History, 10th Street and Constitution Avenue, NW, Washington, DC 20560 USA; and 6 Instituto de Biolog í a, Universidad de Antioquia, AA 1226, Medell í n, Colombia Palms are a monophyletic group with a dominantly tropical distribution; however, their fossil record in low latitudes is strikingly scarce. In this paper, we describe fossil leaves, infl orescences, and fruits of palms from the middle to late Paleocene Cerrej ó n Formation, outcropping in the Rancher í a River Valley, northern Colombia. The fossils demonstrate the presence of at least fi ve palm morphospecies in the basin ca. 60 Ma. We compare the morphology of the fossils with extant palms and conclude that they belong to at least three palm lineages: the pantropical Cocoseae of the subfamily Arecoideae, the monotypic genus Nypa , and ei- ther Calamoideae or Coryphoideae. The fossil fruits and infl orescences are among the oldest megafossil records of these groups and demonstrate that the divergence of the Cocoseae was more than 60 Ma, earlier than has previously been thought. These fossils are useful in tracing the range expansion or contraction of historical or current neotropical elements and also have profound im- plications for the understanding of the evolution of neotropical rainforests. Key words: Arecaceae; Arecoideae; Attaleinae; Cerrej ó n; Cocos ; Colombia; neotropics; Nypa ; Paleocene. Arecaceae, the palm family, is a monophyletic group includ- However, the oldest unequivocal macrofossil records are stems ing 183 genera and 2364 species ( Govaerts and Dransfi eld, (not assignable below the family level) from the lower Upper 2005 ; Dransfi eld et al., 2008 ). At present, most palms are dis- Cretaceous (Turonian, 95 Ma) of France ( Dransfi eld et al., tributed in the tropics with a few species reaching subtropical 2008 ). After their fi rst appearance, palms underwent an impor- areas ( Henderson et al., 1995 ). Fossil records from the tropics tant radiation during the Paleocene – Eocene period ( Harley, are less common, however, than those from middle latitudes 2006 ; Dransfi eld et al., 2008 ), coinciding with long-term global ( Harley and Morley, 1995 ; Dransfi eld et al., 2008 ). The palm warming ( Zachos et al., 2001 ). fossil record refl ects a broader latitudinal distribution of palms The family has been placed in recent studies within the com- in the late Mesozoic and early Cenozoic because of warmer melinid clade of the monocotyledons ( Chase et al., 2006 ; Davis global climate, but also lack of study in the tropics. et al., 2006 ). Arecaceae is composed by fi ve strongly supported Palms are hypothesized to have originated in Australasia (in- subfamilies: Arecoideae, Calamoideae, Ceroxyloideae, Cory- cluding New Guinea, New Caledonia, and New Zealand) and phoideae, and Nypoideae with Calamoideae as sister group to their crown node is estimated to be ca. 110 Myr old (late Ap- the rest of the palms and Nypoideae as the next branch ( Asmus- tian) ( Janssen and Bremer, 2004 ; Bremer and Janssen, 2005 ). sen et al., 2006 ; Dransfi eld et al., 2005 , 2008 ; Baker et al., in press ). The oldest fossils reported for the most basal subfami- lies (Nypoideae and Calamoideae), however, are pollen of 1 Manuscript received 6 November 2008; revision accepted 17 March 2009. Maastrichtian age, while the oldest palm fossil assignable be- The authors thank Carbones del Cerrej ó n, Explorers Club, Fondo para la low family level is 20 Ma older ( Berry, 1914 ) and belongs to Investigaci ó n de Ciencia y Tecnolog í a of Banco de la Rep ú blica – Colombia, the more derived subfamily Coryphoideae ( Dransfi eld et al., Smithsonian Tropical Research Institute, Instituto Colombiano del 2008 ). Petr ó leo, Corporaci ó n Geol ó gica ARES, and NSF grant DEB-0733725 for In this paper, we describe fi ve palm morphospecies from a fi nancial support. Especially they thank F. Chavez, C. Montes, and the geology team at the Cerrej ó n mine for their help and support during fi eld Paleocene (ca. 60 – 58 Ma) rainforest ( Herrera et al., 2005 ) in trips. The Litoteca Nacional and the Universidad de Antioquia Herbarium northeastern Colombia. The fossils are infl orescences, fruits and Palynology Laboratorium provided space for the study of the fossils. and leaves related to three out of the fi ve palm subfamilies Fairchild Tropical Botanic Garden supplied leaf fragments of modern (Arecoideae, Nypoideae, and either Calamoideae or Coryphoid- palms for comparison. S. Manchester, N. Parra, G. Upchurch, and R. eae). Thus, by the Paleocene, the family was represented in Fonnegra provided advice on cuticle preparation; F. Henderson resolved northern South America by more than half of the major extant questions about epidermal anatomy; and J. Dransfi eld, S. Zona, A. palm lineages. Henderson, M. A. Gandolfo, and F. J. Rold á n resolved inquiries in plant The infl orescences collected have affi nities with the subfam- systematics and taxonomy. They also thank W. J. Baker, C. Specht, and the ily Arecoideae, as does one of the fruit morphotypes, which we anonymous reviewers for insightful comments on the manuscript. P. assign to cf. Cocos , a pantropical genus in the tribe Cocoseae. Sucerquia provided the photographs in Figs. 3A, B, 5A, 6I, and G. Bayona the stratigraphic column. The other fruit type we assign to the monotypic genus Nypa 7 Author for correspondence (e-mail: [email protected] ), phone: 507- (Nypoideae). Palm leaves were separated into pinnate and pal- 212-8089 mate morphospecies with uncertain subfamilial affi nity, al- though the palmate type belongs to either Calamoideae or doi:10.3732/ajb.0800378 Coryphoideae. The fossils described here provide information 1300 July 2009] G Ó MEZ-NAVARRO ET AL. — FOSSIL NEOTROPICAL PALMS 1301 about the previous distribution ranges and minimum ages of Cerrejó n fossil fl oral assemblage — The Cerrej ó n megafl ora was fi rst col- extant palm lineages. In particular, the infl orescences and fruits lected over forty years ago ( Doubinger and Pons, 1970 ) and represents one of the very few known fossil fl oral assemblages from the neotropics ( Burnham and are among the oldest megafossil records of the modern groups Johnson, 2004 ). An analysis of leaf morphological characters shows a high pro- to which they are assigned. portion of entire margins and large leaves, which point to a wet tropical climate with a mean annual temperature and precipitation of ca. > 24! C and ~4000 mm, respectively ( Wing et al., 2004 ; Herrera et al., 2005 ). Another estimate of pale- MATERIALS AND METHODS otemperature based on the size of fossil snake vertebrae from the same strata suggested a minimum mean annual temperature of 30 – 34! C ( Head et al., 2009 ). Wing et al. (2004) and Herrera et al. (2005) found affi nities of the Cerrej ó n fl ora Cerrej ó n Formation — The fossil palms were recovered from six localities with typical tropical rainforest families such as Anacardiaceae, Araceae, Are- at the Cerrej ó n open-pit coal mine, Rancher í a Basin, Guajira Department, caceae, Euphorbiaceae, Fabaceae, Lauraceae, Malvaceae, Menispermaceae, northeastern Colombia ( Fig. 1 ). The sampled strata are in the middle and upper and the order Zingiberales ( Doria et al., 2008 ; Herrera et al., 2008 ). part of the Cerrej ó n Formation, a sedimentary sequence dominated by mud- Based on a palynological study of the Cerrej ó n Formation strata, Jaramillo stone, sandstone, and coal, and deposited in a fresh water-infl uenced coastal et al. (2007) concluded that the composition and diversity of the Cerrej ó n fl ora plain ( Jaramillo et al., 2007 ). The six fossil localities are: 0317 (11! 14" N; did not change signifi cantly through the formation. They also found three fossil 72! 57" W), 0318 (11! 13" N; 72! 55" W), 0319 (11! 66" N; 73! 31" W), 0323 palynomorph species that have been assigned to palms, including Arecipites (11! 64" N; 73! 33" W), 0324 (11! 62" N; 73! 32" W), and La Puente M105 – 106 regio , Mauritiidites franciscoi , and Psilamonocolpites medius , all of which are (11! 90" N; 72! 30" W) ( Fig. 2 ). The formation is middle to late Paleocene (ca. abundant. However, a detailed morphological study to assess their natural af- 60 – 58 Ma) based on pollen and carbon isotope studies ( Van der Kaars, 1983 ; fi nities within Arecaceae has not been carried out yet. Spinizonocolpites echi- Jaramillo et al., 2007 ). natus , a fossil pollen species that is related to Nypa ( Germeraad et al., 1968 ) was only found below coal seam 100 ( Fig. 2 ). Fossil material — The megafossils are compressions of reproductive and vegetative organs of palms preserved with external morphological details. The collections are deposited at Ingeominas (Instituto Colombiano de Geolog í a y RESULTS Miner í a) in Bogot á , Colombia. Fossil cuticles were prepared using Schulze ’ s solution and other standard techniques ( Kerp and Krings, 1999 ). Fossil cuticles obtained by maceration were extremely fragmented even with the gentlest Fossil Nypa sp . — Order— Arecales treatment. Cuticle description follows Tomlinson (1961) . Cuticles from mod- ern palm leaves, prepared for comparison, were isolated with commercial Family— Arecaceae Schultz Sch. 1832 bleach, and then stained in 1% aqueous safranin-O. The cellular patterns dis- played by the tissues isolated from the fossil fruits were compared with im- Subfamily— Nypoideae Griffi th 1850 pressions in a transparent resin of the surface of modern palm fruits.