Fossil Evidence for Evolution of The

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14. M. J. Prather, Science 279, 1339 (1998). Table 2. Chemical modes and amplitudes excited by pulses of N2O, CO, and CH4. The modes are identified with perturbation minus control (P – C) simulations. Amplitudes (A) are in globally 15. D. L. Albritton, R. G. Derwent, I. S. A. Isaksen, M. Lal, D. J. Wuebbles, in Climate Change 1994, Intergovernmental integrated teragrams of N for N2O and NOy and in teragrams for other species. The amplitudes of Panel on Climate Change,J.T.Houghtonet al.,Eds. these modes are characterized by the amounts of N2O (mode 1) and CH4 (mode 2), shown in bold. (Cambridge Univ. Press, Cambridge, 1995), pp. 204–231. Relatively small amplitudes are not shown (–). 16. M. J. Prather, Geophys. Res. Lett. 21, 801 (1994). 17. M. Prather et al., in Climate Change 1994, P – C Initial pulse Mode (time) A N2O A NOy A CH4 A O3 A trop O3 Intergovernmental Panel on Climate Change, – – – – J. T. Houghton et al., Eds. (Cambridge Univ. Press, C2 C1 10 Tg of N from N2O 1 (108.4 years) +10.2 +0.011 2.1 0.93 0.01 Cambridge, 1995), pp. 73–126. 2 (12.5 years) –0.002 – +2.8 +0.11 0.03 18. P. Forster et al., in Climate Change 2007: The Physical C3 – C1 100 Tg of CO 1 (108.4 years) +0.0045 –––– Science Basis. Fourth Assessment Report of the 2 (12.5 years) –0.005 –0.00003 +7.4 +0.30 +0.09 Intergovernmental Panel on Climate Change, – –––– S. Solomon et al., Eds. (Cambridge Univ. Press, C4 C1 10 Tg of CH4 1 (108.4 years) +0.006 Cambridge, 2007), pp. 129–234. 2 (12.5 years) –0.007 -0.00004 +9.85 +0.40 +0.12 19. WMO, Scientific Assessment of Ozone Depletion: 2006, C. A. Ennis, Ed. (WMO, Geneva, 2006). 20. K. L. Denman et al., in Climate Change 2007: The This N2O-CH4 coupling will shift with climate 3. M. B. McElroy, J. C. McConnell, J. Atmos. Sci. 28, 1095 (1971). Physical Science Basis. Fourth Assessment Report of the change over the 21st century. For example, the 4. World Meteorological Organization (WMO), Atmospheric Intergovernmental Panel on Climate Change, Ozone 1985: Assessment of Our Understanding of the upper stratosphere cools as CO increases, and this S. Solomon et al., Eds. (Cambridge Univ. Press, 2 Processes Controlling Its Present Distribution and Cambridge, 2007), pp. 499–587. temperature change alters the N2O-NOy-O3 chem- Change, R. T. Watson et al., Eds. (Global Ozone Research 21. J. E. Rosenfield, A. R. Douglass, Geophys. Res. Lett. 25, istry, reducing the impact of N2OonO3 (21). The and Monitoring Project Report No. 16, WMO, Geneva, 4381 (1998). importance of N O as an ozone-depleting sub- 1985). 22. A. R. Ravishankara, J. S. Daniel, R. W. Portmann, Science 2 5. J. Hsu, M. J. Prather, Geophys. Res. Lett. 37, L07805 (2010). stance (22) will thus be reduced, weakening the 326, 123 (2009). 6. Q. Tang, M. J. Prather, Atmos. Chem. Phys. 10, 9681 23. This research was supported by NSF’s Atmospheric coupling described here but still maintaining the (2010). Chemistry program (grant ATM-0550234) and NASA’s 7. Materials and methods are available as supporting negative greenhouse feedback effect of CH4 on Modeling, Analysis, and Prediction/Global Modeling material on Science Online. N2O emissions. Initiative program (grants NNG06GB84G and 8. D. S. Stevenson et al., J. Geophys. Res. 111, D08301 NNX09AJ47G). (2006). References and Notes 9. O. Wild, M. J. Prather, J. Geophys. Res. 105, 24647 (2000). Supporting Online Material 1. A. M. Fiore, J. J. West, L. W. Horowitz, V. Naik, 10.R.G.Derwent,W.J.Collins,C.E.Johnson,D.S.Stevenson,

www.sciencemag.org/cgi/content/full/330/6006/952/DC1 on November 15, 2010 M. D. Schwarzkopf, J. Geophys. Res. 113, D08307 (2008). Clim. Change 49, 463 (2001). Methods 2. M. Prather et al., in Climate Change 2001: The Scientific 11. M. J. Prather, Geophys. Res. Lett. 36, L03811 (2009). References Basis. Third Assessment Report of the Intergovernmental 12. J. Hsu, M. J. Prather, O. Wild, J. Geophys. Res. 110, D19305 Panel on Climate Change,J.T.Houghtonet al.,Eds. (2005). 9 August 2010; accepted 8 October 2010 (Cambridge Univ. Press, Cambridge, 2001), pp. 239–287. 13. J. Hsu, M. J. Prather, J. Geophys. Res. 114, D06102 (2009). 10.1126/science.1196285

Reserve, Peru (10). Diagnosis: Inkayacu para- Fossil Evidence for Evolution of the casensis is diagnosed by the following combi- nation of characters (autapomorphies within Shape and Color of Penguin Feathers Sphenisciformes demarcated by an asterisk): www.sciencemag.org paired grooves meeting at midline on dorsal sur- Julia A. Clarke,1* Daniel T. Ksepka,2,3 Rodolfo Salas-Gismondi,4 Ali J. Altamirano,4 face of premaxilla* (Fig. 1, GR), articular surfaces Matthew D. Shawkey,5 Liliana D’Alba,5 Jakob Vinther,6 Thomas J. DeVries,7 Patrice Baby8,9 of otic and squamosal head of quadrate contacting one another,* furcula with blade-like hypocleidium,* Penguin feathers are highly modified in form and function, but there have been no fossils to inform conspicuous n. coracobrachialis sulcus developed their evolution. A giant penguin with feathers wasrecoveredfromthelateEocene(~36million on the humerus (Fig. 1, CNS), femur with widened years ago) of Peru. The fossil reveals that key feathering features, including undifferentiated primary and sharply distally tapering medial condyle* and Downloaded from wing feathers and broad body contour feather shafts, evolved early in the penguin lineage. Analyses tab-like process projecting from posterior intra- of fossilized color-imparting melanosomes reveal that their dimensions were similar to those of muscular ridge at midshaft* (Fig. 1, MC and T), non-penguin avian taxa and that the feathering may have been predominantly gray and reddish-brown. and weak proximal projection of cnemial crests of In contrast, the dark black-brown color of extant penguin feathers is generated by large, ellipsoidal tibiotarsus (Fig. 1, CNE). See (10) for additional melanosomes previously unknown for birds. The nanostructure of penguin feathers was thus modified diagnosis, figures, and description. after earlier macrostructural modifications of feather shape linked to aquatic flight.

1 uring wing-propelled diving, penguins morphologies (9) and discuss the pattern and Department of Geological Sciences, University of Texas at Austin, Austin, TX 78712, USA. 2Department of Marine, Earth, generate propulsive forces in a fluid en- timing of major events in the evolution of pen- and Atmospheric Sciences, North Carolina State University, Dvironment ~800 times more dense and guin integument. Raleigh, NC 27695–8208, USA. 3Department of Paleontology, ~70 times more viscous than air (1). Recent fossil Systematic paleontology: Aves Linnaeus North Carolina Museum of Natural Sciences, Raleigh, NC 27601– discoveries have yielded information on the se- 1758 sensu Gauthier 1986. Sphenisciformes 1029, USA. 4Departamento de Paleontología de Vertebrados, Museo de Historia Natural–Universidad Nacional Mayor de San quence of early osteological changes in pen- Sharpe 1891 sensu Clarke et al. 2003. Inkayacu 5 paracasensis Marcos (UNMSM), Lima 14, Perú. Integrated Bioscience Pro- guins accompanying the evolution of aquatic flight new gen. and sp. Etymology: gram, University of Akron, Akron, OH 44325, USA. 6Department (2–5), but these specimens have not included Inkayacu—the Quechua, “Inka” for emperor and of Geology and Geophysics, Yale University, New Haven, CT 06511, feathers. Living penguin melanosome morphol- “yacu” for water; paracasensis for the Reserva USA. 7Burke Museum of Natural History and Culture, University 8 ogies have not been described, although the Nacional de Paracas, Peru, the type locality. ofWashington,Seattle,WA98195,USA. Laboratoire des Mécanismes et Transferts en Géologie, Institut de Recherche pour melanin they contain is generally known to pro- Holotype: MUSM 1444, a nearly complete skel- de Développement, 14 Avenue Edouard Belin, F-31400 Toulouse, vide both color and wear-resistance to bird feathers eton with wing feathering, body contour feathers, France. 9Université de Toulouse, F-31400 Toulouse, France. (6–8). Here, we describe a giant fossil penguin and pedal scales (Figs. 1 to 3) (10). Locality and *To whom correspondence should be addressed: julia_clarke@ with feathers recording preserved melanosome horizon: UpperEoceneofYumaquePoint,Paracas jsg.utexas.edu

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Fig. 1. Reconstruction of Inkayacu paracasensis in oblique anterior view showing recovered elements in white and photographs of the holotype specimen (MUSM 1444): skull and mandible in (A and C) dorsal, (B)ventral,and(D) lateral views; scapula in (E) lateral view and humerus in (F) posterior, (G) ventral, (H)anterior,and(I) distal views; femur in (J) dorsal, (K)medial,(L)ventral,and(M) distal views; patella in (N) anterior view; tibiotarsus in (O) lateral view; and tarsometatarsus in (P)proximal,(Q)distal, (R)anterior,and(S) plantar views. AC, acromion; AMB,pathwayofm.ambienstendon;ATR,anterior trochlearprocess;CBC,m.coracobrachialiscaudalis insertion; CF, fibular crest; CNE, cnemial crests; CNS, coracobrachialis nerve sulcus; CT, coracoid tuberos- ity; DEN, dentary; GR, groove on premaxilla; IL, m. iliofemoralis and iliotrochantericus insertions; LF, lacrimal facet; LPVF, lateral proximal vascular fora- men; MHC, medial hypotarsal crest; MC, medial condyle; MTR, middle trochlear process; PIII-1, manual phalanx III-1; PAL, palatine; PATH, pathology; PF, pectoralisfossa;PO,postorbitalprocess;PS,para- sphenoid rostrum; PTR, posterior trochlear process; SC, m. supracoracoideus insertion; SF, salt gland fossa; SU, surangular; T, tab-like process; TF, temporal fossa; V, vomer. Asterisks demarcate autapomorphies refer- enced in the diagnosis (10).

The holotype skeleton of Inkayacu para- on November 15, 2010 casensis is disarticulated, with the exception of regions with extensive soft tissue impressions [distal left flipper (Fig. 2) and distal left pes (10)]. The fossil represents an animal with an estimated swimming length of 1.5 m. It has a hyper-elongate beak with a grooved tip and relatively gracile wing bones as compared with those of other giant penguins [such as Icadyptes (11)]. Conservative estimates of body mass for Inkayacu (~54.6 to www.sciencemag.org 59.7 kg) are approximately twice the average mass of the Emperor Penguin (12); it is among the largest described fossil penguins (10). Isolated contour feathers exhibit the broadened rachis of extant penguins. They grade from a light-colored (pale gray) base to a dark gray- black distal end (Fig. 3), where the rachis narrows and a cluster of distally directed, clumped darker Downloaded from barbs are developed at the tip. This coloration pattern is observed in penguins and other birds, resulting from increasing melanization toward the tip (13). Preserved portions of contour feathers and estimates from rachis diameter are consistent with a maximum length of approximately 3 cm, which is within the range of extant penguin body contour feathers (10) but notably shorter Fig. 2. The wing feathering of Inkayacu paracasensis.(A) Photograph and line drawing of the left wing (scale than contour feathers from several smaller-bodied bar, 1 cm) showing location of insets and samples (circles) taken for scanning electron microscopy (SEM). (B) extant high-latitude species (10). As in extant Close-up of the counterpart showing the surface of imbricated short covert feathers from the leading edge of penguins, these feathers are pennaceous over most the wing and (C) SEM of melanosomes in (B). (D)Close-upofthecounterparttothesurfaceofthecarpo- of their length; barbs are relatively evenly spaced, metacarpus with preserved melanized bases of covert feathers and (E)SEMofmelanosomesfromfeather although barbule structure is not visible. bases in (D) (melanosomes were not observed in surrounding matrix). (F)Close-upoftertiariesand(G) SEM of Preserved feathering along the left distal wing melanosomes in (F). (H)Secondariesand(I) SEM of melanosomes from (H). Scale bar for SEM images, 1 mm, is exposed in dorsal view (Fig. 2) and appears to and for insets, 3 mm. mc, carpometacarpus; r, radius; rl, radiale; t, tibiotarsus; u, ulna; ul, ulnare. be close to life position with only slight peri- depositional posterior movement of the distal somes (Fig. 2, A to C). This darker layer contin- is textured with small regularly distributed raised carpometacarpus. At the leading edge, texturing ues over most of the carpometacarpus and distal knobs (Fig. 2A). Thin, paired impressions in this of a thin layer of gray matrix records the tips of radius. Where it split from the dorsal carpometa- pale matrix preserve melanosomes (Fig. 2, D and tiny, closely packed covert feathers with melano- carpal surface, the underlying, light-colored matrix E) that we interpret as melanized bases of the short,

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Fig. 3. Comparison of darker-tipped covert feathers. Similarly, extant pen- melanosome proportions guin coverts that exhibit dark tips are commonly and body contour feather white proximally but bear melanin stripes where morphology in (A and B) the feathers enters the skin. The absence of mela- Inkayacu paracasensis nosomes in the light matrix surrounding these and (C and D)represent- marks in the fossil is consistent with similarly ative extant penguins. (A) white proximal feathers (9)inInkayacu. Presence SEM of melanosomes pre- of intact lesser covert feather bases and tips (in served in the tip of (B) part and counterpart) represents a dimensionality body contour feathers of rare in feather preservation. I. paracasensis;(C)SEMof Dorsal lesser-wing covert feathers partially large, ellipsoidal melanosomes (shown, Eudyptula overlie the distal wing bones (Fig. 2). Layers of minor) from (D) similarly elongate under-wing coverts pass ventral to the shaped body contour fea- ulnare and carpometacarpus. The morphology and thers (shown, Aptenodytes dark tonality of the feathers originating from the forsteri) in the penguin carpometacarpus and ulna, which comprise the crown clade. trailing edge of the wing, are identical (Fig. 2, A and H). The homology of any one stacked layer of these feathers with the primaries and secondaries (remiges) of other birds is uncertain, but if one layer is considered to represent the remiges, at least one layer of coverts subequal in length must be present. All of these feathers show a broadened rachis and are relatively larger than in any extant penguin. The centers of rachises are light with darker edges. Many barbs are visible in distal feathers, and fewer are decipherable at midshaft. Seven incomplete feathers preserved on November 15, 2010 in the matrix overlying the secondaries appear to be associated with the distal humerus. All preserved feather types in Inkayacu record melanosomes (Figs. 2 and 3) (10)ofdimensions Fig. 4. Phylogenetic within the range for avian taxa other than extant placement of Inkayacu penguins (10). Although the length of extant pen- paracasensis in a strict guin melanosomes was similar to other eumelano- consensus cladogram of somes, (mean of ~900 nm), their width (mean of 45 most-parsimonious trees ~440 nm) was far greater than all other Aves sam- www.sciencemag.org (MPTs) [Crown clade col- 10 pled (mean of ~300 nm) and in some cases ap- lapsed; see ( )forde- proached their length (table S3). We thus analyzed tails of analysis]. Placement them as a separate class in a discriminant analysis in a clade of Eocene giant (10). We used four properties of melanosome mor- penguins (X) implies an — origin for the modified phology and distribution long-axis variation, short- — wing feathering, undifferen- axis skew, aspect ratio, and density to estimate the color predicted from the fossil feather samples

tiated remiges, and broad Downloaded from rachis of body contour fea- (10). All six Inkayacu samples were assigned a thers (insets) no later than gray or reddish-brown color with high probability, the early Eocene (10). En- and none clustered with extant penguin samples. larged melanosomes are The Inkayacu specimen provides evidence phylogenetically supported for an Eocene giant penguin clade (Fig. 4, Clade at minimum as a novelty of X) with a wide Southern Ocean distribution and the penguin crown clade for a third early-stem penguin dispersal to low (insets). Stratigraphic distri- latitudes (11). Phylogenetic analysis of a com- butions from (5). Fossil dis- bined data set (10) finds the new species allied tributions are Antarctica, with three early- to late-Eocene species from New blue; New Zealand, green; Zealand and Antarctica (10). The most recent Africa, dark gray; and South common ancestor of Inkayacu and living pen- America, red. guins (Spheniscidae) is thus inferred to be present by the early Eocene and to have shared the lack of differentiation between stacked remiges and greater coverts, densely packed, squamiform lesser coverts, and broad flattened contour feather rachises seen in extant penguins. Early modifications in the wing feathering seen in Inkayacu created a narrow streamlined flipper and changed the hydrodynamic properties of the body feathers. Broad flat contour

956 12 NOVEMBER 2010 VOL 330 SCIENCE www.sciencemag.org REPORTS feather rachises create less turbulent flow (12), demands of underwater propulsion. Low aspect 15. R. P. Wilson, K. Hustler, P. G. Ryan, A. E. Burger, which is an effect hypothesized to explain a lower ratio, large size, and clustered melanosome distri- E. C. Noldeke, Am. Nat. 140, 179 (1992). 10 16. C. Dawson, J. F. V. Vincent, G. Jeronimidis, G. Rice, observed drag coefficient than predicted from bution ( ) may affect melanin packing and fea- P. Forshaw, J. Theor. Biol. 199, 291 (1999). streamlined penguin body shape alone (14). They ther material properties. Melanin confers resistance 17. K. J. McGraw et al., Pigment Cell Res. 20, 301 (2007). also facilitate reduction of intraplumage air (15). to fracture (6, 21, 22), which is important to mate- 18. H. M. Rowland, Philos. Trans. R. Soc. London Ser. B Most of the insulating properties of extant pen- rials like feathers subjected to cyclical loading (22). Biol. Sci. 364, 519 (2009). 19. A. Berta, in Encyclopedia of Marine Mammals, Second guin contour feathers derive from their plumula- Selective pressures for the color and material prop- Edition, W. Perrin, B. Würsing, J. G. M. Thewissen, Eds. ceous afterfeathers (16), which are not preserved erties of penguin feathers could thus have led to (Academic Press, San Diego, CA, 2009), pp. 861–868. or not present in Inkayacu. nanoscale changes in melanosome morphology. 20. U. Arnason et al., Mol. Phylogenet. Evol. 41, 345 (2006). Inkayacu shows that the large, subround mel- 21. A. A. Voitkevich, The Feathers and Plumage of Birds anosomes of extant penguin feathers were absent (October House, New York, 1966). References and Notes 22. R. H. Bonser, P. P. Purslow, J. Exp. Biol. 198, 1029 (1995). early in penguin evolution. At minimum, an in- 1. M. Denny, Air and Water (Princeton Univ. Press, 23. K. Browne helped produce the figures; W. Aguirre, crease in melanosome size and a decrease in their Princeton, NJ, 1993). P. Brinkman, and V. Schneider prepared the fossil. aspect ratio occurred after the early Eocene diver- 2. R. E. Fordyce, C. M. Jones, in Penguin Biology, L. S. Davis, K. Middleton and M. Stucchi provided discussion. gence of the clade that includes Inkayacu (Fig. 4, J. T. Darby, Eds. (Academic Press, San Diego, CA, 1990), P. Unitt, K. Zyskowski, B. Wang, J. Tejada, J. Reyes, pp. 419–226. E. Díaz, and Z. Jiang provided professional assistance. Clade X) and before the origin of extant penguins 3. K. E. Slack et al., Mol. Biol. Evol. 23, 1144 (2006). The research was funded by the National Science (Spheniscidae) by the late Miocene (5). The spe- 4. P. Jadwiszczak, Polar Res. 30, 3 (2009). Foundation (DEB-0949897 and DEB-0949899), the cific proportions of extant penguin melanosomes, 5. D. T. Ksepka, J. A. Clarke, Bull. Am. Mus. Nat. Hist. National Geographic Society Expeditions Council, the the packing of these melanosomes into clusters 337, 1 (2010). Air Force Office of Scientific Research (FA9550-09-1- 0159), and University of Akron startup funds. MUSM within the barbs and rachis (10), and yellow, pterin- 6. E. H. Burtt Jr., Ornithol. Monogr. 38, 1 (1986). 7. K. J. McGraw, in Bird Coloration, vol.1, Mechanisms and 1444 is permanently deposited at the Museo de Historia 17 – like pigmentation ( ) are so far only known in the Measurements, G. E. Hill, K. J. McGraw (Harvard Univ. Natural UNMSM, Lima, Peru. penguin crown clade. Press, Boston, 2006), pp. 243–294. Shifts in penguin plumage coloration indi- 8. B. Stonehouse, The Biology of Penguins (Macmillan, Supporting Online Material London, 1975). www.sciencemag.org/cgi/content/full/science.1193604/DC1 cated by the fossil may be linked to differences in Materials and Methods 9. J. Vinther, D. E. G. Briggs, R. O. Prum, V. Saranathan, ecology, thermoregulatory demands (18), or the SOM Text Biol. Lett. 4, 522 (2008). Figs. S1 to S9 more recent, predominantly Neogene, diversifi- 10. Materials and methods are available as supporting Tables S1 to S8 cation of their primary mammalian predators material on Science Online.

References on November 15, 2010 (19, 20). However, they do not explain the aberrant 11. J. A. Clarke et al., Proc. Natl. Acad. Sci. U.S.A. 104, Phylogenetic Data Set melanosome morphology associated with extant 11545 (2007). 12. B. Stonehouse, Adv. Ecol. Res 4, 131 (1967). 10 June 2010; accepted 10 September 2010 penguin brown-black color. Indeed, rather than 13. W. L. N. Tickell, Waterbirds 26, 1 (2003). Published online 30 September 2010; selection for color, these changes may represent 14. J. Lovvorn, G. A. Liggins, M. H. Borstad, S. M. Calisal, 10.1126/science.1193604 an unanticipated response to the hydrodynamic J. Mikkelsen, J. Exp. Biol. 204, 1547 (2001). Include this information when citing this paper.

years (1), a rapid and transient northward migration Effects of Rapid Global Warming at the of plants in North America (6), and a mammalian turnover in North America and Europe (7). www.sciencemag.org Paleocene-Eocene Boundary on Efforts to understand the impact of climate change on terrestrial environments have focused on mid- to high-latitude localities, but little is Neotropical Vegetation known of tropical ecosystems during the PETM. Tropical temperature change is poorly constrained, 1 1,2 3,1,4 5 Carlos Jaramillo, * Diana Ochoa, Lineth Contreras, Mark Pagani, but, given the magnitude of temperature change 6,1 6 5 1 Humberto Carvajal-Ortiz, Lisa M. Pratt, Srinath Krishnan, Agustin Cardona, elsewhere, tropical ecosystems are thought to have

1 1,7 3,8 9,3 Downloaded from Millerlandy Romero, Luis Quiroz, Guillermo Rodriguez, Milton J. Rueda, suffered extensively because mean temperatures 3 1,10 1 11,1 1,11 Felipe de la Parra, Sara Morón, Walton Green, German Bayona, Camilo Montes, are surmised to have exceeded the ecosystems’ 12 13 14 15 16 Oscar Quintero, Rafael Ramirez, Germán Mora, Stefan Schouten, Hermann Bermudez, heat tolerance (8). 17 18 16 19 20 Rosa Navarrete, Francisco Parra, Mauricio Alvarán, Jose Osorno, James L. Crowley, For this study, three tropical terrestrial PETM 21 22 Victor Valencia, Jeff Vervoort sites from Colombia and Venezuela were analyzed for pollen and spore content and stable car- Temperatures in tropical regions are estimated to have increased by 3° to 5°C, compared with bon isotopic composition of organic materials Late Paleocene values, during the Paleocene-Eocene Thermal Maximum (PETM, 56.3 million years (Fig. 1) (9). The analysis included 317 pollen ago) event. We investigated the tropical forest response to this rapid warming by evaluating samples, 1104 morphospecies, and 37,952 indi- the palynological record of three stratigraphic sections in eastern Colombia and western Venezuela. vidual occurrences together with 489 carbon We observed a rapid and distinct increase in plant diversity and origination rates, with a set of isotopes samples, 21 plant biomarker samples, new taxa, mostly angiosperms, added to the existing stock of low-diversity Paleocene flora. There is and one radiometric age (9). Localities Mar 2X no evidence for enhanced aridity in the northern Neotropics. The tropical rainforest was able (core), Riecito Mache (outcrop), and Gonzales to persist under elevated temperatures and high levels of atmospheric carbon dioxide, in contrast (outcrop and well) contain sediments that accu- to speculations that tropical ecosystems were severely compromised by heat stress. mulated in fluvial to coastal plain settings. Bio- stratigraphy and carbon isotope stratigraphy, using he Late Paleocene-Eocene Thermal Max- PETM is associated with a large negative carbon bulk d13C and plant wax n-alkanes, confirm the imum [PETM, 56.3 million years ago isotope excursion recorded in carbonate and position of the PETM at the three sites (Figs. 2 (Ma)], lasting only ~100,000 to 200,000 organic materials, reflecting a massive release of and 3) (9), which is not associated with any for- T 13 years, was one of the most abrupt global warming C-depleted carbon (4, 5), an ~5°C increase in mation boundary or major lithological or deposi- events of the past 65 million years (1–3). The mean global temperature in ~10,000 to 20,000 tional environment change. The location of the