The largest extant snakes live in the tropics of South America and southeast Asia1,2,3 where high temperatures facilitate the evolution of large body sizes among air-breathing animals whose body temperatures are dependant on ambient environmental temperatures (poikilothermy)4,5. Very little is known about ancient tropical terrestrial ecosystems, limiting our understanding of the evolution of giant snakes and their relationship to climate in the past. Here we describe a boid snake from the oldest known neotropical rainforest fauna from the Cerrejón Formation (58–60 Myr ago) in northeastern Colombia. We estimate a body length of 13 m and a mass of 1,135 kg, making it the largest known snake6,7,8,9. The maximum size of poikilothermic animals at a given temperature is limited by metabolic rate4, and a snake of this size would require a minimum mean annual temperature of 30–34 °C to survive. This estimate is consistent with hypotheses of hot Palaeocene neotropics with high concentrations of atmospheric CO2 based on climate models10. Comparison of palaeotemperature estimates from the equator to those from South American mid-latitudes indicates a relatively steep temperature gradient during the early Palaeogene greenhouse, similar to that of today. Depositional environments and faunal composition of the Cerrejón Formation indicate an anaconda-like ecology for the giant snake, and an earliest Cenozoic origin of neotropical vertebrate faunas.
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We thank C. Bell, R. Ghent, E. Kowalski, A. M. Lawing, B. MacFadden, R. Reisz and S. Wing for advice and discussion, K. Seymour, K. Krysko, K. deQueiroz and G. Zug for access to comparative specimens, A. Rincon and M. Carvalho for fieldwork, J. Mason, K. Church, J. Mathis and J. Nestler for fossil preparation, and K. Krysko and J. Nestler for photographic assistance. We thank Carbones del Cerrejón, L. Teicher, F. Chavez, C. Montes and G. Hernandez for logistical support and access to the Cerrejón mine. This research was funded by the National Science Foundation, Fondo para Investigaciones del Banco de la Republica de Colombia, Smithsonian Tropical Research Institute Paleobiology Fund, the Florida Museum of Natural History, a Geological Society of America Graduate Student Research Grant to A.K.H., and a National Sciences and Engineering Research Council of Canada Discovery Grant to J.J.H.
Author Contributions J.J.H., J.I.B., C.A.J., P.D.P., A.K.H. and J.R.B. contributed to project planning. J.J.H. and J.I.B. contributed to systematic palaeontology. J.J.H., P.D.P., J.I.B., A.K.H., J.R.B. and E.A.C. contributed to body size estimation. J.J.H., J.I.B., F.A.H., P.D.P. and C.A.J. contributed to palaeoclimatic analysis. J.I.B., A.K.H., E.A.C., F.A.H. and C.A.J. contributed to fieldwork. J.I.B., A.K.H., C.A.J. and J.J.H. contributed to financial support. All authors contributed to manuscript and figure preparation.
This file contains Supplementary Figures 1-4 with Legends, Supplementary Data and Supplementary Tables 1-3. Supplementary table 2 has been corrected since its original online publication.
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Journal of Mammalian Evolution (2010)