1. Department of Biology, University of Toronto, Mississauga, Ontario L5L 1C6, Canada
2. Florida Museum of Natural History, University of Florida, Gainesville, Florida 32611-7800, USA
3. Smithsonian Tropical Research Institute, Box 0843-03092, Balboa, Ancon Republic of Panama
4. Department of Geological Sciences, Indiana University, Bloomington, Indiana 47405-1405, USA

Correspondence to: Jason J. Head¹ Correspondence and requests for materials should be addressed to J.J.H. (Email: jason.head@utoronto.ca).

Abstract

The largest extant snakes live in the tropics of South America and southeast Asia^{1, 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 snake^{6, 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.

1. Department of Biology, University of Toronto, Mississauga, Ontario L5L 1C6, Canada
2. Florida Museum of Natural History, University of Florida, Gainesville, Florida 32611-7800, USA
3. Smithsonian Tropical Research Institute, Box 0843-03092, Balboa, Ancon Republic of Panama
4. Department of Geological Sciences, Indiana University, Bloomington, Indiana 47405-1405, USA

Correspondence to: Jason J. Head¹ Correspondence and requests for materials should be addressed to J.J.H. (Email: jason.head@utoronto.ca).

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