Giant boid snake from the Palaeocene neotropics reveals hotter past equatorial temperatures

Abstract

The largest extant snakes live in the tropics of South America and southeast Asia<U><SUP>1, 2, 3</SUP></U> where high temperatures facilitate the evolution of large body sizes among air-breathing animals whose body temperatures are dependant on ambient environmental temperatures (poikilothermy)<U><SUP>4, 5</SUP></U>. 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<U><SUP>6, 7, 8, 9</SUP></U>. The maximum size of poikilothermic animals at a given temperature is limited by metabolic rate<U><SUP>4</SUP></U>, 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 CO<SUB>2</SUB> based on climate models<U><SUP>10</SUP></U>. 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.