Titanoboa was a coldblooded animal whose body temperature depended on that of its habitat. Reptiles can grow bigger in warmer climates, where they can absorb enough energy to maintain a necessary metabolic rate. That’s why insects, reptiles and amphibians tend to be larger in the tropics than in the temperate zone. In this view, extraordinary heat is what made the snake a titan. The same principle would explain why ancient turtles and lungfish of Cerrejón were, like Titanoboa, much larger than their modern relatives.
The relationship between coldblooded body mass and ambient temperature was the subject of a 2005 study by researchers at the Nuclear Physics Institute in St. Petersburg, Russia. By examining species sizes at a variety of different ambient temperatures, Anastassia Makarieva and colleagues calculated how fossils could be used to estimate temperatures in the distant past.
Head and Bloch used the Russian data, plus information about today’s anacondas and their Amazon habitat, to conclude that Titanoboa would have needed surprisingly warm temperatures to survive in ancient Cerrejón.
Several researchers, however, disagree with their conclusion. Paleoclimatologist Kale Sniderman, of the University of Melbourne in Australia, is skeptical of Makarieva’s approach. He noted that an ancient lizard from temperate Australia grew to at least 16.5 feet in length. Applying the model to that fossil predicts that lizards currently living in tropical areas should be capable of reaching 33 feet. In another critique, Stanford’s Mark Denny, a specialist in biomechanics, says the Titanoboa researchers have it backward: The snake was so large and was producing so much metabolic heat that the ambient temperature must have been four to six degrees cooler than the team’s estimate, or the snake would have overheated.
Head, Bloch, Polly and Jaramillo defended the team’s approach, but they acknowledge that their original estimate may have been a bit high. Recent data derived from nearby marine core samples have suggested temperatures closer to 82 to 88 degrees. Even so, they said, Titanoboa’s forest was much warmer than tropical forests today.
Analyses of fossilized leaves from that forest support the idea that it was sweltering. Jaramillo and Herrera studied carbon isotopes in the leaves and the density of pores that let water in and out. They calculated that the levels of carbon dioxide in the atmosphere were 50 percent higher than today, which would have led to high temperatures on land. This fits with estimates from other techniques that the mean temperature was at least 82.5 degrees, and probably considerably higher.
The temperature has implications for how species survived in the tropics—and how they will survive as the climate changes. The rapid contamination of earth’s atmosphere by greenhouse gases like carbon dioxide is causing global warming, a phenomenon, which, if unchecked, may cause massive die-off in species that can’t cope with the heat.
As temperatures rise, at some point plants should become unable to photosynthesize properly. “Figuring out when the different plant groups max out is a difficult question,” said Wing. “When a plant can’t shed the heat, it eventually dies.”
During the time of Titanoboa, said Jaramillo, “we find a very productive forest, with a lot of biomass.” If Titanoboa and its lush ecosystem were in harmony at high temperatures, then global warming may not lead to ecological catastrophe—at least for some plants. “Perhaps modern plants have the ability to cope,” Jaramillo said.
Jaramillo and other members of the Titanoboa team, however, point out that coping with climate change is a lot easier if you have millions of years to adapt to the warming trend. Making the adjustment in 200 years, as climatologists characterize the pace of today’s greenhouse effect, or even 2,000 years, is a different matter altogether.
The paleontologists will return to Cerrejón this year to look for more fossils, more species and more evidence of what the world was like near the Equator 58 million years ago.
“The hardest thing to know about the past,” Wing said, “is how different it was.”