Anacondas have remained giant for millions of years, a new study finds. The enormous snakes' average body size has remained constant since they first appeared in the fossil record about 12.4 million years ago, during the Middle Miocene (16 million to 11.6 million years ago), researchers revealed in a new study published Monday (Dec. 1) in the Journal of Vertebrate Paleontology. But here's where it gets controversial: despite warm weather and abundant wetlands enabling anacondas to reach their giant size early in their evolutionary history, cooler temperatures and shrinking ranges haven't forced the snakes to get smaller to adapt. This suggests that these weren't the primary factors keeping the snakes large in the intervening millennia. It's still unclear why anacondas have not become smaller over time. The study, led by vertebrate paleontologist Andrés Alfonso-Rojas from the University of Cambridge, measured 183 fossilized anaconda vertebrae from at least 32 individual snakes collected in Venezuela. They also used a technique called ancestral state reconstruction to predict the body lengths of ancient anacondas from characteristics of related snakes. Based on these calculations, the team found that anacondas averaged about 17 feet (5.2 m) long when they first appeared during the Miocene 12 million years ago — roughly the same length as modern anacondas. This is a surprising result because we expected to find the ancient anacondas were seven or eight meters [23 to 26 feet] long, Alfonso-Rojas said. But we don't have any evidence of a larger snake from the Miocene when global temperatures were warmer. Snake quiz: How much do you know about the slithering reptiles?
