Fossil remains discovered in northwestern Venezuela have revealed that ancient giant anacondas once lived in the region some 12.4 million years ago. The findings provide rare insights into how early snakes in South America reached such large sizes and managed to maintain them for millions of years.
Researchers from the University of Cambridge analyzed 183 fossilized backbones, which came from at least 32 different snakes. The fossils were unearthed in the Urumaco region, an area known for its rich fossil history despite difficult conditions for preservation. High heat, humidity, and acidic soils usually destroy remains quickly in tropical climates, making these finds especially valuable.
Experts believe the snakes belonged to an early form of the modern green anaconda, which still holds the record as the world’s heaviest snake. By studying the shape and size of the bones, researchers estimated that these ancient snakes measured over 17 feet long (about 5.2 meters), a size comparable to today’s largest anacondas.
Fossil clues suggest size hasn’t changed much in millions of years
Scientists used a method that compares modern animals with their ancient relatives to estimate the size and traits of the prehistoric anacondas. Their findings showed that these snakes had already reached their large size during the Middle Miocene, a period marked by warm global temperatures and vast wetlands across northern South America.
Surprisingly, the study found no signs that earlier anacondas were much larger than their modern counterparts. While researchers expected to find fossils from snakes reaching lengths of up to 26 feet due to the warm climate at the time, the evidence suggested otherwise.
These results raise new questions about how and why anacondas developed such large bodies. While other massive reptiles from the same period — such as the 39-foot (11.8 meters) caiman Purussaurus and the giant turtle Stupendemys — eventually shrank or went extinct, anacondas remained large and survived long after others disappeared.
Anacondas may have adapted to changing climates
Study lead Andres Alfonso-Rojas, a zoology researcher at the University of Cambridge, noted that the findings challenge assumptions about the relationship between climate and body size. He suggested that early anacondas may have grown large due to abundant prey and widespread wetlands. However, the reason they kept their size while other reptiles declined remains unclear.
As more fossils are uncovered from later periods, researchers hope to better understand how anacondas adapted over time and why they were able to thrive while other large species vanished.
The discovery offers a new perspective on the ancient ecosystems of South America and adds to the growing understanding of how some of today’s most powerful predators came to be.