The anaconda is among the largest surviving snake species in the world. Typically, its length ranges from 4 to 5 meters, although exceptional cases can reach up to 7 meters. A recent study conducted by paleontologists on giant anaconda fossils from South America suggests that these tropical reptiles achieved their maximum size approximately 12.4 million years ago and have maintained their large dimensions continuously since then.

“Current snakes display a broad spectrum of body lengths, averaging about 1 meter, with sizes ranging from 10 centimeters for the smallest leptotyphloid thread snakes to roughly 7 meters for anacondas.” Eunectes Andrés Alfonso Rojas, a PhD student at the University of Cambridge, and his colleagues state:

“Within the Eunectes genus, the green anaconda (Eunectes murinus) is the largest species, averaging 4 to 5 meters in length, with maximum recorded lengths of 6 to 7.2 meters.”

“Limited fossil findings from Brazil, Colombia, Peru, and Venezuela suggest that the evolutionary timeline of anacondas dates back to the mid-to-late Miocene.”

“However, our understanding of the body size of early anacondas, which coexisted with massive crocodilians, turtles, ungulates, and xenartranians, remains scarce.”

In their research, the authors examined 183 fossilized anaconda spines representing at least 32 snakes discovered in the state of Falcón, Venezuela.

By integrating these measurements with fossil data from various South American locations, they concluded that ancient anacondas measured 4 to 5 meters in length, similar to today’s anacondas.

“While other species, including giant crocodiles and colossal turtles, have become extinct since the Miocene—likely due to declining global temperatures and reduced habitats—giant anacondas have persisted. They demonstrate remarkable adaptability,” noted Alfonso Rojas.

“The analysis of fossils indicates that anacondas’ body size evolved significantly soon after their emergence in tropical South America around 12.4 million years ago, and this size has remained consistent ever since.”

The researchers cross-verified their estimates using an alternative method known as ancestral state reconstruction, employing snake family trees to estimate the length of giant anacondas and related modern species like tree boas and rainbow boas.

This method corroborates the notion that when anacondas first appeared in the Miocene, their average size was 4 to 5 meters.

Anacondas inhabit swamps, marshes, and substantial rivers, such as the Amazon. During the Miocene, northern South America resembled the contemporary Amazon region, allowing anacondas to thrive in wider areas than seen today.

Nonetheless, the current environment still offers ample food sources, including capybaras and fish, and suitable habitats that support the continued growth of modern anacondas.

As snakes are particularly sensitive to temperature changes, it was previously believed that anacondas might have grown even larger during earlier warm periods.

“This finding is unexpected, as ancient anacondas were thought to have reached lengths of 7 to 8 meters,” remarked Alfonso Rojas.

“However, we found no evidence supporting the existence of larger snakes during the Miocene, even when global temperatures were higher.”

These findings were published recently in the Journal of Vertebrate Paleontology.

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Andres F. Alfonso-Rojas et al. Early origins of gigantism in anacondas (Serpentes: Eunectes) revealed by the fossil record. Journal of Vertebrate Paleontology published online on December 1, 2025. doi: 10.1080/02724634.2025.2572967