Anacondas are among the largest living snakes in the world. They typically range in length from 4 to 5 m and in rare cases can reach 7 m. In a new study, paleontologists analyzed fossils of giant anacondas from South America and concluded that these tropical snakes reached their maximum size 12.4 million years ago and have remained giants ever since.
“Living snakes have a wide range of body lengths: the modal size is 1 m and varies from 10 cm in the smallest leptotiphlopid filament snakes to approximately 7 m in the genus anaconda. Evnect and giant pythonids,” said Cambridge University graduate student Andres Alfonso-Rojas and colleagues.
“Within Evnect, green anaconda (Mouse eunects) It is the largest species with an average body size of 4-5 m in length and a verifiable maximum size of 6 to 7.2 m.”
“The evolutionary history of anacondas can be minimally limited to the middle to late Miocene, based on limited fossil samples from Brazil, Colombia, Peru and Venezuela.”
“However, little is known about the body size of the earliest anacondas, which coexisted with giant crocodylomorphs, turtles, ungulates and xenarthrans.”
For the study, the authors measured 183 fossilized anaconda vertebrae, representing at least 32 snakes discovered in the state of Falcon in Venezuela, South America.
Combining these measurements with fossil data from other sites in South America allowed them to estimate that ancient anacondas were between 4 and 5 meters long—the size of anacondas that exist today.
“Other species, like giant crocodiles and giant tortoises, have gone extinct since the Miocene, probably due to global cooling and habitat loss, but giant anacondas have survived—they're super hardy,” Alfonso-Rojas said.
“By measuring the fossils, we found that anacondas evolved large body sizes soon after they emerged in tropical South America about 12.4 million years ago, and their size has remained unchanged since then.”
The researchers double-checked their calculations using a second method called ancestral state reconstruction, using the snake family tree as a way to reconstruct the body lengths of giant anacondas and related species of living snakes, including tree boas and rainbow boas.
This confirmed that anacondas had an average body length of 4 to 5 m when they first appeared in the Miocene.
Anacondas live in swamps, swamps and large rivers such as the Amazon. During the Miocene, all of northern South America resembled the modern Amazon region, and anacondas were much more common than they are today.
But there is still enough suitable habitat around with suitable food, such as capybaras and fish, that modern anacondas can continue to remain large.
It was previously thought that anacondas were even larger in the past when it was warmer because snakes are especially sensitive to temperature.
“This is a surprising result because we expected ancient anacondas to be 7 or 8 meters long,” Alfonso-Rojas said.
“But we have no evidence of a larger snake from the Miocene, when global temperatures were higher.”
conclusions were published this week Journal of Vertebrate Paleontology.
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Andres F. Alfonso-Rojas etc.. Early emergence of gigantism in anacondas (Serpentes: Evnect), discovered in the fossil record. Journal of Vertebrate Paleontologypublished online December 1, 2025; doi: 10.1080/02724634.2025.2572967
