Fossils from Venezuela push back the origin of giant anacondas and show these tropical snakes reached their maximum size around 12.4 million years ago, remaining giants ever since.
Overview
Anacondas rank among the world’s largest snakes. Typical lengths are about 4–5 meters, with rare individuals approaching 7 meters. A new study of South American fossil remains indicates that ancient anacondas already reached 4–5 meters in length over 12 million years ago in the Miocene, and this size has persisted through time. The researchers analyzed dozens of fossil backbones from Venezuela and other South American sites to estimate body length and compare it with modern relatives.
Key findings
- Modern anacondas vary widely in length, with the green anaconda (Eunectes murinus) being the largest living species, averaging about 4–5 meters and with verified maxima around 6–7.2 meters. This provides a contemporary scale for interpreting fossil sizes.
- The study involved measurements of 183 fossilized backbones, representing at least 32 individual snakes found in Falcón State, Venezuela, combined with other regional fossil records to reconstruct body sizes. This analysis supports a Miocene-era average length of 4–5 meters, matching today’s giant anacondas.
- An ancestral-state reconstruction using a broader snake family tree confirmed these results, suggesting early anacondas already reached 4–5 meters when they first appeared in tropical South America, and their size has remained relatively stable since then.
Habitat and evolution
Anacondas inhabited swamps, marshes, and large river systems, such as the Amazon. During the Miocene, northern South America had landscapes resembling today’s Amazon basin, with a wider historical distribution of anacondas than we see today. This expansive habitat, along with abundant prey like capybaras and fish, likely supported their continued large size.
Surprising twists
- Contrary to expectations that ancient snakes would be larger during relatively warmer periods, the study found no evidence of Miocene giants exceeding 7–8 meters; this challenges the assumption that warmer climates directly produced bigger snakes.
- The team notes that other contemporary giant reptiles, such as certain crocodylomorphs and turtles, ultimately went extinct, possibly due to climate cooling and habitat shifts, whereas giant anacondas persisted. This highlights their notable resilience.
Publication details
The findings were published in the Journal of Vertebrate Paleontology online on December 1, 2025, with the title: An early origin of gigantism in anacondas (Serpentes: Eunectes) revealed by the fossil record. The DOI is provided in the article.
If you’re curious about the broader implications, this study suggests that gigantism in these snakes emerged earlier than previously believed and has endured through significant climatic and environmental changes, prompting fresh questions about stability of maximal body size and ecological constraints in large snakes. Would you like a layperson-friendly explainer that walks through the methods used to estimate fossil lengths and what this means for our understanding of Miocene ecosystems?
