Study shows Amazon's massive anacondas were at their largest size 12 million years ago

A recent analysis of anaconda fossils reveals that these snakes achieved their largest size around 12.4 million years ago and have maintained it ever since. While modern anacondas typically measure 4 to 5 metres, some can grow up to 7 metres. In this study, a research team from the University of Cambridge examined 183 fossilized vertebrae discovered in Falcn State, Venezuela, representing at least 32 individual snakes. Calculations indicate that these ancient anacondas were also between four and five metres long, similar to their living counterparts in the Amazon.

By examining these fossils, we discovered that anacondas developed a large body size soon after emerging in tropical South America about 12.4 million years ago, and their size has remained stable ever since, explained Andrs Alfonso-Rojas, the studys lead author. This persistence shows that anacondas withstood climate shifts that caused the extinction of other large species.

During the Middle to Upper Miocene, from 12.4 to 5.3 million years ago, many animal species were larger than their modern descendants due to warm climates, expansive wetlands, and abundant food. Massive creatures like the 12-metre caiman Purussaurus and the 3.2-metre freshwater turtle Stupendemys inhabited northern South America, but these giants eventually vanished. In contrast, anacondas survived and retained their impressive size.

Other giant species, such as enormous crocodiles and turtles, disappeared after the Miocene, likely because of cooler temperatures and shrinking habitats, but anacondas proved incredibly resilient, noted Alfonso-Rojas, a PhD student and Gates Cambridge Scholar in the Department of Zoology.

The team confirmed their measurements using ancestral state reconstruction, which maps the evolutionary tree of snakes to estimate the body lengths of ancient anacondas and related species, including tree boas and rainbow boas. This method supported the initial finding that Miocene anacondas averaged four to five metres in length.

These results challenge the assumption that snakes, being cold-blooded, would only reach their maximum size during the warmest periods. We expected to find snakes seven or eight metres long in the Miocene, but no evidence of larger specimens exists from that era, Alfonso-Rojas said.

The true remarkable aspect is not the size itself but the species ability to endure global cooling. Researchers suggest that their aquatic habits and versatile diet played a crucial role. Miocene wetlands in northern South America resembled todays Amazon, offering widespread suitable habitats. Even with environmental changes, sufficient swampy areas and prey, such as capybaras and fish, allowed anacondas to sustain their large size.

The study was published in the Journal of Vertebrate Paleontology on December 1.

Author: Sophia Brooks