A new analysis of South American giant anaconda fossils has revealed the modern land giants reached their maximum size sometime around 12.4 million years ago and have maintained their gigantic status since.
Previous studies have cast doubt on such an ancient timeline for the evolution of giant anacondas, instead suggesting that even larger giants that lived alongside other giant animal species during the Miocene era died out and were replaced by today’s less lengthy anaconda species. However, the University of Cambridge-led team behind the new analysis believes their comparison of ancient and modern anaconda fossils provides compelling support for an evolutionary adaptation that occurred millions of years ago and has persisted to the present day.
According to a statement detailing the team’s research, the team measured 183 fossilized anaconda backbones, representing at least 32 snakes. The specimens were unearthed over several seasons of fieldwork by researchers from the University of Zurich and the Museo Paleontológico de Urumaco in Venezuela, working in Falcón State in Venezuela, South America.
Because these snakes can have more than 300 vertebrae in their backbones, measuring the size of individual fossilized specimens can provide a reliable indication of how long a snake was before it died.
When the research team combined their new measurements with previously collected giant anaconda fossil measurements taken throughout South America, the numbers revealed that ancient anacondas would have been about four or five meters long on average. The team notes that this size “correlates to anacondas today.”
“By measuring the fossils, we found that anacondas evolved a large body size shortly after they appeared in tropical South America around 12.4 million years ago, and their size hasn’t changed since,” explained Andrés Alfonso-Rojas, a PhD student and Gates Cambridge Scholar in the Department of Zoology at the University of Cambridge, lead author of the research.
To double-check the results, the University of Cambridge researcher employed another method, “ancestral state reconstruction,” that uses a snake’s family tree to reconstruct the expected body length of giant anacondas and other snake species. After running the numbers, the researchers said the alternate method “confirmed that the average body length of anacondas was four to five metres” when they first appeared in the region’s fossil record.
Alfonso-Rojas said finding that anacondas were already giants over 12 million years ago during the Miocene era, when there were other giant species that have not survived into the present, was surprising since they had expected to find the animals were much larger in their ancient past and had evolved to their smaller, yet still imressive land giants we see today, due to temperature changes.
“We expected to find the ancient anacondas were seven or eight metres long,” Alfonso-Rojas explained. “But we don’t have any evidence of a larger snake from the Miocene when global temperatures were warmer.”
During the Upper and Middle Miocene, many giant versions of modern animal species existed that no longer exist today. Alfonso-Rojas said other giants like giant crocodiles and giant turtles went extinct during this part of the planet’s history, “probably due to cooling global temperatures and shrinking habitats.”
Conversely, the new analysis shows that giant anacondas, which also reached their maximum size at a time when other giants also roamed the Earth, were able to adapt to tropical zones and maintain their giant status to this day.
“They are super-resilient,” said Alfonso-Rojas.
The study “An early origin of gigantism in anacondas (Serpentes: Eunectes) revealed by the fossil record” was published in the Journal of Vertebrate Paleontology.
Christopher Plain is a Science Fiction and Fantasy novelist and Head Science Writer at The Debrief. Follow and connect with him on X, learn about his books at plainfiction.com, or email him directly at christopher@thedebrief.org.