Anacondas reached their massive form around 12.4 million years ago and have stayed the same since.
A research team, led by the University of Cambridge, made the conclusion after analysing hundreds of giant anaconda
fossils from South America.
The finding was published in the Journal of Vertebrate Palaeontology, and challenges the long-held assumption that
ancient anacondas must have been much larger than today’s snakes because they lived in a warmer world.
GIANTS DIED, ANACONDAS ENDURED
Between 12.4 and 5.3 million years ago, during the Middle to Upper Miocene, many animals grew to enormous sizes.
Warmer global temperatures, widespread wetlands, and abundant prey allowed creatures like the 12-metre Purussaurus (a
giant caiman) and the 3.2-metre Stupendemys, one of the largest freshwater turtles ever, to survive without struggle.
“This is a surprising result because we expected to find the ancient anacondas were seven or eight metres long,” said
lead author Andres Alfonso-Rojas.
But while these mega-reptiles later went extinct as the world got cooler and habitats shrank, anacondas survived as
Modern green anacondas reach 4 to 5 metres, with rare cases of them stretching up to 7 metres.
183 FOSSIL BONES AND A CONCLUSION
Researchers measured 183 fossilised anaconda backbones from at least 32 snakes found in Venezuela's Falcon State.
When they compared these fossils with samples from other sites across South America, they calculated that ancient
anacondas were also 4 to 5 metres long, almost exactly the size of anacondas today.
To confirm their estimates, the team used another method called ancestral state reconstruction, which analyses
evolutionary family trees. That analysis also showed that the earliest anacondas were already large-bodied when they
appeared around 12.4 million years ago.
Rojas, a PhD student and Gates Cambridge Scholar, admitted that the results were stark and could inform future research.
“We expected to find that ancient anacondas were seven or eight metres long. But we don’t have any evidence of a larger
snake from the Miocene when global temperatures were warmer,” he said.
The researchers believe that the consistent presence of suitable habitats, like swamps, marshes and large river systems
like the Amazon, allowed anacondas to keep thriving at the same size.
During those years, much of northern South America resembled today’s Amazon, giving these snakes a huge range. While
their habitat today is more limited, there is still enough waterlogged terrain and prey, from fish to capybaras, to
sustain their giant frames.