Many contemporary animal species would be dwarfed by their distant ancestors. In the Middle to Upper Miocene period, 12.4 to 5.3 million years ago, warm global temperatures and an abundance of food resulted in giant animals, most of which are now either extinct or replaced by far smaller descendants. But according to research by Darwin student Andrés Alfonso-Rojas, anacondas are the striking exception, reaching a peak size of 5.2 metres long, and staying that big for 12 million years.
Andrés, a Gates Cambridge Scholar who is pursuing his PhD in the Department of Zoology, led a team which analysed the fossils of at least 32 snakes, discovered in Falcón State, Venezuela. Combining their measurements with fossil data from other sites in South America, and confirming them using ‘ancestral state reconstruction’ to compare them with related species, he concluded that anacondas have been giants throughout their existence.
“Other species like giant crocodiles and giant turtles have gone extinct since the Miocene, probably due to cooling global temperatures and shrinking habitats, but the giant anacondas have survived – they are super-resilient. 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.”
The research overturns previous assumptions, that anacondas must have been even bigger in the past. But their surviving Amazonian habitat appears to continue providing the right temperature and prey to cultivate massive monsters.
“This is a surprising result because we expected to find the ancient anacondas were seven or eight metres long,” says Andrés. “But we don’t have any evidence of a larger snake from the Miocene when global temperatures were warmer.”
This research was funded by The Gates Cambridge Trust and the Natural Environment Research Council. It was published today in the Journal of Vertebrate Paleontology.
