The Evolutionary Mystery of Anaconda Gigantism

Anacondas (Eunectes), known for their impressive size, have puzzled researchers regarding their evolutionary history and the origins of their gigantism. A recent study led by a team from the University of Cambridge analyzed 183 fossilized vertebrae from at least 32 ancient anacondas discovered in Urumaco, Venezuela. The findings indicate that these reptiles reached their maximum size approximately 12.4 million years ago during the Middle Miocene, measuring around 4 to 5 meters (13 to 16 feet) in length. This size is consistent with that of modern green anacondas, which typically range from 4 to 5 meters but can occasionally grow larger in less accessible habitats.

Bones of giant anacondas found in Venezuela. Here's what scientists discovered when they pieced them togetherGizmodoFossils reveal anacondas have been giants for over 12 million years

During the Middle to Upper Miocene period (12.4 to 5.3 million years ago), many species, including the 12-meter-long caiman Purussaurus and the 3.2-meter-long turtle Stupendemys, thrived in warmer climates and abundant wetlands. Unlike these other giant reptiles, which eventually became extinct and were replaced by smaller relatives, anacondas have maintained their large size throughout the ages. Andrés Alfonso-Rojas, the lead author of the study, noted that while other species diminished in size due to cooling global temperatures and habitat loss, anacondas have shown remarkable resilience.

Fossils reveal anacondas have been giants for over 12 million yearsGizmodoBones of giant anacondas found in Venezuela. Here's what scientists discovered when they pieced them together

The research team initially anticipated that ancient anacondas would be significantly larger, possibly reaching lengths of 7 to 8 meters (23 to 26 feet). However, the fossil evidence did not support this hypothesis, revealing that the size of ancient anacondas has remained stable over millions of years. Alfonso-Rojas remarked, “This is a surprising result because we expected to find the 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.” This unexpected outcome raises questions about the factors that allowed anacondas to retain their size despite environmental changes.

Bones of giant anacondas found in Venezuela. Here's what scientists discovered when they pieced them togetherFossils reveal anacondas have been giants for over 12 million yearsGizmodo

Modern anacondas continue to thrive in habitats such as swamps, marshes, and large rivers, including the Amazon. The availability of prey, such as capybaras and fish, supports their continued gigantism. The study suggests that the extensive wetland ecosystems present during the Miocene may have contributed to the initial evolution of their large body size. Despite the reduction in their range compared to the past, sufficient habitats and food sources remain to sustain their current size.

Fossils reveal anacondas have been giants for over 12 million years

The study highlights the need for further exploration of anaconda fossils from various time periods to deepen the understanding of their evolutionary trajectory. As researchers continue to uncover more fossil evidence, they hope to unravel the mysteries surrounding the persistence of gigantism in anacondas and their adaptation to changing climates.

Bones of giant anacondas found in Venezuela. Here's what scientists discovered when they pieced them together

• “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.” — Andrés Alfonso-Rojas, PhD student, University of Cambridge

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• “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,” — Andrés Alfonso-Rojas, PhD student, University of Cambridge

Gizmodo

• “This is a surprising result because we expected to find the 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.” — Andrés Alfonso-Rojas, PhD student, University of Cambridge

Bones of giant anacondas found in Venezuela. Here's what scientists discovered when they pieced them together