Considered among the planet’s most substantial living reptiles, anacondas typically measure between 4 and 5 meters in length, with exceptional specimens occasionally extending to 7 meters. Recent scholarly investigations involving the analysis of fossilized giant anaconda remains from South America indicate that these tropical constrictors achieved their maximal dimensions approximately 12.4 million years ago and have maintained their colossal stature ever since.
The green anaconda (Eunectes murinus). Image credit: MKAMPIS / CC BY-SA 4.0.
“The spectrum of body lengths observed in extant snakes is quite diverse, with a prevalent size of approximately 1 meter and a range from merely 10 centimeters in the diminutive leptotyphlopid thread snakes to around 7 meters in genera such as Eunectes (anacondas) and formidable pythonids,” stated Andrés Alfonso-Rojas, a doctoral candidate at the University of Cambridge, along with his research associates.
“Within the genus Eunectes, the green anaconda (Eunectes murinus) stands out as the paramount species, exhibiting an average body dimension of 4-5 meters and documented maximum lengths ranging between 6 and 7.2 meters.”
“The phylogenetic trajectory of anacondas can be traced back, at a minimum, to the Middle to Late Miocene epoch, as evidenced by sparse fossil discoveries originating from Brazil, Colombia, Peru, and Venezuela.”
“Nonetheless, there remains a paucity of information concerning the body mass of the most ancient anacondas, which coexisted with colossal crocodylomorphs, chelonians, ungulates, and xenarthrans of the era.”
In the course of this investigation, the researchers meticulously measured 183 fossilized vertebral elements belonging to anacondas, representing at least 32 distinct individuals, unearthed in the Venezuelan state of Falcón, South America.
By integrating these dimensional data with paleontological records from other South American locales, they were able to ascertain that prehistoric anacondas would have possessed lengths of 4 to 5 meters—comparable to the dimensions of anacondas observed in the present day.
“While other colossal fauna, such as giant crocodiles and turtles, have since vanished from existence following the Miocene, likely due to global climatic cooling and habitat fragmentation, the gargantuan anacondas have demonstrated remarkable persistence, showcasing exceptional resilience,” commented Alfonso-Rojas.
“Our analysis of the fossilized remains revealed that anacondas developed their substantial body size relatively soon after their emergence in tropical South America, approximately 12.4 million years ago, and their dimensions have remained consistent since that period.”
The research team validated their computations through a secondary analytical approach known as ancestral state reconstruction. This method utilized a phylogenetic tree of snakes to infer the body length of enormous anacondas and their contemporary reptilian kin, including arboreal boas and rainbow boas.
This corroborative analysis reinforced the finding that the mean length of anacondas was between 4 and 5 meters when they initially appeared during the Miocene epoch.
Anacondas inhabit wetlands, marshes, and major river systems such as the Amazon. During the Miocene, the entirety of northern South America presented an environment akin to the contemporary Amazonian region, and anacondas were far more widely distributed than they are presently.
However, sufficient suitable habitats, complete with prey items like capybaras and fish, continue to exist, enabling modern anacondas to maintain their impressive size.
Prior hypotheses suggested that anacondas might have attained even greater proportions in antiquity when global temperatures were warmer, given the heightened sensitivity of snakes to thermal fluctuations.
“This outcome is rather unexpected, as our prior conjecture anticipated discovering evidence of ancient anacondas measuring 7 or 8 meters,” stated Alfonso-Rojas.
“Yet, we currently lack any empirical data pointing to larger snake specimens from the Miocene era, a period characterized by elevated global temperatures.”
The research findings were disseminated this week within the pages of the Journal of Vertebrate Paleontology.
_____
Andrés F. Alfonso-Rojas et al. An early origin of gigantism in anacondas (Serpentes: Eunectes) revealed by the fossil record. Journal of Vertebrate Paleontology, published online December 1, 2025; doi: 10.1080/02724634.2025.2572967
