During the Middle to Upper Miocene period (12.4 to 5.3 million years ago), giant animals walked—and slithered—the Earth thanks to warmer temperatures, larger wetlands, and greater amounts of food. Many of their descendants today are significantly smaller, but anacondas ( Eunectes ) have proven to be unexpectedly stubborn.

Researchers investigated 12.4-million-year-old fossils from Venezuela to understand how large ancient anacondas were compared to their relatives today. They found that these early serpents would have been 13 to 16 feet (4 to 5 meters) long on average. That aligns with the usual size of today’s anacondas, meaning these tropical reptiles have remained humongous for millions of years.

Unlike other giant species, which reached their peak size during the Miocene before dyi

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