“As the cobra flees for its life, it makes a movement like the flick of a whip around a horse's neck,” Rudyard Kipling wrote about the ferocious Nagaina cobra in his tale of the heroic mongoose Rikki-Tiki-Tavi. And this whiplash movement may have helped real-life cobras and their relatives spread from their native Asia across the globe.
Scientists once believed that the superfamily Elaphoidea, which includes cobras, coral snakes, and mambas, originated in Africa. Fossils of file snakes found in Tanzania and dated to the Oligocene epoch (33.9 million to 23 million years ago), support this hypothesis. They are the oldest relatives of this group found in the fossil record.
But in a new study published August 7 in the journal Royal Society Open Science, researchers used genetic analysis and fossils from other regions to conclude that these snakes, and related colubroid snakes, actually originated in Asia.
“The uncertainty comes primarily from a lack of understanding of how these different species are related to each other,” lead author Jeffrey Weinel, an evolutionary biologist and postdoctoral researcher at the American Museum of Natural History who conducted the study while at the University of Kansas, told Live Science.
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Scientists had never compiled comprehensive genetic data on this group before, he explained. “I was interested in inferring a tree of life that would predict the evolutionary relationships of this group, and then using that tree of life estimate and information about modern species to infer where the ancestors of this group lived,” he added.
In the new study, Weinel and his colleagues analyzed 3,128 sites in the genomes of 65 elapid snake species to determine how they are all related, adding data from 434 species already in genetic databases or collected by the team themselves. They then mapped these species to depict their historical and geographical distribution.
They found that the oldest ancestor of the cobraoidea evolved in Asia between 28.94 million and 45.92 million years ago, while the colubroidea emerged approximately 31.13 million to 48.81 million years ago.
These early Asian ancestors may not be present in the fossil record because of the environment they evolved in. “Tropical Asia is not the best for preserving fossils because of the climate,” Weinel says.
These snakes migrated from Asia to Africa as early as 37.5 million years ago to as long ago as 24.4 years ago, and their descendants subsequently dispersed in several waves to Europe, Australia, and the Americas. Today, 700 species live on every continent except Antarctica, and on many islands. Even the oceans have been colonized by the descendants of these early snakes.
The study found that these snakes have had complex evolutionary histories: elapid and colubroid snakes, for example, may have migrated from Asia to Africa at least 15 times, and have recolonized Africa into Asia at least seven times, illustrating the complexity of land-based migration and highlighting the difficulty of tracing their origins.
As for how they moved from continent to continent, Weinel speculates that these snakes could have taken a variety of routes, including using land bridges or crossing narrow sea routes, to reach their current global distribution.
