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Scientists from Ohio University have found fossil evidence that venomous snakes existed in Africa as early as 25 million years ago.
Ohio University's Jacob McCartney, lead author of a study published in the journal PLOS ONE, said the discovery shows that elapid snakes - such as cobras, kraits and sea snakes which use a variety of methods, including venom, to capture and kill prey - were active foragers In the Oligocene period.
McCartney said: "From about 34 to 23 million years ago, we would have expected to see a fauna dominated by booid snakes, such as boas and pythons. These are generally 'sit and wait' constricting predators that hide and ambush passing prey."
However, the team was surprised when they discovered more colubroids than booids suggesting that the local environment became more open and seasonally dry at an earlier time in Africa than in most other parts of the world, as found in previous studies.
The environment would also have become more hospitable to these active foraging types of snakes, which do not require cover to hide and ambush prey.
Although colubroid fossils are documented as early as 50 million years ago, they were not expected to constitute such a large part of the African snake fauna 25 million years ago, as they became dominant in Europe and North America much later.
Elapids belong to a larger group of snakes known as colubroids. The study describes eight different types of fossil snakes from the Rukwa Rift - five colubroid and three booid - with vertebrae ranging in length from 2.6 mm to just over 5 mm.
The team has been exploring the Rukwa Rift Basin of Tanzania for the last ten years to understand environmental change through time in the East African Rift System.
Their findings include a description of the oldest evidence of African booid snakes which the researchers have named Rukwanyoka holmani, combining the Rukwa region name with the Swahili word for snake.
Nancy Stevens, study co-author, said: "The fossils suggest a fundamental shift toward more active and potentially venomous snakes that could exert very different pressures on the local fauna."
It is hoped that further research from other locations will indicate whether colubroid snakes dominated all of Africa during the Oligocene or just the local region around the Rukwa Rift.