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A vertebrae of the oldest fossil venomous snake
Rukwanyoka holmani in Africa. Photo Credit: Ohio
University. |
Ohio University scientists
have found the oldest definitive fossil evidence of modern, venomous snakes in
Africa, according to a new study published March 19 in the journal PLOS
ONE.
The newly discovered
fossils demonstrate that elapid snakes—such as cobras, kraits and sea
snakes—were present in Africa as early as 25 million years ago, said lead
author Jacob McCartney, a postdoctoral researcher in the Ohio University
Heritage College of Osteopathic Medicine. He's part of a team that has been
examining the Rukwa Rift Basin of Tanzania over the last decade to understand
environmental change through time in the East African Rift System.
Elapids belong to a
larger group of snakes known as colubroids, active foragers that use a variety
of methods, including venom, to capture and kill prey.
Colubroid fossils are
documented as early as 50 million years ago. But they weren't 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.
"In the Oligocene
epoch, 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,"
McCartney said.
In fact, the recent
study includes a description of the oldest evidence of African booid snakes, he
said. The researchers have named this new species Rukwanyoka holmani; the genus
name combines the Rukwa region name with the Swahili word for snake, and the
species name is in honor of J. Alan Holman, a paleontologist and mentor.
However, the team was
surprised to discover that the fauna actually revealed more colubroids than
booids. That higher-than-expected concentration of colubroid snakes suggests
that the local environment became more open and seasonally dry—and, in turn,
more hospitable to these active foraging types of snakes that don't require
cover to hide and ambush prey—at an earlier time in Africa than in most other
parts of the world, as documented in previous studies.
"This finding gives
further strength to the idea that tectonic activity in the East African Rift
has helped to shape animal habitats in fascinating ways," said Nancy
Stevens, an associate professor of biomedical sciences at Ohio University and
co-author of the study. "The fossils suggest a fundamental shift toward
more active and potentially venomous snakes that could exert very different
pressures on the local fauna."
More fossils from
additional locations should indicate whether colubroid snakes dominated all of
Africa during the Oligocene or just the local region around the Rukwa Rift,
McCartney said.
The study published in PLOS
ONE 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.
Citation
McCartney JA, Stevens NJ, O’Connor PM (2014)
The Earliest Colubroid-Dominated Snake Fauna from Africa: Perspectives from the
Late Oligocene Nsungwe Formation of Southwestern Tanzania. PLoS ONE 9(3):
e90415. doi:10.1371/journal.pone.0090415