In 2008, miners off the coast of Namibia stumbled upon a buried treasure: a sunken Portuguese ship known as Bom Jesus, which disappeared on its way to India in 1533. The merchant ship carried gold and silver coins and other valuable materials. . But for a team of archaeologists and biologists, Bom Jesus ’most precious cargo was a run of more than 100 elephant tusks, the largest archeological load of African ivory ever discovered.
Genetic and chemical analyzes have now traced those fangs to several distinct herds of forest elephants that once roamed West Africa. “It’s by far the most detailed and complete attempt to get (archaeological) ivory from an elephant,” says Paul Lane, a Cambridge University archaeologist who is not involved in the work.
The new results, published in the February 8 issue of Current Biology, provide insight into the historic populations of African elephants and ivory trading networks.
Being lost at sea for nearly 500 years, Bom Jesus ivory is incredibly well preserved, says Alida de Flamingh, a molecular biologist at the University of Illinois at Urbana-Champaign. “When the boat sank, copper and lead ingots (stored on the fangs) pushed the ivory toward the seabed,” protecting the fangs from dispersal and erosion. A cold ocean current also flows through this region of the Atlantic. “That really cold current probably helped preserve the DNA that was in the fangs,” Flamingh says.
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She and her colleagues extracted DNA from 44 fangs. The genetic material revealed that all that ivory came from the elephants of the African forest (Loxodonta cyclotis) instead of their relatives from the African savannah (L. africana). By comparing ivory DNA with that of past and present African elephant populations with known origins, the team determined that the wrecked tusks belonged to elephants of at least 17 genetically distinct herds across West Africa, of which only four still exist. It is possible that the other elephant lineages died as a result of hunting or habitat destruction (SN: 11/7/16).
The types, or isotopes, of carbon and nitrogen in the fangs provided more details about where these elephants lived. Carbon and nitrogen build up in the fangs over the life of an elephant through the food the animal eats and the water it drinks. The relative amounts of different isotopes of carbon and nitrogen depend on whether an elephant has spent most of its time, say, in a rainforest or in an arid meadow. The isotopes in the fangs of Bom Jesus revealed that these elephants lived in a mixture of forests and savannas.
National Museum of Namibia
“We were quite surprised,” says study co-author Ashley Coutu, an archaeologist at Oxford University. It is known that modern elephants in the African forest roam forests and also savannas. But researchers thought that forest elephants first ventured into the prairies only in the 20th century, as many savannah elephants were destroyed by poachers and the original habitats of forest elephants were destroyed by human development. The new results suggest that African forest elephants have been susceptible to both forest and savannah habitats.
A better understanding of the habitats historically preferred by African forest elephants could inform efforts to conserve this vulnerable species (SN: 9/9/16). More than 60 percent of these elephants have been poached in the last decade and those that remain only inhabit about a quarter of their historical range, according to the African Wildlife Foundation.
Bom Jesus ’ivory origins also paint a clearer picture of the 16th-century ivory trade on the African continent, Lane says. The fact that the tusks originated in many herds hints that several West African communities participated in the ivory supply. But it is unclear whether Portuguese traders picked up this diverse ivory from several locally sourced ports along the coast or from a single port that has been linked to extensive trade networks on the continent, Lane says. Future analyzes of ivory discovered at historic sites in the port could help solve the mystery.