Scientists have discovered the origins of more than 100 elephant tusks found on a ship that sank in 1533.
Almost 500 years ago the Bom Jesus – a Portuguese trading vessel carrying 40 tonnes of cargo including gold, silver, copper and more than 100 elephant tusks – sank off the coast of Africa near present-day Namibia.
The wreck was found in 2008, and scientists say they now have determined the source of much of the ivory recovered from the ship.
Researchers used various techniques such as DNA analysis of the well-preserved tusks to determine the species of elephants, their geographic origins and the types of environments they lived in before they were killed for their tusks.
The ivory had been stowed in a lower level of the Bom Jesus under a weighty cargo of copper and lead ingots.
Alida de Flamingh at the University of Illinois said: “When the ship sank, the ingots compressed the tusks into the seabed, preventing a lot of physical erosion by sea currents that can lead to the destruction and scattering of shipwreck artefacts.
“There is also an extremely cold sea current in that region of coastal Namibia which likely also helped preserve the DNA in the shipwrecked tusks.”
The team in Namibia, South Africa, the US, and the UK extracted DNA from 44 tusks.
By analysing genetic sequences known to differ between African forest and savanna elephants, the scientists determined that all of the tusks they analysed belonged to forest elephants.
A further examination of mitochondrial DNA, which is passed only from mothers to their offspring, offered a more precise geographic origin of the elephant tusks.
All 44 tusks were from elephants residing in West Africa, and none originated from Central Africa according to the study published in Current Biology.
Ms de Flamingh said: “This is consistent with the establishment of Portuguese trading centres along the West African coast during this period of history.”
The team used DNA to trace the elephants to 17 family lineages, only four of which are known to persist in Africa.
“The other lineages disappeared because West Africa has lost more than 95% of its elephants in subsequent centuries due to hunting and habitat destruction,” said Alfred Roca, a professor in animal sciences at the University of Illinois.
To learn more about the environments the elephants inhabited, University of Oxford Pitt Rivers Museum research fellow and study co-author Ashley Coutu analysed the stable carbon and nitrogen isotopes of 97 tusks.
That analysis revealed that the elephants lived in mixed habitats, switching from forested areas to savannas in different seasons, most likely in response to water availability.
“Our data help us to understand the ecology of the West African forest elephant in its historic landscape which has relevance to modern wildlife conservation,” she said.