Dick-Read says pottery and bronze sculptures found in Nigeria also came from seafarers since they were too far from Saharan trade routes and too sophisticated for indigenous artwork of that time.
Sir Mervyn Brown, Britain's former ambassador to Madagascar and a historian of the region, found Dick-Read's conclusions "generally plausible" and urged fresh research.
"Dick-Read has not provided any great new revelations in this area but has produced more detailed supporting evidence," he said.
"The influence in west Africa is not generally known, even among academics," he said.
Other historians disagree. Robert Soper, an authority on eastern Africa, said there was no known evidence from artefacts, for example, of Indonesians spreading the iron age down the coast.
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