A team of excavators in Bulgaria has resumed a search for fossils of an ape-like creature that may be the oldest-known direct ancestor of man and whose discovery has challenged the central hypothesis that humankind originated in Africa.

The Graecopithecus freybergi, who lived 7.2 million years ago, is known only from a lower jawbone, unearthed in 1944 in Greece, and an isolated tooth, found in 2009 near the Bulgarian town of Chirpan, where excavations have now restarted.

"It would be great to find a whole skeleton but a thigh would also help us a lot," said professor Nikolai Spassov, head of Bulgaria's National Museum of Natural History.

The scientific consensus long has been that humanity's ape-like ancestors, known as hominins, originated in Africa. Until now, the oldest-known hominin was Sahelanthropus, which lived 6 million to 7 million years ago in Chad.

But Spassov hopes new fossils will back up the theory that hominins originated in the Eastern Mediterranean.

"They have most probably migrated to Africa due to climate change," he said.

Surrounded by dangerous predators in a savannah-type environment, life would have been hard for a Graecopithecus freybergi. A male would have weighed around 40 kg and a female around 30 kg, Spassov said.

Scientists in Greece are also expected to resume the search for remains of the hominin, and excavation work will begin in neighboring Macedonia in September.