A tiny drawing of a kangaroo curled in the letters of a 16th-century Portuguese manuscript could rewrite Australian history.

The document, acquired by Les Enluminures Gallery in New York, shows a sketch of an apparent kangaroo (''canguru'' in Portuguese) nestled in its text and is dated between 1580 and 1620. It has led researchers to believe images of the marsupial were already being circulated by the time the Dutch ship Duyfken - long thought to have been the first European vessel to visit Australia - landed in 1606.

Image of what is thought to be a kangaroo on a 16th-century processional could lend weight to the theory that the Portuguese were the first explorers to set foot on Australian soil, before the Dutch or English.

The pocket-sized manuscript, known as a processional, contains text and music for a liturgical procession and is inscribed with the name Caterina de Carvalho, believed to be a nun from Caldas da Rainha in western Portugal.

The European discovery of Australia has officially been credited to the Dutch voyage headed by Willen Janszoon in 1606, but historians have suggested the country may already have been explored by other western Europeans.