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.
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.
''A kangaroo or a wallaby in a manuscript dated this early is proof that the artist of this manuscript had either been in Australia, or even more interestingly, that travellers' reports and drawings of the interesting animals found in this new world were already available in Portugal,'' Les Enluminures researcher Laura Light said.
''Portugal was extremely secretive about her trade routes during this period, explaining why their presence there wasn't widely known.''
Peter Trickett, an award-winning historian and author of Beyond Capricorn, has long argued that a Portuguese maritime expedition first mapped the coast of Australia in 1521-22, nearly a century before the Dutch landing.
''It is not surprising at all that an image of a kangaroo would have turned up in Portugal at some point in the latter part of the 16th century. It could be that someone in the Portuguese exhibition had this manuscript in their possession,'' Mr Trickett said.
National Library of Australia curator of maps Martin Woods said that while the image looked like a kangaroo or a wallaby, it alone was not proof enough to alter Australia's history books.
''The likeness of the animal to a kangaroo or wallaby is clear enough, but then it could be another animal in south-east Asia, like any number of deer species, some of which stand on their hind legs to feed off high branches,'' Dr Woods said.
''For now, unfortunately the appearance of a long-eared big-footed animal in a manuscript doesn't really add much.''
Les Enluminures Gallery, which lists the manuscript's value at $US15,000 ($16,600), acquired the processional from a rare book dealer in Portugal and will exhibit the piece as part of an exhibition.
Portugal was extremely secretive about her trade routes during this period, explaining why their presence there wasn't widely known.
Also entwined in letters of the text are two male figures adorned in tribal dress, baring naked torsos and crowns of leaves, which Ms Light said could be Aborigines.
Fellow of the Australian Academy of the Humanities, John Gascoigne, said proving that the Portuguese were the first Europeans to arrive in Australia would be ''forever difficult to document because of their secrecy and because so many of the records were destroyed in the Lisbon earthquake of 1755''.
''The possible date span for the manuscript goes up to 1620, which would accommodate the arrival of Willen Janszoon in the Duyfken in northern Australia in 1606,'' Professor Gascoigne said.
He speculated the images could come from a 1526 trip to Papua.
''Looking at it from a European perspective, it is surely evocative to wonder what these exotic images must have meant to the Portuguese nun gazing at them from within the confines of her convent's walls,'' Ms Light said.