William A Richardson (2003)
South America on maps before Columbus? Martellus's "Dragon's Tail" peninsula
Imago Mundi(55):25-37.
The article argues that perceived similarities between the river and coastal outlines on this "Dragon's Tail" peninsula and those of South America are fortuitous, and that the non-Ptolemaic place-names on this section of Martellus's map are derived from Marco Polo.