Francisco Javier Muñiz had published details in 1841 of substantial fossil finds in Luján, Argentina; instead of his collection forming the foundation of a National Museum of Natural History in Argentina as Muñiz hoped, it was shipped to Paris after General Juan Manuel Rosas, governor of Buenos Aires, gave it to the French naval commander in the region in 1842 (Novoa and Levine 2010, pp. 31–2). Earlier collections of Argentinian fossils had also been sent to Europe (Podgorny 2013). Macrauchenia patachonica, an extinct llama-like animal the size of a camel, had been determined by Owen from a partial skeleton found by CD at Port St Julian, Patagonia, in 1834, and published in Fossil Mammalia, pp. 35–6 (see also R. D. Keynes 1988, p. 214 n.2).

CD presumably enclosed the issue of the British Packet (the newspaper of the British community in Buenos Aires) in which a letter from Muñiz describing his finds was published; in South America, p. 106, CD noted, ‘lately, within eight leagues of the town of Luxan, Dr. F. X. Muñiz has collected (British Packet, Buenos Ayres September 25th, 1841), from an average depth of eighteen feet, very numerous remains, of no less than, as he believes, nine distinct species of mammifers.’