Back at Montevideo, Darwin was introduced to Conrad Martens, the replacement artist brought on board "Beagle" after Augustus Earle had to leave due to health problems. They sailed south, putting in at Port Desire on 23 December, and the following day Darwin shot a guanaco which provided them with a Christmas meal. Early in the new year, Martens shot a rhea which they enjoyed eating before Darwin realised that this was the elusive smaller rhea and preserved the remains. On 9 January 1834, further south, they reached Port St Julian and exploring the local geology in cliffs near the harbour Darwin found fossils of pieces of spine and a hind leg of "some large animal, I fancy a Mastodon".</ref> On 26 January, they entered the Straits of Magellan, and at St. Gregory's Bay, they met half-civilised Patagonian "giants" over tall, described by Darwin as "excellent practical naturalists". One told him that the smaller rheas were the only species this far south, while the larger rheas kept to the north, the species meeting around the Rio Negro.