National Geographic : 2009 Feb
• "We passed the night in Punta Alta, and I employed myself in searching for fossil bones; this point being a perfect catacomb for monsters of extinct races." AUGUST 1833 themselves were crated up for shipping back to England, mostly to the care of John Stevens Henslow, the gentle botanist who had been Darwin s mentor at Cambridge. "I have been lucky with fossil bones," he told Henslow in a letter. He mentioned the giant rodent, the ground sloths, and the section of bony polygonal scutes, commenting on the last: "Immediately I saw them I thought they must belong to an enormous Armadillo, living species of which genus are so abundant here." And he added: "If it interests you su ciently to unpack them, I shall be very curious to hear something about them." It s important not to overstate how clearly Darwin could even identify, let alone interpret, what he had found. Most of his fossils, apart from the Megatherium, represented species not yet familiar to experts, and he was no expert. He wasn t a comparative anatomist, like the great Cuvier; he wasn t especially knowledgeable about mammals; and the very word "paleontologist" hadn t yet come into use. Darwin entrusted the description and identi cation of his fossils to a brilliant young anatomist back in London named Richard Owen, an up-and-coming authority on extinct mammals. It was Owen who gave names to the unknown sloths, and Owen who suggested (mistakenly, later correcting himself) the a nity between Macrauchenia and a camel. Darwin himself was no Owen. He was just a highly attentive eldman, greedy for specimens, learning as he went. e Beagle invitation had rescued him from an unsuitable future as a country pastor, and since his rst days aboard ship he had applied himself diligently, matur- ing fast to assume (and then transcend) the role of ship s naturalist. His best quali cations for interpreting the fossils were his intense curi- osity, his talent for close observation, and his instinctive sense that everything in the natural world is somehow connected with everything else. Also, he wasn t afraid to speculate boldly--- so long as he could do it in private. but suggestive datum reached him months later, while the Beagle lingered off northern Patagonia and Darwin spent time ashore among another congenial group of gauchos. First it was hearsay: e gauchos mentioned a rare form of ostrich, smaller than the common one, with shorter legs, and more easily killed using their bolas, but otherwise similar. The possibility of finding that bird slipped Darwin s mind until one of his shipmates shot such a smaller "ostrich" (another rhea) for its meat. Darwin paid little attention, assum- ing it was a juvenile. "The bird was skinned and cooked before my memory returned," he wrote, in a passage so candid you can almost see him smacking his forehead with a palm. "But the head, neck, legs, wings, many of the larger feathers, and a large part of the skin, had been preserved." He rescued those scraps and sent them to England, where they were stitched into a presentable specimen for the museum of the Zoological Society. e orni- thologist John Gould, to whom Darwin would consign his Galápagos nches and mocking- birds for identi cation, also got a rst look at this creature. Gould confirmed that it was a distinct species and called it Rhea darwinii (a name later changed because of taxonomic technicalities) for the man who had rescued it from the midden. What intrigued Darwin most about the two rhea species was that, similar as they were, they overlapped very little in geographic distribu- tion. e greater rhea inhabited the Pampas and northern Patagonia, as far south as Argentina s Río Negro, which drained to the coast at about 41° south latitude; the lesser rhea replaced it beyond the Río Negro and occupied southern Patagonia. Together with the evidence of extinct South American mammals, the implications of rhea diversity and distribution would prove almost as suggestive to Darwin as the patterns he would later find among the finches and mockingbirds of the Galápagos.