Friday, August 14, 2015

Adventure classics – The mystery of the vanished giants

The Voyage of HMS Beagle
by Charles Darwin
As the Royal Navy’s HMS Beagle made its way around South America in the mid-1830’s, frequently dropping off its on-board geologist, Charles Darwin, to make inland excursions inland, Darwin had time to wonder about the strange fossils he was collecting along river banks. What were they? And what had happened to sweep them from the earth?

The sheer numbers of fossils troubled him. He struggled to accommodate the huge quantities of bones, seemingly produced by the catastrophic deaths of large numbers of animals, with his enthusiasm for Scottish geologist Charles Lyell’s theory of gradual change over time.

“The number of the remains embedded in the grand estuary deposit which forms the Pampas and covers the granitic rocks of Banda Oriental, must be extraordinarily great. . . Besides those which I found during my short excursions, I heard of many others, and the origin of such names as ‘the stream of the animal’, ‘the hill of the giant’, is obvious,” he wrote in his journal of the voyage of the Beagle.

Darwin published his records in two editions, in 1839 and 1845. The 1957 collectible edition I’m working from is based on the 1845 edition, when Darwin was well on his way to puzzling out his theory of evolution based on natural selection. Some of the South American fossils, such as the extinct giant sloths, were obviously related to still living relatives. But what to make of creatures such as the Macrauchenia, looking like a humpless camel with a long snout, whose 1913 reconstruction illustrates this post? Or the Toxodon, with a rhinocerous-like body and rodent-like teeth, whose skull he bought for 18 pence, which when found “was quite perfect; but the boys knocked out some of the teeth with stones, and then set up the head as a mark to throw at.”

It would require 21st century science to place the giant grazers in the family trees Darwin was starting to create, Scientific American magazine reported March 20, 2015, in “Mystery of Darwin’s ‘Strange Animals’Solved.”

Initially researchers trying to place the animals’ relationships were stumped by a lack of DNA, which degrades quickly in the South American climate. Instead, an international team used a different tactic, extracting collagen protein, to at last give two of Darwin’s mysterious mammals their place in the family tree of mammals.

“Part of a group of more than 250 mammals known as the South American ungulates,” Scientific American reported, “the creatures lived on the continent for around 60 million years before disappearing around 12,000 years ago.”

Purely on the basis of their fossils’ physical appearance, some had been suspected them of being related to elephants. Darwin himself suggested a possible link between the camel-like Macrauchenia and surviving llama-relatives, the wild guanacos of the pampas. But after sequencing proteins from two museum specimens of Toxodon and two of Macrauchenia, scientists finally placed them in a group that includes horses, tapirs and rhinos.

And what caused their disappearance after millions of years of survival? I’m going to suggest a catastrophic cause undreamed of by Darwin – the arrival of humans on the South American continent.

(Next Friday, Adventure classics puts Darwin back on board ship, to continue an August of adventures at sea.)

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