Does the ground sloth, Mylodon darwinii, still survive in South America?

Dr Ross Barnett and Simon Sylvester

In Zoology, nothing is more exciting than the rediscovery of an animal previously thought long extinct. The coelacanth (Latimera chalumnae) and the ivory-bill woodpecker (Campephilus principalis) are two famous recent examples of ‘Lazarus’ taxa. Well-publicised rediscoveries like these promote the idea that refugia containing the last survivors of prehistoric species are still to be found.

One group that has been searched for more optimistically than many others is the South American ground sloth. In particular, one species, Mylodon darwinii (Fig. 1) has been the subject of much speculation. Could it still survive today? And why have people clung on to the possibility of continued survival of this species of ancient animal more than any other, to the extent that expeditions are still being sent to search for the beast (Oren, 2001)?

A last gasp at Last Hope

The history of this optimism can, I think, be traced to an exceptional series of events that took place in Patagonia (Fig. 2) over a century ago.

These were widely reported in the global presses, but have not received the follow up attention they deserve.

The drama began in 1895, at the Chilean site of Ultima Esperanza (‘Last Hope’), when a German landowner, known as Eberhardt (Fig. 4), discovered a strange, shaggy, red hide in an enormous cave (Fig. 3) on his property (Bell, 2002).

He and some labourers had stumbled upon the skin while exploring the cavern, which had also contained some human bones. These were removed from the cave and burned in a bonfire on the shore, to the horror of later archaeologists (Lönnberg, 1896). The large, furry hide was hung upon a tree as a curiosity, and attracted the attention of local folklorists who confidently asserted it to be from a cow that had grown pebbles in its skin, or of an unknown sea creature (Moreno & Woodward, 1899).

It was later chanced upon by Swedish explorers who were passing through on a trip to Tierra del Fuego in 1896 (Lönnberg, 1896). The expedition was led by the famous explorer Dr Otto Nordenskjold. Intrigued by the ‘stones’ visible in the skin, they chopped off a section and took it home for study by the learned men of Uppsala (Lönnberg, 1896).

At around the same time, word of this enigmatic ‘cowhide’ was received by Dr Francisco Moreno of the La Plata museum, who ventured out to examine it for himself. He confirmed that it must belong to the ground sloth Mylodon or a closely related genus due to the unique dermal ossicles (‘pebbles’) that are only possessed by this group of South American mammals (Moreno & Woodward, 1899). The Swedish expedition returned again in 1899 (Lönnberg, 1900), led by Erland Nordenskjold, Otto’s cousin, and conducted some excavations in the cave, only to discover another piece of skin (probably from the extinct horse Hippidion) as well as many other skeletal remains buried in the floor of the cave, under a layer of well-preserved ground sloth dung.

Altogether, the Eberhardt cave has produced the remains of ground sloth, human, sabre-toothed cat, extinct giant bear, jaguar, puma, fox, horse, llama, litoptern (a unique South American herbivore) and giant rat. However, of course, the most interesting puzzle was the skin. It looked fresh, it had hair on it, and it had clearly been skinned from a dead animal by the hand of man and even contained dried blood on its margins. It must have come from a recently killed animal – even the director of the Natural History Museum, Prof R Lankester, was reported to have said “it is quite possible … that he still exists in some of the mountainous regions of Patagonia” (Prichard, 1902).

It lives (maybe)

Into this jumble of supposition, further details suddenly appeared. Florentino Ameghino, also of the La Plata museum, received word from the explorer, Ramon Lista, that he had chanced upon a large, hairy red beast in the pampas (Pritchard, 1902). Ameghino was sure that this must be a living ground sloth and promptly named it ‘Lista’s new Mylodon’ (Neomylodon listai).

The native inhabitants of Patagonia, the Tehuelche, were interrogated for information on anything that might resemble a living ground sloth. Prof Ameghino identified the amphibious ‘Iemisch’ of Tehuelche legend as identical to his Neomylodon and reported that the creature was recently encountered by several indigenous people he knew (Heuvelmans, 1958). One even claimed to have shot and killed an ‘Iemisch’ while on his way to Santa Cruz! Encouraged by such stories, the Daily Express sent the reporter H H Prichard to the tip of South America to report on whether any antediluvian monsters could still be found there (Prichard, 1902).

Yet, amid all the excitement, there were some sceptical voices. Dr Moreno, the first scientist to properly examine the skin, knew that the dry, cold conditions found in caves could act as a wonderful preservative. He drew attention to the mummified remains of extinct Moa found in New Zealand and the curious natural human mummies that he had personally encountered in Patagonia (Moreno & Woodward, 1899).

Dr Moreno was also well acquainted with the stories of the Tehuelche and, although he had never encountered any tales of the‘Iemisch’, he did recognise tales of an ugly, hairy animal known as ‘Ellengassen’. He was assured by his Tehuelche sources that they knew of nothing that could account for the Eberhardt skin or Lista’s mysterious animal (Moreno & Woodward, 1899).

Lista himself suggested that the creature he saw was something like an old world pangolin, too small to be a ground sloth. H H Prichard returned from his sloth-hunting trip a sceptic, having discovered: “no trace whatever either by hearsay or from the evidence of our own experience to warrant the supposition that it continues to exist to the present day” (Prichard, 1902). And that is pretty much where the story was left. Prichard returned to Britain in 1901, but the idea of living ground sloths in Patagonia remained fixed in the public’s imagination.

Dating a ground sloth

So, what new evidence has been collected over the past century pertaining to ground sloth survival in South America? Mylodon darwinii has been one of the most investigated sloth taxa and we now have a good appreciation of its biology. From analysis of the dung found in Eberhardt cave, we know that it lived on grasses, herbs and sedges in an open treeless steppe, due to the absence of tree pollen in the dung (Moor 1978).

The ideal habitat for Mylodon is definitely not jungle or forest, as some sloth-hunters have assumed. It was a creature of the plain and the thought of ground sloths surviving on the wide pampas, unobserved by the vaqueros of southern Argentina is absurd in the extreme. It is true that some genera of ground sloth (for example, Megatherium) may have been browsers of the forest, but there has never been any suggestion that these giants survived to modern times.

When Eberhardt cave was first brought to scientific attention, the age of archaeological and palaeontological remains was almost always a mystery. Relative dating of secure stratigraphic layers was the only way to estimate the age of artefacts. In the 1950s, dating was revolutionised by the discovery of radiocarbon. For the first time ever, absolute dates could be obtained from organic material (Figs. 6 and 7). The incredible assortment of bones, dung and skin from Eberhardt Cave were a treasure trove of dateable, organic riches.

More than anything else, radiocarbon dating held the promise of putting a definite age on the demise of the Mylodon. Almost 30 dates have now been obtained from Mylodon remains (including skin) which all date within the range of 10,200 to 13,600 radiocarbon years BP (Tonni et al, 2003). Sadly, it appears that the last ground sloths in Patagonia were probably hunted to extinction over a hundred centuries ago, soon after the first humans arrived in the southern tip of South America.

References

Oren, D. C. Does the Endangered Xenarthran Fauna of Amazonia Include Remnant Ground Sloths? Edentata, 2-5 (2001).

Bell, C. M. Did elephants hang from trees?-the giant sloths of South America. Geology Today 18, 63-66 (2002).

Lönnberg, E. in Svenska Expeditionen Magellansländerna 149-170 (1896).

Moreno, F. P. & Woodward, A. S. On a Portion of Mammalian Skin named Neomylodon listai, from a Cavern near Consuelo Cove, Last Hope Inlet, Patagonia. Proceedings of the Zoological Society of London 5, 144-156 (1899).

Lönnberg, E. On a remarkable Piece of Skin from Cueva Eberhardt, Last Hope Inlet, Patagonia. Proceedings of the Zoological Society of London, 379-384 (1900).

Hesketh Prichard, H. Through the Heart of Patagonia (D. Appleton & Co., New York, 1902).

Heuvelmans, B. in On the track of unknown animals 253-283 (1958).

Moore, D. M. Post-glacial vegetation in the South Patagonian territory of the giant ground sloth, Mylodon. Botanical Journal of the Linnean Society 77, 177-202 (1978).

Tonni, E. P., Carlini, A. A., Scillato Yane, G. J. & Figini, A. J. Cronologia radiocarbonica y condiciones climaticas en la “Cueva del Milodon” (sur de Chile) durante el Pleistoceno Tardio. Ameghiniana 40, 1-7 (2003).

Stock, C. Problems of Antiquity presented in Gypsum Cave, Nevada. The Scientific Monthly 32, 22-32 (1931).