The Milodón- the Giant Sloths in South America
Milodón is the Spanish word for an unusual extinct animal by today’s standards- the giant sloth. Giant sloths were once widely distributed in the Americas during the Pleistocene. Giant slothes were likely less shy and slower than their tree hugging relatives. They are represented in fossils from the world famous La Brea Tar pits of Los Angeles to the caves from the southern tip of Chile.
Here we review some classic South American localities for Milodón fossils. They belong to the mammalian superorder Xenarthra. These sloths were larger than cattle, featuring thick-boned powerful frames. The sloth family classification includes Megalonychidae (mainly Eocene), Megatheriidae (Oligocene), Nothrotheriidae, Mylodontidae, and Scelidotheriinae.
Giant sloths originated in South America and migrated to North America in the late Miocene upon establishment of a land bridge between the two continents. Fossil remains are widespread throughout Peru (Pujos and Salas, 2004) and are found in Colombia and numerous lesser studied tar pits, such as Inciarte site, in Venezuela. These giants were stomping around everywhere in South America!
Our interest in this topic began for us 20 years ago when finding a mammal fossil in the late Miocene beds of the Huanta Formation in the Ayacucho Intermontane basin. Years later it was determined that the partial skull fragment belonged to a variety of giant sloth, but the species could not be determined. Some of the Peru specimens include those found in the Pliocene Pisco Formation where giant marine sloths once lived (Muizon and McDonald, 1995).
The giant sloths were widespread in the Americas, even leaving behind evidence of living in Rondônia, Brazil, where giant paleo-burrows are thought to be the tunnels excavated by the extinct giant sloths (Rodrigues do Nascimiento, 2008). The two most studied locations in South America are the Cueva del Milodón in southern Chile knows as Monumento Natural Cueva del Milodón run by CONAF, and the Talara tar pits in northern Peru.
Cueva del Milodón, Chile
Then in the year 2014 while traveling through the Chilean Patagonia we visited the Cueva del Milodón- the Giant Sloth Cave located 19-km NNW of Puerto Natales along Route Y-290 (waypoint -51.570393S, -72.601768W). The giant sloth remains were first discovered here in 1895 by Hermann Eberhard. Remarkably, a piece of preserved sloth hide was part of the find.
Carbon analysis of bone material in the cave dates back to 13,560 B.P. (Tonni et al, 2003), a time that pre-dates human occupation at this site. In addition to giant sloths, Cueva del Milodón has remains of Smilodon, or saber-toothed cat, dating from 11,420 B.P. (Prieto et al., 2010) and Hippidion saldiasi, miniature horse (Frassinetti and Alberdi, 2001).
A walk through this 200-meter long quasi-cave (it’s not formed in limestone) leaves little to be seen in the dirt-covered floor today. A few signs and a statue at the site provide visitors with imagination cues for the location’s significance.
Talara tar pits
The Talara oil seeps and preserved fossil record had every chance to retain as significant of a site as La Brea in California, however, the location remains incredibly obscure. I have been thinking upon this topic for two decades while researching the geology of Peru and only recently have encountered the work by Edmund’s excavation of the site for the Royal Ontario Museum in 1958.
The role of this site is completely unappreciated within Peru. Practically all Peruvians have never heard of it. I was thinking that perhaps a dig could be organized to search for fossils, however, Edmunds collected some 28,000 fossils making one wonder how much was left behind? Specimens at this site includes giant sloths, dire wolves, forms of jaguars and saber-toothed cats (Smilodon), and numerous bird species.
Churcher (1966) used carbon dating method from several Talara samples to provide an age range of 13,000 to 14,000 years before present. Does much remain left in the ground to develop the area into a La Brea California type site? Certainly, local funding is not feasible in Peru to undertake such an enterprise. Because of the petroleum association it seems that PetroPeru would be the ideal organization to consider such a proposition.
The tar seeps are located one-kilometer southwest of the Panamericana highway, at the waypoint -4.655215, -81.13089, a location that is 17-km east of the coastal town of Talara. One can clearly see in Google Earth extensive surface disturbance from the old excavations and several active tar seeps and notably zero infrastructure explaining or protecting the site.
In general, the extinction of the giant ground sloth is hypothesized to have coincided with the arrival of human beings in the Americas, which is similar to the demise of the mammoth. Early habitation of southern Chile is marked near Puerto Montt where a hunter’s camp utilized shelters fashioned from mammoth bones and hides (Dillehay, 1999). Combined extinction of the mammoths and giant sloths, plus other large mammals from the Pleistocene also temporally marks the climate shift from the last ice age.
It remains unclear to what extent warming climate versus paleo-hunting was responsible for the demise of these magnificent large animals. There is a certain pervasive pessimistic bias in the sciences that seeks to place the blame upon ourselves, humans, for all past extinctions by projecting back through time our unfortunately poor record of environmental stewardship from these several past centuries. This perhaps is too simplistic and closes the question of what happened to the giant sloths before having all the evidence.
Nonetheless, it is intriguing while travelling in South America to imagine the landscape filled with the paleo-fauna, to once have been able to witness giant sloths walking about the Andes!
References
Bryan, A.L., 1973, Paleo-environments and cultural diversity in late Pleistocene in South America: Quaternary Research, 3: 237-256.
Chucher, C.S., 1959, Fossil Canis from the Tar pits of La Brea, Peru: Science, 130: 564-565.
Chucher, C.S., 1962, Odocoileus salinae and Mazama sp. from the Talara Tar-seeps, Peru: Life Sciences Division, Royal Ontario Museum – University of Toronto, v. 57, p. 1-27.
Chucher, C.S., 1965, Camelid material of the genus Paleolama Gervais from the Talara Tar-seeps, Peru, with a description of a new subgenus, Astylolama: Proceedings of the Zoological Society of London, v. 145(2), p. 161-205.
Chucher, C.S., 1966, The insect fauna from the Talara Tar-seeps, Peru: Canadian Journal of Zoology, v. 44, p. 985-993.
Dillehay, T.D., 1999, The Late Pleistocene Cultures of South America: Evolutionary Anthropology, v. 7 (6), p. 206–216.
Frassinetti, D., and Alberdi, M.T., 2001, Los macromamiferos continentals del Pleistoceno superior de Chile: reseña historica, localidades, restos fosiles, espieces y dataciones conocids: Estudios Geol., v. 57, p. 53-69.
Lemon, R.R.H. and Chucher, C.S., 1961, Pleistocene geology and paleontology of the Talara region, northwest Peru: American Journal of Science, v. 259, p. 410-429.
Marshall, L.G., Hoffstetter, R., and Pascual, R., 1983, Mammals and stratigraphy:
geochronology of the continental mammal-bearing Tertiary of South America:
Paleovertebrata, 93 p. Memoire Extraordinaire.
McDonald, H.G. and Muizon, C. de, 2002, The cranial anatomy of Thalassocnus
(Xenarthra, Mammalia), a derived nothrothere from the Neogene of the Pisco Formation (Peru): Journal of Vertebrate Paleontology, v. 22(2), p. 349-365.
Muizon, C. de, and McDonald, H.G., 1995, An aquatic sloth from the Pliocene of Peru: Nature, v. 375, p. 224-227.
Prieto, A., Labarca, R., and Sierpe, V., 2010, New evidence of the sabertooth cat Smilodon (Carnivora: Machairodontinae) in the late Pleistocene of southern Chilean Patagonia: Revista chilena de historia natural, v. 83, p. 299-307.
Pujos, F., and Salas, R., 2004, A systematic reassessment and paleogeographic review of fossil Xenarthra from Peru: Bulletin de l’Institut français d’études andines, v. 33, p. 331-377.
Rodrigues do Nascimiento A., 2008, Os Xenarthra Pilosa (Megatheriidae), Notoungulata (Toxodontdae) e Proboscidea (Gomphotheriidae) da Formação Madeira do Pleistoceno superior do Estado de Rondênia, Brasil: Monografia de Mestrado, UFRGS, Porto Alegre, 113 pp.
Tonni, E.P., Carlini, A.A., Gustavo J. Scillato Yane, G.J., and Figini, A.J., 2003, Cronología radiocarbónica y condiciones climáticas en la “Cueva del Milodón” (sur de Chile) durante el Pleistoceno Tardío: Rev. Asoc. Paleontol. Argentina, v. 40 (4), p. 609-615.
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South America seems to refuse to show its inexhaustible creative force.
