Giant sloth

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Megatherium

A number of extinct species of sloth are known as giant sloths . They lived on the American continent and sometimes reached a weight of several tons, some species did not become extinct until the end of the Pleistocene . In contrast to today's sloths, giant sloths did not live in the trees, but on the ground.

Causes of extinction

The last giant sloths disappeared at the end of the Pleistocene, roughly simultaneously with climate change and the first appearance of humans in North America. To this day, it remains a matter of dispute whether the Paleo-Indians , the ancestors of the Native Americans, were responsible for the disappearance of the giant sloths. For a long time, rapid climate change at the end of the last glacial period was blamed for this. The warming shifted the precipitation zones, the glaciers melted and the sea level rose. Some scientists argue that many animal species, including the giant sloth, could not adapt quickly enough to the new environmental conditions.

Against this thesis, however, there is the fact that giant sloths survived many climate changes, warm and cold periods for over two million years. In addition, they were among the few South American species that gained a foothold on the North American continent when the land bridge between North and South America was formed and that they were able to spread widely, which also speaks for a pronounced ability to adapt. Recent studies show that smaller species on the Caribbean islands of Hispaniola and Cuba did not become extinct until shortly after the arrival of the Europeans around 1550. Humans settled America 10,000 to 30,000 years ago. The last giant sloths disappeared on the mainland around 10,000 years ago. This suggests that the animals were heavily hunted. They probably couldn't do much to oppose humans because, like their current relatives, they moved very slowly. Presumably, humans were more responsible for the extinction of the giant sloths than the consequences of climate change. Indian legends tell of the Mapinguari , a mythical creature that is very similar to the giant sloth.

Taxonomy

The giant sloths are not a single taxonomic group. Several families of sloths gave birth to large representatives known as giant sloths. For more information, see the sloth system .

Megatheriidae

Skeleton of a Megatherium americanum
Skeleton of the extinct aquatic living thalassocnus

Members of the Megatheriidae family reached the size of elephants. One of the largest genera was Megatherium from the late Pleistocene of South America. It reached a length of six meters. About the same size was Eremotherium , which also survived into the late Pleistocene. His remains have been found in Florida and South America. The other genera of the Megatheriids were smaller. A striking feature of the developed Megatheriidae is their homodontic dentition. Relatively original genera of the group were, for example, Planops and Hapalops , which lived in the Miocene of South America and still had teeth comparable to the megalonychids (with a canine-like front tooth). Hapalops was about four feet long.

Nothrotheriidae

The Nothrotheriidae form a group of giant sloths that is rather poor in shape. Their best-known representatives, Nothrotherium and Nothrotheriops , were very similar to each other and also existed in America until the late Pleistocene, with Nothrotherium being restricted to the South American continent and Nothrotheriops living in North America. With a maximum weight of 460 kg, it was the smallest of the Pleistocene giant sloths in North America. It is often also thalassocnus , the only semi-aquatic members of the sloths, refer to this group.

Megalonychidae

The Megalonychidae family includes the bovine-sized Megalonyx jeffersonii , the remains of which were found in Kentucky as early as 1796 and which is one of the longest known fossil forms. In addition, the representatives of the genus reached the arctic areas of North America, making Megalonyx the sloth form with the northernmost distribution. Other members of the family of similar size include Xibalbaonyx and Nohochichak from Central America. Older forms such as Zacatzontli were definitely smaller. The Megalonychidae were common in both North and South America. A characteristic feature of the family representatives are the hands and feet that are not twisted in contrast to other forms of sloth.

Mylodontidae

The Mylodontidae form another group of giant sloths. The genus Mylodon reached a length of three meters and the size of a bull. The animals wore fur and had skin interspersed with irregularly shaped osteoderms ; both have been preserved partly mummified . Remains of Mylodon were found by the German adventurer Hermann Eberhard in 1895 in a cave east of the Torres del Paine National Park in Chile . They suggest that these animals became extinct around 11,000 years ago. A related species, Paramylodon harlani , has been found in the La Brea Tar Pit in Los Angeles , among others . The largest representative of the Mylodonts is Lestodon from the pampas region of South America. Scelidotherium differed in skull structure from other Mylodontiden and lived from the Upper Pliocene to the late Pleistocene in South America.

Acratocnidae and Parocnidae

The sloths of the Caribbean islands were rather small, sometimes only with the dimensions of today's tree sloths, and therefore do not represent giant sloths in the sense of the word. However, with Megalocnus , they also produced quite large forms. The Caribbean sloths were originally counted among the Megalonychidae and were considered to be the closest relatives of today's two-toed sloths , but genetic studies from 2019 contradicted this view. They therefore form a very original line within the sloth.

literature

  • Paul S. Martin , Richard G. Klein (Eds.): Quaternary Extinctions. A Prehistoric Revolution. The University of Arizona Press, Tucson AZ 1984, ISBN 0-8165-1100-4 .
  • Arno Hermann Müller : Textbook of paleozoology. Volume 3: Vertebrates. Part 3: Mammalia. 2nd revised and expanded edition. Fischer, Jena 1989, ISBN 3-334-00223-3 .
  • Caesar Claude: El mamifero misterioso. The giant sloth and its relatives. Zoological Museum of the University of Zurich, Zurich 2000, ISBN 3-9521043-4-5 .

Individual evidence

  1. ↑ C. Sandom, S. Faurby, B. Sandel, J.-C. Svenning: Global late Quaternary megafauna extinctions linked to humans, not climate change. Proceedings of the Royal Society B: Biological Sciences 281, 2014, p. 20133254, doi : 10.1098 / rspb.2013.3254 .
  2. ↑ Timothy J. Gaudin: Phylogenetic relationships among sloths (Mammalia, Xenarthra, Tardigrada): the craniodental evidence. Zoological Journal of the Linnean Society 140, 2004, pp. 255-305
  3. ↑ H. Gregory McDonald and George T. Jefferson: Distribution of Pleistocene Nothrotheriops (Xrenarthra, Nothrotheriidae) in North America. Science Series 41, 2008, pp. 313-331
  4. ^ Christian de Muizon and H. Gregory McDonald: An aquatic sloth from the Pliocene of Peru. Nature 375, 1995, pp. 224-227 doi: 10.1038 / 375224a0
  5. ↑ Frédéric Delsuc, Melanie Kuch, Gillian C. Gibb, Emil Karpinski, Dirk Hackenberger, Paul Szpak, Jorge G. Martínez, Jim I. Mead, H. Gregory McDonald, Ross DE MacPhee, Guillaume Billet, Lionel Hautier and Hendrik N. Poinar : Ancient mitogenomes reveal the evolutionary history and biogeography of sloths. Current Biology 29, 2019, doi: 10.1016 / j.cub.2019.05.043

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