Eremotherium spp.

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Eremotherium spp.


Life reconstruction of E. laurillardi compared to a modern human and the extant Bradypus variegatus (three-toed sloth). © @ Gabriel Ugueto.

Temporal range: Late Neogene to Late Quaternary; latest Pliocene to early Holocene[1][2][3] (2.588-0.011 Ma)

Scientific classification:

Life
Domain: Eukaryota
(unranked): Unikonta
(unranked): Opisthokonta
(unranked): Holozoa
(unranked): Filozoa
Kingdom: Animalia
Subkingdom: Eumetazoa
(unranked): Bilateria
Clade: Nephrozoa
Superphylum: Deuterostomia
Phylum: Chordata
Clade: Olfactores
Clade: Craniata
Subphylum: Vertebrata
Infraphylum: Gnathostomata
Clade: Eugnathostomata
Clade: Teleostomi
Superclass: Tetrapoda
Clade: Reptiliomorpha
Clade: Amniota
Clade: Synapsida
Clade: Eupelycosauria
Clade: Sphenacodontia
Clade: Sphenacodontoidea
Order: Therapsida
Clade: Eutheriodonta
Suborder: Cynodontia
Clade: Epicynodontia
Infraorder: Eucynodontia
Parvorder: Probainognathia
Superfamily: Chiniquodontoidea
Clade: Prozostrodontia
Clade: Mammaliaformes
Class: Mammalia
(unranked): Pegasoferae
(unranked): Zooamata
Clade: Holotheria
Superlegion: Trechnotheria
Legion: Cladotheria
Sublegion: Zatheria
Infralegion: Tribosphenida
Subclass: Theria
Clade: Eutheria
Infraclass: Placentalia
Superorder: Xenarthra
Order: Pilosa
Suborder: Folivora
Superfamily: Megatherioidea
Family: †Megatheriidae
Subfamily: †Megatheriinae
Genus: †Eremotherium
Species: †E. laurillardi
†E. eomigrans
†E. sefvei[4]

Eremotherium is a genus of ground sloth that lived almost exclusively at low latitudes of North America, Central America, and South America from the latest Pliocene[2] to the early Holocene.[1]

Taxonomy:
There appear to currently be three valid species of Eremotherium. Eremotherium laurillardi is argued to be the only valid megatheriine species in the Pleistocene of intertropical Brazil, with E. rusconii being a junior synonym of E. laurillardi.[5]

Evolution and geographic range:
E. eomigrans may have been ancestral to the later E. laurillardi. However, it was not as geographically widespread as the later species.[6]

Description:
E. laurillardi is the largest species of extinct ground sloth, with estimates in the scientific literature putting its body mass at up to 6,550 kg[7][8] (although, there are also much lower body mass estimates of ~3,300-3400 kg[9][10]). By contrast, E. sefvei is the smallest post-Miocene megatheriine species; the femur of the type specimen has a lateral length of 39.1 cm.[4] E. eomigrans generally had slightly more gracile postcranial bones than E. laurillardi and was similar in size to Megatherium americanum.[6] Eremotherium is recognizable not just by its large size, but also by the triangular shape of the predental part of its rostrum and the lower positioned basilar plane and condyles than in Megatherium.[2]

E. eomigrans is anatomically very similar to E. laurillardi. Its major diagnostic feature is a manus with all five digits (with claws on all except the fifth). By contrast, E. laurillardi had a manus with only three digits (losing the first and second digits, leaving it with only two claws) and Megatherium had a manus with four digits (losing the first digit, leaving it with three claws).[6]


Manus of E. eomigrans. Note the presence of all five digits with claws on all but digit V. From [6].


Manus of E. laurillardi. Note the loss of digits I and II. Screen capture from [11].

Biology:
Multiple studies (incorporating both isotope analysis or tooth microwear analysis) have indicated that E. laurillardi was a generalist mixed feeder.[12][13][14] Like Megatherium, it likely had a well-developed ability to orally process food with a strong bite.[14] Due to its large size and wide niche breadth, Eremotherium was likely to be a key species in the Pleistocene Brazilian Intertropical Region, and an excellent competitor for resources.[12]

A bonebed of E. laurillardi remains at Tanque Loma provides some insight into the biology and behavior of the species. This multigenerational group is thought to have died within the same time frame due to the fact that almost all of them occur in the same layer with little sediment separating the bones. Five hypotheses were proposed as to what led to the mass death of Eremotherium. Of these, it is believed that a biological disaster such as drought or disease is what most likely killed the ground sloths, since multiple lines of evidence support this interpretation. The assemblage has been compared to assemblages of hippopotamuses, which gather in large groups at bodies of water; during droughts, the wallows dry up and become contaminated with hippopotamus feces, and the animals die in large numbers due to starvation and/or disease. Given that the Eremotherium fossil deposit occurs in an anoxic, low-energy aquatic context, and contains what appears to be digested food matter from Eremotherium, suggests that the die-off may have been caused by the wallow being contaminated by the sloths’ own feces. The bonebed also suggests that some species of ground sloth may have been gregarious and formed multigenerational congregations.[15]

Stable carbon and isotope analysis of a ~27,000 year old Eremotherium tooth showed that this individual was able to adapt its diet to a seasonal environment. This individual seems to have preferred open habitat to dense forest.[16] Diet would have varied depending on the habitat; Eremotherium would have grazed in open habitat, but been a mixed feeder in more closed habitats.[14]

In the pes of Eremotherium (and Megatherium), the digital plane was about 35^o to the horizontal plane, meaning that the weight of the animal was largely borne by metatarsal V, as well as metatarsal IV and potentially the claw of digit III.[17] It would have walked on its knuckles with the two claws on each manus turned backward. Eremotherium’s main defense would have been its great size and strength, with the claws likely also being used for defense.[18]

Ground sloths such as Megatherium have been proposed to be omnivores. Based on stable isotope analysis, this suggestion is currently unsupported in Eremotherium, as in Megatherium.[19]

Extinction:
It is most likely that E. eomigrans went extinct during the Irvingtonian, and was then replaced by E. laurillardi as the latter migrated from South America.[6]

A 2012 study modeled the potential distribution of Eremotherium and Megatherium during the last glacial maximum (21 ky BP) and the mid-Holocene (6 ky BP). This model predicted a drastic reduction of the geographic ranges of both species during the mid-Holocene, as well as fragmentation of refugia. However, this model predicted that neither would have been fully extinguished by this point in time due to climate change alone. Because of this, climate change was likely a significant factor in the extinction of Eremotherium, but not the sole reason. Anthropogenic impacts likely would have destroyed any chances for Eremotherium to recover from climatic changes.[20]

References:

[1] Oliveira, J. F., Asevedo, L., Cherkinsky, A., & Dantas, M. A. T. (2020). Radiocarbon dating and integrative paleoecology (ẟ13C, stereomicrowear) of Eremotherium laurillardi (LUND, 1842) from midwest region of the Brazilian intertropical region. Journal of South American Earth Sciences, 102, 102653.
[2] Carlini, A. A., Brandoni, D., Sánchez, R., & Sánchez Villagra, M. R. (2018). A new Megatheriinae skull (Xenarthra, Tardigrada) from the Pliocene of Northern Venezuela–implications for a giant sloth dispersal to Central and North America.
[3] Ribeiro, M. S. L., Varela, S., Nogués-Bravo, D., & Diniz Filho, J. A. F. (2012). Potential suitable areas of giant ground sloths dropped before its extinction in South America: the evidences from bioclimatic envelope modeling.
[4] De Iuliis, G., & St-André, P. A. (1997). Eremotherium sefvei nov. sp. (Mammalia, Xenarthra, Megatheriidae) from the pleistocene of ulloma, Bolivia. Geobios, 30(3), 453-461.
[5] Cartelle, C., De Iuliis, G., & Pujos, F. (2015). Eremotherium laurillardi (Lund, 1842)(Xenarthra, Megatheriinae) is the only valid megatheriine sloth species in the Pleistocene of intertropical Brazil: A response to Faure et al., 2014. Comptes Rendus Palevol, 14(1), 15-23.
[6] www.floridamuseum.ufl.edu/florida-vertebrate-fossils/species/eremotherium-eomigrans/
[7] Larmon, J. T., McDonald, H. G., Ambrose, S., DeSantis, L. R., & Lucero, L. J. (2019). A year in the life of a giant ground sloth during the Last Glacial Maximum in Belize. Science advances, 5(2), eaau1200.
[8] Dantas, M. A. T., Cherkinsky, A., Bocherens, H., Drefahl, M., Bernardes, C., & de Melo França, L. (2017). Isotopic paleoecology of the Pleistocene megamammals from the Brazilian Intertropical Region: Feeding ecology (δ13C), niche breadth and overlap. Quaternary Science Reviews, 170, 152-163.
[9] Dantas, M. A. T. (2019). Atualizando a estimativa da massa corporal da megafauna do Pleistoceno Final da Região Intertropical Brasileira. In Boletim de Resumos, Congresso Brasileiro de Paleontologia. Uberlândia, Minas Gerais.
[10] Dantas, M. A. T., Cherkinsky, A., Lessa, C. M. B., Santos, L. V., Cozzuol, M. A., Omena, É. C., ... & Bocherens, H. (2020). [url=https://sbpbrasil.org/publications/index.php/rbp/article/view/150Isotopic paleoecology (δ13C, δ18O) of a late Pleistocene vertebrate community from the Brazilian Intertropical Region[/url]. Revista Brasileira de Paleontologia, 23(2), 138-152.
[11] De Iuliis, G., & Cartelle, C. (1994). The Medial Carpal and Metacarpal Elements of Eremotherium and Megatherium (Xenarthra: Mammalia). Journal of Vertebrate Paleontology, 13(4), 525-533. Retrieved July 18, 2021, from www.jstor.org/stable/4523536
[12] Dantas, M. A. T., Cherkinsky, A., Bocherens, H., Drefahl, M., Bernardes, C., & de Melo França, L. (2017). [url=https://www.sciencedirect.com/science/article/abs/pii/S0277379117300616Isotopic paleoecology of the Pleistocene megamammals from the Brazilian Intertropical Region: Feeding ecology (δ13C), niche breadth and overlap[/url]. Quaternary Science Reviews, 170, 152-163.
[13] Oliveira, J. F., Asevedo, L., Cherkinsky, A., & Dantas, M. A. T. (2020). Radiocarbon dating and integrative paleoecology (ẟ13C, stereomicrowear) of Eremotherium laurillardi (LUND, 1842) from midwest region of the Brazilian intertropical region. Journal of South American Earth Sciences, 102, 102653.
[14] Dantas, M. A. T., Dutra, R. P., Cherkinsky, A., Fortier, D. C., Kamino, L. H. Y., Cozzuol, M. A., ... & Vieira, F. S. (2013). Paleoecology and radiocarbon dating of the Pleistocene megafauna of the Brazilian Intertropical Region. Quaternary Research, 79(1), 61-65.
[15] Lindsey, E. L., Reyes, E. X. L., Matzke, G. E., Rice, K. A., & McDonald, H. G. (2020). A monodominant late-Pleistocene megafauna locality from Santa Elena, Ecuador: Insight on the biology and behavior of giant ground sloths. Palaeogeography, Palaeoclimatology, Palaeoecology, 544, 109599.
[16] Larmon, J. T., McDonald, H. G., Ambrose, S., DeSantis, L. R., & Lucero, L. J. (2019). A year in the life of a giant ground sloth during the Last Glacial Maximum in Belize. Science advances, 5(2), eaau1200.
[17] Toledo, N., De Iuliis, G., Vizcaíno, S. F., & Bargo, M. S. (2018). [url=http://sedici.unlp.edu.ar/bitstream/handle/10915/80692/Documento_completo.pdf?sequence=1The concept of a pedolateral pes revisited: The giant sloths Megatherium and Eremotherium (Xenarthra, Folivora, Megatheriinae) as a case study[/url]. Journal of Mammalian Evolution, 25(4), 525-537.
[18] Kurtén, B. (1988). Before the Indians. Columbia University Press. p. 81.
[19] Dantas, M. A. T., Omena, É. C., da Silva, J. L. L., & Sial, A. Could Eremotherium laurillardi (Lund, 1842)(Megatheriidae, Xenarthra) be an Omnivore Species?. Anuário do Instituto de Geociências, 44.
[20] Ribeiro, M. S. L., Varela, S., Nogués-Bravo, D., & Diniz Filho, J. A. F. (2012). Potential suitable areas of giant ground sloths dropped before its extinction in South America: the evidences from bioclimatic envelope modeling.

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The paleoecology of Pleistocene giant megatheriid sloths: stable isotopes (δ13C, δ18O) of co-occurring Megatherium and Eremotherium from southern Brazil

The Pampa in subtropical Brazil (State of Rio Grande do Sul) is the only area of South America known so far where fossils of the Pleistocene giant megatheriid sloths Megatherium americanum, characteristic of subtropical-temperate areas, and Eremotherium laurillardi, widespread in the tropical zone, were discovered in the same deposits (Pessegueiro Creek and Chuí Creek), but it is not clear whether this co-occurrence is a product of taphonomic mixture, or co-existence, which would imply niche partitioning. In order to understand their paleoecology and reconstruct the associated paleoenvironments, dentin samples of both megatheriids from the two sites were analyzed for their carbon (δ13C) and oxygen (δ18O) isotope ratios. The δ13C values of Megatherium indicate mixed diet of C3-C4 plants with higher content of the latter in Pessegueiro Creek, whereas the δ13C values of Eremotherium indicate C3-dominated diets, the more negative value in Pessegueiro Creek possibly related to the canopy effect. The δ18O of Eremotherium points to 18O-depleted water sources, possibly also influenced by the diet, whereas Megatherium ingested 18O-enriched water. The results show that co-existence of both megatheriids would have been ecologically possible, and that the Pampa was occupied by open grasslands/woodlands, with closed forests in Pessegueiro Creek. The δ13C of Eremotherium from intertropical Brazil indicate a more generalist habit than Megatherium from subtropical Brazil and Argentina, which probably facilitated its dispersion from the tropics up to subtropical areas along two different routes, one along the coastal plain, and the other along the Paraná River Basin across central South America, following the southward expansion of riparian forests during warmer stages. The reduction of those forests during intervening cold stages possibly led to its disappearance in southern Brazil.

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