Ground sloth diet overview

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Since ground sloth diet has been making the rounds again due to the recent omnivore Mylodon paper, I decided to make a thread that summarizes diet in four extinct ground sloth families.

Megalonychids:

A specimen of Megalonyx jeffersonii from New York was found to have had a diet of only C₃ plants.

The first record of the Jefferson ground sloth, Megalonyx jeffersonii, in New York is reported. The specimen consists of a partial synsacrum recovered from a peat deposit near Newburgh, Orange County. Compared to other synsacra of Megalonyx, the number of vertebrae is anomalous with one less caudal vertebra than expected. Stable isotope analysis of the bone shows a δ13C value of 20.5‰ and implies a diet of only C₃ plants. The specimen has a radiocarbon date of 11,450 ± 55 BP indicating the presence of this taxon in the region immediately prior to the extinction of the North American Pleistocene megafauna.

Finally, there appears to be a +3–5‰ shift in δ¹⁵N values with each rise in trophic level (DeNiro and Epstein, 1981; Minagawa and Wada, 1984; France et al., 2007; Fox-Dobbs et al., 2007). Based on our current understanding of the late Pleistocene flora of New York State (MaenzaGmelch, 1997; Dyke, 2005) as well as ecological information on M. jeffersonii from previous studies (France et al., 2007; Bocherens et al., 1994). This M. jeffersonii specimen exhibits δ¹³C values in the C₃ range and δ¹⁵N values similar to other herbivores as it is suspected to have been a forest dwelling browser

Source: McDonald, H. G., Feranec, R. S., & Miller, N. (2019). First record of the extinct ground sloth, Megalonyx jeffersonii,(Xenarthra, Megalonychidae) from New York and contributions to its paleoecology. Quaternary International, 530, 42-46.

The youngest known remains of M. jeffersonii (found near Millersburg, Ohio) also suggest a diet of only C₃ plants.

The − 20.2‰ δ¹³C value for this specimen indicates a diet of only C₃ plants, which is consistent with other specimens of Megalonyx. These include the 400 ka, middle Irvingtonian (Interglacial) Camelot fauna in South Carolina (Kohn et al., 2005) and Megalonyx jeffersonii specimens from the late Pleistocene faunas from Saltville, Virginia (France et al., 2007) and Edmonton, Alberta (Bocherens et al., 1994). The δ¹⁵N value of 5.0‰ is similar to previous values on this species and indicates that the animal's diet was that of a typical herbivore. The habitat of this animal was one containing only C₃ plants and was most likely a forest, although pure C₃ grasslands and wooded C₃ grasslands would yield a similar C₃-dominated, δ¹³C value of approximately − 20‰.

Source: McDonald, H. G., Stafford Jr, T. W., & Gnidovec, D. M. (2015). Youngest radiocarbon age for Jefferson's ground sloth, Megalonyx jeffersonii (Xenarthra, Megalonychidae). Quaternary Research, 83(2), 355-359.

Nitrogen and carbon isotopic data for a specimen of M. jeffersonii (a femur) also groups it as a herbivore.

The Megalonyx specimen presented a unique opportunity to examine the debate concerning the potential carnivorous nature of the giant ground sloths. The data show a relatively high δ₁₅N value (+ 4.65 ± 0.11‰, 2σ) for this particular sloth. Based on sister taxa and modern sloths, the giant ground sloths of the Pleistocene are generally considered to be non-ruminants. This study supports this view due to the similarity in δ₁₅N values between the Megalonyx and other non-ruminants. However, previous research has also suggested that the giant ground sloths may have been omnivorous based on the biomechanical structure of their forearms allowing for precise butchering of captured prey; furthermore they may have evolved highly developed brains allowing for the necessary sensory aptitude for hunting (Aramayo, 1988; Dozo, 1989; Farina, 1996). Our ability to obtain only one quality sloth specimen from the Saltville locality prevents a statistical comparison between the Megalonyx and the other herbivores, yet the fact that the Megalonyx δ₁₅N and δ₁₃C values plot well within the range of the rest of the herbivores (Figs. 5 and 6) strongly suggests a herbivorous diet. The possibility of a small meat component in the Megalonyx diet remains possible, but it is highly unlikely that this animal partook of a strict meat diet. This is in agreement with previous findings for a Pleistocene Megalonyx from Alberta (Bocherens et al., 1994b) and the Pleistocene sloth Paramylodon harlani (Coltrain et al., 2004), which exhibited carbon and nitrogen isotopic values similar to those of strict herbivores from the same ecosystem.

France, C. A., Zelanko, P. M., Kaufman, A. J., & Holtz, T. R. (2007). Carbon and nitrogen isotopic analysis of Pleistocene mammals from the Saltville Quarry (Virginia, USA): Implications for trophic relationships. Palaeogeography, Palaeoclimatology, Palaeoecology, 249(3-4), 271-282.

Megatheres:

An isotopic study found that two specimens of Megatherium (mandible and molariform dentin) were completely herbivorous, with no evidence of carnivore or insectivore.

The diet of extinct giant Xenarthrans is a debated topic, especially for ground sloths, for which herbivory, insectivory, and carnivory through scavenging or active hunting have been suggested. In this study, stable carbon isotopic composition of collagen and carbonate fraction of well-preserved fossil bones was used as a tracer of trophic level. N200 modern mammal bones of species with a variety of diets were used as a reference dataset. The good preservation of the carbonate isotopic composition was checked using different diagenetic indicators and by using fossil carnivorous and herbivorous taxa from the same sites as test-taxa. The results on modern mammals indicate a clear distinction in the difference between the carbon isotopic composition of carbonate and collagen between faunivores (carnivores, insectivores, piscivores, omnivores) and herbivores. Using this framework, the results on the fossil megafaunal Xenarthrans indicate a herbivorous diet for both Glyptodontids and are also consistent with a herbivorous diet for giant ground sloths, including Megatherium. The hypothesis that Megatherium could be a cryptic meat-eater or an insectivore is not supported by the results obtained in the present study.

Source: Bocherens, H., Cotte, M., Bonini, R. A., Straccia, P., Scian, D., Soibelzon, L., & Prevosti, F. J. (2017). Isotopic insight on paleodiet of extinct Pleistocene megafaunal Xenarthrans from Argentina. Gondwana Research, 48, 7-14.

Stable isotopes from Megatherium and Eremotherium remains suggest a mixed diet of C₃-C₄ plants and a C₃-dominated diet, respectively.

The ¹³C values of Megatherium indicates mixed diet of C₃-C₄ plants with higher content of the latter in Pessegueiro Creek, whereas the ¹³C values of Eremotherium indicate C₃-dominated diets, the more negative value in Pessegueiro Creek possibly related to the canopy effect.

Source: Lopes, RP, Dillenburg, SR, Pereira, JC, & Sial, AN (2021). The paleoecology of Pleistocene giant megatheriid sloths: stable isotopes (δ13C, δ18O) of co-occurring Megatherium and Eremotherium from southern Brazil. Brazilian Journal of Paleontology , 24 (3), 245-264. doi.org/10.4072/rbp.2021.3.06

A Brazilian specimen of Eremotherium laurillardi was found to have a mixed C₃-C₄ diet. Stereomicrowear results also suggest a mixed diet, with possible significant consumption of grass.

The results include a ¹⁴C AMS dating of 32,390 ± 100 (34,705-33,947 cal yr BP), and a δ¹³C value of −8.99‰, which indicates a generalist diet (BA = 0.96) with similar proportions of C₃ (pi = 57%) and C₄ (pi = 43%) plants consumed. The stereomicrowear results also suggests a mixed diet, although the high values of scratches could be associated to the significant consumption of grasses.

Source: 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.

A study that examined carbon and nitrogen stable isotope data from an adult Eremotherium tooth from Pernambuco, Brazil found no evidence of carnivory.

We present carbon (δ¹³C_collagen = -10.1 ‰) and nitrogen (δ¹⁵N = 6.8 ‰) stable isotopes data for Eremotherium laurillardi (Megatheriidae, Xenarthra) from the late Pleistocene of Brejo da Madre de Deus, Pernambuco (Brazil) and discuss the possibility of an omnivore diet for the species. Our data, although ponctual, reinforce the inferences that E. laurillardi was a herbivore species.

The δ¹⁵N value of E. laurillardi was 6.8 ‰, which is expected for a grazer, since C₄ plants can have higher values of δ¹⁵N (e.g. Bocherens & Drucker, 2013). Whether E. laurillardi was an omnivore species, it could feed prey taxa with δ¹⁵N values of 3.8 ‰ or 1.8 ‰, considering the most common enrichments of trophic niche +3 ‰ and +5 ‰, respectively (Bocherens & Drucker, 2013). However, these δ¹⁵N values could represent browser taxa, that would have lived in closed habitats, as low-density forests or arboreal savanna, thus in a different habitat expected for this E. laurillardi individual according to its carbon isotope value. Therefore, the proposition made by Fariña (1996) for Megatherium americanum suggesting that it could be an omnivore species, could not be attributed for E. laurillardi.

Source: 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.

Nothrotheres:

Coprolites from Nothrotheriops have only yielded direct evidence for the consumption of plant matter.

DNA from excrements can be amplified by means of the polymerase chain reaction. However, this has not been possible with ancient feces. Cross-links between reducing sugars and amino groups were shown to exist in a Pleistocene coprolite from Gypsum Cave, Nevada. A chemical agent, N-phenacylthiazolium bromide, that cleaves such cross-links made it possible to amplify DNA se- quences. Analyses of these DNA sequences showed that the coprolite is derived from an extinct sloth, presumably the Shasta ground sloth Nothrotheriops shastensis. Plant DNA sequences from seven groups of plants were identified in the coprolite. The plant assemblage that formed part of the sloth's diet exists today at elevations about 800 meters higher than the cave.

Source: Poinar, H. N., Hofreiter, M., Spaulding, W. G., Martin, P. S., Stankiewicz, B. A., Bland, H., ... & Pääbo, S. (1998). Molecular coproscopy: dung and diet of the extinct ground sloth Nothrotheriops shastensis. Science, 281(5375), 402-406.

Seven coprolites of the extinct Shasta ground sloth (Nothrotheriops shastense) were recently discovered in the Los Angeles County Museum collection from Shelter Cave, New Mexico. Three dung balls provided radiocarbon ages of 11,330, 12,330 and 12,430 yr B.P. Packrat (Neotoma) middens disclose a xeric juniper woodland at Shelter Cave during the sloth's occupation. Plant cuticles from the dung indicate that the ground sloth had a diet dominated by mormon tea (Ephedra) and other xerophytic shrubs. Pollen spectra from the coprolites have high representations of anemophilous plants and low representations of the dietary items shown in the cuticle analysis.

Source: Thompson, R. S., Van Devender, T. R., Martin, P. S., Foppe, T., & Long, A. (1980). Shasta ground sloth (Nothrotheriops shastense Hoffstetter) at Shelter Cave, New Mexico: environment, diet, and extinction. Quaternary Research, 14(3), 360-376.

DNA was extracted from five coprolites, excavated in Gypsum Cave, Nevada and radiocarbon dated to approximately 11 000, 20 000 and 28 500 years bp. All coprolites contained mitochondrial DNA sequences identical to a DNA sequence determined from a bone of the extinct ground sloth Nothrotheriops shastensis. A 157-bp fragment of the chloroplast gene for the large subunit of the ribulosebisphosphate carboxylase (rbcL) was amplified from the boluses and several hundred clones were sequenced. In addition, the same DNA fragment was sequenced from 99 plant species that occur in the vicinity of Gypsum Cave today. When these were compared to the DNA sequences in GenBank, 69 were correctly (two incorrectly) assigned to taxonomic orders. The plant sequences from the five coprolites as well as from one previously studied coprolite were compared to rbcL sequences in GenBank and the contemporary plant species. Thirteen families or orders of plants that formed part of the diet of the Shasta ground sloth could be identified, showing that the ground sloth was feeding on trees as well as herbs and grasses. The plants in the boluses further indicate that the climate 11 000 years BP was dryer than 20 000 and 28 500 years BP. However, the sloths seem to have visited water sources more frequently at 11 000 BP than at earlier times.

Source: Hofreiter, M., Poinar, H. N., Spaulding, W. G., Bauer, K., Martin, P. S., Possnert, G., & Pääbo, S. (2000). A molecular analysis of ground sloth diet through the last glaciation. Molecular Ecology, 9(12), 1975-1984.

Microwear analysis of the teeth of Nothrotheriops shastensis also suggest herbivory.

Microwear patterns in N. shastensis are most comparable to extant folivores based on scratch number and hierarchical cluster analysis. This strongly supports an herbivorous diet for N. shastensis that is corroborated by multiple independent lines of evidence. Thus, orthodentine microwear analysis can be used to reconstruct diet in extinct xenarthrans.

Source: Jeremy L. Green, Dental microwear in the orthodentine of the Xenarthra (Mammalia) and its use in reconstructing the palaeodiet of extinct taxa: the case study of Nothrotheriops shastensis (Xenarthra, Tardigrada, Nothrotheriidae), Zoological Journal of the Linnean Society, Volume 156, Issue 1, May 2009, Pages 201–222, doi.org/10.1111/j.1096-3642.2008.00486.x

Isotopic analysis has also confirmed herbivory in N. shastensis.

The Δδ¹⁵N_Glx − δ¹⁵N_Phe values for Mylodon overlap those of taxa within the omnivore category (median = 2.7‰) while Nothrotheriops best fit values in the herbivore category (median = 1.9‰, Fig. 1, Table S5).

Assessing the results of all analyses together (∆δ¹⁵N_Glx − δ¹⁵N_Phe and linear relationships between δ¹⁵N_Glx and δ¹⁵N_Phe in extant mammals) suggests that while the Shasta ground sloth Nothrotheriops shastensis was likely an obligate herbivore, Darwin’s sloth Mylodon darwinii was not, instead occupying a higher trophic position.

Source: Tejada, J. V., Flynn, J. J., MacPhee, R., O’Connell, T. C., Cerling, T. E., Bermudez, L., ... & Popp, B. N. (2021). Isotope data from amino acids indicate Darwin’s ground sloth was not an herbivore. Scientific Reports, 11(1), 1-10.

Mylodontids:

Recently, stable nitrogen isotopes from Mylodon darwinii have suggested omnivory in this species.

The Δδ¹⁵N_Glx − δ¹⁵N_Phe values for Mylodon overlap those of taxa within the omnivore category (median = 2.7‰) while Nothrotheriops best fit values in the herbivore category (median = 1.9‰, Fig. 1, Table S5).

Assessing the results of all analyses together (∆δ¹⁵N_Glx − δ¹⁵N_Phe and linear relationships between δ¹⁵N_Glx and δ¹⁵N_Phe in extant mammals) suggests that while the Shasta ground sloth Nothrotheriops shastensis was likely an obligate herbivore, Darwin’s sloth Mylodon darwinii was not, instead occupying a higher trophic position.

Source: Tejada, J. V., Flynn, J. J., MacPhee, R., O’Connell, T. C., Cerling, T. E., Bermudez, L., ... & Popp, B. N. (2021). Isotope data from amino acids indicate Darwin’s ground sloth was not an herbivore. Scientific Reports, 11(1), 1-10.

Otherwise, coprolites from Mylodon have only suggested the consumption of plant matter.

The oldest deposits, carbon-dated as c. 12,400 B.P., comprise dung of the extinct ground sloth Mylodon darwinii and show the animal to have fed entirely on Cyperaceae, Gramineae and species associated with these in the modern cool, wet sedge-grasslands of western Patagonia, communities which would be expected after the retreat of the ice.

Source: D.M. Moore, Post-glacial vegetation in the South Patagonian territory of the giant ground sloth, Mylodon, Botanical Journal of the Linnean Society, Volume 77, Issue 3, October 1978, Pages 177–202, doi.org/10.1111/j.1095-8339.1978.tb01398.x

Stable carbon and nitrogen isotopes from Lestodon armatus and Glossotherium robustum also suggest C₃ plant bulk feeding. The nitrogen values in particular were high, and it has been suggested that one possible cause for this is some degree of carnivory. However, multiple potential reasons (e.g. non-ruminant physiology and CO₂ concentration on ecosystem) could easily (indeed, are seemingly favored) explain this.

Biogeochemical techniques have become most useful in the determination of the dietary niches of fossil mammalian species and in the reconstruction of past communities. Stable isotopes analyses (¹³C and ¹⁵N) were applied to study the diet of the mylodontids Lestodon and Glossotherium and other Late Pleistocene megamammals. Only the samples for these ground sloths yielded reliable values. The results of the δ¹⁵N for L. armatus and G. robustum could be related to a non-ruminant herbivorous physiology or to the climate inferred for the Pampean region in the Late Pleistocene, colder and drier than present. The results of δ¹³C for L. armatus and G. robustum indicate a preference for C₃ vegetation in open environments. This is also congruent with the trophic habits inferred for these ground sloths from morphological and biomechanical evidence that point them out as bulk feeders.

Finally, a more diverse diet than strict herbivory, and possibly including animal matter, has been proposed for ground sloths (Fariña 1996), particularly Megatherium americanum. Although a more general view on this topic is still lacking, this could be another factor to take into account at interpreting the high values obtained.

The results of the δ¹⁵N obtained for Lestodon armatus are consistent with the values obtained previously (Fariña & CasTilla 2007). Those results, as well as those obtained for Glossotherium robustum could be related to a non-ruminant herbivorous physiology or to the dryer and colder climate inferred for their respective ages. The results of δ¹⁵N obtained for L. armatus and G. robustum are congruent with the climate inferred for the Pampean region in the Late Pleistocene during the OIS 2, colder and drier than present (iriondo & garCía 1993; iriondo 1999; Tonni & Cione 1997; Tonni et al. 1999).

Source: Czerwonogora, A., Fariña, R. A., & Tonni, E. P. (2011). Diet and isotopes of Late Pleistocene ground sloths: first results for Lestodon and Glossotherium (Xenarthra, Tardigrada). Neues Jahrbuch fur Geologie und Palaontologie-Abhandlungen, 262(3), 257.

Stable isotope analysis of the remains of Paramylodon harlani from Rancho La Brea has grouped this species in with contemporaneous herbivores.

Source: Coltrain, J. B., Harris, J. M., Cerling, T. E., Ehleringer, J. R., Dearing, M. D., Ward, J., & Allen, J. (2004). Rancho La Brea stable isotope biogeochemistry and its implications for the palaeoecology of late Pleistocene, coastal southern California. Palaeogeography, Palaeoclimatology, Palaeoecology, 205(3-4), 199-219.

Conclusion:

Given current evidence, only some mylodontids may be said to possibly be omnivorous. This includes Mylodon itself. Although there is some bit of suggestion that high stable nitrogen values in Lestodon and Glossotherium may possibly be the result of faunivory, the non-ruminant physiology or environmental conditions could easily account for these, and are, in fact, suggested. One mylodontid, Paramylodon, shows no evidence of faunivory. All other ground sloths are confirmed to be herbivorous by multiple lines of evidence.