Giant's Diet

 Despite discussing the bipedal implications of biomechanical analyses yesterday, it is important to note that many of the foods Megatherium was thought to have consumed are on the ground. Unlike present day sloths, Megatherium was more of a grasslands and edge of the forest dweller. The open ground of the entirety of the genus' range was different depending on where in the range we discuss. However, the generally accepted diet, aside from trees, consists of lower growing plants like yucca, agave, and grass. As we probably all recognize, herbivores are often large bodied animals. There are a number of reasons for this. The explanation in its simplest form is that plant matter needs to be consumed in large quantities and the digestive anatomy needed to extract the most nutritional value from this material needs to be extensive in these large herbivores (e.g. Westoby 1974; Danell et al. 2006, and Felton et al. 2016). 

Understanding the guts of extinct animals like Megatherium that relied on the leaves of trees and low-lying plants like those mentioned above can be accomplished using living examples that we know well to draw conclusions. The understanding of how Megatherium processed, and even ate, all of that material can also be inferred from living animals, but thankfully for us, we have the capability to model feeding and the technology to do so. This has led to biomechanical and morphometric analyses of Megatherium skulls. Bargo (2001) is one such study that analyzes both the biomechanical capabilities of these sloths and takes into account the morphometrics of the skull as well as dietary limits. What we learned from Bargo (2001) is that Megatherium teeth and jaws were well suited to biting and cutting medium to soft vegetation and do not appear to have been used for grinding tough and fibrous plant materials. 

It has also been suggested that Megatherium was an opportunistic omnivore, and not a strict herbivore. These sorts of occasional carnivory have been documented, anecdotally, at least, in deer that have been reported eating mice. Hummingbirds have been known to feed arthropods to their offspring and augment their nectar diets with fruit flies (Young 1971, Brice 1992, Yanega and Rubega 2004). Occasional carnivory possibly (probably) occurs in other animals as well. Fariña and Blanco (1996) originally put forth the hypothesis that Megatherium may have engaged in scavenging of carcasses based on the muscle attachments of the elbow. This view remains controversial, but hinges (elbow pun intended) on the idea that the anatomical configuration of the Megatherium elbow is like that in other carnivores and accentuates speed of movement rather than force. The authors contended that this permitted Megatherium to use their large curved claws like daggers to stab prey or lash out at carnivores that they were attempting to wrest carcasses away from. Isotope data (and other studies) appears to completely refute this hypothesis, however (e.g. Bargo 2001, Bocherens et al. 2017)

Literature Cited

Bargo, M. S. (2001). "The ground sloth Megatherium americanum: Skull shape, bite forces, and diet". Acta Palaeontologica Polonica. 46 (2): 173–192.

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. doi:10.1016/j.gr.2017.04.003

Brice, A. T. (1992). The essentiality of nectar and arthropods in the diet of the Anna's hummingbird (Calypte anna). Comparative Biochemistry and Physiology Part A: Physiology, 101(1), 151-155.

Danell, K., Bergström, R., Duncan, P., & Pastor, J. (Eds.). (2006). Large herbivore ecology, ecosystem dynamics and conservation (Vol. 11). Cambridge University Press.

Fariña, R. A.; R. E. Blanco (1996). Megatherium, the stabber. Proceedings of the Royal Society of London. 263. pp. 1725–1729. doi:10.1098/rspb.1996.0252

Felton, A. M., Felton, A., Raubenheimer, D., Simpson, S. J., Krizsan, S. J., Hedwall, P. O., & Stolter, C. (2016). The nutritional balancing act of a large herbivore: an experiment with captive moose (Alces alces L). PloS one, 11(3), e0150870.

Westoby, M. (1974). An analysis of diet selection by large generalist herbivores. The American Naturalist, 108(961), 290-304.

Yanega, G. M., & Rubega, M. A. (2004). Hummingbird jaw bends to aid insect capture. Nature, 428(6983), 615-615.

Young, A. M. (1971). Foraging for insects by a tropical hummingbird. The Condor, 73(1), 36-45.