In 1788, a remarkable specimen of Megatherium americanum, one of the largest known terrestrial sloths, was shipped from the Viceroyalty of the Río de la Plata (present-day Argentina and Uruguay) to the Royal Cabinet of Natural History in Madrid, Spain.
This fossil would become the type specimen for the species and a cornerstone in the early study of extinct megafauna.
Megatherium belonged to the order Pilosa within the superorder Xenarthra—a group that includes modern sloths, anteaters, and armadillos.
These colossal herbivores thrived in South America from the Pliocene to the end of the Pleistocene, approximately 2 million to 10,000 years ago. Megatherium, whose name means "great beast," could grow up to 6 meters (20 feet) in length and weigh over 4 tons, rivaling modern elephants in size.
This sloth's immense skeletal structure, including robust pelvic and femoral bones, suggests it could rear up on its hind limbs, using its tail as a supportive tripod. This stance allowed it to browse high vegetation, possibly stripping branches and reaching tree canopies with its elongated forelimbs and curved claws. Such a feeding adaptation was critical, as an adult Megatherium required vast quantities of plant matter to sustain its bulk.
Intriguingly, the Megatherium may have played a key role in the dispersal of large-fruited plants like Persea americana—the avocado. Its gut was capable of processing such large fruits, and it likely defecated the intact pits over great distances, contributing to the avocado’s prehistoric range. Modern ecological studies support the idea that many now-domesticated fruit species evolved in tandem with megafaunal seed dispersers (Guimarães et al., 2008).
The specimen sent to Spain was assembled and illustrated by Spanish artist and anatomist Juan Bautista Bru de Ramón. Though Bru’s reconstruction, completed in 1788, was not anatomically correct by today’s standards—it depicts the sloth standing upright with straight legs and a curved spine—it was a pioneering attempt at skeletal reconstruction.
The mount remains on display at the Museo Nacional de Ciencias Naturales in Madrid in its original form, preserving its historical and scientific significance.
French naturalist Georges Cuvier, often regarded as the father of paleontology, later studied Bru’s illustrations and used them to describe Megatherium scientifically in 1796. Cuvier recognized the sloth’s herbivorous nature and its relation to modern tree sloths, a conclusion that helped shape early theories of extinction and comparative anatomy (Cuvier, 1796).
Today, the Megatherium skeleton in Madrid stands not only as a monument to a vanished giant but also as a testament to international collaboration in the early days of paleontology—where artists, anatomists, and naturalists together unveiled the grandeur of life’s ancient past.
If you look closely, you'll see it is not anatomically correct. But all good paleontology is teamwork. Based upon the drawings of Juan Bautista Bru, George Cuvier used this specimen to describe the species for the very first time.
References:
Cuvier, G. (1796). Mémoire sur le squelette d’une très grande espèce de quadrupède inconnue jusqu’à présent. Mémoires de l’Institut National des Sciences et Arts.
Fariña, R. A., Vizcaíno, S. F., & Bargo, M. S. (1998). Body mass estimations in Lujanian (late Pleistocene–early Holocene of South America) mammal megafauna. Mastozoología Neotropical, 5(2), 87–108.
Guimarães Jr, P. R., Galetti, M., & Jordano, P. (2008). Seed dispersal anachronisms: Rethinking the fruits extinct megafauna ate. PLoS ONE, 3(3), e1745. https://doi.org/10.1371/journal.pone.0001745
McDonald, H. G. (2005). Paleoecology of extinct xenarthrans and the Great American Biotic Interchange. Bulletin of the Florida Museum of Natural History, 45, 313–333.
