The first fossils ever assembled into a freestanding mount belonged to the giant ground sloth Megatherium. The fossils, which were unearthed near Luján in what is now Argentina, were described and mounted in 1795 by Juan Bautista Bru at the Royal Cabinet of Natural History in Madrid. But while the Megatherium mount played an important part in the history of paleontology and in our understanding of the changing Earth, the man who made it possible is scarcely mentioned in the literature. Instead, Bru’s work on Megatherium is typically overshadowed by the involvement of the much better known anatomist Georges Cuvier. Drawing principally from José López Piñero ‘s 1988 paper on Bru, this entry is intended to highlight and acknowledge Bru’s contribution to the practice of mounting fossils for public display.
The Megatherium in question was discovered in 1789 in what was then the Viceroyalty of Rio de la Plata, on the banks of the Luján River, “a league and a half” from the town of the same name. As region was controlled by the Spanish monarchy at the time (although the Argentine War of Independence was not far off), it was standard procedure for viceroy Marqués de Lorento to ship the important find to Spain with all haste. Packed into seven crates, the nearly complete skeleton was delivered to the Royal Cabinet of Natural History in Madrid, which curated natural specimens from Spanish territories and was among the most respected scientific institutions in Europe.
By the late 1700s, the European Enlightenment was well established, and the pursuit of knowledge about the world through reason and scientific deduction rather than legend or dogma was popular among the societal elite. The study of natural history was deemed particularly important, and institutions like the Royal Cabinet which collected, quantified and published knowledge about the natural world were well-respected and well-funded. However, the meaning of the fossil record still eluded the top minds of the era. A century earlier, Nicolaus Steno had determined that fossils were the remains of once-living organisms, and by the late 1700s some naturalists were starting to come around to the idea that species that once existed had become extinct. Nevertheless, when the Megatherium arrived in Madrid, naturalists still lacked the most important part of the puzzle presented by the fossil record: an understanding of evolution and the interrelatedness of life on Earth.
The task of interpreting the Luján fossils went to Juan Bautista Bru, the “Artist and First Dissector” at the Royal Cabinet. Born in Valencia, Bru had initially tried his hand as a traditional artist, but found little success. After shifting his focus to natural science, Bru joined the Royal Cabinet in 1771 and remained there until his death in 1799. Bru primarily served as a scientific illustrator, combining his artistic skill with his extensive anatomical knowledge to produce gorgeously detailed drawings of biological specimens, as was required before photography became commonplace. He was also responsible for producing taxidermy pieces and occasionally, mounted skeletons of animals. In 1777, Bru prepared and mounted the skeleton of an elephant that had died at the royal estate in Aranjuez, a task which doubtlessly provided useful practice for mounting the gigantic Megatherium.
Bru devoted four years to studying the Luján fossils, which were complete except for the animal’s tail. He completed his monograph in 1793, which included detailed descriptions of every skeletal element, in addition to 22 plates illustrating the bones from various angles. Among the illustrations was the completely articulated skeleton shown above, which is, incidentally, the first recorded instance of a skeletal drawing illustrating the living form of an extinct animal. Since the mounted skeleton did not go on display until 1795, it is unclear whether Bru based the illustration on the mount or vice versa. Unfortunately, little is known about how Bru created the Megatherium mount, and his drawing provides no information about the armature that supported the massive bones. Since Bru did not discuss the mount’s construction in his monograph, one can only surmise that the techniques he refined over the years building mounts of modern animal skeletons were applicable to the fossils. Wooden armatures were used to mount fossils in the early 1800s, and it is plausible that Bru pioneered this technique. Regardless of how it was supported, the rhino-sized Megatherium mount was placed on a rectangular wooden platform in a room of the Royal Cabinet already devoted to fossils and minerals.
It is unclear why, but Bru never published his monograph, and this unfortunately resulted in him effectively being scooped by Georges Cuvier in 1796. A representative of the French government working in Santa Domingo acquired a set of proofs of Bru’s monograph and illustration, and passed them along to the Institut de France. The proofs made their way to Cuvier, who was well established as one of the world’s leading experts in anatomy and natural history. Although he had not yet seen the actual fossils, Cuvier wrote a brief article in the journal Magasin Encyclopedique on the South American creature, in which he coined the rather vague name Megatherium americanum, meaning American giant beast. Cuvier’s article was not without error (he claimed the fossils were found in Paraguay), but he did correctly recognize that the animal was an edentate* and was curiously similar to modern tree sloths**. In contrast, Bru’s description of the fossils, while thorough, contained no attempt at classification.
As it happened, Cuvier published a second important article on fossil animals in 1796: his Mémoires sur les espèces d’éléphants vivants et fossiles, in which he established that the mammoth fossils found in the Americas belonged to an extinct relative of modern elephants. The wave of attention Cuvier received that year for his contributions to the young field of paleontology apparently eclipsed any recognition of Bru’s multi-year study of the Megatherium. Bru ended up selling his monograph and illustrations to a publisher, and a translated version eventually appeared in a widely disseminated booklet with Cuvier’s Megatherium article in 1804, five years after Bru’s death.
Megatherium would continue to be important to 19th century paleontologists. Charles Darwin became interested in South American fossils during the second voyage of the HMS Beagle. In particular, the relationship between the extinct ground sloths and their modern relatives contributed to Darwin’s ideas about the succession of species over geologic time. In 1849, the British Museum produced a Megatherium mount of their own, a composite of two skeletons found very near to where the Spanish specimen was first discovered. Plaster casts of this mount would appear in museums on both sides of the Atlantic, and the original cast is still on display in London today (some of the fossils were destroyed during World War II). But while the discovery of Megatherium would be recounted often over the subsequent two centuries, it was Cuvier, not Bru, who was always given credit for introducing the animal to the world. Only in recent years has Bru’s name begun to circulate again in historical accounts.
However, there is a bit of happiness at the end of this story. Unlike other early mounts like Peale’s mastodon and Hydrarchos, Bru’s Megatherium has survived to the present day. Remounted on a new steel armature in an approximation of the original quadrupedal pose, the Luján Megatherium fossils are on display at the Royal Cabinet’s spiritual successor, the National Museum of Natural Science in Madrid. On public display for a nearly uninterrupted 218 years, this specimen can surely be said to have taken on a second life. It was once a giant beast that roamed across the ancient Argentinian plains, and now it is a monument to scientific achievement.
*Edentata is a historic paraphyletic group that includes sloths, anteaters, pangolins and aardvarks. Modern biologists recognize that the new world sloths and anteaters and old world pangolins and aardvarks are not closely related. The name Xenarthra is now used for sloths and their new world relatives.
**Cuvier was working many decades before Charles Darwin published On the Origin of Species, and as such, did not subscribe to the idea that species could change and diversify over time. It is therefore worth noting that while he recognized the similarity between Megatherium and modern sloths, he did not conceive of their relationship in an evolutionary sense (that is, related species sharing a common ancestor).
Argot, C. (2008). Changing Views in Paleontology:
The Story of a Giant (Megatherium, Xenarthra). Mammalian Evolutionary Morphology. Pp 37-50.
López Piñero , J.M. (1988). Juan Bautista Bru (1740-1799) and the Description of the Genus Megatherium. Journal of the History of Biology. 21:1:147-163.