The research history of Anoplotherium spans back to 1804 when Georges Cuvier first described the fossils of this extinct artiodactyl and named the genus after describing Palaeotherium, making it one of the first fossil mammal genera to be described as well as having one of the earliest official taxonomic authorities. It was also amongst the first fossil genera to be reconstructed by drawings and biomechanics. Subsequent descriptions of fossil evidence by Cuvier are also said to have been some of the earliest instances of palaeoneurology and palaeopathology. Anoplotherium was a significant find in palaeontological history and was once an iconic element of text and classroom sources of palaeontology, geology, and natural history. Today, it has a lessened cultural status compared to the 19th century as a result of public interest in Mesozoic dinosaurs or Neogene-Quaternary mammals, but it is still regularly acknowledged in sources of the history of palaeontology.
Cuvier recognized four species of Anoplotherium the same year he first created the genus name, among them the type species A. commune. From 1807 to 1812, he described two skeletons of A. commune from the French communes of Pantin and Antony, noting the distinct lack of anatomical analogues among modern mammals and making a hypothesis based on its unique anatomy that it was semi-aquatic. The two other species he named in 1804, A. medium, A. minus, and A. minimum, had their paleobiologies speculated on in 1812 and had their names emended in 1822 to A. (Xiphodon) gracile, A. (Dichobune) leporinum, and A. murinus. The former two species' subgenera were converted into distinct genera in later decades while A. murinus was later assigned to its own genus Amphimeryx. Cuvier in 1822 also named two additional species A. secundaria and A. obliquum, later reassigned to newer genera Diplobune and, provisionally, Haplomeryx respectively.
Many species assigned to Anoplotherium were named in later decades and were then subsequently assigned to other genera by other works. Several other species that were also erected within Anoplotherium remain within the genus today, namely A. laurillardi, A. latipes, and A. pompeckji; as a result, four species of Anoplotherium are recognized. In addition, the hypothesis that Anoplotherium was semi-aquatic was proven incorrect by M. Dor in 1938 and replaced by another of facultative bipedalism by Jerry J. Hooker in 2007.
Early Identification First described remains
In 1804, French naturalist Georges Cuvier wrote about a "remarkable" fossil mammal genus from the gypsum quarries of the outskirts of Paris (known as the Paris Basin), making comparisons of its fossils with those of Palaeotherium, which he had already described shortly before it. These fossils were known by Cuvier as early as 1800 but were not formally described yet. He described Anoplotherium as having tooth sizes similar to Palaeotherium that are otherwise different in form. He considered that the most important trait of the newer genus is the apparent lack of canines, leaving a large gap between the incisors and molars. The fossil specimen of the peculiar animal, Cuvier observed, contained nine teeth leading from the last three-pointed molar to the lateral incisors. To the zoologist, the distinct lack of canines was an unusual trait that few "pachyderms", namely rhinoceroses and hyraxes, had. The difference between the genus and certain "pachyderms," according to Cuvier, was that rhinos and hyraxes either had only four lower incisors total or lacked them while a hemimandible (half a mandible) specimen had three lower incisors. There was a lack of any upper jaw attributable to it, however, making its upper dental diagnoses unknown or only up to speculation at the time. Therefore, he erected the genus name Anoplotherium, basing the etymology on an apparent lack of "offensive" arms and canines by which characterized it. The genus name means "unarmed beast," for which the etymology is a compound of the Greek prefixes () meaning 'not', () meaning 'armor, large shield' and the suffix () meaning 'beast' or 'wild animal'.
Cuvier named three species of Anoplotherium in the same year, the first of which was the "sheep-sized" A. commune and the other three of which were "smaller species" that he named A. medium, A. minus, and A. minimum. The etymology of the species name A. commune refers to how "common" fossils of the species were while the etymologies of the other two species were based on sizes compared to A. commune. He also attributed a cloven hoof (or didactyl hoof) to A. commune since the specimen appeared to be large-sized. The naturalist had great difficulty in distinguishing between Palaeotherium fossils and Anoplotherium fossils especially since he rejected that idea that the head's proportions automatically indicated limb proportions. However, he figured that the head Palaeotherium''' was pig-sized and the similar to a tapir compared to that of Anoplotherium and that the tridactyl fossils belonged it. By contrast, Anoplotherium had all cloven hoof fossils attributed to it and was diagnosed in part by having incisors but no canines, which he thought makes it more similar to ruminants or camels. In 1805, Cuvier reinforced the idea of Anoplotherium having didactyl hooves, justifying that based on additional limb bone remains, it had two toes on its front legs and its hind legs.
Skeletal Discoveries In 1807, Cuvier conducted another series of analyses on Anoplotherium. In comparing the unguals (toes) of the limbs of A. commune, he noticed that the two unguals of the hind foot, are more pointed and elongated than those of the front foot, although he did not know if age correlates in any way with elongations or bluntness of the unguals. He determined that Anoplotherium in terms of extant relatives must have been closest to camelids based on the shapes of the unguals, but he also mentioned that the shortness of the front two pairs of unguals are similar in proportions to the bluntness of the hind unguals of pigs compared to those of their front legs. In addition to the two large toes, A. commune appeared to also have a third index toe of smaller size.
In the same year, he wrote about two incomplete skeletons found within communes nearby Paris. The first, found in the quarries of Montmartre in the commune of Pantin, had helped to confirm Cuvier's diagnoses of A. commune. The embedded skeleton, embedded in stone fragments was the size of a small horse and contained partial skull fragments (the parts connecting them to the body scattered, meaning that the workers did not collect them), scattered remains of a hind foot, a partial femur, ribs, a pelvis, and a large portion of the tail. The incomplete skeleton of A. commune confirmed the genus having large didactyl hind feet and 44 teeth in individuals total, 11 on each side of its jaw with an apparent lack of canine. There were also 11 complete ribs and a small fragment of a 12th rib, similar to camelids. Cuvier expressed his disappointment at how the neglect of the way the fossil was collected caused damage to it, frustrated that the vertebrae could not be fully examined as a result. The most surprising element of the skeleton to the naturalist was the enormous tail with at least twenty-two vertebrae, which he immediately recognized as having no modern analogue in any large quadrupedal mammal.
A second skeleton from Antony was described shortly after by Cuvier his preceding article of the first skeleton. The skeleton was removed more carefully by workers with supervision of experts but was still fragmentary and missing critical bone pieces needed for more thorough diagnoses. Still, he was able to count six lumbar vertebrae, the last four of which were long, wide, and slightly forward similar to those of ruminants and pigs. He also recalled three sacral vertebrae, all of which were extremely strong and were probably able to support large tails. Most notable to Cuvier was the confirmation that Anoplotherium had two large fingers and one small finger on its front legs.
Early depictions Cuvier's reconstruction
In 1812, Cuvier published his summary on his years of research on the two extinct genera that lived in modern-day France. Previously cautious about synthesizing information about the two taxa due to potential criticism, Cuvier had the good scientific reputation and information needed to publish his reconstructions of the fossil mammals based on synthesized information. Because of A. commune's robust build, short limbs, and enormous tail, he hypothesized that its body position, except for its legs, were similar to otters, that A. commune likely exhibited semi-aquatic swimming behaviors within marshy environments. According to Cuvier's theory, Anoplotherium was a herbivore that consumed aquatic plants and their roots, had sleek hair like otters or little to no hair like hippopotamuses, and did not have long ears that would have been counterproductive to its aquatic life. Therefore, Cuvier suggested that underwater quadrupeds like the hippo and water-adapted muroids are living analogues to it. In comparison, A. medium adopted a more terrestrial, cursorial lifestyle similar to gazelles or roe deer, grazing on plants or browsing on shrubs and traveling on marshes that A. commune lived in. It was thought to have short hair, a timid nature, and lack of rumination that modern ruminants have. A. minus was thought to be similar to A. medium but hare-sized. Of all species of Anoplotherium to be described and drawn, only A. commune remained accurate, the rest of the reconstructions being erroneous.
Crystal Palace Dinosaurs A. commune is particularly well-known for being represented as 3 "Tertiary Island" sculptures of the famous Crystal Palace Dinosaurs attraction in the Crystal Palace Park in the United Kingdom, being the last mammals that could be seen based on their positions being closest to the "Secondary Island." However, there are some confusions of the "species" of Anoplotherium that is represented, which is the result of the Crystal Palace guides of the 1850s-1860s listing both A. commune and "A. gracile" (= Xiphodon gracilis) as being present on the Tertiary Island. It was originally proposed by multiple sources in the 1990s that within the herd of Anoplotherium, the two standing statues represent A. commune while the third statue that is in a reposed position represents "A. gracile". In 2022, however, authors Mark Witton and Elinor Michel argued that there are no anatomical differences between the three A. commune statues, and A. commune was always known to have largely differentiated anatomically from "A. gracile." They instead pointed out that the Megaloceros "fawn" was in fact an "A. gracile" individual, the three other individuals being lost in time.
The three statues of A. commune, located along the banks of the Tidal Lake, are large ( long) and resemble hybrids of deer and big cats. The genus is considered perhaps the most obscure of all Crystal Palace Dinosaur genera to visitors of the modern day but are well-known to palaeontological or 1800s palaeoart specialists. Anoplotherium was once an iconic component of palaeontology, geology, and natural history, being incorporated regularly in both palaeontological texts and within classrooms (mineralogists and science professors of the National Museum of Natural History, France Claude-Henri Gorceix and Alfred Des Cloizeaux considered an Anoplotherium head to be amongst the few palaeontological items of "utmost importance"). Public interest in Anoplotherium decreased in the turn of the 20th century when more extraordinary prehistoric animals were described.