Anoplotherium is the type genus of the extinct Palaeogene artiodactyl family Anoplotheriidae, which was endemic to Western Europe. It lived from the Late Eocene to the earliest Oligocene. It was the fifth fossil mammal genus to be described with official taxonomic authority, with a history extending back to 1804 when its fossils from Montmartre in Paris, France were first described by the French naturalist Georges Cuvier. Discoveries of incomplete skeletons of A. commune in 1807 led Cuvier to thoroughly describe unusual features for which there are no modern analogues. His drawn skeletal and muscle reconstructions of A. commune in 1812 were amongst the first instances of anatomical reconstructions based on fossil evidence. Cuvier's contributions to palaeontology based on his works on the genus were revolutionary for the field, not only proving the developing ideas of extinction and ecological succession but also paving the way for subfields such as palaeoneurology. Today, there are four known species.
Anoplotherium was amongst the largest non-whippomorph artiodactyls of the Palaeogene period, weighing on average to and measuring at least in head and body length and in shoulder height. It was an evolutionarily advanced and unusual artiodactyl, sporting three-toed feet in certain species like A. latipes, a long and robust tail, and a highly-developed brain with strong support for both sense of smell and sensory perception. Its overall robust build and elongate tail has been suggested to have allowed it to stand bipedally like a gerenuk to browse on plants at greater heights, reaching approximately tall, effectively competing with the few other medium to large herbivores it lived with. The full extent of its bipedalism needs to be confirmed by more research, however. The larger, two-toed A. commune and slightly smaller, three-toed A. latipes may be sexual dimorphs in that the former is female and the latter male, but this idea remains speculative. Its closest relative was Diplobune, which similarly is hypothesized to have had specialized behaviours.
The artiodactyl lived in western Europe back when it was an archipelago that was isolated from the rest of Eurasia, meaning that it lived in an environment with various other faunas that also evolved with strong levels of endemism. Its exact origins are unknown, but it arose long after a shift towards drier but still subhumid conditions that led to abrasive plants and the extinctions of the large-sized Lophiodontidae, achieving gigantism and establishing itself as a dominant herbivore throughout the entirety of the western European region given its abundant fossil evidence.
Anoplotherium was recorded up to the earliest Oligocene, which largely coincided with shifts towards further glaciation and seasonality as part of the Grande Coupure extinction and faunal turnover event in the earliest Oligocene of western Europe. Tropical and subtropical forests were rapidly replaced by more temperate environments, and most ocean barriers previously separating western Europe from eastern Eurasia closed, allowing for large faunal dispersals from Asia. Although the specific causes are uncertain, Anoplotherium was likely unable to adapt to these major changes for long and succumbed to extinction.
Taxonomy Research history
Identifications
While Georges Cuvier knew about fossil bones from the gypsum quarries of the outskirts of Paris (known as the Paris Basin) as early as at least 1800, it was not until 1804 that he would describe them. After describing Palaeotherium, he wrote about the next set of fossils that he was able to discern as being different from Palaeotherium based on dentition form, including the apparent lack of canines that left a large gap between the incisors and premolars. He observed that the hemimandible (half a mandible) had three lower incisors instead of four incisors or none which he said characterized other "pachyderms". Cuvier, basing the name on its apparent lack of suitable arms and canines for offensive attacks, erected the name Anoplotherium.
The genus name Anoplotherium means "unarmed beast" and is a compound of the Greek words (, 'not'), (, 'armor, large shield'), and (, 'beast, 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. He thought that Anoplotherium had didactyl hooves instead of tridactyl hooves, which would have separated it from Palaeotherium. Based on the hooves and dentition, he concluded that Anoplotherium was similar to ruminants or camelids. However, in 1807, Cuvier found out that Anoplotherium commune had three toes on its hind limbs, although the third index toes were of smaller sizes compared to the other two.
Skeletons
In 1807, Cuvier wrote about two incomplete skeletons that were recently uncovered, although the first was partially damaged because it was not collected carefully (which he expressed as having frustrated his understanding of the skeletal anatomy of Anoplotherium initially). The first skeleton, found in the quarries of Montmartre in the commune of Pantin, helped to confirm Cuvier's earlier diagnoses of Anoplotherium as correct. The embedded skeleton was the size of a small horse and helped to confirm the large didactyl feet and the 44 total teeth that it had (11 in each side of its jaw). It also had 11 complete ribs and a fragment of a 12th, matching with the number of ribs of camelids. The most surprising element to Cuvier, however, was the enormous tail with 22 vertebrae in the skeleton, a feature that he said he would not have known about previously, as there are no modern analogues of the elongated and thick tail in any large quadrupedal mammal.
The second incomplete skeleton came from Antony, this time more carefully removed with supervision from experts than the first skeleton. In it, he was able to confirm six lumbar vertebrae and three sacral vertebrae, all of which were extremely strong and probably supported the long tail. Most notable to Cuvier was the confirmation that Anoplotherium had two large fingers and one small finger on its front legs, which was unusual for mammals related to it.
Significance in palaeontological history
Although Palaeotherium and Anoplotherium are not well-recognized compared to fossil animals of other periods (i.e. Mesozoic dinosaurs and Neogene-Quaternary mammals), their fossil discoveries in Montmartre and formal descriptions by Cuvier are recognized as critical moments that pioneered palaeontology to the modern era. Unlike Pleistocene fossil genera in the Americas in early palaeontological history such as Megatherium and Mammut, Palaeotherium and Anoplotherium were not found in surface-level deposits but embedded in deeper, harder rock deposits dating to the Eocene. People in Paris had been previously familiar with animal skeletons being in their area for centuries, some of which were later kept and formally described. However, it was Cuvier who formally erected two fossil genera that came from older deposits, and from his homeland in the continent of Europe instead of the Americas where Megatherium and Mammut were found. The Palaeogene-aged fossils left no evidence of any later descendants, extinct or extant, although the similarities of Palaeotherium to tapirs made proving the theory more difficult. He noticed that below the gypsum was older sediments of seashells and reptiles like what Cuvier described as a giant "crocodile", which would later be known as Mosasaurus. Cuvier knew then that the world that Anoplotherium and Palaeotherium came from was a different span of time before that of the preceding time of sea reptiles and the proceeding times of Megatherium and Mammut, thereby proving the concept of natural extinction.
Cuvier's descriptions of an endocast (fossilized brain case) of a cerebral hemisphere belonging to a broken skull of A. commune from Montmartre, starting from 1804 up to 1822, are recognized as the first true instance of palaeoneurology, the study of brain evolution. The very first definition of an "endocast" dates back to 1822 when Cuvier described a mould of the brain of A. commune, noticing that it offered hints to the true shape of the brain of the now-extinct mammal (although it was later found to be a portion of the brain rather than the entirety of it). Since the first endocast study, many other brain studies were conducted for other fossil mammals throughout the second half of the 19th century onward. An 1822 description by Cuvier of a healed fractured femur of A. commune is cited as an early instance of palaeopathology, the study of ancient diseases and injuries on prehistoric organisms.
Early depictions
In 1812, Cuvier published his drawing of a skeletal reconstruction of A. commune based on known fossil remains of the species including the aforementioned incomplete skeletons. Based on the robust build of the mammal species, he hypothesized that its body structure was similar to otters except for its legs, that it was adapted for semi-aquatic life by swimming for consumption of aquatic plants, lacking long ears similar to semi-aquatic mammals, and living in marshy environments. Cuvier suggested that its lifestyle was therefore similar to semi-aquatic quadrupedal mammals like hippopotamuses and muroid rodents. He thought that in comparison, other species of Anoplotherium such as A. medium and A. minus were adapted for terrestrial behaviours and mixed feeding (browsing and grazing). Today, the reconstruction for the skeletal anatomy has aged well, mostly standing the test of time since 1812. Anoplotherium and Palaeotherium were also depicted in 1822 drawings by the French palaeontologist Charles Léopold Laurillard under the direction of Cuvier, although the restorations were not as detailed as Cuvier's.
The reconstruction of Anoplotherium as an aquatic swimmer was supported by multiple 19th century European palaeontologists and persisted for over a century until 1938 when M. Dor rejected the theory of the genus as being aquatic-adapted based on anatomical differences from otters and hippopotamuses that contradict semi-aquatic behaviours and are more consistent with terrestrial life. This rejection was supported by Jerry J. Hooker in 2007 and Svitozar Davydenko et al. in 2023 based on anatomical traits, although the former disagreed with Dor's observations on the tail. Hooker argued that although the distal caudal vertebrae of the anoplothere are less prominent than those of kangaroos (Macropus), the vertebrae patterns of Anoplotherium are more similar to Macropus than ungulates like Bos or Equus. Today, Anoplotherium is thought to be a terrestrial browser with specialized behaviours.
A. commune was notably depicted in the Crystal Palace Dinosaurs attraction in the Crystal Palace Park in the United Kingdom, open to the public since 1854 and constructed by English sculptor Benjamin Waterhouse Hawkins. More specifically, three statues of A. commune were made, two of which are standing and the third of which is in a reposed position. These statues resemble hybrids of deer and big cats and measure long. Its inclusion in the Crystal Palace Park reflects the popularity and public interest in Anoplotherium in the 19th century, as it was an icon of palaeontology, geology, and natural history that it was regularly incorporated in palaeontological texts and classrooms (its popularity diminished since the 20th century).