Anoplotherium Commune

''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 may have allowed it to stand bipedally 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.

Its success was abruptly halted by the Grande Coupure extinction and faunal turnover event in the earliest Oligocene of western Europe, which was caused by shifts towards further glaciation and seasonality. 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 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).

The sculptures of ''A. commune'' were overall based on Hawkins closely following Cuvier's description of the genus based on known remains, including Cuvier's unpublished robust muscle speculations which are seen as accurate by modern-day standards. Hawkins did also deviate outside of Cuvier's descriptions, however, likely basing its facial designs and the inaccurate presence of tetradactyl limbs (four toes on each foot) instead of didactyl or tridactyl limbs on extant camelids. Besides these errors, the statues have largely been accurate to modern-day depictions of ''Anoplotherium''.

Confusions with other mammal groups

For much of the 19th century, palaeontologists confused mammals of other families with ''Anoplotherium'' largely due to palaeontology being at its early stages. One of the earlier examples is 1822, when Cuvier erected the names ''A. gracile'', ''A. murinum'', ''A. obliquum'', ''A. leporinum'', and ''A. secundaria'', replacing earlier species names within ''Anoplotherium'' outside of ''A. commune''. In ''A. gracile'', he noticed differences in the molars that he erected the subgenus ''Xiphodon''. For ''A. leporinum'', ''A. murinum'', and ''A. obliquum'', the subgenus ''Dichobune'' was created by Cuvier based on its small size. In 1848, French palaeontologist Auguste Pomel promoted the 2 subgenera to genus ranks and erected an additional genus '' Amphimeryx'' for ''A. murinus'' and ''A. obliquus''. The revised taxonomies were followed by subsequent palaeontologists like another Paul Gervais. Therefore, the species are no longer classified as ''Anoplotherium'' but distant genera.

Other mammals initially confused with the genus ''Anoplotherium'' but eventually reclassified within the 19th century represented the endemic European artiodactyl family Cainotheriidae ('' Cainotherium''), European and Indian subcontinental members of the perissodactyl family Chalicotheriidae ('' Anisodon'' and ''Nestoritherium''), and even endemic South American members of the order Litopterna (''Scalabrinitherium'').

Revisions within the Anoplotheriidae

In 1851, Pomel observed that ''Anoplotherium'' species could be determined as having either didactyl hooves (lessened third index) or tridactyl hooves (greater-developed third index) and that the only previously erected species that are valid are ''A. commune'' and ''A. secundaria''. In addition, he erected three new species based on additional remains: ''A. duvmoyi'' (based on Cuvier's fossil illustrations of ''A. commune''), ''A. platypus'', ''A. laurillardi'' (convex incisors on the anterior surface), and ''A. cuvieri''. ''A. laurillardi'' derives as a species name from Charles Laurillard.

French palaeontologist Paul Gervais in 1852 named the genus ''Eurytherium'' based on its presence of tridactyl hooves instead of didactyl hooves, for he made the new species ''E. latipis'' the type species and ''A. platypus'' a synonym of the former. Henri Filhol would follow Gervais by erecting ''E. quercyi'' and ''E. minus'' based on dental sizes and reclassifying ''A. secundarium'' (or ''A. secundaria'') to ''Eurytherium''.

In 1862, Ludwig Rütimeyer erected the subgenus ''Diplobune'' for the genus ''Dichobune'' on the basis that it was an evolutionary transition between ''Anoplotherium secundarium'' and the dichobunid. It was promoted to a distinct genus with one species ''D. bavaricum'' being placed into the genus by Oscar Fraas by 1870, however.

In 1883, Max Schlosser made ''Eurytherium'' a synonym of ''Anoplotherium'' because he argued that the limb anatomies and dentitions were specific differences in characteristics rather than major ones that defined an entire genus. Sclosser pointed out that all species of ''Anoplotherium'' in some form had three indexes despite ''A. commune'' having less developed third indexes than ''A. latipes''. He also reinforced the idea that "''A. platypus''" is a synonym of ''A. latipes''. The name ''A. latipes'' takes priority over ''A. platypus'' to the modern day because Pomel in 1851 did not list any specimen for the species, effectively making it a nomen dubium. He also mentioned that the status of ''A. duvmoyi'' was not stable due to being based on illustrations, which he considered to be a "hopeless effort". He also supported ''Diplobune'' being a valid genus in that he argued that ''A. secundaria'' should be renamed to ''D. secundaria'' based on dentition and smaller sizes. Schlosser also said that ''A. cuvieri'' was an invalid species because the diagnosis based on isolated metatarsal bones was valid-enough.

Richard Lydekker erected the species ''A. cayluxense'' in 1885 based on its smaller size and unique variations in the molar cusps. He also demoted the genus ''Diplobune'' as a synonym of ''Anoplotherium'', meaning that the former's species were added/readded to ''Anoplotherium'' as ''A. secundarium'', ''A. quercyi'', ''A. modicum'', ''A. bavaricum'', and ''A. minus'' (= ''A. minor'', Filhol 1877). The synonymy of ''Diplobune'' with ''Anoplotherium'' was not supported by Hans Georg Stehlin in 1910, as he argued that the former was generically distinct from the latter despite their close relations, thus restoring the previous species into ''Diplobune'' (with the exception of ''D. modicum'', which he synonymized with ''D. bavarica'') and adding "''A. secundarium''" into ''Diplobune'' as ''D. secundaria''. He also wrote that ''A. cayluxense'' was a synonym of ''D. secundaria''. Stehlin also tentatively referred "''A.''" ''obliquum'' to the genus ''Haplomeryx'' as ''H? obliquum''. As a result of the revisions, the only valid species of ''Anoplotherium'' were ''A. commune'', ''A. latipes'', and ''A. laurillardi''.

In 1922, Wilhelm Otto Dietrich erected the fourth species ''A. pompeckji'' from the locality of Mähringen in Germany, named in honor of German palaeontologist Josef Felix Pompeckj. The species was described as a medium-sized tridactyl species with 4-fingered front limbs and 3-toed hind limbs with slimmer hand bone proportions and a smaller astragalus. ''A. pompeckji'' is the least characterized species and has similar dentition to ''A. laurillardi'', making its status less certain compared to the three other species.

In 1964, palaeontologist Louis de Bonis reviewed briefly the taxonomic synonyms of ''Anoplotherium'', considering that ''A. duvernoyi'' was based on a young individual with incisor characteristics that Pomel did not specify and that ''A. cuvieri'' does not differ in metacarpal dimensions from ''A. laurillardi''. He followed Stehlin in recognizing the three main species of ''Anoplotherium'', although he did not mention ''A. pompeckji'' in his review.

Classification

''Anoplotherium'' is the type genus of the Anoplotheriidae, a Palaeogene artiodactyl family endemic to western Europe that lived from the Middle Eocene to the Early Oligocene (~44 to 30 Ma, possible earliest record at ~48 Ma). The exact evolutionary origins and dispersals of the anoplotheriids are uncertain, but they exclusively resided within the continent when it was an archipelago that was isolated by seaway barriers from other regions such as Balkanatolia and the rest of eastern Eurasia. The Anoplotheriidae's relations with other members of the Artiodactyla are not well-resolved, with some determining it to be either a tylopod (which includes camelids and merycoidodonts of the Palaeogene) or a close relative to the infraorder and some others believing that it may have been closer to the Ruminantia (which includes tragulids and other close Palaeogene relatives).

The Anoplotheriidae consists of two subfamilies, the Dacrytheriinae and Anoplotheriinae, the latter of which is the younger subfamily that ''Anoplotherium'' belongs to. The Dacrytheriinae is the older subfamily of the two that first appeared in the Middle Eocene (since the Mammal Palaeozone Zones unit MP13, possibly up to MP10), although some authors consider them to be a separate family in the form of the Dacrytheriidae. Anoplotheriines made their first appearances by the Late Eocene (MP15-MP16), or ~41-40 Ma, within western Europe with ''Duerotherium'' and ''Robiatherium''. By MP17a-MP17b, however, there is a notable gap in the fossil record of anoplotheriines overall as the former two genera seemingly made their last appearances by the previous MP level MP16.

By MP18, ''Anoplotherium'' and ''Diplobune'' made their first appearances in western Europe, but their exact origins are unknown. The two genera were widespread throughout western Europe based on abundant fossil evidence spanning from Portugal, Spain, United Kingdom, France, Germany, and Switzerland for much of pre-Grande Coupure Europe (prior to MP21), meaning that they were typical elements of the Late Eocene up until the earliest Oligocene. The earlier anoplotheriines are considered to be smaller species whereas the later anoplotheriines were larger. ''Anoplotherium'' and ''Diplobune'' are considered the most derived (or evolutionarily recent) anoplotheriids based on dental morphology and achieved gigantism amongst non- whippomorph artiodactyls, making them some of the largest non-whippomorph artiodactyls of the Palaeogene as well as amongst the largest mammals to roam western Europe at the time (all species of ''Anoplotherium'' were large to very large whereas not all species of ''Diplobune'' were large).

Conducting studies focused on the phylogenetic relations within the Anoplotheriidae has proven difficult due to the general scarcity of fossil specimens of most genera. The phylogenetic relations of the Anoplotheriidae as well as the Xiphodontidae, Mixtotheriidae, and Cainotheriidae have also been elusive due to the selenodont morphologies of the molars, which were convergent with tylopods or ruminants. Some researchers considered the selenodont families Anoplotheriidae, Xiphodontidae, and Cainotheriidae to be within Tylopoda due to postcranial features that were similar to the tylopods from North America in the Palaeogene. Other researchers tie them as being more closely related to ruminants than tylopods based on dental morphology. Different phylogenetic analyses have produced different results for the "derived" selenodont Eocene European artiodactyl families, making it uncertain whether they were closer to the Tylopoda or Ruminantia.

In an article published in 2019, Romain Weppe et al. conducted a phylogenetic analysis on the Cainotherioidea within the Artiodactyla based on mandibular and dental characteristics, specifically in terms of relationships with artiodactyls of the Palaeogene. The results retrieved that the superfamily was closely related to the Mixtotheriidae and Anoplotheriidae. They determined that the Cainotheriidae, Robiacinidae, Anoplotheriidae, and Mixtotheriidae formed a clade that was the sister group to the Ruminantia while Tylopoda, along with the Amphimerycidae and Xiphodontidae split earlier in the tree. The phylogenetic tree used for the journal and another published work about the cainotherioids is outlined below:

In 2020, Vincent Luccisano et al. created a phylogenetic tree of the basal artiodactyls, a majority endemic to western Europe, from the Palaeogene. In one clade, the "bunoselenodont endemic European" Mixtotheriidae, Anoplotheriidae, Xiphodontidae, Amphimerycidae, Cainotheriidae, and Robiacinidae are grouped together with the Ruminantia. The phylogenetic tree as produced by the authors is shown below:

In 2022, Weppe created a phylogenetic analysis in his academic thesis regarding Palaeogene artiodactyl lineages, focusing most specifically on the endemic European families. The phylogenetic tree, according to Weppe, is the first to conduct phylogenetic affinities of all anoplotheriid genera, although not all individual species were included. He found that the Anoplotheriidae, Mixtotheriidae, and Cainotherioidea form a clade based on synapomorphic dental traits (traits thought to have originated from their most recent common ancestor). The result, Weppe mentioned, matches up with previous phylogenetic analyses on the Cainotherioidea with other endemic European Palaeogene artiodactyls that support the families as a clade. As a result, he argued that the proposed superfamily Anoplotherioidea, composing of the Anoplotheriidae and Xiphodontidae as proposed by Alan W. Gentry and Hooker in 1988, is invalid due to the polyphyly of the lineages in the phylogenetic analysis. However, the Xiphodontidae was still found to compose part of a wider clade with the three other groups. ''Anoplotherium'' and ''Diplobune'' compose a clade of the Anoplotheriidae because of their derived dental traits, supported by them being the latest-appearing anoplotheriids.

Description

Skull

The Anoplotheriidae is characterized in part by low-proportioned skulls with elongated muzzles (the muzzle aligns with the top of the cranium in the case of ''Anoplotherium''), and a wide-open skull orbit. ''Anoplotherium'' lacks bony processes and lacrimal fossae. It has large paroccipital processes and shorter postorbital process projections of the lacrimal bone.

The skull of ''Anoplotherium'' is narrow and elongated, with a constricted postorbital bone indicating poor brain development. It features robust sagittal and nuchal crests, the former having high elevations and emerging from low postorbital ridges and the latter having complicated elevation shifts. The back has a circular foramen magnum and large occipital condyles. The underside has an elongated palate with glenoid surfaces and strong post-glenoid processes of the squamosal bone.

The skull's bones are robust, with the spongy diploë bone being greatly developed. The skull's strength is attributed to massive temporal muscles as part of an overall strong body build. The skull has a shallow sella turcica, a pear-shaped cranial fossa, extensive parietal bones, large squamosal bone, narrow occipital bone, and two small occipital buns for muscle attachment. Many cranial traits seen in ''Anoplotherium'' are also found in the closely related ''Diplobune''.

In the auditory region (including the temporal bones), the periotic bone of the inner ear is extensive, the internal auditory meatus and facial canal openings of the temporal bone being visible in the lower triangular area of the periotic bone. The tympanic part of the temporal bone is connected partially to the squamosal bone, remains separate from the periotic bone, and consists of a small but thick auditory bulla (hollow bony structure of the auditory region), which projects underneath the petrous part of the temporal bone.

In a skull fragment of ''A. laurillardi'' with incisors and canine alveoli, the known length of the nasal region is large, measuring . The trait of large nasals is similar to what was observed in a skull of ''Diplobune secundaria'', which are recorded to be massive, elongated, and connected to each other and the maxilla. Cyril Gagnaison and Jean-Jacques Leroux proposed in the case of ''D. secundaria'' that the elongated nasal region supports the presence of a very tapered tongue, which similar to giraffes may have allowed it to pull plant branches.

Endocast anatomy

In 1913, R.W. Palmer conducted studies on the brain cast from a cranium of ''Anoplotherium commune'', originating from the Phosphorites of Quercy within the British Museum collections (the endocast is now in the National Museum of Natural History, France as the specimen BMNH 3753). The individual in question was estimated to have weighed by its death similar to extant llamas, weighing considerably less than typical estimates of adult ''Anoplotherium''. The total length of the brain is under , its volume measuring approximately .

The form of the brain is naturally narrow and elongated. The cerebellum and cerebrum are both at high positions compared to modern ungulates that have brain hemispheres located above the cerebellum. Palmer noticed that the brain was similar to the modern aardvark (''Orycteropus afer''). The highly-developed cerebrum that enables a strong sense of smell from ''Anoplotherium'' makes it macrosmatic (derived in sense of smell), as also indicated by the enlarged olfactory bulbs and the small size of the neocortex. In both ''Anoplotherium'' and ''Diplobune'', the rhinal fissure divides the brain hemisphere horizontally and equally in half. The cerebellar vermis of the cerebellum is divided almost equally by the primary fissure of cerebellum (or "fissura prima").

Additionally, the olfactory bulbs are thick, and the olfactory tubercles take the form of smooth circular elevations that are curved more backwards than the aardvark and are easily noticeable. In another endocast for ''Anoplotherium'', the olfactory bulbs compose 7.5% of the total volume of the brain, above average for both extinct and extant artiodactyls.

The neocortex area of the brain, responsible for sensory perception and other sensory brain functions, covers 28% of the medium-sized ''A. commune'' endocast's surface area. Another endocast, which belongs to ''Anoplotherium'' sp., measures ² in the cerebrum surface, ² in neopallium surface, and ³ in endocranial volume. The former two data when calculated together (neopallium surface/cerebrum surface) compose 61.6% in the total neocortical surface area of the brain, meaning that adult ''Anoplotherium'' has massive brain and neocortical surface area measurements compared to most Palaeogene artiodactyls, the latter measurement being on par with or less than those of modern artiodactyls.

''Anoplotherium'' and other anoplotheriids share traits of generally elongated and parallel sulci (shallow furrows) in the cerebral cortex, as well as a vertical (cordial) sulcus corresponding to the lateral (side) sulcus. The fissures (deep furrows) on the surface of the central area of the brain show clear formations of a complex lateral sulcus (also known as the Sylvian fissure) in a process known as operculization. The operculization of the brain of anoplotheriids is similar to the Anthracotheriidae but does not indicate any close phylogenetic relation, which means that the similarities are an instance of parallel evolution. The measurements of the endocasts of ''Anoplotherium'' are larger than those of other Palaeogene artiodactyls in a 2015 study by Ghislain Thiery and Stéphane Ducrocq.

Dentition

Unlike most mammal fossil genera, ''Anoplotherium'' is diagnosed mainly based on postcranial morphology than dental morphology, but it does have diagnoses based on the latter. The dental formula of ''Anoplotherium'' and other anoplotheriids is for a total of 44 teeth, consistent with the primitive dental formula for early-middle Palaeogene placental mammals. Anoplotheriids have selenodont (crescent-shaped ridge form) or bunoselenodont (bunodont and selenodont) premolars (P/p) and molars (M/m) made for leaf-browsing diets. The canines (C/c) of the Anoplotheriidae are overall undifferentiated from the incisors (I/i). The lower premolars of the family are piercing and elongated. The upper molars are bunoselenodont in form while the lower molars have selenodont labial cuspids and bunodont (or rounded) lingual cuspids. The subfamily Anoplotheriinae differs from the Dacrytheriinae by the molariform premolars with crescent-shaped paraconules and the lower molars that lack a third cusp between the metaconid and entoconid.

The upper molars of ''Anoplotherium'' are characterized by trapezoidal outlines in occlusal views (or top views of the tooth enamel), W-shaped ectolophs (crests or ridges of upper molar teeth), and specific differences in cusps. More specifically, the upper molars of the genus contain near-central and conical protocone cusps closely aligned with the mesostyle cusps, conical paraconules that are connected to the parastyle by posterior crests, and compressed parastyles and mesostyles. The lower molars of the anoplotheriid contains the paraconid and metaconid cusps which have pronounced separations by a valley between them.

Vertebrae and ribs

''Anoplotherium'' has 7 total cervical vertebrae for a series of C1-C7, typical of most mammals. The atlas (C1) is similar to those of camelids such as ''Lama'' in form as well as the position of the "alar foramina" in association with facet joint connections involving the axis (C2). An axis that was attributed to ''A. commune'' (but also possibly belonging to its close relative ''Diplobune secundaria'') is elongated in length and has a diminished spinous process. The vertebrae C3-C7 are analogous to ''Cainotherium''. The C4 vertebra appears slanted, which hints towards the neck changing in orientation from vertebra C3 to C4 as a potential bending in the front area of the neck, similar to modern bears. As a result of the neck vertebrae morphology, ''Anoplotherium'' likely had a sloped, upward position of the neck.

''Anoplotherium'' also had 12 thoracic vertebrae, 6 lumbar vertebrae, and 3 sacral vertebrae. The lumbar vertebrae, especially L4-L6, contain transverse processes that are wide, long, and point slightly towards a forward direction. The 3 sacral vertebrae are robust and contain apophyses for strong attachments to the long tail. The vertebrae of the anoplotheriid genus are built for typical ungulate movement.

The most unusual postcranial aspect of ''Anoplotherium'' compared to other artiodactyls is the long and thick tail, which is made up of 22 caudal vertebrae for strong muscle support. The frontal vertebrae had well-pronounced process, and all vertebrae except for the farthest distal ones have haemal arches on them.

Like the chalicothere ''Chalicotherium'' and unlike other mammals like caprines of the genus ''Ovis'' and ''Cainotherium'', the ribs curve in wider areas and their tubercles do not project as much in the dorsal direction. The ribs of ''Anoplotherium'' form a barrel-shaped trunk, meaning that the rib cage is much wider than those of modern ruminants. The ribs generally project sideways due to the very curved positions of them, the position of the tubercle, and the thoracic vertebrae projecting on the upper sides.

Limbs

''Anoplotherium'' has short limbs and is thought to have been unguligrade in limb positions, with most species having three toes on both their front and hind limbs. ''A. commune'' is differentiated from the similar ''A. latipes'' by its didactyl ("two-toed") as opposed to tridactyl ("three-toed") digits.

Front limbs

The scapula (or shoulder blade) has a convex coracoid border and is similar to that of ''Diplobune''. Similar to camels (''Camelus''), the supraspinous fossa is broader than the infraspinous fossa, but camels have narrower scapulae, especially in distal (back) ends of the supraspinous fossa. The scapular spine is robust, thick, and gradually rises in height distally up until it reaches the edge of the glenoid cavities like camels but unlike most other modern artiodactyls. The coracoid process (normally resembling a small hooklike structure) is reduced to a blunt knob that only slightly projects. The wide supraspinous fossa and broadly curved coracoid edge of the scapulae of ''Anoplotherium'' are unlike ''Cainotherium'' and '' Merycoidodon'' because ''Anoplotherium'' shares neither any triangular shape of the shoulder blades nor narrow supraspinous fossae.

The elbow morphology of ''Anoplotherium'', based on the structures and articulations of elbow bones like the humerus, radius, and ulna, shows evidence of adaptations to moving the elbow up and down in supination-pronation rotations by 13° maximum. A fully extended elbow could make an angle between the ulna and humerus that measures approximately 135°, indicating high flexibility compared to other artiodactyls, including the already semi-flexible elbows of ''Cainotherium''.

Similar in wrist morphology to pigs of the genus '' Sus'', the hooves of ''Anoplotherium'' spread out by ~16° when downward, supported by footprint morphology. The wrist may have been able to rotate up and down but only to a limited degree and nowhere near the flexible wrist morphologies of primates, suggesting that the adaptation was not a main feature of the artiodactyl genus but the result of regaining a primitive trait.

The carpus consists of the scaphoid, lunate, triquetrum, and pisiform in its first row and the trapezium, trapezoid, capitate, and hamate in its second. ''Anoplotherium'' has four digit bones, but those of digit V and, in the case of ''A. commune'', digit II are poorly developed. The second finger (digit II) of ''Anoplotherium'' has no capability of rotation or flexible movements, which signifies that it does not play any thumb-like role like in primates or the giant panda.

Hind limbs

The ilium, part of the hip bone of the greater pelvis bone, is broad and has a firmly rounded iliac crest that meets with the concave underside edge at a sharp angle. The ilium of ''Anoplotherium'' can be differentiated from ''Palaeotherium'' by the shorter iliac body, the longer ischium (the lower and back area of the hip bone), and a straighter back edge of pelvis that results in a longer pubic symphysis. The acetabular fossa region of the acetabulum surface of the pelvis is large, its acetabular notch being in a posterior (or back) position similar to that in ''Chalicotherium''.

The femur is larger than the tibia, has only two trochanters similar to other basal artiodactyls, has a narrow gap between its femoral head and greater trochanter, and has a long femoral neck. The trochanteric fossa, a hollow at the surface of the greater trochanter, is wide in depth and narrow in shape, deepening by the sides. The tibia is robust, strongly supporting muscle attachments based on its crests and processes. The distal end of the fibula plus the medial malleolus prominence of the tibia enclose the center area of the astragalus in order to prevent it from moving sideways.

Anoplotheriids with known postcranial fossils have proportionally wide, stocky, and oblique astragali (or talus or ankle bone), differing widely from other artiodactyls. ''A. latipes'' differs from ''A. commune'' in part by morphologies of the facets plus fossae of the astragalus and a shorter and more robust calcaneum (heel bone). The astragali of anoplotheres share levels of elevations and positions of specific facets with the merycoidodonts that no modern artiodactyls share, possibly an instance of convergent evolution. The medial (sustentacular) facet of ''Anoplotherium'' and ''Diplobune'' is concave, contrasting with the flat to slightly convex facet of ''Dacrytherium''.

The tarsus consists of the navicular, three cueniform bones, and a cuboid bone. The foot of ''A. commune'' consisted of two toes, as indicated by the relatively small outermost and middle cuneiform bones.

Footprints

Large-sized footprints from southern France and north Spain that date to the Late Eocene may have been from ''Anoplotherium''. The ichnogenus is named '' Anoplotheriipus'' and was first described from the department of Gard

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