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. 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. sculptures on the Tertiary Island of the
Crystal Palace Park, United Kingdom 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. 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 and
Proterotherium).
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. 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. ,
astragalus, and partial
fibula of
A. commune 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. 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 , the French naturalist who described
Palaeotherium and
Anoplotherium in 1804
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). 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. 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. {{clade| style=font-size:85%; line-height:85% 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: == Description ==