Pseudamphimeryx Temporal range: Middle Eocene to Late Eocene | |
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Pseudamphimeryx renevieri mandible, Natural History Museum of Basel | |
Scientific classification | |
Domain: | Eukaryota |
Kingdom: | Animalia |
Phylum: | Chordata |
Class: | Mammalia |
Order: | Artiodactyla |
Family: | † Amphimerycidae |
Genus: | † Pseudamphimeryx Stehlin, 1910 |
Type species | |
†Pseudamphimeryx renevieri | |
Other species | |
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Pseudamphimeryx is an extinct genus of Palaeogene artiodactyls belonging to the Amphimerycidae that was endemic to the central region of western Europe and lived from the Middle to Late Eocene. It was first erected in 1910 by the Swiss palaeontologist Hans Georg Stehlin, who assigned to it multiple species and noted specific differences from another amphimerycid Amphimeryx . As of present, it is known by six species, although the validity of P. valdensis has been questioned while the earliest-appearing species P. schosseri has been suggested to not be an amphimerycid.
Pseudamphimeryx is very similar to Amphimeryx with its selenodont (crescent-like ridges) dentition and its fused "cubonavicular bone" (cuboid bone and navicular bone) of its hind legs, both of which are recorded in ruminants in an instance of parallel evolution. Both amphimerycid genera had large orbits and long snouts. Pseudamphimeryx has very specific differences with Amphimeryx such as the occipital crest forms. Its selenodont dentition suggests that it had a preference for leaf-eating diets. Pseudamphimeryx was a tiny-sized artiodactyl that likely weighed less than 1 kg (2.2 lb).
It inhabited western Europe back when it was an archipelago that was isolated from the rest of Eurasia, meaning that it lived in a tropical-subtropical environment with various other faunas that also evolved with strong levels of endemism. This meant that it coexisted with a wide variety of other artiodactyls and perissodactyls. Although it survived a major faunal turnover by the Middle Eocene, it was eventually replaced by Amphimeryx in the Late Eocene.
In 1910, the Swiss palaeontologist Hans Georg Stehlin erected the genus Pseudamphimeryx, introducing it as an artiodactyl that differed from Amphimeryx only by specific cranial and dental traits. He first recognized the species Pseudamphimeryx Renevieri, which was previously classified to Cainotherium then Xiphodontherium (the latter synonymized with Amphimeryx); it was first named by the naturalists François Jules Pictet de la Rive and Aloïs Humbert in 1869. The second species that he classified to Pseudamphimeryx was P. Schlosseri, first named as a species of Dichobune by Ludwig Ruetimeyer in 1891. Stehlin then named the species P. valdensis based on lower fossil molars from the Swiss locality of Mormont, stating that it was smaller than P. renevieri in size. He also recognized two additional taxa from the Phosphorites du Quercy site: P. Renevieri var. Pavlowiae and P. decedens. [a] [1] [2] [3]
In 1928, English palaeontologist Clive Forster-Cooper erected P. hantonensis based on two upper molars from Hordle in England. [4] In 1978, French palaeontologist Jean Sudre recognized P. pavloviae as a distinct species and erected another named P. salesmei based on a mandible from the French locality of Salesmes. [5] [6]
In 1974, the French palaeontologist Colette Dechaseaux noted that P. decedens had notably large orbits along with preorbital fossae in front of them like in deer; these morphologies previously gave palaeontologists ideas of the appearance of the skull of Pseudamphimeryx. She cast doubt that the species actually belonged to Pseudamphimeryx because of the molar forms. Similarly in 1978, Sudre expressed that P. decedens actually belonged to Pseudamphimeryx, stating that the short premolars, large orbits, and preorbital fossae are not present in any other skull of other amphimerycid species. In 1984, Sudre tentatively reassigned P. decedens to the tragulid genus Cryptomeryx as C? decedens, building on to Dechaseaux's study by confirming that the now-lost skull would have belonged to a small ruminant. [7] [5] [8] In 1986, however, Geneviève Bouvrain, Denis Geraads and Jean Sudre revised Cryptomeryx as a synonym of Lophiomeryx , [9] but it was alternatively considered a synonym of Iberomeryx by Bastien Mennecart et al. in 2010. C? decedens had tentatively been placed in Iberomeryx in a 2012 PhD thesis by Mennecart. [b] [10] [11]
In 2000, the palaeontologists Jerry J. Hooker and Marc Weidmann suggested that P. pavloviae be emended back to P. pavlowiae based on Stehlin's original spelling and argued that P. valdensis was both a nomen dubium and potentially a junior synonym of P. renevieri. [6] In 2007, palaeontologists Jörg Erfurt and Grégoire Métais listed P. valdensis as a valid species without referencing Hooker and Weidmann's invalidation of the species. [12]
Pseudamphimeryx belongs to the Amphimerycidae, a Palaeogene artiodactyl family endemic to western Europe that lived from the middle to the earliest Oligocene (~44 to 33 Ma). Like the other contemporary endemic artiodactyl families of western Europe, the evolutionary origins of the Amphimerycidae are poorly known. [12] The family is generally thought to have made its first appearance by the unit MP14 of the Mammal Palaeogene zones, making them the first selenodont dentition artiodactyl representatives to have appeared in the landmass along with the Xiphodontidae. [13] The first representative of the Amphimerycidae to have appeared was Pseudamphimeryx, lasting from MP14 to MP17. Amphimeryx made its first appearance in MP18 as the only other known amphimerycid genus and lasted up to MP21, after the Grande Coupure faunal turnover event. [12]
Because of its similar anatomical traits with ruminants, some palaeontologists had originally included it within the suborder Ruminantia while some others rejected the placement. Today, its similarities with ruminants is thought to have been an instance of parallel evolution, in which amphimerycids and ruminants independently gained similar traits. [12] [14] While amphimerycids have typically been excluded from the Ruminantia due to dental characteristics, it does not eliminate the possibility of them being sister taxa to ruminants by the latter independently gaining longer legs and more selenodont (crescent-shaped) dentition. [15] Its affinities, along with those of other endemic European artiodactyls, are unclear; the Amphimerycidae, Anoplotheriidae, Xiphodontidae, Mixtotheriidae, and Cainotheriidae have been determined to be closer to either tylopods (i.e. camelids and merycoidodonts) or ruminants. 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. [14] [16] [17]
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. [17] The phylogenetic tree used for the journal and another published work about the cainotherioids is outlined below: [18]
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: [16]
In 2022, Weppe conducted a phylogenetic analysis in his academic thesis regarding Palaeogene artiodactyl lineages, focusing most specifically on the endemic European families. One large monophyletic set consisted of the Hyperdichobuninae, Amphimerycidae, Xiphodontidae, and Cainotherioidea based on dental synapomorphies, of which the hyperdichobunines are paraphyletic in relation to the other clades. In terms of the amphimerycids, while the clade consisting of P. renevieri and A. murinus was recovered as a sister group to the other endemic artiodactyl clades, the placement of P. schlosseri has rendered the Amphimerycidae paraphyletic in relation to the derived amphimerycid species and other families. He argued that the Amphimerycidae thus needs a systemic revision for which P. schlosseri would be assigned to a new genus and removed from the Amphimerycidae. [14]
The Amphimerycidae is defined in part as having an elongated snout and large orbits that are widened in their backs. [12] Pseudmphimeryx specifically is described as having a skull whose peak appears initially concave at the occipital crest's front, ascends slightly, and then finally slopes down. The skull is also diagnosed as having strong body orifices in its basicranium and projecting occipital crests. [5] Pseudamphimeryx and Amphimeryx, both known by multiple skull specimens, have very similar forms but differ based on a few characteristics. [7] Amphimeryx is also distinguished from Pseudamphimeryx by the more well-developed occipital crest. Its skull additionally resembles those of both Dacrytherium and Tapirulus . [19]
The overall skull of Pseudamphimeryx is very elongated especially in comparison to Mouillacitherium but falls short of that of Amphimeryx. The parietal bone and squamosal bone both make up a prominent portion of the cranial cavity's wall. Both amphimerycid genera have especially prominent occipital and sagittal crests, the latter of which divides into two less prominent branches behind the fronto-parietal suture that extend up to the supraorbital foramen. This is unlike Mouillacitherium where the crest's extension only goes up to the foramen's back. [7] The glenoid surface of Pseudamphimeryx is positioned slightly above the overall base of the skull and has a slightly convex form as opposed to a flat one like in primitive ruminants. The glenoid region of the skull also has a deep concavity above it like in ruminants but unlike in anoplotheriids. The zygomatic arch, or cheek bone, is thin. [19] The orientation of the occipital crest differs by amphimerycid genus, with that of Pseudamphimeryx being straight and vertical. Amphimerycids have primitive "mastoid" forms (in which the periotic bone of the ear is exposed to the skull's surface) akin to those of the dichobunids Dichobune and Mouillacitherium. [7]
The frontal bones of both amphimerycid genera are large plus flat, being particularly sizeable in their supraorbital portions; this trait is more pronounced in Amphimeryx. That of Amphimeryx is close to the orbits' upper edges and is more prominent in position between the two orbits than that of Pseudamphimeryx. The supraorbital foramen of Amphimeryx is wider than it is long and is proportionally larger than that of Pseudamphimeryx. It is also more perpendicular to the sagittal plane in its back edge, which is not oriented backwards like in Pseudamphimeryx. The lacrimal bone of both amphimerycids, but especially in Amphimeryx, has an extensive pars facialis and is quadrangular in shape, narrowing at its front. The orbit is large, is positioned back in relation to the overall skull, is wide at its back area, and is more curved at its upper compared to lower edge. There is no difference between both amphimerycids in terms of the orbits, suggesting based on their morphologies that the snouts of both genera are elongated. The optic foramen, located in the sphenoid bone, extends more forward in Amphimeryx than in Pseudamphimeryx. While the nasal bone is not as well-preserved in Amphimeryx fossils, the frontonasal suture is implied to have formed a W shape on the skull's upper surface like that of Pseudamphimeryx. Both amphimerycid genera also have similar, although not identical, medial positions of the infraorbital foramen in the maxilla. The palatine bones of Amphimeryx and Pseudamphimeryx are narrower at their front than back ends. [7]
The mandible of Pseudamphimeryx is undulated at the lower edge of its horizontal branch, or the mandibular corpus, and, like in Amphimeryx, has a large and slightly rounded angular border. The coronoid process of the mandible is positioned lower in relation to the overall skull unlike in ruminants, and the temporomandibular joint is also lower than in Amphimeryx. [7] [12]
Pseudamphimeryx is also known from a brain endocast, although the endocasts of it and Amphimeryx were not as closely described in detail. Its neocortex was described by Dechaseaux as being of a primitive and simple type in the larger evolutionary scale of artiodactyls. [7] [20]
The dental formula of the Amphimerycidae is 3.1.4.33.1.4.3 for a total of 44 teeth, consistent with the primitive dental formula for early-middle Palaeogene placental mammals. [5] [21] The canines (C/c) are incisiform (incisor (I/i) form) and therefore differ little with the incisors themselves. The premolars (P/p) are elongated and may generally be separated by diastemata (gaps between teeth). The lower premolars have three lobes, or developed areas on their crowns. The upper molars (M/m) are more developed in form and are generally subtriangular in shape, although some may be more rectangular. They have five crescent-shaped (selenodont) tubercles and sometimes a partial hypocone cusp that may be present in all species. [5] [12] Amphimerycids differ from ruminants, particularly the basal clade Tragulina, in the retentions of their first premolars and their high levels of specialization in their selenodonty and number of cusps in their molars. [22] Their dentitions more closely resemble those of xiphodonts or dacrytheriines than of ruminants. [12]
Pseudamphimeryx specifically is diagnosed in part as having moderate diastemata between P1 and P2. P1 is similarly separated from P2 by a diastema but is closer to the lower canine. Its upper molars have five tubercles along with a single front cingulum each. In the lower molars, the labial cuspids are crescent-shaped whereas the lingual cuspids are subconical. The peak of the crescent formed by the metaconid and entoconid cusps is rounder in the molars of Pseudamphimeryx than in those of Amphimeryx, a diagnostic trait separating the two genera. [5] [12]
In terms of non-diagnostic features of the amphimerycids, both genera have incisors that are shovel-shaped, have sharp edges on their crowns, and have horizontal positions in relation to the dental row. The canines are similar to incisors but differ by their somewhat asymmetrical shapes. [1] P1 and P2 have both been described as narrow and elongated, but the former tooth is larger than the latter. [7] The overall selenodonty and brachyodonty (low-crowned teeth) of amphimerycids suggest that they were adapted towards folivorous (leaf-eating) dietary habits. [23]
According to Sudre and Cécile Blondel in 1995 and Erfurt and Métais in 2007, there are three reports of postcranial fossils classified to Pseudamphimeryx: a "cubonavicular" bone (fused cuboid bone and navicular bone of the hind legs) of P. pavloviae from La Bouffie plus P. salesmei from Salesmes and an astragalus of P. renevieri from the French commune of Euzet. The latter fossil is suggested to prove the presence of a fused cubonavicular bone in P. renevieri. The fused cubonavicular bone trait has also been reported in Amphimeryx, which appeared after Pseudamphimeryx and is known from postcranial fossils from multiple localities, and is also generally a defining trait of ruminants in an instance of parallel evolution. [12] [24]
The later relative Amphimeryx, unlike Pseudamphimeryx, is known by complete hind leg evidence including the cubonavicular bone. The overall morphology of the hind leg's bones are reminiscent of those of derived (including extant) ruminants. More specifically, Amphimeryx was functionally didactyl (two-toed) because, as in derived ruminants, its two middle toes, making up a single cannon bone, are elongated while its two side digits are greatly reduced. On the other hand, Amphimeryx differs from ruminants by the primitive morphology of the astragalus. [25] [5]
The Amphimerycidae consists only of small-sized species within Amphimeryx and Pseudamphimeryx. [12] According to Blondel, amphimerycid species would have ranged from 0.4 kg (0.88 lb) to 1.5 kg (3.3 lb) total. [23] Similarly, Hooker et al. stated that Pseudamphimeryx was a tiny artiodactyl genus that weighed less than 1 kg (2.2 lb) total. [26] In comparison, Amphimeryx, while still small-sized compared to most other Palaeogene artiodactyls, was larger with estimated weights of 1.846 kg (4.07 lb) based on its M1 and 1.511 kg (3.33 lb) based on the astragalus. [25]
Some species of Pseudamphimeryx had been differentiated based on size in addition to morphology, with Sudre differing P. pavloviae from P. renevieri (both of which coexisted with each other) by the former being larger in size and having more elongated premolars. Hooker and Weidmann suggested that Sudre's measures for proportional sizes between the two species could be potentially challenged by the variations in dental morphology and gaps in quantitative analyses. Therefore, they argued that additional statistical analyses need to be conducted that identify and separate different molar types (first to third molars) to better represent species size differences. [5] [6]
For much of the Eocene, a hothouse climate climate with humid, tropical environments with consistently high precipitations prevailed. Modern mammalian orders including the Perissodactyla, Artiodactyla, and Primates (or the suborder Euprimates) appeared already by the early Eocene, diversifying rapidly and developing dentitions specialized for folivory. The omnivorous forms mostly either switched to folivorous diets or went extinct by the middle Eocene (47–37 Ma) along with the archaic "condylarths". By the late Eocene (approx. 37–33 mya), most of the ungulate form dentitions shifted from bunodont (or rounded) cusps to cutting ridges (i.e. lophs) for folivorous diets. [27] [28]
Land connections between western Europe and North America were interrupted around 53 Ma. From the early Eocene up until the Grande Coupure extinction event (56–33.9 mya), western Eurasia was separated into three landmasses: western Europe (an archipelago), Balkanatolia (in-between the Paratethys Sea of the north and the Neotethys Ocean of the south), and eastern Eurasia. [29] The Holarctic mammalian faunas of western Europe were therefore mostly isolated from other landmasses including Greenland, Africa, and eastern Eurasia, allowing for endemism to develop. [28] Therefore, the European mammals of the late Eocene (MP17–MP20 of the Mammal Palaeogene zones) were mostly descendants of endemic middle Eocene groups. [30]
The Amphimerycidae, and by extent the first genus Pseudamphimeryx, is first recorded by the appearance of P. schlosseri in the Swiss locality of Egerkingen α + β, dating back to MP14. [13] [31] [32] Both families would have coexisted with perissodactyls (Palaeotheriidae, Lophiodontidae, and Hyrachyidae), non-endemic artiodactyls (Dichobunidae and Tapirulidae), endemic European artiodactyls (Choeropotamidae, Cebochoeridae, and Anoplotheriidae), and primates (Adapidae). [23] [13] [33] The stratigraphic ranges of the early species of Amphimeryx also overlapped with metatherians (Herpetotheriidae), cimolestans (Pantolestidae, Paroxyclaenidae), rodents (Ischyromyidae, Theridomyoidea, Gliridae), eulipotyphlans, bats, apatotherians, carnivoraformes (Miacidae), and hyaenodonts (Hyainailourinae, Proviverrinae). [31] Other MP13-MP14 sites have also yielded fossils of turtles and crocodylomorphs, [34] and MP13 sites are stratigraphically the latest to have yielded remains of the bird clades Gastornithidae and Palaeognathae. [35]
In addition to P. schlosseri, other mammals that appeared in Egerkingen α + β include the herpetotheriid Amphiperatherium , ischyromyids Ailuravus and Plesiarctomys , pseudosciurid Treposciurus , omomyid Necrolemur , adapid Leptadapis , proviverrine Proviverra , palaeotheres ( Propalaeotherium , Anchilophus , Lophiotherium , Plagiolophus , Palaeotherium ), hyrachyid Chasmotherium , lophiodont Lophiodon , dichobunids Hyperdichobune and Mouillacitherium, choeropotamid Rhagatherium , anoplotheriid Catodontherium , cebochoerid Cebochoerus , tapirulid Tapirulus, mixtotheriid Mixtotherium , and the xiphodonts Dichodon and Haplomeryx . [31]
The unit MP16 records the appearances of P. renevieri and P. pavloviae, both of which are recorded from the MP16 French locality of Robiac. Other mammal genera that cooccur in the site include the herpetotheriids Amphiperatherium and Peratherium , apatemyid Heterohyus , nyctitheriid Saturninia , rodents ( Glamys , Elfomys , Plesiarctomys , Ailuravus , Remys ), omomyids Pseudoloris and Necrolemur, adapid Adapis , hyaenodonts Paroxyaena and Cynohyaenodon , carnivoraformes Paramiacis and Quercygale , palaeotheres ( Propalaeotherium , Anchilophus , Plagiolophus , Pachynolophus , Palaeotherium ), lophiodont Lophiodon , hyrachyid Chasmotherium , cebochoerids Acotherulum and Cebochoerus, choeropotamid Choeropotamus , tapirulid Tapirulus, anoplotheriids (Dacrytherium, Catodontherium , Robiatherium ), robicinid Robiacina , and xiphodonts ( Xiphodon , Dichodon, Haplomeryx). [31]
After MP16, a faunal turnover occurred, marking the disappearances of the lophiodonts and European hyrachyids as well as the extinctions of all European crocodylomorphs except for the alligatoroid Diplocynodon . [13] [34] [36] [37] The causes of the faunal turnover have been attributed to a shift from humid and highly tropical environments to drier and more temperate forests with open areas and more abrasive vegetation. The surviving herbivorous faunas shifted their dentitions and dietary strategies accordingly to adapt to abrasive and seasonal vegetation. [38] [39] However, the environments were still subhumid and covered by subtropical evergreen forests. The Palaeotheriidae was the sole remaining European perissodactyl group, and frugivorous-folivorous or purely folivorous artiodactyls became the dominant group in western Europe. [40] [23]
The late Eocene unit MP17 records as many as four total species of Pseudamphimeryx: P. renevieri, P. havloviae, P. salesmei, and P. hantonensis. [32] [41] MP17a confirms the continued occurrence of P. renevieri in the French locality of Fons 4; MP17b is the latest unit that Pseudamphimeryx occurs and records both P. renevieri and P. pavloviae from another French locality of Perrière. Starting at MP18, Amphimeryx makes its first appearance and therefore succeeds Pseudamphimeryx. [31] [32] In Perrière, Pseudamphimeryx fossils have been found along with those of the herpetotheriids Peratherium and Amphiperatherium, pseudorhyncocyonid Pseudorhyncocyon , apatemyid Heterohyus, nyctitheriid Saturninia, various rodents and bats, omomyids Pseudoloris and Microchoerus , adapid Leptadapis , hyaenodontid Hyenodon , miacid Quercygale, palaeotheres ( Lophiotherium , Palaeotherium, and Plagiolophus), dichobunid Mouillacitherium, cebochoerid Acotherulum, mixtothere Mixtotherium, anoplotheriid Dacrytherium, tapirulid Tapirulus, and the xiphodonts Dichodon and Haplomeryx. [31]
Artiodactyls are placental mammals belonging to the order Artiodactyla. Typically, they are ungulates which bear weight equally on two of their five toes. The other three toes are either present, absent, vestigial, or pointing posteriorly. By contrast, most perissodactyls bear weight on an odd number of the five toes. Another difference between the two orders is that many artiodactyls digest plant cellulose in one or more stomach chambers rather than in their intestine. Molecular biology, along with new fossil discoveries, has found that cetaceans fall within this taxonomic branch, being most closely related to hippopotamuses. Some modern taxonomists thus apply the name Cetartiodactyla to this group, while others opt to include cetaceans within the existing name of Artiodactyla. Some researchers use "even-toed ungulates" to exclude cetaceans and only include terrestrial artiodactyls, making the term paraphyletic in nature.
Entelodontidae is an extinct family of pig-like artiodactyls which inhabited the Northern Hemisphere from the late Eocene to the early Miocene epochs, about 38-19 million years ago. Their large heads, low snouts, narrow gait, and proposed omnivorous diet inspires comparisons to suids and tayassuids (peccaries), and historically they have been considered closely related to these families purely on a morphological basis. However, studies which combine morphological and molecular (genetic) data on artiodactyls instead suggest that entelodonts are cetancodontamorphs, more closely related to hippos and cetaceans through their resemblance to Pakicetus, than to basal pigs like Kubanochoerus and other ungulates.
Palaeotherium is an extinct genus of equoid that lived in Europe and possibly the Middle East from the Middle Eocene to the Early Oligocene. It is the type genus of the Palaeotheriidae, a group exclusive to the Palaeogene that was closest in relation to the Equidae, which contains horses plus their closest relatives and ancestors. Fossils of Palaeotherium were first described in 1782 by the French naturalist Robert de Lamanon and then closely studied by another French naturalist, Georges Cuvier, after 1798. Cuvier erected the genus in 1804 and recognized multiple species based on overall fossil sizes and forms. As one of the first fossil genera to be recognized with official taxonomic authority, it is recognized as an important milestone within the field of palaeontology. The research by early naturalists on Palaeotherium contributed to the developing ideas of evolution, extinction, and succession and demonstrating the morphological diversity of different species within one genus.
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.
Xiphodontidae is an extinct family of herbivorous even-toed ungulates, endemic to Europe during the Eocene 40.4—33.9 million years ago, existing for about 7.5 million years. Paraxiphodon suggests that they survived into the Lower Oligocene, at least.
Anoplotheriidae is an extinct family of artiodactyl ungulates. They were endemic to Europe during the Eocene and Oligocene epochs about 44—30 million years ago. Its name is derived from the Ancient Greek: ἂνοπλος ("unarmed") and θήριον ("beast"), translating as "unarmed beast".
Duerotherium is an extinct genus of artiodactyl that lived during the Middle Eocene and is only known from the Iberian Peninsula. The genus is a member of the family Anoplotheriidae and the subfamily Anoplotheriinae, and contains one species, D. sudrei. Like other anoplotheriids, it was endemic to Western Europe. The genus was described based on a left fragment of a maxilla from the Mazaterón Formation of the Duero Basin, from which its name derives, in 2009. Its dentition is mostly typical of the Anoplotheriinae but differs from related genera in the elongated and triangular third upper premolar and traits of the molars. It is thought to have been part of an endemic fauna that evolved in the Iberian Peninsula during the Middle Eocene, when climates were subtropical.
Xiphodon is the type genus of the extinct Palaeogene artiodactyl family Xiphodontidae. It, like other xiphodonts, was endemic to Western Europe and lived from the middle Eocene up to the earliest Oligocene. Fossils from Montmartre in Paris, France that belonged to X. gracilis were first described by the French naturalist Georges Cuvier in 1804. Although he assigned the species to Anoplotherium, he recognized that it differed from A. commune by its dentition and limb bones, later moving it to its own subgenus in 1822. Xiphodon was promoted to genus rank by other naturalists in later decades. It is today defined by the type species X. gracilis and two other species, X. castrensis and X. intermedium.
Plagiolophus is an extinct genus of equoids belonging to the family Palaeotheriidae. It lived in Europe from the middle Oligocene to the early Oligocene. The type species P. minor was initially described by the French naturalist Georges Cuvier in 1804 based on postcranial material including a now-lost skeleton originally from the Paris Basin. It was classified to Palaeotherium the same year but was reclassified to the subgenus Plagiolophus, named by Auguste Pomel in 1847. Plagiolophus was promoted to genus rank by subsequent palaeontologists and today includes as many as seventeen species. As proposed by the French palaeontologist Jean A. Remy in 2004, it is defined by three subgenera: Plagiolophus, Paloplotherium, and Fraasiolophus.
Cainotheriidae is an extinct family of artiodactyls known from the Late Eocene to Middle Miocene of Europe. They are mostly found preserved in karstic deposits.
Dichodon is an extinct genus of Palaeogene artiodactyls belonging to the family Xiphodontidae. It was endemic to Western Europe and lived from the middle Eocene up to the earliest Oligocene. The genus was first erected by the British naturalist Richard Owen in 1848 based on dental remains from the fossil beds in Hordle, England. He noticed similar dentitions to contemporary artiodactyls like those of the Anoplotheriidae and Dichobunidae and references the name of the genus Dichobune. Eventually, it was found to be more closely related to Xiphodon and now includes 11 species, although one of them may be synonymous.
Bachitherium is an extinct genus of Paleogene ruminants that lived in Europe from the late Eocene to the late Oligocene. The genus was erected in 1882 by Henri Filhol based on fossil remains found in the Quercy Phosphorites Formation. Bachitherium curtum was defined the type species, and another species called B. insigne; five more species have since been named although one, B. sardus, is currently pending reassessment. The genus name derives from "Bach", the French locality where its first fossils were found, and the Greek θήρ/therium meaning "beast". Bachitherium has historically been assigned to various families within the ruminant infrorder Tragulina, but was reclassified to its own monotypic family Bachitheriidae by Christine Janis in 1987.
Diplobune is an extinct genus of Palaeogene artiodactyls belonging to the family Anoplotheriidae. It was endemic to Europe and lived from the late Eocene to the early Oligocene. The genus was first erected as a subgenus of Dichobune by Ludwig Rütimeyer in 1862 based on his hypothesis of the taxon being a transitional form between "Anoplotherium" secundaria, previously erected by Georges Cuvier in 1822, and Dichobune. He based the genus etymology off of the two-pointed pillarlike shapes of the lower molars, which had since been a diagnosis of it. However, in 1870, Diplobune was elevated to genus rank by Oscar Fraas, who recognized that Diplobune was a distinct genus related to Anoplotherium and not Dichobune. After several revisions of the anoplotheriids, there are currently four known species of which D. minor is the type species.
Dacrytherium is an extinct genus of Palaeogene artiodactyls belonging to the family Anoplotheriidae. It occurred from the Middle to Late Eocene of Western Europe and is the type genus of the subfamily Dacrytheriinae, the older of the two anoplotheriid subfamilies. Dacrytherium was first erected in 1876 by the French palaeontologist Henri Filhol, who recognised in his studies that it had dentition similar to the anoplotheriids Anoplotherium and Diplobune but differed from them by a deep preorbital fossa and a lacrimal fossa, the latter of which is where the genus name derives from. D. ovinum, originally classified in Dichobune, is the type species of Dacrytherium. Henri Filhol named D. elegans in 1884, and Hans Georg Stehlin named the species D. priscum and D. saturnini in 1910.
Catodontherium is an extinct genus of Palaeogene artiodactyls belonging to the family Anoplotheriidae. It was endemic to Western Europe and had a temporal range exclusive to the middle Eocene, although its earliest appearance depends on whether C. argentonicum is truly a species of Catodontherium. It was first named Catodus by the French palaeontologist Charles Depéret in 1906, who created two species for the genus and later changed the genus name to Catodontherium in 1908. The Swiss palaeontologist Hans Georg Stehlin renamed one species and classified two other newly erected species to Catodontherium in 1910. Today, there are four known species, although two remain questionable in genus placement.
Ephelcomenus is an extinct genus of Palaeogene artiodactyls endemic to Western Europe. It contains one species E. filholi, which was first described by Richard Lydekker in 1889 but eventually classified to its own genus by the Swiss palaeontologist Johannes Hürzeler in 1938. It has an uncertain stratigraphic range, but some sources suggest that it was present in the Oligocene after the Grande Coupure turnover event of western Europe.
Robiatherium is an extinct genus of Palaeogene artiodactyls containing one species R. cournovense. The genus name derives from the locality of Robiac in France where some of its fossil were described plus the Greek θήρ/therium meaning "beast" or "wild animal". It was known only from the middle Eocene and, like other anoplotheriids, was endemic to Western Europe. The genus was erected by Jean Sudre in 1988 for a species originally attributed to the xiphodont genus Paraxiphodon in 1978. Robiatherium had dentitions typical of the subfamily Anoplotheriinae, differing from other genera by specific differences in the molars. It is one of the earliest-appearing anoplotheriine species in the fossil record as well as the earliest to have appeared in Central Europe.
Mixtotherium is an extinct genus of Palaeogene artiodactyls belonging to the monotypic family Mixtotheriidae. Known informally as mixtotheriids or mixtotheres, these artiodactyls were endemic to western Europe and occurred from the middle to late Eocene. The genus and type species were both first established by the French naturalist Henri Filhol in 1880. Several species are well known by good skull fossils, which were informative enough to allow for classifications of the species to their own family. The Mixtotheriidae, first recognized by Helga Sharpe Pearson in 1927, is currently known by 7 valid species, although M. priscum is thought by several authors to be synonymous with M. gresslyi. The affinities of the Mixtotheriidae in relation to other artiodactyl families is uncertain, but it is currently thought to have been related to the Cainotherioidea and Anoplotheriidae.
Haplomeryx is an extinct genus of Palaeogene artiodactyls belonging to the family Xiphodontidae. It was endemic to Western Europe and lived from the middle Eocene up to the earliest Oligocene. Haplomeryx was first established as a genus by the German naturalist Max Schlosser in 1886 based on a molar tooth set from Quercy Phosphorites deposits. Three additional species were erected and classified to the xiphodontid genus while one other species, first recognized in 1822, was tentatively classified to it and remains unresolved in affinity.
Amphimeryx is an extinct genus of Palaeogene artiodactyls belonging to the Amphimerycidae that was endemic to the central region of western Europe and lived from the Late Eocene to the Early Oligocene. It was erected in 1848 by the French palaeontologist Auguste Pomel, who argued that its dentition was roughly similar to those of ruminants. Hence, the etymology of the genus name means "near ruminant," of which it derives from the ancient Greek words ἀμφί (near) and μήρυξ (ruminant). The type species A. murinus was previously recognized as a species of Dichobune by the French palaeontologist Georges Cuvier in 1822 before its eventual reclassification to its own genus. Two other species A. collotarsus and A. riparius are recognized also today although the former may be synonymous with A. murinus while the latter is known solely by a now-lost fossil specimen.