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 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.

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.

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.

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.

[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.

[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).

[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.

[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.

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] Eurodexis russelli Dichobune leporina Amphimeryx murinus Xiphodon castrense Paratoceras coatesi Eotylopus reedi Parvitragulus priscus Lophiomeryx chalaniati Archaeomeryx optatus Mixtotherium cuspidatum Anoplotherium latipes Dacrytherium ovinum Robiacina lavergnesis Robiacina minuta Robiacina quercyi Palembertina deplasi Paroxacron bergeri Paroxacron valdense Oxacron courtoisii Cainotherium laticurvatum Caenomeryx filholi Caenomeryx procommunis Plesiomeryx cadurcensis Plesiomeryx huerzeleri In 2020, Vincent Luccisano et al. created a phylogenetic tree of the basal artiodactyls, a majority endemic to western Europe, from the Palaeogene.

The phylogenetic tree as produced by the authors is shown below:[16] Bunophorus Gunophorus Diacodexis Protodichobune Eurodexis Buxobune Mouillacitherium Meniscodon Hyperdichobune Dichobune robertiana Dichobune leporina Homacodon Gobiohyus Khirtharia Entelodon Palaeocheorus Perchoerus Haplobunodon Cuisitherium Lophiobunodon Mixtotherium Robiacina Dacrytherium Diplobune Xiphodon Paraxiphodon Cainotherium Paroxacron Archaeomeryx Amphimeryx Pseudamphimeryx Aumelasia Hallebune Amphirhagatherium Cebochoerus Gervachoerus Choeropotamus Siamotherium 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.

[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.

[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.

[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.

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.

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.

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.

[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.

[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).

[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.

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), robiacinid Robiacina, and xiphodonts (Xiphodon, Dichodon, Haplomeryx).

[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.

[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.