Literally meaning "sword tooth" in Ancient Greek, Xiphodon had specialized bladelike selenodont dentition, with its brachyodont (low-crowned) incisors, canines, and premolars having sharp edges for cutting through higher vegetation such as leaves and shrubs.

Its skull morphology, combined with slender and elongated limbs, suggest similar behaviours to North American Palaeogene camelids such as Poebrotherium, including cursoriality (running adaptations).

It and other xiphodont genera went extinct by the Grande Coupure extinction/faunal turnover event, coinciding with shifts towards further glaciation and seasonality plus dispersals of Asian immigrant faunas into western Europe.

The causes of its extinction are attributed to negative interactions with immigrant faunas (resource competition, predation), environmental turnover from climate change, or some combination of the two.

He stated that in contrast to the more robust A. commune, A. medium was more gracile in form and therefore would have been built for cursoriality similar to extant ungulates such as gazelles or roe deer.

[8] The genus name Xiphodon means "sword tooth" and is a compound of the Ancient Greek words ξίφος (xiphos, 'sword') and ὀδούς (odoús, 'tooth').

The sculpture's appearance overall matches up with Cuvier's anatomical description of the species, the main inaccuracy being the reconstruction of additional small digits similar to A. commune.

[27] The phylogenetic relations of the Xiphodontidae as well as the Anoplotheriidae, Mixtotheriidae and Cainotheriidae have been elusive due to the selenodont morphologies (or having crescent-shaped ridges) of the molars, which were convergent with tylopods or ruminants.

[28] 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.

[24] 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.

[31] The phylogenetic tree published in the article and another work about the cainotherioids is outlined below:[32] 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:[30] 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 created a phylogenetic analysis in his academic thesis regarding Palaeogene artiodactyl lineages, focusing most specifically on the endemic European families.

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.

[35] The hard palate for the upper mouth appears concave and has a visible premaxillary-maxillary suture extending from the outer edge of the jaw to the back.

[35] In addition to the large and hollow tympanic bullae, the ear canal has elevated edges and opens in a slanted position slightly in front of the suture of the occipital bone.

[35] Both Xiphodon and Dichodon display complete sets of 3 three incisors, 1 canine, 4 premolars, and 3 molars on each half of the upper and lower jaws,[35][37] consistent with the primitive placental mammal dental formula of 3.1.4.33.1.4.3 for a total of 44 teeth.

[35] Jean Sudre in 1978 argued that Xiphodon displayed the evolutionary trend of the molars becoming more quadrangular in shape and that their selenodont forms were already present in the most basal species X.

[33] Xiphodon is the only member of its family for which postcranial evidence is known, primarily represented by the gypsum quarries of Montmartre in the case of X. gracilis as previously described by Cuvier.

The body mass formula based on astragali was previously established by Jean-Noël Martinez and Sudre in 1995 for Palaeogene artiodactyls, although Xiphodon was not included in the initial study.

[40][41] The Xiphodontidae is a selenodont artiodactyl group in western Europe, meaning that the family was likely adapted for folivorous (leaf-eating) dietary habits.

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.

[45] 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.

[42][25][48] It also cooccurred with metatherians (Herpetotheriidae), rodents (Ischyromyidae, Theridomyoidea, Gliridae), eulipotyphlans, bats, apatotherians, carnivoraformes (Miacidae), and hyaenodonts (Hyainailourinae, Proviverrinae).

[26] Within Robiac, fossils of X. castrensis were found with those of other mammals like the herpetotheriids Peratherium and Amphiperatherium, apatemyid Heterohyus, nyctithere Saturninia, rodents (Glamys, Elfomys, Plesiarctomys, Remys), omomyids Pseudoloris and Necrolemur, adapid Adapis, hyaenodonts Paroxyaena and Cynohyaenodon, carnivoraformes Paramiacis and Simamphicyon, palaeotheres (Palaeotherium, Plagiolophus, Anchilophus, Leptolophus), lophiodont Lophiodon, hyrachyid Chasmotherium, cebochoerids Acotherulum and Cebochoerus, choeropotamid Choeropotamus, tapirulid Tapirulus, anoplotheriids Dacrytherium and Catodontherium, dichobunid Mouillacitherium, robiacinid Robiacina, amphimerycid Pseudamphimeryx, and the other xiphodonts Dichodon and Haplomeryx.

[25][49][50][51] 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 xiphodont largely coexisted with the same artiodactyl families as well as the Palaeotheriidae within western Europe,[26] although the Cainotheriidae and the derived anoplotheriids Anoplotherium and Diplobune all made their first fossil record appearances by MP18.

Based on the MP19 French locality of Escamps, it coexisted with the likes of the herpetotheriids Peratherium and Amphiperatherium, pseudorhyncocyonid Pseudorhyncocyon, nyctitheres Saturninia and Amphidozotherium, various bats and rodents, omomyid Microchoerus, adapid Palaeolemur, hyainailourine Pterodon, amphicyonid Cynodictis, palaeotheres Palaeotherium and Plagiolophus, dichobunid Dichobune, choeropotamid Choeropotamus, anoplotheriids Anoplotherium and Diplobune, cainothere Oxacron, amphimerycid Amphimeryx, and the other xiphodonts Dichodon and Haplomeryx.

The Turgai Strait, which once separated much of Europe from Asia, is often proposed as the main European seaway barrier prior to the Grande Coupure, but some researchers challenged this perception recently, arguing that it completely receded already 37 Ma, long before the Eocene-Oligocene transition.

[27][58][24] The extinctions of Xiphodon and many other mammals have been attributed to negative interactions with immigrant faunas (competition, predations), environmental changes from cooling climates, or some combination of the two.