It is also recognised as having two evolutionary paths in the forms of D. elegans-D. saturnini and D. priscum-D. ovinum given the anatomical changes and size increases of dentitions over time, although the researcher who proposed the lineages later expressed doubt that the validity of the latter.

Dacrytherium itself was likely folivorous, but its lifestyle is unknown given the general scarcity of post-cranial evidence and the unusual variations of hypothesized behaviours in the derived anoplotheriines Anoplotherium and Diplobune.

In 1876, French palaeontologist Henri Filhol described fossils from recent excavations at the phosphorite deposits of Quercy in France, including bones that he identified as belonging to new genera or species.

[1] The same year, French palaeontologist Paul Gervais compared Dacrytherium to hipparionines and merycoidodonts based on the upper maxilla of the complete skull having a similarly deep lateral (or outer) hollowing.

However, before Lydekker wrote his 1892 article, Arthur Smith Woodward presented him with more fossil evidence from the French phosphorites including a well-preserved mandible of D. cayluxi, leading him to synonymize it with D. ovinum.

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.

[26] The Dacrytheriinae has recently been suggested to have been a paraphyletic subfamily based on dental morphology from which the Anoplotheriinae, Mixtotheriidae, and Cainotherioidea stemmed, but further research is required to confirm if this is true.

[27] Conducting studies focused on the phylogenetic relations within the Anoplotheriidae has proven difficult due to the general scarcity of fossil specimens of most genera.

[27] 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.

[23][29] 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.

[29] The phylogenetic tree published in the article and another work about the cainotherioids is outlined below:[22] 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:[23] 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.

[30][17][27] Dacrytherium has fairly complete skull material since 1876 and is best known for its large-sized lacrimal fossa in front of its eye, or "tear pit", hence the derivation of the genus name.

Historically the trait, along with the fusion of the front internal cusps in the lower molar teeth, were used to justify Dacrytherium as being a different evolutionary lineage from other anoplotheres.

The cerebellar hemispheres are lower in position than the vermis and contains a large superior petrosal sinus on the surface in an arclike form, which is attached to the base of the neocerebellum but gradually moves away from it in the front area.

[45] The morphology of the astragalus of Dacrytherium being similar to the astragali of the anoplotheriines Anoplotherium and Diplobune, as originally proposed by Viret and Prudant, was supported by Jean-Noël Martinez and Jean Sudre in 1995.

The astragali are common bones in fossil assemblages due to their reduced vulnerability to fragmentation as a result of their stocky shape and compact structure, explaining their choice for using it.

[46] In 2014, Takehisa Tsubamoto reexamined the relationship between astragalus size and estimated body mass based on extensive studies of extant terrestrial mammals, reapplying the methods to Palaeogene artiodactyls previously tested by Sudre and Martinez.

[21] Hooker in 1986 also pointed out that Dacrytherium and Mixtotherium, despite belonging to different artiodactyl families, had similar dentitions based on their low-crowned and strongly selenodont molars.

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.

[18] 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.

[51][25][56] The stratigraphic ranges of the early species of Dacrytherium also overlapped with metatherians (Herpetotheriidae), cimolestans (Pantolestidae, Paroxyclaenidae), rodents (Ischyromyidae, Theridomyoidea, Gliridae), eulipotyphlans, bats, apatotherians, carnivoraformes (Miacidae), and hyaenodonts (Hyainailourinae, Proviverrinae).

elegans fossils cooccurred with those of many other mammals such as the herpetotheriid Amphiperatherium, miacid Quercygale, proviverrine Proviverra, equoid Hallensia, palaeotheres Propalaeotherium and Plagiolophus, lophiodont Lophiodon, choeropotamids (Haplobunodon, Rhagatherium and Amphirhagatherium), and the cebochoerid Cebochoerus.

[55][57][17] Undisputed fossil remains of D. elegans occur in several sites of France and Switzerland that date back to MP16, such as Mormont Eclépens, Le Bretou, and Robiac.

[34] The locality of Robiac indicates that D. elegans coexisted with similar mammal faunas as earlier species of the genus, such as the herpetotheriids Peratherium and Amphiperatherium, hyaenodonts Paroxyaena and Cynohyaenodon, miacids Paramiacis and Quercygale, palaeotheres (Palaeotherium, Plagiolophus, Anchilophus), lophiodont Lophiodon, cebochoerids Cebochoerus and Acotherulum, choeropotamid Choeropotamus, dichobunid Mouillacitherium, robiacinid Robiacina, xiphodonts (Xiphodon, Dichodon, and Haplomeryx), amphimerycid Amphimeryx, and other anoplotheriids Catodontherium and Robiatherium.

[25][58][61][62] 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.

[34][55] Both lineages largely coexisted with the same artiodactyl families as well as the Palaeotheriidae within western Europe,[57] although the Cainotheriidae and the derived anoplotheriids Anoplotherium and Diplobune all made their first fossil record appearances by MP18.

[67] The MP18 locality of La Débruge of France indicates that D. saturnini coexisted with a wide variety of mammals, namely the herpetotheriid Peratherium, rodents (Blainvillimys, Theridomys, Plesiarctomys, Glamys), hyaenodonts (Hyaenodon and Pterodon), amphicyonid Cynodictis, palaeotheres (Plagiolophus, Anchilophus, Palaeotherium), dichobunid Dichobune, choeropotamid Choeropotamus, cebochoerids Cebochoerus and Acotherulum, anoplotheriids Anoplotherium and Diplobune, tapirulid Tapirulus, xiphodonts Xiphodon and Dichodon, cainothere Oxacron, amphimerycid Amphimeryx, and anthracothere Elomeryx.