Dichodon (mammal)

Dichodon Temporal range: Middle Eocene – Early Oligocene 43.5–33.4 Ma PreꞒ Ꞓ O S D C P T J K Pg N
Dichodon spp. dental remains, Natural History Museum of Basel (clockwise from top left) - D. ruetimeyeri, D. sp., D. cervinum
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Class:	Mammalia
Order:	Artiodactyla
Family:	†Xiphodontidae
Genus:	†Dichodon Owen, 1848
Type species
†Dichodon cuspidatum Owen, 1848
Other species
†D. cervinum Owen, 1841 †D. frohnstettensis Meyer, 1852 †D. simplex Kowalevsky, 1874 †D. cartieri Rütimeyer, 1891 †D. subtilis Stehlin, 1910 †D. ruetimeyeri Stehlin, 1910 †D. lugdunensis Sudre, 1972 †D. stehlini Sudre, 1973 †D. vidalenci? Sudre, 1988 †D. biroi Hooker & Weidmann, 2000
Synonyms
Genus synonymy Tetraselenodon Schlosser, 1886 Synonyms of D. cervinum Tetraselenodon Kowalevskii Schlosser, 1886

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.

Dichodon had brachyodont (low-crowned) dentition, its premolars being elongated similar to other xiphodonts. However, it differs from them by the generally stronger but varied degrees of elongation of the premolars and "molarization" of the fourth premolars, in which the earliest species had triangular top fourth premolars while later species had quadrangular ones. Its snout is also shorter and narrower compared to that of Xiphodon. The different morphologies of the two genera suggest different dietary specializations of folivory (leaf-eating), but the postcranial morphology of Dichodon remains poorly known compared to that of Xiphodon.

Dichodon lived in western Europe 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 animals that also evolved with strong levels of endemism. The genus was speciose, composed of many small-sized species as well as medium-sized ones. D. cuspidatum and D. stehlini were especially large but are known only from single fossil localities. The small-sized D. frohnstettensis and the medium-sized D. cervinum, in comparison, frequently occur in many localities dating from the late middle to late Eocene.

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.