Xiphodon

Xiphodon Temporal range: Middle Eocene – early Oligocene 40–33.4 Ma PreꞒ Ꞓ O S D C P T J K Pg N
Xiphodon gracilis skull, National Museum of Natural History, France
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Class:	Mammalia
Order:	Artiodactyla
Family:	†Xiphodontidae
Genus:	†Xiphodon Cuvier, 1822
Type species
†Xiphodon gracilis Cuvier, 1822
Other species
†X. castrensis Kovalevsky, 1876 †X. intermedium Stehlin, 1910
Synonyms
Synonyms of X. gracilis Anoplotherium medium Cuvier, 1804 Dubious species Xiphodon tragulinum Gervais, 1876

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.

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. It also retained primitive molars compared to its relative Dichodon, indicating different dietary specializations. Xiphodon is also the only xiphodontid to be known from postcranial fossils. Its skull morphology, combined with slender and elongated limbs, suggest similar behaviours to North American Palaeogene camelids such as Poebrotherium, including cursoriality (running adaptations). However, the full extent of its behaviour and evolutionary relationships remain uncertain, and its resemblances to camelids are probably an instance of convergent evolution.

Xiphodon lived in western Europe back when it was an archipelago that was isolated from the rest of Eurasia, meaning that it lived in an environment with various other endemic faunas. The xiphodont made its first appearance in the Middle Eocene shortly before a shift towards drier but still subhumid conditions, which led to increasingly abrasive plants. Species of Xiphodon were relatively small with the second-appearing species X. intermedium having an estimated weight of 4.6 kg (10 lb). X. gracilis was the last and largest species within the genus in an evolutionary size increase trend.

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.