Bachitherium

Bachitherium Temporal range: Late Eocene to Late Oligocene, 37.71–24 Ma PreꞒ Ꞓ O S D C P T J K Pg N
Bachitherium cf. insigne skeleton, Pierre Martel Museum of Vachères
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Class:	Mammalia
Order:	Artiodactyla
Suborder:	Ruminantia
Infraorder:	Tragulina
Family:	†Bachitheriidae Janis, 1987
Genus:	†Bachitherium Filhol, 1882
Type species
†Gelocus curtus (= †Bachitherium curtum) Filhol, 1877
Other species
†Bachitherium insigne Filhol, 1877 †Bachitherium vireti Sudre, 1986 †Bachitherium lavocati Sudre, 1986 †Bachitherium guirounetensis Sudre, 1995 †Bachitherium thraciensis Mennecart et al., 2018 Species pending reassessment †Bachitherium sardus van der Made, 2008
Synonyms
Synonyms of B. curtum Gelocus curtus Filhol, 1877 Bachitherium medium Filhol, 1882 Synonyms of B. insigne Gelocus insignis Filhol, 1877

Bachitherium is an extinct genus of Paleogene ruminants that lived in Europe from the late Eocene to the late Oligocene. The genus was erected in 1882 by Henri Filhol based on fossil remains found in the Quercy Phosphorites Formation. Bachitherium curtum was defined the type species, and another species called B. insigne; five more species have since been named although one, B. sardus, is currently pending reassessment. The genus name derives from "Bach", the French locality where its first fossils were found, and the Greek θήρ/therium meaning "beast". Bachitherium has historically been assigned to various families within the ruminant infrorder Tragulina, but was reclassified to its own monotypic family Bachitheriidae by Christine Janis in 1987.

For much of its taxonomic history, Bachitherium was only known from incomplete remains, making assessments difficult. However, a nearly complete skeleton of B. cf. insigne was uncovered in the commune of Céreste in France in 1981, which helped palaeontologists understand its morphology compared to other ruminants. The complete fossil revealed that Bachitherium had cursorial limb builds unlike typical tragulines and like smaller-sized members of the infraorder Pecora. In addition, its dentition differs from other traguline families such as the Tragulidae, Hypertragulidae, and Leptomerycidae by a combination of a tusklike but reduced bottom first incisor, strong upper canine, caniniform first bottom premolar, and other evolutionarily derived traits unique to the genus.

Based on its dental and limb morphologies, B. curtum, weighing 7 kg (15 lb) to 8 kg (18 lb), was well-adapted to closed forest environments and ate a mix of leaves, fruit, and herbages. In comparison, the larger B. insigne, weighing up to 36 kg (79 lb), was more cursorial and therefore built for more open forested environments and a diet consisting mainly of leaves. The morphological differences between the species, combined with their frequent appearances in the same fossil deposits, imply niche partitioning based on their different ecological niches. The last species B. lavocati probably evolved from B. curtum and was likely better adapted to open forested environments than other species of its genus, coinciding with major climatic and faunal restructurings.

Bachitherium is the earliest-known ruminant to have appeared in the European fossil record, originating in eastern Europe during the late Eocene and migrating to western Europe by the early Oligocene after major seaway barriers fell. The genus remained endemic to the continent and survived several waves of climatic changes of the Oligocene without evolving into a new genus. The Microbunodon Event in the late Oligocene, however, led to its extinction as it faced a combination of a warming climate plus subsequent habitat turnover and competition from a new wave of migrating species.