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 for Bachitherium curtum, the type species, and 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 / 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 to , 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 , 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.
Taxonomy
Early history
The French palaeontologist Henri Filhol described two fossil artiodactyl genera from the lime phosphate deposits of the French province of Quercy that he thought indicated the Eocene epoch in 1882. He thought that the first genus belonged to the Moschidae family and must be closely affiliated with Gelocus. According to Filhol, the lower dental formula of the genus was 3:1:3:3, and the genus was characterized by its compressed lower premolars, with the posterior edge extending as a deep furrow. It was therefore differentiated from Gelocus in that the newer genus had all compressed lower premolars whereas only the last premolar of Gelocus, which has four premolars total, was compressed. The incisors, he observed, were quite small, while the canine immediately following them was strong. Based on these traits, Filhol erected the genus name Bachitherium, basing its etymology on "Bach," a location of phosphorite deposits. The first species, B. insigne, was determined to be a large animal while B. medium was much smaller than B. insigne but larger than the smallest species B. minus.
In 1885, the English naturalist Richard Lydekker placed Bachitherium provisionally in the family Tragulidae (chevrotains/mouse-deer/tragulids) and listed the species Bachitherium curtum, for which he made "Gelocus curtum" and "Bachitherium medium" synonyms of because the specimens appeared to have belonged to the same species (notably, Filhol described the species "Gelocus curtus" and "Gelocus insignis" in 1877 prior to the erection of Bachitherium). Lydekker stated that Bachitherium was known only by some portions of the mandible and maxilla, that it was said to be closely allied to Gelocus but differed by its first lower premolar. He stated that the dental formula of Bachitherium was , that the upper cheek of the genus closely resemble that of Prodremotherium. Additionally, he also confirmed B. insigne as a valid species.