Plagiolophus (mammal)

Plagiolophus Temporal range: Middle Eocene – Early Oligocene 44.9–27.3 Ma PreꞒ Ꞓ O S D C P T J K Pg N (Possible earliest record of up to 46.3 Ma)
Plagiolophus minor skeleton from Baden-Württemberg, State Museum of Natural History Stuttgart
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Class:	Mammalia
Order:	Perissodactyla
Family:	†Palaeotheriidae
Subfamily:	†Palaeotheriinae
Genus:	†Plagiolophus Pomel, 1847
Type species
†Plagiolophus minor Cuvier, 1804
Other species
†P. ovinus Aymard, 1846 †P. annectens Owen, 1848 †P. fraasi von Meyer, 1852 †P. javali Filhol, 1877 †P. lugdunensis Depéret & Carrière, 1901 †P. cartailhaci Stehlin, 1904 †P. cartieri Stehlin, 1904 †P. oweni Depéret, 1917 †P. curtisi Hooker, 1986 †P. major Brunet & Jehenne, 1989 †P. ministri Brunet & Jehenne, 1989 †P. casasecaensis Cuesta, 1994 †P. mazateronensis Cuesta, 1994 †P. huerzeleri Remy, 2000 †P. ringeadei Remy, 2004 †P. mamertensis Remy, 2004 For subspecies suggested, see below.
Synonyms
Genus synonymy Paloplotherium Owen, 1848 Synonyms of P. minor Plagiolophus tenuirostris Pomel, 1853 Synonyms of P. ovinus Palaeotherium ovinum Aymard, 1846 Synonyms of P. annectens Paloplotherium annectens Owen, 1848 Synonyms of P. javali Paloplotherium javalii Filhol, 1877 Synonyms of P. lugdunensis Paloplotherium lugdunense Depéret & Carrière, 1901 Synonyms of P. major Paloplotherium majus Brunet & Jehenne, 1989 Dubious species Plagiolophus minutus Ruetimeyer, 1862

Plagiolophus (Ancient Greek: πλαγιοϛ (oblique) + λοφος (crest) meaning "oblique crest") is an extinct genus of equoids belonging to the family Palaeotheriidae. It lived in Europe from the middle Oligocene to the early Oligocene. The type species P. minor was initially described by the French naturalist Georges Cuvier in 1804 based on postcranial material including a now-lost skeleton originally from the Paris Basin. It was classified to Palaeotherium the same year but was reclassified to the subgenus Plagiolophus, named by Auguste Pomel in 1847. Plagiolophus was promoted to genus rank by subsequent palaeontologists and today includes as many as seventeen species. As proposed by the French palaeontologist Jean A. Remy in 2004, it is defined by three subgenera: Plagiolophus, Paloplotherium, and Fraasiolophus.

Plagiolophus is an evolutionarily derived member of its family with tridactyl (or three-toed) forelimbs and hindlimbs. It has longer postcanine diastemata (gaps between teeth) compared to Palaeotherium and brachyodont (low-crowned) dentition that evolutionarily progressed towards hypsodonty (high-crowned) in response to climatic trends. It is also defined in part by an elongated facial region, deep nasal notch, and orbits for the eyes that are more positioned backwards compared to those of Palaeotherium. Plagiolophus, as a species-rich genus, has a wide body mass range extending from less than 10 kg (22 lb) in the smallest species P. minor to over 150 kg (330 lb) in the largest species P. javali. The postcranial builds of several species suggest that some had stockier body builds (P. annectens, P. fraasi, P. javali) while some others were lightly built for cursorial (running) adaptations (P. minor, P. ministri, P. huerzeleri).

Plagiolophus and other members of the Palaeotheriinae likely descended from the earlier subfamily Pachynolophinae in the middle Eocene. Western Europe, where Plagiolophus was largely present, was an archipelago that was isolated from the rest of Eurasia, meaning that it lived in an environment with various other faunas that also evolved with strong levels of endemism. While many species had short temporal ranges, P. minor was long-lasting to the extent that researchers observed trends in changes in its dietary habits. More specifically, P. minor over time was observed to have consumed less hard foods (fruits, seeds) and became more specialized but less selective towards tough, abrasive, and older leaves in response to environmental trends in the late Eocene to early Oligocene. Its dietary habits would have allow it to niche partition with other palaeotheres like Palaeotherium and Leptolophus. Plagiolophus was consistently diverse for much of its evolutionary history and survived far past the Grande Coupure extinction event, likely because some of its species were well-adapted towards major environmental trends as a result of their dietary changes and cursorial nature. It was able to adapt to more seasonal climates after the Grande Coupure and coexisted with immigrant faunas from the faunal turnover event. Its eventual extinction by the later early Oligocene marked the complete extinction of the Palaeotheriidae.