Palaeoloxodon

In 1924, Hikoshichiro Matsumoto circumscribed Palaeoloxodon as a subgenus of Loxodonta. It included the "E. antiquus—namadicus group", and he designated "E. namadicus naumanni Mak." as its type species.[1]

Palaeoloxodon was later thought to be a subgenus of Elephas, but this was abandoned by 2007.[4] In 2016, a mitochondrial DNA study of P. antiquus found that it was more closely related to African forest elephant, Loxodonta cyclotis, than the African bush elephant, L. africana. The authors suggested that this invalidated the genus Palaeoloxodon as currently recognized.[5] A second study published in 2018 based on the nuclear genome suggested P. antiquus had a complex hybridization history, with over 60% of its DNA coming from a lineage closest to but outside the two extant Loxodonta species, around 6% from Mammuthus and 30% from a lineage closer to L. cyclotis than L. africana. The hybridisation probably took place in Africa, where Palaeoloxodon was dominant for most of the Pliocene and Early Pleistocene.[6]

Life restoration of P. namadicus

Size diagram of the largest Palaeoloxodon species

Most species of Palaeoloxodon (aside from P. turkmenicus) are noted for their distinctive parieto-occipital crests present at the top of the cranium, which was used to anchor the splenius as well as possibly the rhomboid muscles to support the skull, which is proportionally large in comparison to other elephants. The development of the crest is variable depending the species, growth stage and gender, with females and juvenliles having less developed or absent crests. The tusks have relatively little curvature, and are proportionally large.[10]

Palaeoloxodon namadicus, showing the parieto-occipital crest at the top of the skull typical of Palaeoloxodon.

Palaeoloxodon first appears in the fossil record in Africa during the early Pliocene, around 4 Mya as the species Palaeoloxodon recki. P. recki was the dominant elephant in Africa for the Pliocene and most of the Pleistocene. A population of P. recki migrated out of Africa between 0.8 and 0.6 Mya, diversifying into the radiation of Eurasian Palaeoloxodon species, including P. antiquus, P. namadicus, and P. naumanni, the precise relationships of the Eurasian taxa to each other are obscure in the absence of molecular evidence. P. recki became extinct in Africa around 0.5 Mya, being replaced by the modern genus Loxodonta.[11] The arrival of P. antiquus in Europe co-incides with the extinction of Mammuthus meridionalis and its replacement by Mammuthus trogontherii, suggesting that it might have shared a similar dietary niche and outcompeted the former.[11] P. antiquus was able to disperse onto many islands in the Mediterranean, undergoing insular dwarfism and speciating into numerous distinct varieties of dwarf elephants. Palaeoloxodon fossils are abundant in China and are assigned to three species, P. namadicus, P. naumanni and P. huaihoensis.[12] However, the relationships of Chinese Palaeoloxodon are currently unresolved and it is unclear how many species were present in the region.[10]

The last Paleoloxodon species in Africa, P. iolensis, became extinct at the end of the Middle Pleistocene, around 130,000 years ago.[13] Most Eurasian species of Palaeoloxodon became extinct towards the end of the last glacial period. The youngest record of P. antiquus are footprints from the southern Iberian Peninsula, dating to approximately 28,000 years ago.[14] The youngest Japanese records of P. naumanni date to around 24,000 years ago.[15] Similar dates have been reported for Indian P. namadicus and Chinese Palaeoloxodon.[16][17] Some of the Mediterranean dwarf species held on for longer, with the youngest dates for the Cyprus dwarf elephant P. cypriotes around 12,000 years ago.[18] P. tiliensis from the Greek island of Tilos was suggested to have survived as recently as 3,500 years Before Present based on preliminary radiocarbon dating done in the 1970s, which would make it the youngest surviving elephant in Europe, but this has not been thoroughly investigated.[19]

In a 2012 paper, Li Ji and colleagues from the Institute of Geographic Sciences and Natural Resources Research, Beijing, argued that 3000 year old teeth from Northern China previously believed to belong to Asian elephants were actually those of Palaeoloxodon. They also argued that Chinese ritual bronze vessels depicting trunks with two "fingers" must be Palaeoloxodon (which are only known from bones; their trunk characteristics are unknown) because Asian elephants only have one.[20][21] Fossil elephant experts Victoria Herridge and Adrian Lister disagree with the assignment, stating that the claimed diagnostic dental features are actually contrast artifacts created due to the low image resolution of the figures in the scientific paper, which are not evident in better-quality photographs, and that the Bronze age vessels could be the result of stylistic choice.[22]