Palaeoloxodon is an extinct genus of elephant. It originated in Africa during the Early Pleistocene, and expanded into Eurasia at the beginning of the Middle Pleistocene. Palaeoloxodon contains the largest known species of elephants, with mature bulls over tall at the shoulders and over in weight, representing among the largest land mammals ever, including the African Palaeoloxodon recki, the European straight-tusked elephant (Palaeoloxodon antiquus) and the South Asian Palaeoloxodon namadicus. P. namadicus has been suggested to be the largest known land mammal by some authors based on extrapolation from fragmentary remains, though these estimates are highly speculative. In contrast, the genus also contains many species of dwarf elephants (an example of insular dwarfism) on islands in the Mediterranean, some like Palaeoloxodon falconeri less than in shoulder height as fully grown adults, making them the smallest elephants known. The genus has a long and complex taxonomic history, and at various times, it has been considered to belong to Loxodonta or Elephas, but today is usually considered a valid and separate genus in its own right.
History of research and taxonomy Remains of Palaeoloxodon species have probably been noted since ancient times where their remains like those of other fossil proboscideans were interpreted as those of giants or other mythical beings. In 1695, remains of a straight-tusked elephant were collected from travertine deposits near Burgtonna in what is now Thuringia, Germany. While these remains were originally declared by the Collegium Medicum in the nearby city of Gotha to be purely mineral in nature, Wilhelm Ernst Tentzel, a polymath in the employ of the ducal court of Saxe-Gotha-Altenburg, correctly recognised that they represented the remains of an elephant. Prior to 1845, the remains of Eurasian species of Palaeoloxodon were considered to be those of woolly mammoths. The earliest species of Palaeoloxodon to be described, the European straight-tusked elephant (Palaeoloxodon antiquus) and the South Asian Palaeoloxodon namadicus, were named by British paleontologists Hugh Falconer and Proby Cautley in 1846-47. Prior to the description of the genus, Palaeoloxodon species were initially placed in the genus Elephas (which includes the Asian elephant).Davies, Paul; (2002) The straight-tusked elephant (Palaeoloxodon antiquus) in Pleistocene Europe. Doctoral thesis (Ph.D), UCL (University College London).
In 1924, Matsumoto Hikoshichirō coined Palaeoloxodon, and circumscribed it as a subgenus of Loxodonta (which include the living species of African elephants). It included the "E. antiquus—namadicus group", and he designated the Japanese "E. namadicus naumanni Mak." as its type species. Also in 1924, American paleontologist Henry Fairfield Osborn named the genera Sivalika and Pilgrimia, with the former covering the Asian species and the latter covering the African and Mediterranean island dwarf species of Palaeoloxodon. In 1931 Osborn named the genus Hesperoloxodon to include Palaeoloxodon antiquus. In a 1942 posthumous publication, Osborn recognised Sivalika and Pilgrimia as junior synonyms of Palaeoloxodon, while still recognising Hesperoloxodon as valid. This publication was the first to consider Palaeoloxodon a valid genus in its own right, an opinion followed by later authors such as Emiliano Aguirre in 1969. Later authors have considered Hesperoloxodon another synonym of Palaeoloxodon. Vincent J. Maglio in a 1973 publication controversially synonymised Palaeoloxodon with Elephas based on morphological similarities between the two genera. Later authors either considered Palaeoloxodon a valid genus or a subgenus of Elephas. Cladistic analyses finding Elephas and Palaeoloxodon to not be each other's closest relatives led to the placement of Palaeoloxodon species within Elephas to be questioned by other authors. By the 2010s Palaeoloxodon was widely regarded as a valid genus separate from Elephas. During the 19th and 20th centuries, species of Palaeoloxodon were subject to numerous phylogenetic hypotheses regarding their relationship to other elephantids. Some scholars like Hans Pohlig in 1891 and Osborn in 1935 considered the species of Palaeoloxodon to be closely related to African elephants, while others like Wolfgang Soergel in 1915 considered them to be closely related to mammoths.Zhang, Steven "The Rise and Fall of The Straight-Tusked Elephants" June 2021 East Tennessee State University Natural History Museum & Gray Fossil Site Paleotalks Episode 49. Relevant content begins around 12:20 From the late 20th century to the first decade of the 21st century, Palaeoloxodon was usually considered to be closely related the Asian elephant and other members of the genus Elephas.
In 2016, a study of the straight-tusked elephant (P. antiquus) mitochondrial genome and part of the nuclear genome found that the mitochondrial sequences were nested within the diversity of those of the African forest elephant, Loxodonta cyclotis, with the partial nuclear genome supporting P. antiquus as more closely related to L. cyclotis than the African bush elephant, L. africana. A later study published in 2018 by the same authors based on the complete nuclear genome revised these results, and suggested P. antiquus resulted from reticulate evolution and had a complex ancestry tree, with the majority (~60%) of its nuclear genome coming from a lineage more closely related to modern African elephants than to Asian elephants and mammoths, but which diverged before the split between the two living species, with significant introgressed ancestry resulting from hybridization with African forest elephants (~36% of total genome) and to a lesser extent mammoths (~6%). The ancestry from L. cyclotis was more closely related to modern West African populations of the forest elephant than to other forest elephant populations, while the mammoth ancestry came from a lineage that diverged prior to the split between woolly and Columbian mammoths, probably from shortly after the split between the ancestors of mammoths and Asian elephants. Mitochondrial genomes obtained from Chinese and Japanese Palaeoloxodon specimens indicate that the forest elephant ancestry was ubiquitous among Eurasian Palaeoloxodon populations. Both hybridization events probably took place in Africa, where Palaeoloxodon was dominant for most of the Early Pleistocene, with the mammoth hybridisation suggested to have taken place earlier than the hybridisation with forest elephants.
Analysis of mitochondrial genomes, including Palaeoloxodon individuals from Northern China and Japanese Palaeoloxodon naumanni indicate that African forest elephant mitochondrial genomes completely replaced those originally present in Palaeoloxodon, and that Palaeoloxodon harboured multiple separate mitochondrial genome lineages derived from African forest elephants, some being more closely related to some West African forest elephant groups than to others. It is unclear as to whether this is the result of multiple hybridisation events, or whether multiple mitochondrial lineages were introgressed in a single event. The hybridisation with forest elephants is likely to have occurred around 1 million years ago in Palaeoloxodon recki. It has been found that mitochondrial genome of Chinese Palaeoloxodon specimens clustered with a P. antiquus individual from western Europe, which belonged to a separate clade than other sampled European P. antiquus specimens. The relatively low divergence between the mitochondrial genomes of the European P. antiquus individual and the Chinese Palaeoloxodon specimens may indicate that the populations of Palaeoloxodon across Eurasia maintained gene flow with each other, but this is uncertain.
List of species P. recki (Synonym: Elephas recki) (East Africa), the oldest species and ancestor of all later species P. jolensis (Synonym: Elephas iolensis) the last (late Middle-Late Pleistocene) representative of Palaeoloxodon in Africa P. antiquus (Synonym: Elephas antiquus) (Straight tusked elephant) (Europe, Western Asia) P. huaihoensis (China) P. namadicus (Synonym: Elephas namadicus)Kevrekidis, C., & Mol, D. (2016). A new partial skeleton of Elephas (Palaeoloxodon) antiquus Falconer and Cautley, 1847 (Proboscidea, Elephantidae) from Amyntaio, Macedonia, Greece. Quaternary International, 406, 35–56. https://doi.org/10.1016/j.quaint.2015.11.110 (Indian subcontinent, possibly also elsewhere in Asia), the largest in its genus, and possibly the largest terrestrial mammal ever P. naumanni (Synonym: E. namadicus naumanni) (Naumann's elephant) (Japan, possibly also China and Korea) P. turkmenicus known from a specimen found in the Middle Pleistocene of Turkmenistan in Central Asia, as well as a specimen from the Kashmir Valley in the northwest Indian subcontinent.
Mediterranean island dwarfs These Mediterranean insular dwarf elephant species are almost certainly descended from P. antiquus
P. creutzburgi (Crete) P. xylophagou (Cyprus) P. cypriotes (Cyprus) P. lomolinoi (Naxos) P. tiliensis (Tilos) P. mnaidriensis (Sicily and Malta) P. falconeri (Sicily and Malta) Other indeterminate dwarf Palaeoloxodon species are known from other Greek islands, including Rhodes and Kasos.
Description
Many species of Palaeoloxodon are noted for the distinctive parieto-occipital crest (POC), a bone growth at the top of the skull above the nasal opening which projects forwards and overhangs the rest of the skull. The crest probably functioned to anchor muscle tissue, including the splenius as well as an additional muscle layer called the "extra splenius" (which was likely similar to the "splenius superficialis" found in Asian elephants, and which may have been an extension of the rhomboideus cervicis muscle) which wrapped around the top of the head to support it. The development of the crest is depending, growth stage and gender, with females and juveniles having less developed or absent crests. The crest likely developed as a response to the large size of the head, which in proportional and absolute terms are the largest in size of any proboscideans. The crest shows differences in development depending on species, with the earliest species P. recki as well as the Japanese P. naumanni and Central Asian P. turkmenicus only having weakly developed crests (the so-called "Stuttgart morph"), while P. antiquus, P. namadicus and Chinese Palaeoloxodon have strongly developed crests (the so-called "namadicus morph"). It is thought that the weakly developed morphology of the POC is the ancestral condition in Palaeoloxodon, with the strongly developed "namadicus morph" having evolved following the migration of Palaeoloxodon into Eurasia.
The skull is proportionally short and tall, with the premaxillary bones containing the tusks being flared outwards. The tusks have relatively little curvature, and are proportionally large, and somewhat twisted, with the tusk alveoli (sockets) being divergent from each other at least in Pleistocene species. These tusks could reach in length, and probably over in weight in the largest species, larger than any recorded in modern elephants.