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.
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 Species 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
Paleoloxodon. 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.
'' in relation to other elephantids based on nuclear genomes, after Palkopoulou et al. 2018, showing
introgression from African forest elephants and
Mammoth]]
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
Mammoth.
[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 hybridization history, 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
Introgression ancestry from African forest elephants (~36%) 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 was basal to the split between
Woolly mammoth and Columbian mammoths, probably from shortly after the split between the ancestors of mammoths and Asian elephants. The hybridisation 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 indicates Palaeoloxodon individuals 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 Introgression in a single event. 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.
Diagram of the relationships of elephant mitochondrial genomes, after Lin et al. 2023:
List of species
Mainland 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
/ref> (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, 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 muscles 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 variable depending on the species, 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 skull is proportionally short and tall,
with the
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.
The molar teeth of Palaeoloxodon species typically show a "dot-dash-dot" wear pattern,
Species of Palaeoloxodon varied widely in size. Fully grown bulls of Palaeoloxodon recki, Palaeoloxodon antiquus, Palaeoloxodon namadicus and Chinese Palaeoloxodon grew substantially larger than living elephants, with some mature bulls exceeding tall at the shoulder and in body mass, making them some of the largest known terrestrial mammals to have ever lived.
Ecology
Species of
Palaeoloxodon are thought to have had similar social behaviour to modern elephants, with herds of adult females and juveniles, as well as solitary adult males.
The African species of
Palaeoloxodon, as well as
P. namadicus are suggested to have been grazers,
while
P. antiquus is suggested to have been a variable mixed feeder that consumed a considerable amount of browse.
Evolution
Palaeoloxodon first unambiguously appears in the fossil record in Africa during the Early Pleistocene, around 1.8 million years ago as the species
Palaeoloxodon recki ileretensis (it is contested whether earlier "
E. recki" subspecies are related to
Palaeoloxodon).
was the dominant elephant in East Africa for most of the Pleistocene. A population of
P. recki migrated out of Africa at the beginning of the Middle Pleistocene around 800,000 years ago, diversifying into the radiation of Eurasian
Palaeoloxodon species, including
P. antiquus, and
P. namadicus. The precise relationships of the Eurasian taxa to each other are obscure.
The arrival of
P. antiquus in Europe co-incides with the extinction of the temperate adapted
mammoth species
Mammuthus meridionalis (sometimes called the southern mammoth) and its replacement by
Steppe mammoth (the steppe mammoth) in Europe, with the extinction of
M. meridionalis possibly in part a result of competition with
P. antiquus.
was able to disperse onto many islands in the Mediterranean, undergoing insular dwarfism and speciating into numerous distinct varieties of
.
Palaeoloxodon fossils are abundant in China and are assigned to three species,
P. namadicus, P. naumanni and
P. huaihoensis. However, the relationships of Chinese
Palaeoloxodon are currently unresolved and it is unclear how many species were present in the region.
Relationship with humans
Evidence of interaction with
Palaeoloxodon by
archaic humans extends back over 1 million years ago in Africa, with a number sites with
Palaeoloxodon recki in Africa showing evidence of butchery.
There is extensive evidence for butchery and to a lesser extent hunting of the European straight-tusked elephant by archaic humans like
Homo heidelbergensis and
Neanderthal.
Evidence has been found for butchery of
Palaeoloxodon turkmenicus by archaic humans in the Indian subcontinent.
Based on the association of their remains with stone artefacts, it has been suggested modern humans encountered and butchered the Japanese
P. naumanni and the Cyprus dwarf elephant
P. cypriotes during the Last Glacial Period.
Extinction
The timing of the extinction of the last
Paleoloxodon species in Africa,
P. jolensis, is uncertain. While often suggested to have gone extinct during the
Late Pleistocene, most specimens of the species are poorly dated and dating of specimens from Kenya suggests that it went extinct there around 130,000 years ago, at the end of the Middle Pleistocene.
Most Eurasian species of
Palaeoloxodon became extinct towards the end of the Last Glacial Period as part of the Late Pleistocene extinction event of most large terrestrial mammals globally, probably as a result of climate change, human activity, or a combination of both.
The youngest records of
P. antiquus are from the Iberian Peninsula, dating to around 44-43,000 years ago, with footprints from the southern part of the peninsula possibly extending the record to 28,000 years ago.
The youngest Japanese records of
P. naumanni date to around 24,000 years ago.
The timing of extinction of Chinese
Palaeoloxodon and Indian
P. namadicus is uncertain, but claims of a
Holocene survival are not substantiated for either region.
The youngest dates for the Sicilian dwarf elephant
P. cf
. mnaidriensis are around 32-20,000 years ago,
while those of Cyprus dwarf elephant
P. cypriotes are around 12,000 years ago.
The dwarf elephant
P. tiliensis from the Greek island of
Tilos is suggested by some authors to have survived as recently as 3,500 years
Before Present (around 1500 BC) 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.
