| Palaeoloxodon | |
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| Skeleton of thestraight-tusked elephant (Palaeoloxodon antiquus) at the paleontological museum of theSapienza University of Rome | |
Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Mammalia |
| Order: | Proboscidea |
| Clade: | Elephantida |
| Superfamily: | Elephantoidea |
| Family: | Elephantidae |
| Genus: | †Palaeoloxodon Matsumoto, 1924[1] |
| Type species | |
| Elephas namadicus naumanni Makiyama, 1924 | |
| Species | |
| Synonyms | |
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Palaeoloxodon is an extinctgenus ofelephant. It originated in Africa during theEarly Pleistocene, and expanded into Eurasia at the beginning of theMiddle Pleistocene.Palaeoloxodon contains the largest known species of elephants, with mature bulls over 4 metres (13 ft) tall at the shoulders and over 13 tonnes (29,000 lb) in weight, representing among the largest land mammals ever, including the AfricanPalaeoloxodon recki, the Europeanstraight-tusked elephant (Palaeoloxodon antiquus) and the South AsianPalaeoloxodon namadicus. P. namadicus has been suggested to be thelargest known land mammal by some authors based on extrapolation from fragmentary remains, though these estimates are highly speculative.[2] In contrast, the genus also contains many species ofdwarf elephants (an example ofinsular dwarfism) on islands in the Mediterranean, some likePalaeoloxodon falconeri less than 1 metre (3.3 ft) 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 toLoxodonta orElephas, but today is usually considered a valid and separate genus in its own right.
Remains ofPalaeoloxodon 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.[3] In 1695, remains of astraight-tusked elephant were collected fromtravertine deposits near Burgtonna in what is nowThuringia, Germany. While these remains were originally declared by theCollegium Medicum in the nearby city ofGotha to be purely mineral in nature, Wilhelm Ernst Tentzel, a polymath in the employ of the ducal court ofSaxe-Gotha-Altenburg, correctly recognised that they represented the remains of an elephant.[4] Prior to 1845, the remains of Eurasian species ofPalaeoloxodon were considered to be those ofwoolly mammoths. The earliest species ofPalaeoloxodon to be described, the European straight-tusked elephant (Palaeoloxodon antiquus) and the South AsianPalaeoloxodon namadicus, were named by British paleontologistsHugh Falconer andProby Cautley in 1846-47. Prior to the description of the genus,Palaeoloxodon species were initially placed in the genusElephas (which includes theAsian elephant).[5] In 1924,Matsumoto Hikoshichirō coinedPalaeoloxodon, andcircumscribed it as a subgenus ofLoxodonta (which include the living species of African elephants). It included the "E. antiquus—namadicusgroup", and he designated the Japanese "E. namadicus naumanni Mak." as itstype species.[1] Also in 1924, American paleontologistHenry Fairfield Osborn named the generaSivalika andPilgrimia, with the former covering the Asian species and the latter covering the African and Mediterranean island dwarf species ofPalaeoloxodon. In 1931 Osborn named the genusHesperoloxodon to includePalaeoloxodon antiquus. In a 1942 posthumous publication, Osborn recognisedSivalika andPilgrimia as junior synonyms ofPalaeoloxodon, while still recognisingHesperoloxodon as valid.[3] This publication was the first to considerPalaeoloxodon a valid genus in its own right, an opinion followed by later authors such asEmiliano Aguirre in 1969.[6] Later authors have consideredHesperoloxodon another synonym ofPalaeoloxodon. Vincent J. Maglio in a 1973 publication controversially synonymisedPalaeoloxodon withElephas based on morphological similarities between the two genera.[3] Later authors either consideredPalaeoloxodon a valid genus or asubgenus ofElephas.Cladistic analyses findingElephas andPalaeoloxodon to not be each other's closest relatives led to the placement ofPalaeoloxodon species withinElephas to be questioned by other authors.[7][3] By the 2010sPalaeoloxodon was widely regarded as a valid genus separate fromElephas.[3]
During the 19th and 20th centuries, species ofPalaeoloxodon 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 ofPalaeoloxodon to be closely related to African elephants, while others like Wolfgang Soergel in 1915 considered them to be closely related tomammoths.[8] 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 genusElephas.[6][8] In 2016, a study of thestraight-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 theAfrican forest elephant,Loxodonta cyclotis, with the partial nuclear genome supportingP. antiquus as more closely related toL. cyclotis than theAfrican bush elephant,L. africana.[9] A later study published in 2018 by the same authors based on the completenuclear genome revised these results, and suggestedP. antiquus resulted fromreticulate evolution and had a complexhybridization 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 significantintrogressed ancestry from African forest elephants (~36%) and to a lesser extent mammoths (~6%). The ancestry fromL. cyclotis was more closely related to modern West African populations of the forest elephant than to other forest elephant populations, while the mammoth ancestry wasbasal to the split betweenwoolly andColumbian mammoths, probably from shortly after the split between the ancestors of mammoths and Asian elephants. The hybridisation probably took place in Africa, wherePalaeoloxodon was dominant for most of the Early Pleistocene, with the mammoth hybridisation suggested to have taken place earlier than the hybridisation with forest elephants.[10]
Analysis of mitochondrial genomes, includingPalaeoloxodon individuals from Northern China indicatesPalaeoloxodon 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 wereintrogressed in a single event. It has been found that mitochondrial genome of ChinesePalaeoloxodon specimens clustered with aP. antiquus individual from western Europe, which belonged to a separate clade than other sampled EuropeanP. antiquus specimens. The relatively lowdivergence between the mitochondrial genomes of the EuropeanP. antiquus individual and the ChinesePalaeoloxodon specimens may indicate that the populations ofPalaeoloxodon across Eurasia maintainedgene flow with each other, but this is uncertain.[11]
Diagram of the relationships of elephant mitochondrial genomes, after Lin et al. 2023:[11] (note:mitochondrial genomes are only a singlegenetic locus and in contrast to the nuclear genome, do not necessarily accurately reflect true ancestral history)
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These Mediterranean insulardwarf elephant species are almost certainly descended fromP. antiquus
Other indeterminate dwarfPalaeoloxodon species are known from other Greek islands, includingRhodes andKasos.[14]
Many species ofPalaeoloxodon 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 thesplenius 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.[6] The crest shows differences in development depending on species, with the earliest speciesP. recki as well as the JapaneseP. naumanni and Central AsianP. turkmenicus only having weakly developed crests (the so-called "Stuttgart morph"), whileP. antiquus,P. namadicus and ChinesePalaeoloxodon have strongly developed crests (the so-called "namadicus morph"). It is thought that the weakly developed morphology of the POC is the ancestral condition inPalaeoloxodon, with the strongly developed "namadicus morph" having evolved following the migration ofPalaeoloxodon into Eurasia.[15]
The skull is proportionally short and tall,[3] with thepremaxillary bones containing the tusks being flared outwards. The tusks have relatively little curvature, and are proportionally large,[6] and somewhat twisted, with the tusk alveoli (sockets) being divergent from each other at least in Pleistocene species.[3] These tusks could reach 4 metres (13 ft) in length, and probably over 190 kilograms (420 lb) in weight in the largest species, larger than any recorded in modern elephants.[16]
The lamellae (pockets of dentin surrounded by a layer of enamel, forming a ridge-like structure) of molar teeth ofPalaeoloxodon species typically show a "dot-dash-dot" wear pattern when they are found early in their wear life cycle,[17] with the enamel folds concentrated into a major central structure at the midline of the tooth, which are flanked by smaller folds on either side, and the crowns of the tooth are generally proportionally narrow.[18] The teeth are typically veryhypsodont (high crowned) with a substantial number of lamellae (up to 19[6] to 21[19] on the third molar), though the lamellae frequency is distinctly lower than that reached by advancedmammoth species.[3] The morphology of the teeth varies little between non-dwarf EurasianPalaeoloxodon species, meaning that they generally cannot be distinguished based on tooth morphology alone.[20]
Species ofPalaeoloxodon varied widely in size. Fully grown bulls ofPalaeoloxodon recki, Palaeoloxodon antiquus,Palaeoloxodon namadicus andChinesePalaeoloxodon grew substantially larger than living elephants, with some mature bulls exceeding 4 metres (13 ft) tall at the shoulder and 13 tonnes (29,000 lb) in body mass, making them some of the largest known terrestrial mammals to have ever lived.[21][2] In a 2015 study, one fragmentary unlocated femur ofP. namadicus described in the 19th century was estimated to have belonged to an individual 5.2 metres (17 ft) tall and 22 tonnes (49,000 lb) in weight, exceeding the estimates for the otherwise largest known land mammals, theparaceratheres. However, this estimate is highly speculative and the author suggested that it should be "taken witha grain of salt".[2] In contrast, some of the island dwarf species are the smallest elephants known. The smallest species,P. cypriotes andP. falconeri, only reached 1 metre (3.3 ft) tall as fully grown adults,[22][23] with fully grown adult bulls ofP. falconeri having an estimated body mass of only 250 kg (550 lb).[23]
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Species ofPalaeoloxodon are thought to have had similar social behaviour to modern elephants, with herds of adult females and juveniles, as well as solitary adult males.[24] The African species ofPalaeoloxodon, as well asP. namadicus are suggested to have been grazers,[25][26] whileP. antiquus is suggested to have been a variable mixed feeder that consumed a considerable amount ofbrowse.[27]
Palaeoloxodon first unambiguously appears in the fossil record in Africa during theEarly Pleistocene, around 1.8 million years ago as the speciesPalaeoloxodon recki ileretensis (it is contested whether earlier "E. recki" subspecies are related toPalaeoloxodon).[28]P. recki was the dominant elephant in East Africa for most of the Pleistocene. A population ofP. recki migrated out of Africa at the beginning of theMiddle Pleistocene around 800,000 years ago, diversifying into the radiation of EurasianPalaeoloxodon species, includingP. antiquus, andP. namadicus. The precise relationships of the Eurasian taxa to each other are obscure.[29] The arrival ofP. antiquus in Europe co-incides with the extinction of the temperate adaptedmammoth speciesMammuthus meridionalis (sometimes called the southern mammoth) and its replacement byMammuthus trogontherii (the steppe mammoth) in Europe, with the extinction ofM. meridionalis possibly in part a result of competition withP. antiquus.[29]P. antiquus was able to disperse onto many islands in theMediterranean, undergoing insular dwarfism and speciating into numerous distinct varieties ofdwarf elephants.Palaeoloxodon fossils are abundant in China and are assigned to three species,P. namadicus, P. naumanni andP. huaihoensis.[30] However, the relationships of ChinesePalaeoloxodon are currently unresolved and it is unclear how many species were present in the region.[6]
Evidence of interaction withPalaeoloxodon byarchaic humans extends back over 1 million years ago in Africa, with a number sites withPalaeoloxodon recki in Africa showing evidence of butchery.[31] There is extensive evidence for butchery and to a lesser extent hunting of the European straight-tusked elephant by archaic humans likeHomo heidelbergensis andNeanderthals.[32] Evidence has been found for butchery ofPalaeoloxodon turkmenicus by archaic humans in the Indian subcontinent.[33] Based on the association of their remains with stone artefacts, it has been suggested modern humans encountered and butchered the JapaneseP. naumanni and the Cyprus dwarf elephantP. cypriotes during theLast Glacial Period.[34][35]
The timing of the extinction of the lastPaleoloxodon species in Africa,P. jolensis, is uncertain. While often suggested to have gone extinct during theLate 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.[25] Most Eurasian species ofPalaeoloxodon became extinct towards the end of theLast Glacial Period as part of theLate Pleistocene extinction event of most large terrestrial mammals globally, probably as a result of climate change, human activity, or a combination of both.[36] The youngest records ofP. 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.[37] The youngest Japanese records ofP. naumanni date to around 24,000 years ago.[38] The timing of extinction of ChinesePalaeoloxodon and IndianP. namadicus is uncertain, but claims of aHolocene survival are not substantiated for either region.[39][40][41] The youngest dates for the Sicilian dwarf elephantP. cf. mnaidriensis are around 32-20,000 years ago,[42] while those of Cyprus dwarf elephantP. cypriotes are around 12,000 years ago, shortly after humans arrived to the island.[43] The dwarf elephantP. tiliensis from the Greek island ofTilos is suggested by some authors to have survived as recently as 3,500 yearsBefore 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.[14]
Genera of the orderProboscidea | ||||||||||||||||||||||||||||||
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