| Palaeoloxodon namadicus | |
|---|---|
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| Skull at theIndian Museum, Kolkata | |
Scientific classification | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Mammalia |
| Order: | Proboscidea |
| Family: | Elephantidae |
| Genus: | †Palaeoloxodon |
| Species: | †P. namadicus |
| Binomial name | |
| †Palaeoloxodon namadicus | |
| Synonyms | |
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Palaeoloxodon namadicus is an extinctspecies of prehistoric elephant known from theMiddle Pleistocene toLate Pleistocene of theIndian subcontinent, and possibly also elsewhere in Asia. The species grew larger than any living elephant, and some authors have suggested it to have been the largest known land mammal based on extrapolation from fragmentary remains, though these estimates are speculative.
Remains now recognised as belonging toP. namadicus were unearthed duringthe rule of the British East India Company in India at least as early as the 1830s.[1][2] The species was named asElephas namadicus by British paleontologistsHugh Falconer andProby Cautley in 1846,[3] based on a skull collected from the valley of theGodavari River in central India.[4] In 1924, American paleontologistHenry Fairfield Osborn placed it within the newly coined genusSivalika.[5] Also in that year, Japanese paleontologistMatsumoto Hikoshichirō placed it within his newly coined subgenusPalaeoloxodon, which he placed withinLoxodonta (which contains the living African elephants).[6] In his posthumous 1942 monograph, Osborn placed the species withinPalaeoloxodon, which he regarded as a genus in its own right rather than as a subgenus,[7] with both positions widely supported by modern authors.[8] A number of authors, including Vincent J. Maglio in his widely referenced 1973 workOrigin and Evolution of the Elephantidae, have historically regardedP. namadicus and the largely Europeanstraight-tusked elephant (P. antiquus) as the same species due to their similar skull and tooth morphology.[a][4][9] This was questioned by later authors and the two species are now generally considered distinct.[8]
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P. namadicus shares similarities to other species ofPalaeoloxodon, which includes a large growth of bone (the parieto-occipital crest) at the top of the skull that overhangs the forehead region, which likely anchored thesplenius muscles used to support the head. This structure is more developed in males than in females. Recent research has suggested thatP. namadicus can be distinguished fromP. antiquus by its less robust (proportionally more slender) limb bones and more stout cranium (including a better developed parieto-occipital crest), and the presence of a teardrop shaped indentation/depression in the infraorbital region behind the eyesocket not found inP. antiquus.[8]Palaeoloxodon turkmenicus, also known from the Indian subcontinent, is distinguished fromP. namadicus by its much more weakly developed parietal-occipital crest.[11] Like other largePalaeoloxodon species, the tusks ofP. namadicus were proportionally large, though no complete tusks are known. One partial tusk was estimated to be 3.66 metres (12.0 ft) long and over 120 kilograms (260 lb) in weight when complete, larger than the largest recordedAfrican bush elephant tusk.[12]
Like living elephants,Palaeoloxodon namadicus is thought to have beensexually dimorphic, with males considerably larger than females, with the skull of aP. namadicus male found in the Godavari valley described in 1905 being a full 40% larger than that of a mature female (NHMUK PV M3092, which is thelectotype specimen of the species).[8]
Palaeoloxodon namadicus is the largest species in the genusPalaeoloxodon and one of the largest known proboscideans, and considerably larger than living elephants. A 2015 study by Asier Larramendi attempted to estimate the size ofP. namadicus, as well as other prehistoric proboscideans. Based on a fragmentary skeleton of an adult male, comprising two femurs (the left one of which was measured to be 1.6 metres (5.2 ft) in length when excavated in 1834), a left ulna and a right humerus, from Sagauni inNarsinghpur district,Madhya Pradesh, Larramendiextrapolated a shoulder height of 4.35 metres (14.3 ft) and a weight of 13 tonnes (29,000 lb) for this individual.[1]
A fragmentary lower portion of a femur described in 1834 in the same publication that described the femurs of the Sagauni specimen, stated that this femur was almost a quarter larger than that from Sagauni. Assuming it was about 20% larger, Larramendi calculated an extrapolated femur length of 1.9 metres (6.2 ft) and a speculative size estimate of 5.2 metres (17.1 ft) tall at the shoulder and 22 tonnes (49,000 lb) in body mass, which if correct would makeP. namadicus possibly the largest land mammal ever, exceeding evenparaceratheres in size. However, Larramendi stated that this estimate should be "taken witha grain of salt" (treated with caution), as they could not locate the specimen, but speculated that it may be stored in the Indian Museum of Kolkata.[1]
In 2023, a publication byGregory S. Paul and Larramendi estimated that another specimen identified as cf.P. namadicus, also only known from a partial femur, would have weighed 18–19 tonnes (40,000–42,000 lb).[13] Other authors have noted that weight estimates for proboscideans based on single bones can lead to estimates that are "highly improbable" compared to accurate estimates from complete skeletons.[14] In 2024, Biswas, Chang and Tsai estimated a maximum shoulder height of 4.51 metres (14.8 ft) an body masses between 13.22 to 18.47 tonnes (29,100 to 40,700 lb) for 5 specimens ofP. namadicus from the Indian subcontinent.[15]including supplemental table S4
Fossils ofPalaeoloxodon namadicus are known from the northern and central Indian subcontinent, including theNarmada andGodavari valleys, and theIndo-Gangetic Plain.[16] Some authors have also reported that the species was present inSri Lanka.[17] Based onstable isotope ratios of carbon and oxygen and the morphology of their teeth, it is suggested thatP. namadicus had agrazing to grazing predominant mixed feeding (bothbrowsing and grazing) diet,[18][19] with a specimen found on the banks of theDhasan River suggested to have primarily consumedC4 grasses.[19] The species is suggested to have primarily inhabited opengrassland habitats.[18][19] Its arrival on the subcontinent coincides with a shift in the diet of contemporaneousElephas hysudricus (the ancestor of the livingAsian elephant) from a grazing diet towardsbrowsing-mixed feeding, possibly as a result ofniche partitioning.[18]
P. namadicus is primarily known from the Indian subcontinent.[8] Remains attributed toP. namadicus have also been reported across Southeast Asia (including Malaysia, Myanmar, Laos, and Vietnam, and the island ofSulawesi in Indonesia) and as well as China.[20][21] However, the status of ChinesePalaeoloxodon is unresolved, with other authors considering the remains to belong toP. naumanni (otherwise known from Japan, and originally described as subspecies ofP. namadicus) or the separate speciesP. huaihoensis. The postcranial remains ofPalaeoloxodon from China are substantially more robust than IndianP. namadicus and in many respects are more similar to those ofP. antiquus and their skulls lack the infraorbital depression characteristic of IndianP. namadicus specimens, making their referral toP. namadicus questionable.[8] In the 2020s, some authors began suggesting that ChinesePalaeoloxodon remains were attributable to the largely EuropeanP. antiquus.[11]
P. namadicus is thought to have ultimately evolved, like other EurasianPalaeoloxodon species from a migration of a population ofPalaeoloxodon recki out of Africa.[22] The earliest records ofPalaeoloxodon in the Indian subcontinent are uncertain, though date to sometime in theMiddle Pleistocene, with most remains ofPalaeoloxodon in the Indian subcontinent from the late Middle Pleistocene onwards having the characteristic skull morphology ofP. namadicus.[11]Palaeoloxodon namadicus is thought to have becomeextinct during theLate Pleistocene, making it one of fourmegafauna species native to the Indian subcontinent suggested to have become extinct during the Late Pleistocene, alongside fellowproboscideanStegodon namadicus, the equineEquus namadicus, and the hippopotamusHexaprotodon, along with the local extinction ofostriches, as part of aglobal wave of megafaunal extinctions during the Late Pleistocene.[23][24] The exact time of extinction of these taxa is unclear due to the uncertainties regarding dating, but indirect dating from several sites suggests thatP. namadicus became extinct within the last 50,000 years, with some records possibly as late as 25,000 years ago, implying thatP. namadicus overlapped with modern humans in the region.[24][23] There is little to no current evidence of human interaction withP. namadicus.[10]