Palaeoloxodon namadicus
Palaeoloxodon namadicus is an extinct species of prehistoric elephant known from the Middle Pleistocene to Late Pleistocene of the Indian subcontinent, and possibly also elsewhere in Asia. The species grew larger than any living elephant, and is one of the largest known proboscideans alongside the mastodon "Mammut" borsoni. Some authors have suggested P. namadicus to have been the largest known land mammal based on extrapolation from fragmentary remains, though these estimates are speculative.
Taxonomic history
Remains now recognised as belonging to P. namadicus were unearthed during the rule of the British East India Company in India at least as early as the 1830s. The species was named as Elephas namadicus by British paleontologists Hugh Falconer and Proby Cautley in 1846, based on a skull collected from the valley of the Godavari River in central India. In 1924, American paleontologist Henry Fairfield Osborn placed it within the newly coined genus Sivalika. Also in that year, Japanese paleontologist Matsumoto Hikoshichirō placed it within his newly coined subgenus Palaeoloxodon, which he placed within Loxodonta, with the type species being the Japanese Loxodonta (Palaeoloxodon) naumanni, which had previously been named also in 1924 as a subspecies of P. namadicus.In his posthumous 1942 monograph, Osborn placed the species within Palaeoloxodon, which he regarded as a genus in its own right rather than as a subgenus, with both positions widely supported by modern authors. A number of authors, including Vincent J. Maglio in his widely referenced 1973 work Origin and Evolution of the Elephantidae, have historically regarded P. namadicus and the largely European straight-tusked elephant as the same species due to their similar skull and tooth morphology. This was questioned by later authors and the two species are now generally considered distinct.
Description
P. namadicus shares similarities to other species of Palaeoloxodon, which includes a large growth of bone at the top of the skull that overhangs the forehead region, which likely anchored the splenius muscles used to support the head. This structure is more developed in males than in females. Recent research has suggested that P. namadicus can be distinguished from P. antiquus by its less robust limb bones and more stout cranium, and the presence of a teardrop shaped indentation/depression in the infraorbital region behind the eyesocket not found in P. antiquus.Palaeoloxodon turkmenicus, also known from the Indian subcontinent, is distinguished from P. namadicus by its much more weakly developed parietal-occipital crest. Like other large Palaeoloxodon species, the tusks of P. namadicus were proportionally large, though no complete tusks are known. One partial tusk was estimated to be long and over in weight when complete, larger than the largest recorded African bush elephant tusk.
Size
Like living elephants, Palaeoloxodon namadicus is thought to have been sexually dimorphic, with males considerably larger than females, with the skull of a P. namadicus male found in the Godavari valley described in 1905 being a full 40% larger than that of a mature female.Palaeoloxodon namadicus is the largest species in the genus Palaeoloxodon and one of the largest known proboscideans along with the mastodon "Mammut" borsoni, and considerably larger than living elephants. A 2015 study by Asier Larramendi attempted to estimate the size of P. namadicus, as well as other prehistoric proboscideans. Based on a fragmentary skeleton of an adult male, comprising two femurs, a left ulna and a right humerus, from Sagauni in Narsinghpur district, Madhya Pradesh, Larramendi extrapolated a shoulder height of and a weight of for this individual.
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 and a speculative size estimate of tall at the shoulder and in body mass, which if correct would make P. namadicus possibly the largest land mammal ever, exceeding even paraceratheres in size. However, Larramendi stated that this estimate should be "taken with a grain of salt", as they could not locate the specimen, but speculated that it may be stored in the Indian Museum of Kolkata.In 2023, a publication by Gregory S. Paul and Larramendi estimated that another specimen identified as cf. P. namadicus, also only known from a partial femur, would have weighed. 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. In 2024, Biswas, Chang and Tsai estimated a maximum shoulder height of and body masses between for 5 specimens of P. namadicus from the Indian subcontinent. including supplemental table S4
Ecology
Fossils of Palaeoloxodon namadicus are known from the northern and central Indian subcontinent, including the Narmada and Godavari valleys, and the Indo-Gangetic Plain. Some authors have also reported that the species was present in Sri Lanka. Based on stable isotope ratios of carbon and oxygen and the morphology of their teeth, it is suggested that P. namadicus had a grazing to grazing predominant mixed feeding diet, with a specimen found on the banks of the Dhasan River suggested to have primarily consumed C4 grasses.The species is suggested to have primarily inhabited open grassland habitats. Its arrival on the subcontinent coincides with a shift in the diet of contemporaneous Elephas hysudricus from a grazing diet towards browsing-mixed feeding, possibly as a result of niche partitioning. Species of Palaeoloxodon probably had similar social behaviour to living elephants, with females and juveniles living in matriarchal herds, while males left these herds to live solitarily upon reaching adolescence around 14-15 years of age.
Evolution and extinction
P. namadicus is primarily known from the Indian subcontinent. Remains attributed to P. namadicus have also been reported across Southeast Asia and as well as China. However, the status of Chinese Palaeoloxodon is unresolved, with other authors considering the remains to belong to P. naumanni or the separate species P. huaihoensis. The postcranial remains of Palaeoloxodon from China are substantially more robust than Indian P. namadicus and in many respects are more similar to those of P. antiquus and their skulls lack the infraorbital depression characteristic of Indian P. namadicus specimens, making their referral to P. namadicus questionable. By the early 2020s, it was generally considered that Chinese Palaeoloxodon remains are more closely related or even attributable to the largely European P. antiquus, rather than to P. namadicus.P. namadicus is thought to have ultimately evolved, like other Eurasian Palaeoloxodon species from a migration of a population of Palaeoloxodon recki out of Africa. The earliest records of Palaeoloxodon in the Indian subcontinent are uncertain, though date to sometime in the Middle Pleistocene, with most remains of Palaeoloxodon in the Indian subcontinent from the late Middle Pleistocene onwards having the characteristic skull morphology of P. namadicus. Palaeoloxodon namadicus is thought to have become extinct during the Late Pleistocene, making it one of four megafauna species native to the Indian subcontinent suggested to have become extinct during the Late Pleistocene, alongside fellow proboscidean Stegodon namadicus, the equine Equus namadicus, and the hippopotamus Hexaprotodon, along with the local extinction of ostriches, as part of the Late [Pleistocene extinctions|Late Quaternary extinction event] during the Late Pleistocene, where most large mammals globally became extinct. The exact time of extinction of these taxa is unclear due to the uncertainties regarding dating, but indirect dating from several sites suggests that P. namadicus became extinct within the last 50,000 years, with some records possibly as late as 25,000 years ago, implying that P. namadicus overlapped with modern humans in the region. There is little to no current evidence of human interaction with P. namadicus.