Palaeoloxodon namadicus

Palaeoloxodon namadicus Temporal range: Middle Pleistocene–Late Pleistocene PreꞒ Ꞓ O S D C P T J K Pg N ↓
Skull at the Indian 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 (Falconer & Cautley, 1846)

Palaeoloxodon namadicus is an extinct species of prehistoric elephant known from the early Middle to Late Pleistocene of the Indian 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.

Description[edit]

Some authorities historically regarded P. namadicus and the European straight-tusked elephant (P. antiquus) as the same species due to their similar skull morphology.^[1] P. namadicus shares similarities to other species of Palaeoloxodon, which includes a large crest (the parieto-occipital crest) at the top of the skull that anchored the splenius muscles used to support the head, which is more developed in males than in females. Later research suggested that P. namadicus can be distinguished from P. antiquus by its less robust (more elongate) limb bones and more stout cranium (including a better developed parieto-occipital crest).^[2] Like other large Palaeoloxodon species, the tusks were likely proportionally large, though no known 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.^[3]

Size[edit]

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 (the left one of which was measured to be around 1.6 metres (5.2 ft) in length when excavated in 1834), a left ulna and a right humerus, from Sagauni in Narsinghpur district, Madhya Pradesh, Larramendi extrapolated a shoulder height of 4.35 metres (14.3 ft) and a weight of 13 tonnes (14.3 short tons) for this individual.^[4]

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 (24.3 short tons) in body mass, which if correct would make P. namadicus possibly the largest land mammal ever, exceeding even paraceratheres in size. However, the author stated should be "taken with a grain of salt", as Larramendi stated that he could not locate the specimen, but speculated that it may be stored in the Indian Museum of Kolkata.^[4]

In 2023, 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 (19.8–20.9 short tons).^[5] 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.^[6]

Ecology[edit]

Based on stable isotope ratios of carbon and oxygen and the morphology of their teeth, it is suggested that P. namadicus tended towards a grazing diet. Its arrival on the subcontinent co-incides with a shift in the diet of contemporaneous Elephas hysudricus (the ancestor of the living Asian elephant) from a grazing diet towards browsing-mixed feeding, possibly as a result of niche partitioning.^[7]

Evolution and extinction[edit]

P. namadicus is primarily known from the Indian subcontinent.^[2] Remains attributed to P. namadicus have also been reported across Southeast Asia (including Malaysia, Myanmar, Laos, and Vietnam, and the island of Sulawesi in Indonesia) and as well as China.^[8][9] However, the status of Chinese Palaeoloxodon is unresolved, with other authors considering the remains to belong to P. naumanni (otherwise known from Japan) 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, making their referral to P. namadicus questionable.^[2]

The oldest specimens of P. namadicus in India are thought to be over 700,000 years old, dating to the early Middle Pleistocene,^[2] having evolved, like other Eurasian Palaeoloxodon species from a migration of a population of Palaeoloxodon recki out of Africa.^[10] 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.^[11][12] The exact time of extinction of these taxa is unclear due to the uncertanties regarding dating, but indirect dating from several sites suggests that P. namadicus became extinct within the last 50,000 years.^[12]

References[edit]