Palaeoloxodon namadicus

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.

Life restoration

Asian straight-tusked elephant
Temporal range:
Skull at the Indian Museum, Kolkata
Scientific classification edit
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Proboscidea
Family: Elephantidae
Genus: †Palaeoloxodon
Species:
†P. namadicus
Binomial name
†Palaeoloxodon namadicus
(Falconer & Cautley, 1846)

Some authorities historically regarded it to be a subspecies of Palaeoloxodon antiquus, the European straight-tusked elephant, due to extreme similarities of the tusks.[1] P. namadicus shares similarities to other species 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. Later research suggested that P. namadicus can be distinguished from P. antiquus by its less robust limb bones and more stout cranium (including a better developed parieto-occipital crest).[2]

Based on the stable isotope ratios of carbon and oxygen and the morphology of their teeth, it is suggested that P. namadicus tended towards a grazing diet, as opposed to the sympatric Stegodon and Elephas species, which tended more towards browsing.[3]

The oldest specimens of P. namadicus in India are thought to be over 700,000 years old, dating to the early Middle Pleistocene.[2] Palaeoloxodon namadicus is thought to have become extinct during the Late Pleistocene, making it one of four megafaunal species native to India suggested to have become extinct during the Late Pleistocene, alongside fellow proboscidean Stegodon namadicus, the equine Equus namadicus, and a species of hippopotamus belonging to the genus Hexaprotodon.[4][5] The exact time of extinction of these taxa is unclear to the uncertainly surrounding known dates, many of which were taken decades ago and based on methods that did not involve directly dating the bone itself, with methods that are prone to error.[5]

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 southern China.[6][7] 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]

Size
Estimated size of the largest possible specimen of P. namadicus (known only from a fragmentary femur) with human and Paraceratherium.

Several studies have attempted to estimate the size of the Asian straight-tusked elephants, as well as other prehistoric proboscideans, usually using comparisons of thigh bone length and knowledge of relative growth rates to estimate the size of incomplete skeletons.

One partial skeleton found in India in 1905 had thigh bones that likely measured 165 centimetres (5.41 ft) when complete, suggesting a total shoulder height of 4.5 metres (14.8 ft) for this individual elephant.

Two partial thigh bones were found in the 19th century and would have measured 160 cm (5.2 ft) when complete. A fragment (currently unlocated) from the same locality was said to be almost a quarter larger; volumetric analysis then yields a very speculative size estimate of 5 metres (16.4 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 this estimate based on the "distal femur portion" requires reexamination, as the author himself could only suspect that "fossils are likely stored in the Indian Museum of Kolkata; until such a collection can be revised, this size estimate will remain speculative."[8]

References
  1. Ferretti, M.P. (May 2008). "The dwarf elephant Palaeoloxodon mnaidriensis from Puntali Cave, Carini (Sicily; late Middle Pleistocene): Anatomy, systematics and phylogenetic relationships". Quaternary International. 182 (1): 90–108. Bibcode:2008QuInt.182...90F. doi:10.1016/j.quaint.2007.11.003.
  2. Larramendi, Asier; Zhang, Hanwen; Palombo, Maria Rita; Ferretti, Marco P. (February 2020). "The evolution of Palaeoloxodon skull structure: Disentangling phylogenetic, sexually dimorphic, ontogenetic, and allometric morphological signals". Quaternary Science Reviews. 229: 106090. Bibcode:2020QSRv..22906090L. doi:10.1016/j.quascirev.2019.106090. S2CID 213676377.
  3. Patnaik, Rajeev; Singh, Ningthoujam Premjit; Paul, Debajyoti; Sukumar, Raman (2019-11-15). "Dietary and habitat shifts in relation to climate of Neogene-Quaternary proboscideans and associated mammals of the Indian subcontinent". Quaternary Science Reviews. 224: 105968. doi:10.1016/j.quascirev.2019.105968. ISSN 0277-3791. S2CID 210307849.
  4. Jukar, A.M.; Lyons, S.K.; Wagner, P.J.; Uhen, M.D. (January 2021). "Late Quaternary extinctions in the Indian Subcontinent". Palaeogeography, Palaeoclimatology, Palaeoecology. 562: 110137. doi:10.1016/j.palaeo.2020.110137. S2CID 228877664.
  5. Turvey, Samuel T.; Sathe, Vijay; Crees, Jennifer J.; Jukar, Advait M.; Chakraborty, Prateek; Lister, Adrian M. (January 2021). "Late Quaternary megafaunal extinctions in India: How much do we know?". Quaternary Science Reviews. 252: 106740. doi:10.1016/j.quascirev.2020.106740. S2CID 234265221.
  6. Louys, Julien; Curnoe, Darren; Tong, Haowen (January 2007). "Characteristics of Pleistocene megafauna extinctions in Southeast Asia". Palaeogeography, Palaeoclimatology, Palaeoecology. 243 (1–2): 152–173. doi:10.1016/j.palaeo.2006.07.011.
  7. Geer, Alexandra A. E.; Bergh, Gerrit D.; Lyras, George A.; Prasetyo, Unggul W.; Due, Rokus Awe; Setiyabudi, Erick; Drinia, Hara (August 2016). "The effect of area and isolation on insular dwarf proboscideans". Journal of Biogeography. 43 (8): 1656–1666. doi:10.1111/jbi.12743. ISSN 0305-0270. S2CID 87958022.
  8. Larramendi, Asier (2015). "Proboscideans: Shoulder Height, Body Mass and Shape". Acta Palaeontologica Polonica. doi:10.4202/app.00136.2014.
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