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Palaeoloxodon namadicus

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Palaeoloxodon namadicus
Temporal range: Middle Pleistocene–Late Pleistocene
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Skull at the Indian Museum, Kolkata
Scientific classification Edit this 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 Middle Pleistocene 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

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Partial skull of a female individual, NHMUK PV M3092, showing parieto-occipital crest at the top of the skull

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 growth of bone (the parieto-occipital crest) at the top of the skull that overhangs the forehead region, which likely served 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 (more elongate) 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 in P. antiquus.[2] Palaeoloxodon turkmenicus, also known from the Indian subcontinent, is distinguished from P. namadicus by its much more weakly developed parietal-occipital crest.[3] 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 3.66 metres (12.0 ft) long and over 120 kilograms (260 lb) in weight when complete, larger than the largest recorded African bush elephant tusk.[4]

Size

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Size comparison of the Sagauni 1 specimen, estimated to be 4.35 metres tall, compared to a human

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 (NHMUK PV M3092, which is the lectotype specimen of the species).[2]

Palaeoloxodon namadicus is the largest species in the genus Palaeoloxodon and one of the largest known proboscideans, 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 (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 in Narsinghpur district, Madhya Pradesh, Larramendi extrapolated a shoulder height of 4.35 metres (14.3 ft) and a weight of 13 tonnes (29,000 lb) for this individual.[5]

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 make P. namadicus possibly the largest land mammal ever, exceeding even paraceratheres in size. However, Larramendi stated that is estimate should be "taken with a 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.[5]

Highly speculative size estimate of P. namadicus based on a lost partial femur measured in the 19th century, compared to the paracerathere Paraceratherium asiaticum (labelled as Indricotherium transouralicum)

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 18–19 tonnes (40,000–42,000 lb).[6] 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.[7] In 2024, Biswas, Chang and Tsai estimated a maximum shoulder height of 4.51 metres (14.8 ft) and suggested that the body mass for 5 measured specimens ranged from 13.2 to 18.5 tonnes (29,000 to 41,000 lb).[8]

Ecology

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Life restoration

Fossils of Palaeoloxodon namadicus are known from the northern and central Indian subcontinent, including the Narmada and Godavari valleys, and the Indo-Gangetic Plain.[9] Based on stable isotope ratios of carbon and oxygen and the morphology of their teeth, it is suggested that P. namadicus tended had a grazing-mixed feeding diet,[10][11] with a specimen found on the banks of the Dhasan River suggested to have primarily consumed C4 grasses.[11] The species is suggested to have primarily inhabited open grassland habitats.[10][11] Its arrival on the subcontinent coincides 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.[10]

Evolution and extinction

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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.[12][13] 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 and their skulls lack the infraorbital depression characteristic of Indian P. namadicus specimens, making their referral to P. namadicus questionable.[2]

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.[14] 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.[3] 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 a global wave of megafaunal extinctions during the Late Pleistocene.[15][16] 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.[16][15]

References

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  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. ^ a b c d 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. ^ a b Jukar, Advait M.; Bhat, Ghulam; Parfitt, Simon; Ashton, Nick; Dickinson, Marc; Zhang, Hanwen; Dar, A. M.; Lone, M. S.; Thusu, Bindra; Craig, Jonathan (2024-10-11). "A remarkable Palaeoloxodon (Mammalia, Proboscidea) skull from the intermontane Kashmir Valley, India". Journal of Vertebrate Paleontology. doi:10.1080/02724634.2024.2396821. ISSN 0272-4634.
  4. ^ Larramendi, Asier (2023-12-10). "Estimating tusk masses in proboscideans: a comprehensive analysis and predictive model". Historical Biology: 1–14. doi:10.1080/08912963.2023.2286272. ISSN 0891-2963.
  5. ^ a b Larramendi, Asier (2015). "Proboscideans: Shoulder Height, Body Mass and Shape". Acta Palaeontologica Polonica. doi:10.4202/app.00136.2014.
  6. ^ Paul, Gregory S.; Larramendi, Asier (June 9, 2023). "Body mass estimate of Bruhathkayosaurus and other fragmentary sauropod remains suggest the largest land animals were about as big as the greatest whales". Lethaia. 56 (2): 1–11. Bibcode:2023Letha..56..2.5P. doi:10.18261/let.56.2.5. Retrieved June 9, 2023.
  7. ^ Romano, Marco; Bellucci, Luca; Antonelli, Matteo; Manucci, Fabio; Palombo, Maria Rita (2023-06-13). "Body mass estimate of Anancus arvernensis (Croizet and Jobert 1828): comparison of the regression and volumetric methods". Journal of Quaternary Science. 38 (8): 1357–1381. Bibcode:2023JQS....38.1357R. doi:10.1002/jqs.3549. ISSN 0267-8179.
  8. ^ Biswas, Deep Shubhra; Chang, Chun-Hsiang; Tsai, Cheng-Hsiu (July 2024). "Land of the giants: Body mass estimates of Palaeoloxodon from the Pleistocene of Taiwan". Quaternary Science Reviews. 336: 108761. Bibcode:2024QSRv..33608761B. doi:10.1016/j.quascirev.2024.108761. Supplementary Data
  9. ^ Ghosh, Rupa; Sehgal, R. K.; Srivastava, Pradeep; Shukla, U. K.; Nanda, A. C.; Singh, D. S. (November 2016). "Discovery of Elephas cf. namadicus from the late Pleistocene strata of Marginal Ganga Plain". Journal of the Geological Society of India. 88 (5): 559–568. doi:10.1007/s12594-016-0521-7. ISSN 0016-7622.
  10. ^ a b c 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. Bibcode:2019QSRv..22405968P. doi:10.1016/j.quascirev.2019.105968. ISSN 0277-3791. S2CID 210307849.
  11. ^ a b c Maurya, Sakshi; Ghosh, Rupa; Sehgal, Ramesh Kumar; Srivastava, Pradeep; Shukla, Uma Kant; Singh, Abhishek Pratap; Sarangi, Shushanta (September 2022). "Stable Isotopic studies of the herbivorous mammals from the Marginal Ganga Plain, India: implication for the palaeo-environmental reconstruction". Geological Journal. 57 (9): 3935–3948. doi:10.1002/gj.4522. ISSN 0072-1050.
  12. ^ Louys, Julien; Curnoe, Darren; Tong, Haowen (January 2007). "Characteristics of Pleistocene megafauna extinctions in Southeast Asia". Palaeogeography, Palaeoclimatology, Palaeoecology. 243 (1–2): 152–173. Bibcode:2007PPP...243..152L. doi:10.1016/j.palaeo.2006.07.011.
  13. ^ 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. Bibcode:2016JBiog..43.1656V. doi:10.1111/jbi.12743. ISSN 0305-0270. S2CID 87958022.
  14. ^ Lister, Adrian M. (2004), "Ecological Interactions of Elephantids in Pleistocene Eurasia", Human Paleoecology in the Levantine Corridor, Oxbow Books, pp. 53–60, ISBN 978-1-78570-965-4, retrieved 2020-04-14
  15. ^ a b 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. Bibcode:2021PPP...56210137J. doi:10.1016/j.palaeo.2020.110137. S2CID 228877664.
  16. ^ a b 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. Bibcode:2021QSRv..25206740T. doi:10.1016/j.quascirev.2020.106740. S2CID 234265221.
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