Palaeoloxodon namadicus

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Palaeoloxodon namadicus


Reconstruction of P. namadicus. © @ RJ Palmer.

Temporal range: Quaternary; >700,000-29,000 or 14,000 years ago[1][2] (Chibanian to Late Pleistocene)

Scientific classification:

Life
Domain: Eukaryota
(unranked): Unikonta
(unranked): Opisthokonta
(unranked): Holozoa
(unranked): Filozoa
Kingdom: Animalia
Subkingdom: Eumetazoa
(unranked): Bilateria
Superphylum: Deuterostomia
Phylum: Chordata
Infraphylum: Gnathostomata
Clade: Eugnathostomata
Clade: Teleostomi
Clade: Tetrapoda
Clade: Reptiliomorpha
Clade: Amniota
Clade: Synapsida
Clade: Eupelycosauria
Clade: Sphenacodontia
Clade: Sphenacodontoidea
Order: Therapsida
Clade: Cynodontia
Clade: Prozostrodontia
Clade: Mammaliaformes
Class: Mammalia
Legion: Cladotheria
Sublegion: Zatheria
Infralegion: Tribosphenida
Subclass: Theria
Clade: Eutheria
Infraclass: Placentalia
Subcohort: Exafroplacentalia
Magnorder: Atlantogenata
Superorder: Afrotheria
Clade: Paenungulata
Order: Proboscidea
Suborder: Elephantiformes
Clade: Elephantimorpha
Clade: Elephantida
Superfamily: Elephantoidea
Family: Elephantidae
Tribe: Elephantini
Subtribe: †Palaeoloxodontini
Genus: †Palaeoloxodon
Species: †P. namadicus

Palaeoloxodon namadicus is an extinct species of elephant that lived in India from the earliest Chibanian (Middle Pleistocene) to the Late Pleistocene.

Description:
P. namadicus can be distinguished from the European P. antiquus in having a more robust cranium and occipital. The parieto-occipital crest (POC, a feature unique to Palaeoloxodon), is considerably more developed (thicker) than in P. antiquus. This allowed for a more powerful extra splenius muscle in order to hold up a more massive head than in P. antiquus (due to the deeper and more massively built parietal region).[1] However, the postcranial skeleton is consistently less robust than in P. antiquus; the slender proportions of the limb bones are similar to those seen in P. recki.[1][3]

Sexual dimorphism in the POC is particularly evident in P. namadicus. This muscle attachment was more robust and more expanded (closer to the external choanes) in males than in females. Likewise, the POC in males had strong intermuscular occipital lines, whereas these were absent or weakly developed in females.[1]

Two specimens have had their body size estimated. These were originally found in 1834 in Sagauni at Narsinghpur district, India. One of the individuals, Sagauni I, is comprised of limb elements, and was estimated to have had a shoulder height of 435 cm, with a body mass of ~13 tonnes. Asier Larramendi argues that because the right proximal femoral head was completely detached, it was a young adult. The second specimen, Sagauni II, is a distal femur fragment said to be nearly one-quarter larger than Sagauni I’s femur. Under the assumption that the femur fragment was 20% larger, this suggests a femur length of 190 cm. Such an elephant is estimated to have been 520 cm tall at the shoulder and weighed 22 tonnes. If so, this would make P. namadicus the largest terrestrial mammal that ever lived. However, this fragmentary specimen must be restudied; Asier Larramendi believes this estimate is speculative and must be taken with a grain of salt.[3]

Extinction:
Palaeoloxodon namadicus is one of the four mammalian species that went extinct in India during the Late Pleistocene. Terminal radiocarbon dates for P. namadicus fall within Marine Isotope Stage (MIS) 2; this period dates from 29-14 kya. Species that went extinct in India during this time were all endemic to the Indian subcontinent and/or had small litters and long intervals between litters (inferred from extant relatives).

The limited number of Indian megafaunal extinctions, including that of P. namadicus, has been linked to fluctuating monsoon intensity, but this alone cannot account for their extinction. In India, evidence for a shift to microlith usage begins at the Middle Paleolithic to Late Paleolithic transition (45,000-35,000 years BP). This suggests the use of composite tools by humans (e.g. bows and arrows), making them more efficient hunters and allowing them to put more pressure on Indian megafauna.[2]

References:

[1] Larramendi, A., Zhang, H., Palombo, M. R., & Ferretti, M. P. (2020). The evolution of Palaeoloxodon skull structure: Disentangling phylogenetic, sexually dimorphic, ontogenetic, and allometric morphological signals. Quaternary Science Reviews, 229, 106090. doi:10.1016/j.quascirev.2019.106090
[2] Jukar, A. M., Lyons, S. K., Wagner, P. J., & Uhen, M. D. (2020). Late Quaternary extinctions in the Indian Subcontinent. Palaeogeography, Palaeoclimatology, Palaeoecology, 110137. doi:10.1016/j.palaeo.2020.110137 
[3] Larramendi, A. 2016. Shoulder height, body mass, and shape of proboscideans. Acta Palaeontologica Polonica 61 (3): 537–574.

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I've written about how well I think the argument that P. namadicus really weighed 22 tonnes holds up in the animal sizes thread. In this post, I'm going to grant this assumption to make a separate point. I believe that, if Sagauni II really weighed 22 tonnes, then it was most likely a very large or record sized individual of its species. Here's why.


Normally, I assume that a fossil specimen was of average size for its species in the absence of a sufficiently large sample size that proves otherwise. However, let's look at Table 8 of Larramendi (2016).



Two of the proboscidean species in this table (both extinct) are projected to have reached or exceeded 20 tonnes in body mass throughout their entire size range. Are you noticing something, though? Such individuals are predicted to be very large or record sized individuals. A 20+ tonne M. borsoni is a very large individual, and a 20+ tonne P. antiquus is at around the absolute cap for the species' size.

I realize this isn't a huge sample size of species, but if weights of 20+ tonnes are regarded as exceptionally large for these two extinct proboscideans, then it's well within possibility that a 22 tonne P. namadicus was too, suggesting a consistent max weight of 20+ tonnes (and <30 tonnes) for proboscideans.

Alternatively, P. namadicus really was 22 tonnes on average and max sized individuals could get astonishingly enormous, but I regard this as less likely. One of the other specimens of P. namadicus mentioned by Asier Larramendi was estimated to have weighed ~13 tonnes in life. Larramendi argues that this individual was a young adult on the grounds of the proximal head of the femur being detached (note that he calls it a young adult in the Appendix). If so, then I think it was getting close to the average adult size of the species, even though it could have had the potential to grow considerably more if it had lived longer (depending on how much longer).

Larramendi also mentions a partial skeleton of P. namadicus found in the alluvial deposits of the Godari River at Nandur in 1905, with femora estimated to measure 165 cm, and therefore suggesting a 4.5 meter tall individual. Scaling down or up from Sagauni II and I (respectively) both suggest an animal weighing ~14.2-14.3 tonnes. A more recently described femur found in the Narmada River basin in India is 149 cm long, suggesting a 4 meter tall individual. So, at least from what I could get from Larramendi's paper, known P. namadicus specimens seem to be more consistently in the range of large to very large Columbian mammoths (~11-15 tonnes).

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Thanks to razor45dino for finding this originally.

The body mass distribution of the Taiwan specimens corresponds to that of other mainland species from the genus (Fig. 6, Table S4). The mean body mass values for Loxodonta africana, Palaeoloxodon recki and Palaeoloxodon antiquus are observed to be 5.13, 10.47 and 9.05 tonnes respectively. However, Palaeoloxodon namadicus exhibited a very high mean body mass of 15.97 tonnes. The Games-Howell pairwise test also suggested a significant difference in the body size distribution between the compared species (p < 0.05). P. namadicus is significantly heavier than L. africana, P. antiquus and Palaeoloxodon specimens of Taiwan (Fig. 6). The standard deviation values for all the distributions were considerably high due to smaller size of the datasets (Table S4).

www.sciencedirect.com/science/article/pii/S0277379124002622