Palaeoloxodon falconeri

Palaeoloxodon falconeri Temporal range: Middle Pleistocene
Mounted skeleton, Nebraska State Museum of Natural History
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Class:	Mammalia
Order:	Proboscidea
Family:	Elephantidae
Genus:	†Palaeoloxodon
Species:	†P. falconeri
Binomial name
†Palaeoloxodon falconeri (Busk, 1867)
Synonyms
Elephas falconeri Busk, 1867 Elephas melitensis Palaeoloxodon melitensis

Palaeoloxodon falconeri is an extinct species of dwarf elephant from the Middle Pleistocene (around 500–200,000 years ago) of Sicily and Malta. It is amongst the smallest of all dwarf elephants at under 1 metre (3.3 ft) in height. A member of the genus Palaeoloxodon, it derived from a population of the mainland European straight-tusked elephant (Palaeoloxodon antiquus).

Chronology

Palaeoloxodon falconeri derives from the 4 metre tall straight-tusked elephant (P. antiquus), which arrived in Europe approximately 800,000 years ago. The oldest radiometrically dated fossils of Palaeoloxodon on Sicily date to around 500,000 years ago, with the colonisation possibly occurring as early as 690,000 years ago or earlier. P. falconeri's ancestors most likely reached Sicily from the Italian mainland, likely via a series of islands that now form part of the southern Calabrian peninsula. The chronology of the species compared to that of the larger endemic species of Palaeoloxodon on Malta and Sicily, the 2 m (6.6 ft) tall Palaeoloxodon mnaidriensis, is somewhat uncertain. It is generally thought that P. falconeri is the earlier species dating to the Middle Pleistocene, and that P. mnaidriensis descends from a subsequent separate late Middle Pleistocene colonisation of the island by P. antiquus, suggested to date to approximately 200,000 years ago. P. falconeri also occurs on Malta, but is generally shorter making it a possible subspecies. It likely dispersed to Malta from Sicily during episodes of low sea level. The chronology of Maltese localities is poorly constrained. The important locality of Spinagallo Cave in southeast Sicily where a large sample of P. falconeri individuals have been found is suggested to date to around 366-233,000 years ago based on optically stimulated luminescence dating and uranium–thorium dating.

Taxonomy

In 1867, George Busk had proposed the species Elephas falconeri for many of the smallest molars selected from the material originally ascribed by Hugh Falconer (for whom the species is named) to Palaeoloxodon melitensis for the Maltese dwarf elephant, a possible subspecies of P. falconeri. The species Elephas/Palaeoloxodon melitensis, formerly considered a distinct species, is now considered a synonym of P. falconeri.

Description

Size comparison of Palaeoloxon falconeri compared to a human

Palaeoloxodon falconeri is considered to be a textbook example of insular dwarfism, with adult individuals around the size of modern elephant calves, drastically smaller than their mainland ancestors. In a 2015 study of specimens from Spinagallo Cave, a composite adult male specimen MPUR/V n1 was estimated to measure 96.5 cm (3 ft 2.0 in) in shoulder height about 305 kg (672 lb) in weight, a composite adult female specimen MPUR/V n2 80 cm (2 ft 7.5 in) in shoulder height and about 168 kg (370 lb) in weight, and a composite newborn male specimen MPUR/V n3 33 cm (1 ft 1.0 in) in shoulder height and about 6.7 kg (15 lb) in weight. A later 2019 volumetric study revised the weight estimates for the adult male and adult female to about 250 kg (551 lb) and 150.5 kg (332 lb) respectively. The newborn male of the species was estimated in the same study to weigh 7.8 kg (17 lb). This makes P. falconeri the smallest known elephant species, along with the roughly equivalently sized but much more poorly known Palaeoloxodon cypriotes of Cyprus.

The morphology of the skull demonstrates neotenic traits similar to those present in juvenile elephants, including the loss of the fronto-parietal crest present in other Palaeoloxodon species. The brain was around the size of a human's, and proportionally much larger relative to skull and body size than P. antiquus. In comparison to adult P. antiquus individuals, the neck was elongated, the torso was proportionally wider and longer, and the forelimbs were shorter while the hindlimbs were longer, resulting in a concave back. The limbs were proportionally more slender than P. antiquus, presumably because they needed to bear less weight. The feet were more digitigrade than modern elephants due to being proportionally narrower and higher. The morphology of the limbs and feet suggest that P. falconeri may have been more nimble than living elephants, and better able to move on steep and uneven terrain. Female members of the species were tuskless. Due to the much smaller body size resulting in increased heat loss, it is possible that the species was covered by a more dense coat of hair than present in living elephants in order to maintain a stable body temperature, though if it was present it was still likely sparse, due to elephants lacking sweat glands. The ears were also likely proportionally much smaller than living elephants for similar thermodynamic reasons. Histology analysis of their bones, teeth and tusks demonstrates that despite their small size, individuals of P. falconeri grew very slowly, reaching sexual maturity at around 15 years of age (older than living elephants), with some individuals aged around 22 still having unfused limb bone epiphyses, indicating that they were still growing. The growth rate was only slightly lower post-sexual maturity, which constrasts with African bush elephants, whose growth slows considerably after sexual maturity. At least one individual reached a lifespan of at minimum 68 years, comparable to full-sized elephants. Dental microwear suggests that P. falconeri was a mixed feeder (both browsing and grazing).

Ecology

Sicily and Malta during the time of P. falconeri exhibited a depauperate fauna, with the only other terrestrial mammal species on the islands being the cat-sized giant dormouse Leithia (the largest dormouse ever) as well as the giant dormouse Maltamys, the otter Nesolutra, and the shrew Crocidura esuae which is possibly the ancestor of the living Sicilian shrew, C. sicula though this is disputed (the presence of a fox of the genus Vulpes has been suggested but is unconfirmed). Sicily was also inhabited by a variety of bird species, as well as frogs (Discoglossus, Bufotes, Hyla), lizards (Lacerta), snakes (Hierophis, Natrix), pond turtles, tortoises (including the large Solitudo and smaller Hermann's tortoise), and bats.

Extinction

Palaeoloxodon falconeri became extinct on Sicily around 200,000 years ago, due to the tectonic uplift of northeast Sicily and Calabria resulting in a narrowing of the distance between the island and the Italian mainland, similar to the geography in the region today, allowing a number of large mammal species from mainland Italy to colonise the island, including carnivores like cave hyenas, cave lions, grey wolves, brown bears, and red foxes, and herbivores like wild boar, red deer, fallow deer, aurochs, steppe bison and the hippo Hippopotamus pentlandi. The straight-tusked elephant again recolonised the island during this episode, giving rise to Palaeoloxodon mnaidriensis, which though strongly dwarfed, was considerably larger than P. falconeri, with its larger body size likely a reaction to these large predators and competitors.

Gallery

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  Reconstruction
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  Skeletons in Milan Natural History Museum
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  Skull at MUSE - Science Museum in Trento