Straight-tusked elephant

The straight-tusked elephant (Palaeoloxodon antiquus) is an extinct species of elephant that inhabited Europe and Western Asia during the Middle and Late Pleistocene (781,000–30,000 years Before Present). One of the largest known elephant species, mature bulls on average had a shoulder height of 3.81 - 4.2 m and a weight of 10.8-15 tonne. Like modern elephants, the straight-tusked elephant lived in herds, flourishing during interglacial periods, when its range would extend as far north as Great Britain. Skeletons found in association with stone tools and wooden spears suggest they were scavenged and hunted by early humans, including Neanderthals. It is the ancestral species of most dwarf elephants that inhabited islands in the Mediterranean.

Description


Like many other members of the genus Palaeoloxodon, P. antiquus possesses a well developed parieto-occipital crest at the top of the cranium. The crest functioned to anchor muscle tissue, including the splenius as well as an additional muscle layer called the "extra splenius" (which was likely similar to the "splenius superficialis" found in Asian elephants) which wrapped around the top of the head. The crest likely developed to support the very large size of the head, as the skulls of Palaeoloxodon are the largest proportionally and in absolute size among proboscideans. Two morphs of P. antiquus were previously suggested to exist in Europe on the basis of parieto-occipital crest variation, one more similar to P. namadicus, but these were shown to be the result of ontogenetic variation and taphonomic distortion. P. antiquus can be distinguished from the Indian P. namadicus based on its less stout cranium and more robust limb bones. The premaxillary bones (which contain the tusks) are fan-shaped and very broad in front-view. The tusks are very long relative to body size and vary from straight to slightly curved. The teeth are high crowned (hypsodont), with each third molar having approximately 16–21 ridges/lamellae. The forelimbs of P. antiquus, particuarly the humerus and scapular, are proportionally longer than those of living elephants, resulting in the high position of the shoulder. The head represents the highest point of the animal, with the back being somewhat sloped though irregular in shape. The spines of the back vertebrae are noticeably elongate. The body (including the pelvis) was broad relative to extant elephants. The tail was relatively long. Although not preserved, the body was probably only sparsely covered in hair, similar to extant elephants, and probably had large ears.

As with modern elephants, the species was sexually dimorphic, with males being substantially larger than females, with this size dimorphism being more pronounced than in living elephants. P. antiquus was on average considerably larger than any living elephant. The average mature straight-tusked elephant bull has been estimated to have had a shoulder height of 3.8-4.2 m (average 4 m) and a weight of around 10.8-15 t (average 13 t) (for comparison, mature bulls of the largest living elephant species, the African bush elephant on average have a shoulder height of 3.04 to 3.36 m and a mass of 5.2-6.9 t). Adult males had tusks typically around 3.5-4 m long, with masses comfortably exceeding 100 kg, with the preserved portion of one particularly large tusk from Aniene, Italy measured to be 3.9 m in length, having an estimated mass of over 190 kg. Females probably reached shoulder heights exceeding 3 m and weights exceeding 5.5 t (for comparison, female African bush elephants reach an average shoulder height of 2.6 m and body mass of 3 t. A largely complete 5 year old calf from Cova del Rinoceront in Spain was estimated to have a shoulder height of 178–187 cm and a body mass of 1.45-1.5 t, which is comparable to a similarly aged African bush elephant.

History of discovery and taxonomy
In 1695, remains of a straight-tusked elephant were collected from travertine deposits near Burgtonna in what is now Thuringia, Germany. While these remains were originally declared by the Collegium Medicum in the nearby city of Gotha to be purely mineral in nature, Wilhelm Ernst Tentzel, a polymath in the employ of the ducal court of Saxe-Gotha-Altenburg, correctly recognised that they represented the remains of an elephant. The species was named in 1847 by Hugh Falconer and Proby Cautley for remains found in East Sussex as Elephas antiquus. The genus Palaeoloxodon was first named in 1924 by Matsumoto Hikoshichirō as a subgenus of Loxodonta, and E. antiquus subsequently assigned to the genus. Some experts historically regarded the larger Asian species Palaeoloxodon namadicus as a variant or subspecies, but they are now considered distinct. Historically, the genus Palaeoloxodon has at times been regarded as a subgenus of Elephas (which contains the living Asian elephant), but this is no longer supported. In 2016, a mitochondrial DNA sequence analysis of P. antiquus found their mitochondrial genomes were nested within the mitochondrial genome diversity of the African forest elephant (Loxodonta cyclotis), with analysis of a partial nuclear genome supporting a closer relationship with L. cyclotis than to the African bush elephant (L. africana). A subsequent study published in 2018 by the same authors based on the complete nuclear genome indicated a more complicated relationship between straight-tusked elephants and other species of elephants; according to this study, the biggest genetic contribution to straight-tusked elephants comes a lineage of elephants that was most closely related but basal to the common ancestor of forest and bush elephants (~60% of total genomic contribution), which hybridized with African forest elephants (>33%) and to a lesser extent with mammoths (~5%). The African forest elephant ancestry was more closely related to modern West African forest elephants than to other African forest elephant populations. This hybridisation likely occurred in Africa, prior to migration of Palaeoloxodon into Eurasia, and appears to be shared with other Palaeoloxodon species.

Evolution
Like other Eurasian Palaeoloxodon species, P. antiquus is believed to derive from the African ''Palaeoloxodon recki. P. antiquus'' first appears during the early Middle Pleistocene, with its first records around 780,000 years ago in Italy and Israel. Its earliest known appearance in northern Europe is in England around 600,000 years ago. Its arrival coincided with the extinction of the European mammoth species Mammuthus meridionalis and the migration of Mammuthus trogontherii (the steppe mammoth) into Europe from Asia. There appears to be no overlap between M. meridionalis and P. antiquus, which suggests that the latter might have outcompeted the former. During P. antiquus 's hundreds of thousands of years of existence, its morphology remained relatively static, unlike European mammoth populations.

Distribution and habitat


Palaeoloxodon antiquus is known from abundant finds across Europe, ranging northwards to Great Britain and as far east as European Russia during interglacial periods. Fossils are also known from Israel, Iran and probably Turkey in West Asia, and also possibly from Kazakhstan and Tajikistan. During glacial periods P. antiquus permanently resided in the Mediterranean region. Many of the remains attributed to the species from Western Asia are primarily done so for geographical reasons, and it has been suggested that some of these, such as those from Israel, actually belong to P. recki. The straight-tusked elephant is primarily associated with temperate and Mediterranean forest and woodland habitats, as opposed to the colder open steppe environments inhabited by contemporary mammoths, though the species is also known to have inhabited open grasslands. Straight-tusked elephants rarely coexisted alongside mammoths, although they occasionally did so, like at the Ilford locality in Britain dating to the Marine Isotope Stage 7 interglacial where both steppe mammoths and P. antiquus are found. At this locality, the two species appear to have engaged in dietary niche partitioning.

During interglacial periods, P. antiquus existed as part of the Palaeoloxodon antiquus large-mammal assemblage, along with other temperate adapted megafauna species, including the hippopotamus (Hippopotamus amphibius), rhinoceroses belonging to the genus Stephanorhinus (Merck's rhinoceros S. kirchbergensis and the narrow-nosed rhinoceros S. hemitoechus), the European water buffalo (Bubalus murrensis), Irish elk (Megaloceros giganteus), aurochs (Bos primigenius), European fallow deer (Dama dama), roe deer (Capreolus capreolus), red deer (Cervus elaphus), moose (Alces alces) and wild boar (Sus scrofa), with carnivores including European leopards (Panthera pardus spelaea), cave hyenas (Crocuta spelaea) cave/steppe lions (Panthera spelaea), wolves (Canis lupus) and brown bears (Ursus arctos). The effect of straight tusked elephant and other extinct megafauna on vegetation likely resulted in increased openness of woodland habitats.

Behaviour and paleoecology
As with modern elephants, female and juvenile straight-tusked elephants are thought to have lived in matriarchal herds of related individuals, with the adult males living solitary lives. Like modern elephants, the herds would have been restricted to areas with available fresh water due to the greater hydration needs and lower mobility of the juveniles. Fossil tracks of newborns, calves and adults likely of a herd of P. antiquus have been found in dune deposits southern Spain, dating to MIS 5 (130-80,000 years ago). Due to their larger size, straight-tusked elephants are suggested to have finished growing 10 to 15 years later than living elephants, continuing to grow after 50 years of age. They may also have lived longer than extant elephants, with lifespans perhaps in excess of 80 years.

Dental microwear studies suggest that the diet of P. antiquus was highly variable according to the local conditions, ranging from almost completely grazing to nearly totally browsing (feeding on leaves, stems and fruits of high-growing plants), though microwear only reflects the diet in the last few days or weeks before death, so this may be reflecting seasonal dietary variation, as is found in living elephants. Isotopic analysis of a specimen from Greece suggests that it alternately consumed more browse during the dry (presumably summer) months and more grass during the wet (presumably winter) months. A dental mesowear study of specimens from Britain found that most examined specimens had a browsing predominant mixed feeding diet, similar to that inferred for modern African bush elephants and Asian elephants.

Potential gnaw marks suggested to have been made by hyenas and lions on the bones of straight-tusked elephants have been reported at some localities, which suggests that these species likely at least scavenged on the remains of straight-tusked elephants like lions and hyenas do on elephants in Africa today.

Relationship with humans
Remains of straight-tusked elephants at numerous sites are associated with stone tools and/or bear cut and percussion marks indicative of butchery. In the case of most sites, it is unclear whether the elephants were hunted or were scavenged, though scavenging of already dead elephants as well as active hunting are likely to have occurred. These include the Gesher Benot Ya'akov (c. 780 kya, though other authors attribute the remains to P. recki ) and Revadim Quarry (sometime between 780 kya and 300-500 kya ) sites in Israel, the Ambrona AS3 (MIS 12 c. 478-425 kya), Aridos 1 (MIS 11-9 424-300 kya) & 2 (MIS 11 c. 425-375 kya) sites in Spain, the Notarchirico (c. 670-610 kya, though the evidence for butchery at this site is disputed ), Ficoncella (c. 500 kya), Castel di Guido (c. 400 kya ), La Polledrara di Cecanibbio (325–310 kya) and Poggetti Vecchi (c. 171 kya) sites in Italy, the Marathousa 1 site (c. 500-400 kya) in Greece, the Ebbsfleet site (c. 425-375 kya) in England, and the Schöningen (c. 300 kya) Gröbern Taubach Lehringen  and Neumark Nord (all dating to the Eemian interglacial, c. 130-115 kya) sites in Germany.

The creation of these sites is likely attributable to Homo heidelbergensis and Neanderthals. Stone tools used at these sites include flakes, choppers, bifacial tools like handaxes, as well as cores''. '' At some sites, the bones of straight-tusked elephants and in some cases their ivory were used to make tools. There is evidence that exploitation of straight-tusked elephants in Europe increased and became more systematic from the mid-Middle Pleistocene (around 500,000 years ago) onwards. Based on analysis of sites of straight-tusked elephants with cut marks and/or artifacts, it has been argued that there is little evidence that straight-tusked elephants were targeted preferentially over smaller animals. Most individuals at these sites are subadult to adult and primarily male in sex. The male sex bias likely both represents the fact that adult males, despite their larger size, were more vulnerable targets due to their solitary nature, as well as the tendency of adult male elephants to engage in risky behavior causing them to more frequently die in natural traps, as well as being weakened or killed by injures caused by combat with other male elephants during musth.

At the Lehringen site in north Germany, a skeleton of P. antiquus was found with a spear made of yew wood between its ribs, with flint artifacts found close by, providing clear evidence that this specimen was hunted. Studies in 2023 proposed that in addition to Lehringen, the Neumark Nord, Taubach and Gröbern sites, which show evidence of systematic butchery, provided evidence of widespread hunting of straight-tusked elephants by Neanderthals during the Eemian in Germany. The remains of at least 57 elephants were found at Neumark Nord, which the authors suggested accumulated over around 300 years, with them estimating that one elephant was hunted around once every 5–6 years at the site.

There are no cave paintings that unambiguously depicts P. antiquus, though an outline drawing of an elephant in El Castillo cave in Cantabria, Spain, as well as a drawing from Vermelhosa in Portugal have been suggested to possibly depict it, but could also potentially depict woolly mammoths.

Extinction
Palaeoloxodon antiquus retreated from northern Europe after the end of the Eemian interglacial around 115,000 years ago due to climatic conditions becoming unfavourable, and fossils after that time during the Last Glacial Period are rare. A molar from the cave deposits of Grotta Guattari in central Italy has been suggested to date to around 57,000 years ago (though other studies have found it to have an older early Late Pleistocene age), with later dating done in 2023 suggesting an age of deposition in the cave of around 66-65,000 years ago. Another late Italian record has been reported from Mousterian layers in Barma Grande cave in northwest Italy, probably dating to around the same time as Grotta Guattari, which has been suggested to display evidence of butchery by Neanderthals. Other late remains have been reported from several sites in the Iberian Peninsula, including El Castillo cave in northern Spain, dating to 43,000 years ago, and Foz do Enxarrique (a sequence of terrace deposits of the Tagus river) in central-eastern Portugal, originally dated to around 34-33,000 years ago, but later revised to around 44,000 years ago. A late date of around 37,400 years ago has been reported from a single molar found in the North Sea off the coast of the Netherlands, but it has been suggested that this date needs independent confirmation, due to only representing a single sample. It has been suggested that P. antiquus likely survived until around 28,000 years ago in the southern Iberian Peninsula based on footprints found in Southwest Portugal and Gibraltar. Its extinction is likely to be due to climatic deterioration, possibly in association with human hunting.

The extinction of P. antiquus and other temperate adapted European megafauna has resulted in the severe loss of functional diversity in European ecosystems.

Dwarfed descendants
Dwarf elephants that presumably evolved from the straight-tusked elephant are known from many Mediterranean islands, spanning from Sicily and Malta in the west to Cyprus in the east. The responsible factors for the dwarfing of island mammals are thought to be the reduction in food availability, predation and competition.