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Mammuthus lamarmorae

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Mammuthus lamarmorae

Dwarf elephants are prehistoric members of the order Proboscidea that, through the process of allopatric speciation on islands, evolved much smaller body sizes (around 1.5-2.3 metres) in comparison with their immediate ancestors. Dwarf elephants are an example of insular dwarfism, the phenomenon whereby large terrestrial vertebrates (usually mammals) that colonize islands evolve dwarf forms, a phenomenon attributed to adaptation to resource-poor environments and selection for early maturation and reproduction. Some modern populations of Asian elephants have also undergone size reduction on islands to a lesser degree, resulting in populations of pygmy elephants.

Fossil remains of dwarf elephants have been found on the Mediterranean islands of Cyprus, Malta (at Ghar Dalam), Crete (in Nomos Chanion at Vamos, Stylos and in an now under water cave on the coast), Sicily, Sardinia, the Cyclades Islands and the Dodecanese Islands. Other islands where dwarf stegodon have been found are Sulawesi, Flores, Timor and other islands of the Lesser Sundas. The Channel Islands of California once supported a dwarf species descended from Columbian mammoths,[1] while small races of woolly mammoths were once found on Saint Paul Island; the mammoths on Wrangel island are no longer considered dwarfs.

Mediterranean Islands

Dwarf elephants first inhabited the Mediterranean islands during the Pleistocene, including all the major islands with the apparent exception of Corsica and the Balearics. Mediterranean dwarf elephants have generally been considered as members of the genus paleoloxodontine, derived from the continental straight-tusked elephant, Elephas (Palaeoloxodon) antiquus Falconer & Cautley, 1847. An exception is the dwarf Sardinian mammoth, Mammuthus lamarmorae (Major, 1883), the first endemic elephant of the Mediterranean islands recognized as belonging to the mammoth line. A genetic study published in 2006 theorized that the Elephas creticus could be from the mammoth line too. A scientific study of 2007 demonstrates the mistakes of the DNA research of 2006.[2]

During low sea levels, the Mediterranean islands were colonised again and again, giving rise, sometimes on the same island, to several species (or subspecies) of different body sizes. The island of Sicily appears to have been colonised by proboscideans in at least three separate waves of colonisation. These endemic dwarf elephants were taxonomically different on each island or group of very close islands, like the Cyclades archipelago.

There are many uncertainties about the time of colonisation, the phylogenetic relationships and the taxonomic status of dwarf elephants on the Mediterranean islands. Extinction of the insular dwarf elephants has not been correlated with the arrival in the islands of man. Furthermore, it has been suggested by the palaeontologist Othenio Abel in 1914,[3] that the finding of skeletons of such elephants sparked the idea that they belonged to giant cyclopses, because the center nasal opening was thought to be a cyclopic eye socket.

Sardinia

  • Mammuthus lamarmorae (Major, 1883)

Sicily and Malta

  • Elephas (Palaeoloxodon) antiquus leonardii Aguirre, 1969
  • Elephas (Palaeoloxodon) 'mnaidriensis' (Adams, 1874)
  • Elephas (Palaeoloxodon) melitensis Falconer, 1868
  • Elephas (Palaeoloxodon) falconeri Busk, 1867

Crete

  • Mammuthus creticus (Bate, 1907)
  • Palaeoloxodon creutzburgi (Kuss, 1965)
  • Palaeoloxodon chaniensis (Symeonides et al., 2001)[4]

After DNA research, published in 2006, it has been proposed to rename Elephas (Palaeoloxodon) creticus into Mammuthus creticus (Bate, 1907). Others proposed (in 2002) to rename all the described specimens of larger size under the new subspecies name Elephas antiquus creutzburgi (Kuss, 1965). In a recent study of 2007, it was argued for the groundlessness of the theory by Poulakakis et al. in 2006,[5] showing the weak points of that DNA research.[2] However, morphological data is at least equivocal, and may also support placement in Mammuthus.

Cyprus

The Cyprus dwarf elephant survived at least until 11,000 BP. Its estimated body weight was only 200 kg, only 2% of its 10,000 kg ancestor. Molars of this dwarf are reduced to approximately 40% the size of mainland straight-tusked elephants.

Remains of the species were first discovered and recorded by Dorothea Bate in a cave in the Kyrenia hills of Cyprus in 1902 and reported in 1903.[6][7]

Cyclades Islands

Remains of paleoloxodontine elephants have been reported from the islands of Delos, Naxos, Kythnos, Serifos and Milos. The Delos elephant is of similar size to a small Elephas antiquus, while the Naxos elephant is of similar size to Elephas melitensis. The remains from Kythnos, Serifos and Milos have not been described.

Dodecanese Islands

On the island of Rhodes, bones of an endemic dwarf elephant have been discovered. This elephant was similar in size to Elephas mnaidriensis.

Two groups of remains of dwarf elephants have been found on the island of Tilos. They are similar in size to Elephas mnaidriensis and the smaller Elephas falconeri, but the two groups indicate sexual dimorphism.[8][9] The remains had originally been designated to Palaeoloxodon antiquus falconeri (Busk, 1867). However, this name refers to the dwarf elephants from the island of Malta. As a result, since no migration route between the two islands can be proved, this name should not be used when referring to the elephant remnants from Tilos. The species has now been described as Elephas tiliensis.[10]

The Tilos dwarf elephant is the first dwarf elephant whose DNA sequence has been studied. The results of this research are consistent with previous morphological reports, according to which Palaeoloxodon is more closely related to Elephas than to Loxodonta or Mammuthus. After the study of new osteological material that has been excavated in anatomical connection in the Charkadio Cave on Tilos island the new species name Elephas tiliensis has been assigned to the Tilos dwarf elephants. It was the latest paleoloxodontine to survive in Europe. They became extinct just less than 4,000 years BP, so this elephant survived well into the Holocene. A exhibition is available at the Municipality of Tilos Island, soon to be transferred to the new building near Charkadio Cave.

Channel Islands of California

The Columbian mammoth (Mammuthus columbii) produced a separate, isolated population at the end of the Pleistocene. One of these isolated groups was formed on the Channel Islands of California, most likely about 40,000 years ago (although the time of isolation is not fully known). Selective forces on the Channel Islands resulted in smaller animals, forming a new species, the Pygmy Mammoth Mammuthus exilis. Channel Islands mammoths ranged from 150–190 cm in shoulder height.

St. Paul Island and Wrangel Island

Mammoths also survived longer on Saint Paul Island in the Bering Sea until 6000 BCE.[11] Survival of a mammoth population may be explained by local geographic, topographic and climatic features, which entailed preservation of communities of steppe plants, as well as a degree of isolation sufficient to delay colonization by humans. St. Paul Island shares this characteristic of geographic isolation, implying that human hunting may have played a role in the disappearance of the woolly mammoth.

During the last ice age, woolly mammoths (Mammuthus primigenius) lived on Wrangel Island in the Arctic Ocean and survived until 1700 BCE, the most recent survival of any known mammoth population. Wrangel Island is thought to have become separated from the mainland by 12,000 years BP. It was assumed that Wrangel Island mammoths ranged from 180–230 cm in shoulder height and were for a time considered "dwarf mammoths".[12] However this classification has been re-evaluated and since the Second International Mammoth Conference in 1999, these mammoths are no longer considered to be true "dwarf mammoths".[13]

Indonesia

On Sulawesi and Flores, evidence of a succession of distinct endemic island faunas has been found, including dwarfed elephants, dating until the Middle Pleistocene. Around the early Middle Pleistocene these dwarfed elephants were replaced by new immigrants of larger to intermediate sizes.

Flores

The present understanding of the succession of Stegodon species on Flores is that endemic dwarfs, represented by the Early Pleistocene species Stegodon sondaarii, became extinct around 840,000 years ago. These dwarf forms were then replaced by the medium to large-sized Stegodon florensis, a species closely related to the Stegodon trigonocephalus group found both in Java and in the islands of biogeographical Wallacea, separated by deep water from the Asian and Australian continental shelves. This Stegodon species went extinct about 12,000 years ago, presumably because of a volcanic eruption.

Sulawesi

The dwarfed Stegodon sompoensis lived during the Pleistocene on the island of Sulawesi. They had a shoulder height of only 1.5m.

References

Paleontology portal
ko:난쟁이코끼리

id:Gajah kerdil pt:Elefante-pigmeu

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