Dwarf elephant
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 Skeleton of a Cretan Dwarf Elephant.
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Extinct (fossil)
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Dwarf elephants are prehistoric members of the order Proboscidea, that, through the process of allopatric speciation, evolved to a fraction of the size of their modern relatives. Insular dwarfism is a biological phenomenon by which the size of animals isolated on an island shrinks dramatically over time. Skeletal remains of dwarf elephants have been found on the Mediterranean islands of Cyprus, Malta (at Ghar Dalam), Crete, Sicily, Sardinia, the Cyclades Islands and the Dodecanese Islands. Other islands where dwarf elephants have been found are Sulawesi, Flores, Timor and other islands of the Lesser Sundas. The Channel Islands of California once supported a dwarf race of mammoth[2].
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[edit] Mediterranean Islands
Dwarf elephants were once part of the Pleistocene fauna of several Mediterranean islands. Mediterranean dwarf elephants have generally been considered as 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 only endemic elephant of the Mediterranean islands belonging to the mammoth line. A DNA research published in 2006 theorized that the Elephas creticus could be from the mammoth line too. This old theory, proposed by Bate ever since 1905, is not widely accepted. Today most of scientists disagree, and a scientific study of 2007 demonstrates the mistakes of the DNA research of 2006.[1]
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. These endemic dwarf elephants were taxonomically different on each island or group of very close islands, like the Cyclades archipelago.
There are many uncertainty about the time of colonisation, the phylogenetic relationships, and the taxonomic status of dwarf elephants on the Mediterranean islands.
[edit] Sardinia
- Mammuthus lamarmorae (Major, 1883)
- Elephas antiquus (Acconci, 1881)
- Elephas melitensis (Caria, 1965)
[edit] Sicily & Malta
- Elephas (Palaeoloxodon) antiquus leonardii Aguirre, 1969
- Elephas (Palaeoloxodon) mnaidriensis (Adams, 1874)
- Elephas (Palaeoloxodon) melitensis Falconer, 1868
- Elephas (Palaeoloxodon) falconeri Busk, 1867
[edit] Crete
- Elephas (Palaeoloxodon) creticus Bate, 1907
- Elephas (Palaeoloxodon) creutzburgi (Kyuss, 1965)
- Elephas (Palaeoloxodon) chaniensis Symeonides et al., 2001
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). Modern scientists, in a recent study of 2007, have demonstrated the groundlessness of the theory showed by Poulakakis et al. in 2006, showing the weak points of that DNA research.[1]
[edit] Cyprus
- Elephas (Palaeoloxodon) cypriotes Bate, 1903
The Cyprus dwarf elephant survived at least until 11,000 BP. Its estimated body weight was only 200 kg, which is a weight reduction of 98% from the 10.000 kg ancestor. Molars of this dwarf are reduced to approximately 40% the size of mainland straight-tusked elephants.
[edit] 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.
[edit] 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.[2][3] 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, although some scientists have accepted the temporal use of this name until further material can be examined.[2]
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.
The Tilos dwarf elephant was the latest paleoloxodontine to survive in Europe. They became extinct just less than 4000 years BP, so this elephant survived well into the Holocene.
[edit] 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 Californian Channel Islands, 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 150-180 cm in shoulder height.
[edit] Wrangel Island
During the last ice age, woolly mammoths (Mammuthus primigenius) lived on Wrangel Island in the Arctic Ocean. It has been shown that mammoths survived on Wrangel Island until 1700 B.C.E., 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. Survival of a mammoth population may be explained by local topography and climatic features, which permitted relictual preservation of communities of steppe plants. Wrangel Island mammoths ranged from 180-230 cm in shoulder height and were for a time considered "dwarf mammoths".[4] 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".[5]
[edit] 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.
[edit] 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.
[edit] Sulawesi
The dwarfed Stegodon sompoensis lived during the Pleistocene on the island of Sulawesi. They had a shoulder height of only 1.5m.
[edit] See also
[edit] References
- ^ a b Orlando, L., Pagés, M., Calvignac, S., et al. (2007-02-22). "Does the 43bp sequence from an 800000 year old Cretan dwarf elephantid really rewrite the textbook on mammoths?". Biology Letters 3 (1): 57-59. DOI:10.1098/rsbl.2006.0536.
- ^ a b Theodorou, G. (1983). The dwarf elephants of the Charkadio cave on the island of Tilos (Dodekanese, Greece). Phd Thesis Athens University, 321 pp.
- ^ Theodorou, G.E. (1988). "Environmental factors affecting the evolution of islands endemics: The Tilos example for Greece". Modern Geology 13: 183-188.
- ^ Vartanyan, S.L., Garutt, V.E., Sher, A.V. (March 1993). "Holocene dwarf mammoths from Wrangel Island in the Siberian Arctic". Nature (362): 337-340.
- ^ [1]
