|
The Tasmanian devil (''Sarcophilus harrisii'') is a carnivorous marsupial of the family Dasyuridae, now found in the wild only on the Australian island state of Tasmania. The size of a small dog, it became the largest carnivorous marsupial in the world following the extinction of the thylacine in 1936. It is characterised by its stocky and muscular build, black fur, pungent odour, extremely loud and disturbing screech, keen sense of smell, and ferocity when feeding. The Tasmanian devil's large head and neck allow it to generate amongst the strongest bite per unit body mass of any extant mammal land predator, and it hunts prey and scavenges carrion as well as eating household products if humans are living nearby. Although it usually is solitary, it sometimes eats with other devils and defecates in a communal location. Unlike most other dasyurids, the devil thermoregulates effectively and is active during the middle of the day without overheating. Despite its rotund appearance, the devil is capable of surprising speed and endurance, and can climb trees and swim across rivers. It is believed that ancient marsupials migrated from what is now South America to Australia tens of millions of years ago during the time of Gondwana, and that they evolved as Australia became more arid. Fossils of species similar to modern devils have been found, but it is not known whether they were ancestors of the contemporary species, or whether the current devils co-existed with these species. The date that the Tasmanian devil became locally extinct from the Australian mainland is unclear; most evidence suggests they had contracted to three relict populations around 3000 years ago. A tooth found in Augusta, Western Australia has been dated to 430 years ago, but archaeologist Oliver Brown disputes this and considers the devil's mainland extinction to have occurred around 3000 years ago. This disappearance is usually blamed on dingoes, which are absent from Tasmania. Because they were seen as a threat to livestock and animals that humans hunted for fur in Tasmania, devils were hunted and became endangered. In 1941, the devils, which were originally seen as implacably vicious, became officially protected. Since then, scientists have contended that earlier concerns that the devils were the most significant threat to livestock were overestimated and misplaced. Devils are not monogamous, and their reproductive process is very robust and competitive. Males fight one another for the females, and then guard their partners to prevent female infidelity. Females can ovulate three times in as many weeks during the mating season, and 80% of two-year-old females are seen to be pregnant during the annual mating season. Females average four breeding seasons in their life and give birth to 20–30 live young after three weeks' gestation. The newborn are pink, lack fur, have indistinct facial features and weigh around at birth. As there are only four nipples in the pouch, competition is fierce and few newborns survive. The young grow rapidly and are ejected from the pouch after around 100 days, weighing roughly . The young become independent after around nine months, so the female spends most of her year in activities related to childbirth and rearing. Since the late 1990s, devil facial tumour disease has drastically reduced the devil population and now threatens the survival of the species, which in 2008 was declared to be endangered. Programs are currently being undertaken by the Government of Tasmania to reduce the impact of the disease, including an initiative to build up a group of healthy devils in captivity, isolated from the disease. While the thylacine was extant it preyed on the devil, which targeted young and unattended thylacine cubs in their dens. Localised populations of devils have also been severely reduced by collisions with motor vehicles, particularly when they are eating roadkill. The devil is an iconic symbol of Tasmania and many organisations, groups and products associated with the state use the animal in their logos. It is seen as an important attractor of tourists to Tasmania and has come to worldwide attention through the ''Looney Tunes'' character of the same name. As of 2013, Tasmanian devils are again being sent to zoos around the world. ==Taxonomy== Believing it to be a type of opossum, naturalist George Harris wrote the first published description of the Tasmanian devil in 1807, naming it ''Didelphis ursina'', due to its bearlike characteristics such as the round ear.〔Owen and Pemberton, p. 79.〕 He had earlier made a presentation on the topic at the Zoological Society of London.〔 However, that particular binomial name had been given to the common wombat (later reclassified as ''Vombatus ursinus'') by George Shaw in 1800, and was hence unavailable. In 1838 a specimen was named ''Dasyurus laniarius'' by Richard Owen, but by 1877 he had relegated it to ''Sarcophilus''. The modern Tasmanian devil was named ''Sarcophilus harrisii'' ("Harris's meat-lover") by French naturalist Pierre Boitard in 1841.〔http://palaeontology.palass-pubs.org/pdf/Vol%206/Pages%20615-624.pdf〕 A later revision of the devil's taxonomy, published in 1987, attempted to change the species name to ''Sarcophilus laniarius'' based on mainland fossil records of only a few animals. However, this was not accepted by the taxonomic community at large; the name ''S. harrisii'' has been retained and ''S. laniarius'' relegated to a fossil species.〔 "Beelzebub's pup" was an early vernacular name given to it by the explorers of Tasmania, in reference to a religious figure who is a prince of hell and an assistant of Satan;〔Owen and Pemberton, p. 8.〕 the explorers first encountered the animal by hearing its far-reaching vocalisations at night.〔Owen and Pemberton, p. 7.〕 Related names that were used in the 19th century were ''Sarcophilus satanicus'' ("Satanic meatlover") and ''Diabolus ursinus'' ("ursine devil"), all due to early misconceptions of the devil as implacably vicious.〔 The Tasmanian devil (''Sarcophilus harrisii'') belongs to the family Dasyuridae. The genus ''Sarcophilus'' contains two other species, known only from Pleistocene fossils: ''S. laniarius'' and ''S. moomaensis''. The relationships between the three species are not clear. Phylogenetic analysis shows that the devil is most closely related to quolls. The roots of Australian marsupials are thought to trace back tens of millions of years to when much of the current Southern Hemisphere was part of the supercontinent of Gondwana; marsupials are believed to have originated in what is now South America and migrated across Antarctica, which had a temperate climate at the time.〔Owen and Pemberton, p. 33.〕 As soil degradation took hold, it is believed that the marsupials adapted to the more basic flora of Australia.〔 According to Pemberton, the possible ancestors of the devil may have needed to climb trees to acquire food, leading to a growth in size and the hopping gait of many marsupials. He speculated that these adaptations may have caused the contemporary devil's peculiar gait.〔Owen and Pemberton, p. 34.〕 The specific lineage of the Tasmanian devil is theorised to have emerged during the Miocene, molecular evidence suggesting a split from the ancestors of quolls between 10 and 15 million years ago, when severe climate change came to bear in Australia, transforming the climate from warm and moist to an arid, dry ice age, resulting in mass extinctions.〔 As most of their prey died of the cold, only a few carnivores survived, including the ancestors of the quoll and thylacine. It is speculated that the devil lineage may have arisen at this time to fill a niche in the ecosystem, as a scavenger that disposed of carrion left behind by the selective-eating thylacine.〔 The extinct ''Glaucodon ballaratensis'' of the Pliocene age has been dubbed an intermediate species between the quoll and devil. Fossil deposits in limestone caves at Naracoorte, South Australia, dating to the Miocene include specimens of ''S. laniarius'', which were around 15% larger and 50% heavier than modern devils.〔Owen and Pemberton, p. 35.〕 Older specimens believed to be 50–70,000 years old were found in Darling Downs in Queensland and in Western Australia.〔 It is not clear whether the modern devil evolved from ''S. laniarius'', or whether they coexisted at the time.〔Owen and Pemberton, p. 36.〕 Richard Owen argued for the latter hypothesis in the 19th century, based on fossils found in 1877 in New South Wales.〔 Large bones attributed to ''S. moornaensis'' have been found in New South Wales,〔 and it has been conjectured that these two extinct larger species may have hunted and scavenged.〔 It is known that there were several genera of thylacine millions of years ago, and that they ranged in size, the smaller being more reliant on foraging.〔Owen and Pemberton, p. 37.〕 As the devil and thylacine are similar, the extinction of the co-existing thylacine genera has been cited as evidence for an analogous history for the devils.〔Owen and Pemberton, p. 38.〕 It has been speculated that the smaller size of ''S. laniarius'' and ''S. moornaensis'' allowed them to adapt to the changing conditions more effectively and survive longer than the corresponding thylacines.〔 As the extinction of these two species came at a similar time to human habitation of Australia, hunting by humans and land clearance have been mooted as possible causes.〔Owen and Pemberton, p. 39.〕 Critics of this theory point out that as indigenous Australians only developed boomerangs and spears for hunting around 10,000 years ago, a critical fall in numbers due to systematic hunting is unlikely. They also point out that caves inhabited by Aborigines have a low proportion of bones and rock paintings of devils, and suggest that this is an indication that it was not a large part of indigenous lifestyle. A scientific report in 1910 claimed that Aborigines preferred the meat of herbivores rather than carnivores.〔Owen and Pemberton, pp. 40–42.〕 The other main theory for the extinction was that it was due to the climate change brought on by the most recent ice age.〔 While dingoes are seen as the main reason for the disappearance of devils from the mainland, another theory is that the increasing aridity of the mainland caused it, while the population in Tasmania has been largely unaffected as the climate remains cool and moist.〔Owen and Pemberton, p. 40.〕 According to this theory, the dingo was only a secondary cause.〔Owen and Pemberton, p. 41.〕 As the devil is the thylacine's closest relative, there has been speculation that the thylacine could be revived by combining DNA from museum samples of thylacines with ova of the devil.〔Tyndale-Biscoe, pp. 159–165.〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Tasmanian devil」の詳細全文を読む スポンサード リンク
|