23:03
Planet Worldwide
A mammoth is any species of the extinct genus Mammuthus, proboscideans commonly equipped with long, curved tusks and, in northern species, a covering of longhair. They lived from the Pliocene epoch (from around 5 million years ago) into theHolocene at about 4,500 years ago in Africa, Europe, Asia, and North America. They were members of the family Elephantidae which contains, along with mammoths, the two genera of modern elephants and their ancestors.
Evolution
The earliest known proboscideans, the clade which contains the elephants, existed about 55 million years ago around the Tethys Sea area. The closest relatives of the Proboscidea are the sirenians and the hyraxes. The family Elephantidae is known to have existed six million years ago in Africa, and includes the living elephants and the mammoths. Among many now extinct clades, the mastodon is only a distant relative of the mammoths, and part of the separate Mammutidae family which diverged 25 million years before the mammoths evolved. The following cladogram shows the placement of the genus Mammuthus among other proboscideans, based on hyoid characteristics:
| ||||||||||||||||||||||||||||||||||
Since many remains of each species of mammoth are known from several localities, it is possible to reconstruct the evolutionary history of the genus through morphological studies. Mammoth species can be identified from the number of enamel ridges on their molars; the primitive species had few ridges, and the amount increased gradually as new species evolved and replaced the former ones. At the same time, the crowns of the teeth became longer, and the skulls become higher from top to bottom and shorter from the back to the front over time to accommodate this.
The first known members of the genus Mammuthus are the African species M. subplanifrons from the Pliocene and M. africanavus from the Pleistocene. The former is thought to be the ancestor of later forms. Mammoths entered Europe around 3 million years ago; the earliest known type has been named M. rumanus, which spread across Europe and China. Only its molars are known, which show it had 8-10 enamel ridges. A population evolved 12-14 ridges and split off from and replaced the earlier type, becoming M. meridionalis. In turn, this species was replaced by the steppe mammoth, M. trogontherii, with 18-20 ridges, which evolved in East Asia ca. 1 million years ago. Mammoths derived from M. trogontherii evolved molars with 26 ridges 200,000 years ago in Siberia, and became the woolly mammoth, M. primigenius. The Columbian mammoth, M. columbi, also evolved from a population of M. trogontherii which had entered North America. A 2011 genetic study showed that two examined specimens of the Columbian mammoth were grouped within a subclade of woolly mammoths. This suggests that the two populations interbred and produced fertile offspring. It also suggested that a North American form known as "M. jeffersonii" may be a hybrid between the two species.
From 3 Ma to the late Pleistocene, mammoths in continental Eurasia has undergone a major transformation, including a shortening and heightening of the cranium and mandible, increase in molar hypsodonty index, increase in plate number, and thinning of dental enamel. Due to this drastic change in physical appearance, people started grouping European mammoths separately into distinguishable clusters:
1) Early Pleistocene Mammuthus meridionalis
2) Middle Pleistocene Mammuthus trogontherii
3) Late Pleistocene Mammuthus primigenius
There is speculation to how variation occurred within the three chronospecies. Deviations in environment, climate change, and migration have also played a role in the evolutionary process of the mammoths. Take M. primigenius for example, during their lifespan, woolly mammoths would have lived in opened grassland biomes. The cool steppe-tundra of the Northern Hemisphere was the ideal place for mammoths to thrive because of the resources it supplied. Of course, with the warmings during the ice age, climate would also change the landscape and what was available to the mammoths altered drastically.
Description
Like their modern relatives, mammoths were quite large. The largest known species reached heights in the region of 4 m (13 ft) at the shoulder and weights up to 8 tonnes (9 short tons), while exceptionally large males may have exceeded 12 tonnes (13 short tons). However, most species of mammoth were only about as large as a modern Asian elephant (which are about 2.5m to 3m high at the shoulder, and rarely exceeding 5.4 tonnes). Both sexes bore tusks. A first, small set appeared at about the age of six months and these were replaced at about 18 months by the permanent set. Growth of the permanent set was at a rate of about 1 to 6 inches (2.5 to 15 cm) per year.
Based on studies of their close relatives, the modern elephants, mammoths probably had agestation period of 22 months, resulting in a single calf being born. Their social structure was probably the same as that of African and Asian elephants, with females living in herds headed by a matriarch, whilst bulls lived solitary lives or formed loose groups after sexual maturity.
Scientists discovered and studied the remainders of a mammoth calf and found that the fat in a mammoth plays a major role to the mammoth's form and ability. One of the major roles of mammoth fat is their ability to store large amounts of nutrients to accommodate to the colder climate they live in. The fat also allowed the mammoths to increase their muscle mass, allowing the mammoths to fight against enemies and live longer.
Extinction
The woolly mammoth (M. primigenius) was the last species of the genus. Most populations of the woolly mammoth in North America and Eurasia, as well as all the Columbian mammoths(M. columbi) in North America, died out around the time of the last glacial retreat, as part of amass extinction of megafauna in northern Eurasia and the Americas. Until recently, the last woolly mammoths were generally assumed to have vanished from Europe and southern Siberia about 12,000 years ago, but new findings show some were still present there about 10,000 years ago. Slightly later, the woolly mammoths also disappeared from continental northern Siberia. A small population survived on St. Paul Island, Alaska, up until 3750 BC, and the small mammoths of Wrangel Island survived until 1650 BC. Recent research of sediments in Alaska indicates mammoths survived on the American mainland until 10,000 years ago.
A definitive explanation for their extinction has yet to be agreed upon. The warming trend (Holocene) that occurred 12,000 years ago, accompanied by a glacial retreat and rising sea levels, has been suggested as a contributing factor. Forests replaced open woodlands and grasslands across the continent. The available habitat may have been reduced for some megafaunal species, such as the mammoth. However, such climate changes were nothing new; numerous very similar warming episodes had occurred previously within the ice age of the last several million years without producing comparable megafaunal extinctions, so climate alone is unlikely to have played a decisive role. The spread of advanced human hunters through northern Eurasia and the Americas around the time of the extinctions was a new development, and thus might have contributed significantly.
Whether the general mammoth population died out for climatic reasons or due to overhunting by humans is controversial. During the transition from the Late Pleistocene era to the Holocene era, there was shrinkage of the distribution of the mammoth because of the progressive warming at the end of the Pleistocene era resulted in change in the mammoth's environment. The mammoth steppe was a periglacial landscape with rich herb and grass vegetation that disappeared along with the mammoth because of environmental changes in the climate. Mammoths had moved to isolated spots in Eurasia, where they disappeared completely. Also, it is said that Late Paleolithic and Mesolithic human hunters may have affected the size of the last mammoth populations in Europe. There is evidence to suggest that humans did cause the mammoth extinction, although there is no definitive proof. It was found that humans living south of a mammoth steppe learned to adapt themselves to the harsher climates north of the steppe, where mammoths resided. It was concluded that if humans could survive the harsh north climate of that particular mammoth steppe that it was possible humans could hunt (and eventually extinguish) mammoths everywhere.</ref> Another theory suggests mammoths may have fallen victim to an infectious disease.</ref> A combination of climate change and hunting by humans may be a possible explanation for their extinction. Homo erectus is known to have consumed mammoth meat as early as 1.8 million years ago.This may mean only successful scavenging, rather than actual hunting. A site in Ukraine suggests Neanderthals built dwellings using mammoth bones. However, the American Institute of Biological Sciences also notes bones of dead elephants, left on the ground and subsequently trampled by other elephants, tend to bear marks resembling butchery marks, which have previously been misinterpreted as such by archaeologists.
Another theory said to be the cause of mammoths in Siberia, comes from the idea that many may have drowned. While traveling to the Northern River many of these mammoths broke through the ice and drowned. This also explains bones remains in the Arctic Coast and islands of the New Siberian Group.
Dwarfing occurred with the pygmy mammoth on the outer Channel Islands of California, but at an earlier period. Those animals were very likely killed by early Paleo-Native Americans, and habitat loss caused by a rising sea level that split Santa Rosae into the outer Channel Islands.
De-Extinction
As of 2014, there are ongoing projects such as that from Sooam attempting to recover the mammoth population. Similar to the method popularised in the film Jurassic Park, the projects are based on finding suitable DNA in frozen bodies. The next step is to recover and, if possible, combine the DNA with similar living animals such as the elephant, which may give birth to some mammoth-related or mammoth species.
This work is licensed under a Creative Commons Attribution-ShareAlike 3.0 Unported License.
Posted in: ANIMAL LIFE AREA
0 comments:
Post a Comment