Mammoth
From Wikipedia, the free encyclopedia
A
mammoth is any
species of the
extinct genus Mammuthus,
proboscideans commonly equipped with long, curved
tusks and, in northern species, a covering of long
hair. They lived from the
Pliocene epoch (from around 5 million years ago) into the
Holocene at about 4,500 years ago
[1][2] in Africa, Europe, Asia, and North America. They were members of the family
Elephantidae, which also contains the two genera of modern
elephants and their ancestors. Mammoths stem from an ancestral species called
M. africanavus,
the African mammoth. These mammoths lived in northern Africa and
disappeared about 3 or 4 million years ago. Descendants of these
mammoths moved north and eventually covered most of Eurasia. These were
M. meridionalis, the 'southern mammoths'.
[3]
Evolution
The earliest known
proboscideans, the
clade that 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.
[4]
The following
cladogram shows the placement of the genus
Mammuthus among other proboscideans, based on
hyoid characteristics:
[5]
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.
[6]
Tooth of M. africanavus, one of the earliest known species of mammoth, from North Africa.
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.
[6] The Columbian mammoth,
M. columbi, evolved from a population of
M. trogontherii
that 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.
[7]
By the late Pleistocene, mammoths in continental Eurasia had
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
change in physical appearance, it became customary to group European
mammoths separately into distinguishable clusters:
- Early Pleistocene – Mammuthus meridionalis
- Middle Pleistocene – Mammuthus trogontherii
- Late Pleistocene – Mammuthus primigenius
There is speculation as to what caused this variation within the
three chronospecies. Variations in environment, climate change, and
migration surely played roles in the evolutionary process of the
mammoths. Take
M. primigenius for example: Woolly mammoths 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. With occasional warmings during the ice age,
climate would change the landscape, and resources available to the
mammoths altered accordingly.
[6][8][9]
Etymology and early observations
The word
mammoth was first used in Europe during the early 1600s, when referring to
maimanto tusks discovered in Siberia.
[10] John Bell,
[11]
who was on the Ob River in 1722, said that mammoth tusks were well
known in the area. They were called "mammon's horn" and were often found
in washed-out river banks. Some local people claimed to have seen a
living mammoth, but they only came out at night and always disappeared
under water when detected. He bought one and presented it to
Hans Sloan who pronounced it an elephant's tooth.
The folklore of some native peoples of Siberia, who would routinely
find mammoth bones, and sometimes frozen mammoth bodies, in eroding
river banks, had various interesting explanations for these finds. Among
the
Khanty people of the
Irtysh River
basin, a belief existed that the mammoth was some kind of a water
spirit. According to other Khanty, the mammoth was a creature that lived
underground, burrowing its tunnels as it went, and would die if it
accidentally came to the surface.
[12]
The concept of the mammoth as an underground creature was known to the
Chinese, who received some mammoth ivory from the Siberian natives;
accordingly, the creature was known in China as
yin shu 隐鼠, "the hidden rodent".
[13]
Thomas Jefferson, who famously had a keen interest in
paleontology, is partially responsible for transforming the word
mammoth
from a noun describing the prehistoric elephant to an adjective
describing anything of surprisingly large size. The first recorded use
of the word as an adjective was in a description of a large wheel of
cheese (the "
Cheshire Mammoth Cheese") given to Jefferson in 1802.
[14]
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 of up to 8
tonnes (8.8
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 2.5 m to 3 m high at the shoulder, and rarely
exceeding 5 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 2.5 to 15.2 cm (1 to 6 in) per year.
[15]
Size of various mammoth species compared with a human
Based on studies of their close relatives, the modern elephants, mammoths probably had a
gestation 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.
[16]
Scientists discovered and studied the remainders of a mammoth calf
and found that the fat in a mammoth plays a major role in the mammoth's
form and ability to store large amounts of nutrients to accommodate to
the colder climate they live in, thereby surviving temperatures as low
as −50 °C (−58 °F).
[17]
The fat also allowed the mammoths to increase their muscle mass,
allowing the mammoths to fight against enemies and live longer.
[18]
Diet
Depending on the species or race of mammoth, the diet differed
somewhat depending on location, although all mammoths ate similar
things. For the Columbian mammoth,
M. columbi, the diet was mainly
grazing.
American Columbian mammoths fed primarily on cacti leaves, trees, and
shrubs. These assumptions were based on mammoth feces and mammoth teeth.
Mammoths, like modern day elephants, have
hypsodont molars. These features also allowed mammoths to live an expansive life because of the availability of grasses and trees.
[19]
For the Mongochen mammoth, its diet consisted of herbs, grasses, larch, and shrubs, and possibly
alder.
These inferences were made through the observation of mammoth feces,
which scientists observed contained non-arboreal pollen and moss spores.
[20]
European mammoths had a major diet of
C3 carbon fixation plants. This was determined by examining the isotopic data from the European mammoth teeth.
[21]
The Yamal baby mammoth Lyuba, found in 2007 in the Yamal Peninsula in
Western Siberia, suggests that baby mammoths, as do modern baby
elephants, ate the dung of adult animals. The evidence to show this is
that the dentition (teeth) of the baby mammoth had not yet fully
developed to chew grass. Furthermore, there was an abundance of
ascospores of
coprophilous fungi
from the pollen spectrum of the baby's mother. Coprophilous fungi are
fungi that grow on animal dung and disperse spores in nearby vegetation,
which the baby mammoth would then consume. Spores might have gotten
into its stomach while grazing for the first few times. Coprophagy may
be an
adaptation, serving to populate the infant's gut with the needed
microbiome for digestion.
Mammoths alive in the
Arctic during the
Last Glacial Maximum consumed mainly
forbs, such as
Artemisia;
graminoids were only a minor part of their diet.
[22]
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 a
mass 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.
[23] A small population survived on
St. Paul Island, Alaska, up until 3750 BC,
[2][24][25] and the small
[26] mammoths of
Wrangel Island survived until 1650 BC.
[27][28] Recent research of sediments in Alaska indicates mammoths survived on the American mainland until 10,000 years ago.
[29]
A definitive explanation for their extinction has yet to be agreed.
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 would 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.
[30][31] The spread of advanced human hunters through northern
Eurasia and the
Americas around the time of the extinctions, however, was a new development, and thus might have contributed significantly.
[30][31]
Mammuthus primigenius "Hebior Mammoth specimen" bearing tool/butcher marks
Whether the general mammoth population died out for climatic reasons or due to
overhunting by humans is controversial.
[32]
During the transition from the Late Pleistocene epoch to the Holocene
epoch, there was shrinkage of the distribution of the mammoth because
progressive warming at the end of the Pleistocene epoch changed 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 thought that Late Paleolithic and
Mesolithic human hunters might have affected the size of the last
mammoth populations in Europe.
[citation needed]
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 then it was possible humans could hunt (and
eventually extinguish) mammoths everywhere. Another hypothesis suggests
mammoths fell victim to an infectious disease. 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,
[33]
though this may mean only successful scavenging, rather than actual
hunting. Later humans show greater evidence for hunting mammoths;
mammoth bones at a 50,000-year-old site in South Britain suggest that
Neanderthals butchered the animals,
[34] while various sites in Eastern Europe dating from 15,000 to 44,000 years old suggest humans (probably
Homo sapiens) built dwellings using mammoth bones (the age of some of the earlier structures suggests that Neanderthals began the practice).
[35] 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.
[citation needed]
Many hypotheses also seek to explain the regional extinction of
mammoths in specific areas. Scientists have speculated that the mammoths
of
Saint Paul Island,
an isolated enclave where mammoths survived until about 8,000 years
ago, died out as the island shrank by 80–90% when sea levels rose,
eventually making it too small to support a viable population.
[36]
Similarly, genome sequences of the Wrangel Island mammoths indicate a
sharp decline in genetic diversity, though the extent to which this
played a role in their extinction is still unclear.
[37]
Another hypothesis, said to be the cause of mammoth extinction 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.
[citation needed]
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.
[citation needed]
De-extinction
The use of preserved genetic material to create living mammoth
specimens, particularly in regard to the woolly mammoth, has long been
discussed theoretically but has only recently become the subject of
formal effort. As of 2015, there are three major ongoing projects, one
led by
Akira Iritani of
Japan, another by
Hwang Woo-suk of
South Korea, and the Long Now Foundation,
[38][39] attempting to create a mammoth-elephant hybrid.
[40]
In April 2015, Swedish scientists published the complete
genome (complete DNA sequence) of the woolly mammoth.
[41]
Meanwhile, a Harvard University team is already attempting to study the
animals' characteristics by inserting some mammoth genes into Asian
elephant
stem cells.
[42]
So far, the team placed mammoth genes involved in blood, fat and hair
into elephant stem cells in order to study the effects of these genes in
laboratory cultured cells. It is still unknown if the actual cloning of
a living woolly mammoth is possible.
[42]
The projects are based on finding suitable mammoth DNA in frozen
bodies, sequencing its genome and, if possible, gradually combining the
DNA with
elephant cells.
[38][39][43][44] If the cells turn viable in laboratory tests, the next challenge would be creating a viable "mammoth" hybrid
embryo by inseminating an elephant
egg in vitro. The percent mammoth contribution to the genome would be gradually increased on each hybrid embryo produced
in vitro. If a viable hybrid embryo is obtained, it may be possible to implant it into a female Asian elephant housed in a zoo.
[38]
With the current knowledge and technology, it is still unlikely that
the hybrid embryo would be carried through the two-year gestation.
[45]
See also
The dictionary definition of
mammoth at Wiktionary
References
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.[6]Comparison of a woolly mammoth (left) and an American mastodon (right).
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.[6] The Columbian mammoth, M. columbi, evolved from a population of M. trogontherii that 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.[7]Tooth of M. africanavus, one of the earliest known species of mammoth, from North Africa.
The word mammoth was first used in Europe during the early 1600s, when referring to maimanto tusks discovered in Siberia.[10] John Bell,[11] who was on the Ob River in 1722, said that mammoth tusks were well known in the area. They were called "mammon's horn" and were often found in washed-out river banks. Some local people claimed to have seen a living mammoth, but they only came out at night and always disappeared under water when detected. He bought one and presented it to Hans Sloan who pronounced it an elephant's tooth.
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 of up to 8 tonnes (8.8 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 2.5 m to 3 m high at the shoulder, and rarely exceeding 5 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 2.5 to 15.2 cm (1 to 6 in) per year.[15]Restoration of a steppe mammoth
Based on studies of their close relatives, the modern elephants, mammoths probably had a gestation 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.[16]Size of various mammoth species compared with a human
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 a mass 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.[23] A small population survived on St. Paul Island, Alaska, up until 3750 BC,[2][24][25] and the small[26] mammoths of Wrangel Island survived until 1650 BC.[27][28] Recent research of sediments in Alaska indicates mammoths survived on the American mainland until 10,000 years ago.[29]
Whether the general mammoth population died out for climatic reasons or due to overhunting by humans is controversial.[32] During the transition from the Late Pleistocene epoch to the Holocene epoch, there was shrinkage of the distribution of the mammoth because progressive warming at the end of the Pleistocene epoch changed 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 thought that Late Paleolithic and Mesolithic human hunters might have affected the size of the last mammoth populations in Europe.[citation needed] 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 then it was possible humans could hunt (and eventually extinguish) mammoths everywhere. Another hypothesis suggests mammoths fell victim to an infectious disease. 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,[33] though this may mean only successful scavenging, rather than actual hunting. Later humans show greater evidence for hunting mammoths; mammoth bones at a 50,000-year-old site in South Britain suggest that Neanderthals butchered the animals,[34] while various sites in Eastern Europe dating from 15,000 to 44,000 years old suggest humans (probably Homo sapiens) built dwellings using mammoth bones (the age of some of the earlier structures suggests that Neanderthals began the practice).[35] 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.[citation needed]Mammuthus primigenius "Hebior Mammoth specimen" bearing tool/butcher marks
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