Wie Wollmammuts funktionierten

Reisen Sie rund 4.000 Jahre in der Zeit zurück zu einer abgelegenen russischen Arktisinsel, und Sie werden vielleicht ein paar zottelige braune Vierbeiner mit Rüsseln sehen, die Büschel grasbewachsener Bodendecker hochziehen und sie in ihre stoßzahnbewehrten Münder schieben. Aber trotz ihrer vier kräftigen Beine und dünnen, peitschenden Schwänze würde man sie niemals mit haarigen Elefanten verwechseln. Oh, sicher, wenn Ihre Brille auf der Reise zerbrochen ist, werden Sie vielleicht die markante Abwärtsneigung ihres Rückens, die fingerartigen Greifer an den Enden ihrer Rüssel und ihren kleinen, kälteangepassten Schwanz und ihre Ohren vermissen.

Aber keine noch so große Hornhautverkrümmung könnte Sie übersehen lassen, dass diese Tiere nicht viel größer sind als Sie. Denn Sie haben die Mammuts von Wrangel Island gefunden, den zwerghaften Nachkommen von Mammuthus primigenius , dem wolligen Mammut . Sie sind die letzten ihrer Art.

Im Gegensatz zu den 25 Prozent größeren Wollmäusen, die in ihrer Blütezeit in Eurasien und Nordamerika mehrere Millionen zählten, überlebten diese winzigen Nachkommen den ungefähr von Süd nach Nord verlaufenden Domino des Aussterbens, der so viele große Säugetiere mehr als 6.000 Jahre zuvor erledigt hatte . Sie liefen über Wrangel Island, als Menschen in Ägypten Pyramiden bauten und Stonehenge in Großbritannien bauten. Aber bald, vielleicht von denselben Kräften erledigt, die ihre Vorfahren getötet haben – wahrscheinlich Klimawandel , menschliche Jagd oder eine Kombination aus beidem –, würde die Zeit auch sie einholen [Quellen: Lister und Bahn; MGP ].

Wir wissen wahrscheinlich mehr über Wollmammuts und Mammuts im Allgemeinen als über jede andere ausgestorbene Art. Im Vergleich zu den letzten Dinosauriern, die vor etwa 65 Millionen Jahren ausstarben, haben Mammuts erst vor kurzem diese sterbliche Hülle abgelegt – vor kurzem genug, dass alte Menschen sie jagten, aßen, ihr Elfenbein als Werkzeuge verwendeten und sie in einigen der frühesten bekannten darstellten Skulptur und Höhlenkunst [Quellen: Conard ; Lister und Bahn; MGP ]. Ihre gut erhaltenen Überreste, die manchmal aus ganzen Kadavern bestehen, die in gefrorenen anaeroben Böden eingelegt wurden, können Muskeln, Blut, Zähne, Knochen, Stoßzähne und sogar Gehirn enthalten. Wir haben sogar Mammut-DNA gewonnen und sequenziert [Quellen: Lister und Bahn; Müller ; Poinar ].

Darüber hinaus haben wir drei lebende, wenn auch entfernte Cousins, mit denen wir arbeiten können: zwei Loxodonta -Arten, der afrikanische Busch- und afrikanische Waldelefant, und eine Elephas -Art, der asiatische Elefant, der nächste lebende Verwandte des Mammuts [Quelle: Krause et al. ]. Indem wir das, was wir über moderne Elefanten wissen, mit Beweisen aus Wollmammut-Fossilien, konserviertem Stuhl- und Darminhalt und anderen physischen Beweisen kombinieren, können wir zuversichtlich ein Bild davon zeichnen, wie diese Wollwunder wirklich waren – und wie sie funktionierten.

Springen Sie also zurück in diese Zeitmaschine, stellen Sie die Uhr ein paar hunderttausend Jahre zurück und sehen wir uns an, wie das Leben war, als Mammuts die Erde durchstreiften.

1. Ein Tag im Leben eines Wollmammuts
2. Alle in der Mammutfamilie
3. Das Schicksal des Mammuts

Wir stellen uns oft wollige Mammuts vor, die durch die schneebedeckte arktische Tundra stapfen oder sich ihren Weg durch eine sumpfige russische Steppe schnüffeln. Tatsächlich durchstreiften diese Säugetiere Landschaften, die es heute noch nicht gibt. Während vieler Teile des Pleistozäns – einer Epoche, die vor 1,7 Millionen bis 11.500 Jahren dauerte und mit der letzten Eiszeit endete – breitete sich eine reiche und vielfältige Mischung aus Gräsern, Kräutern und Seggen über die Bering-Landbrücke von Irland bis nach Sibirien aus zu einem Großteil des modernen Kanada. Diese Mammutsteppe wurde von einem anderen Klima unterstützt. Als wachsende Gletscher Wasser einschlossen, sank der Meeresspiegel und legte große Landstriche frei, die von einem trockenen, klaren und luftigen blauen Himmel dominiert wurden [Quellen: Lister und Bahn; Müller ; Saiy; Willerslevet al. ].

Auf der Jagd nach Nahrung 20 Stunden am Tag grasten unzählige Mammuthus primigenius , Kreaturen von der Größe moderner Elefanten, durch diese Landschaft. Diese wolligen Mammuts kamen als einzelne Männchen vor, die jeweils etwa 3 bis 4 Meter groß waren und etwa 6 Tonnen wogen, oder in matriarchalischen Familiengruppen von 2 bis 20 kleineren Weibchen und Kälbern. Sie widerstanden der Kälte ihrer nördlichen Gefilde durch eine Reihe von Anpassungen, darunter eine 3 bis 4 Zoll (8 bis 10 Zentimeter) große Fettschicht, eine Zoll dicke ölige Haut und eine wollige Unterwolle. Letzteres war mit gröberen Schutzhaaren bedeckt, die von wenigen Zoll bis zu 1 Meter lang waren, wobei das längste in einem moschusochsenartigen Rock entlang der Flanken und des Bauches des Mammuts hing [Quellen: BBC ; Lister und Bahn; Müller ;National Geographic]. Even their hemoglobin had heat-retaining properties, a trait echoed in many modern, cold-adapted mammals [sources: Campbell; Rummer].

Woolly mammoths shared these lands with other massive mammals, including grazers like woolly rhinoceroses and long-horned bison and predators such as saber-tooth cats and cave hyenas. Given their bulk and massive tusks, healthy adult mammoths could take all comers in a standup fight, especially if gathered in a protective group, so predators likely preyed on sick or injured adults, or picked off the occasional straggling calf [sources: Lister and Bahn; Mueller].

Mammoth calves were mostly born in spring, when fresh growth could support lactating mothers. A 22-month gestation period meant that conception occurred in late summer. Detecting a female in estrus, competing males would demonstrate their fitness via tusk displays, ritualistic sparring or out-and-out fights. Like modern elephants, male woolly mammoths had a musth gland, which secreted a fluid that helped establish reproductive hierarchy during their aggressive, unpredictable musth phase [source: Lister and Bahn].

If, as experts suspect, mammoths resembled today's elephants, then they were likely highly social, educating their calves and perhaps even guarding and burying their dead. They may have periodically come together in great migratory herds and could probably swim to islands a few miles offshore [sources: BBC; Lister and Bahn; Poinar]. In short, they were animals that had evolved to become well adapted to their environment.

A Lifetime of Teething

Beyond fighting, a mammoth's twisted, inward-curling tusks were also handy for stripping and felling trees or shovel-plowing through dirt and snow. Evolved from the mammoth's upper incisors, these tusks would grow throughout the animal's lifetime. The rest of its teeth consisted of foot-long molars with side-to-side grooves that aided in breaking down its tough food. Like today's elephants , a mammoth would go through six sets of teeth in its 60-year life span, typically dying after the last set wore out [sources: Lister and Bahn; National Geographic].

Woolly mammoths are one of a number of large herbivores, including mastodons , elephants and other mammoth species, descended from primitive proboscideans (from the Greek proboskis, or "nose"), which split off the mammalian tree around 55 million years ago [sources: BBC; Lister and Bahn; UCMP].

The first mammoths showed up in Africa around 5-6 million years ago, but they weren't woolly [sources: Perkins; Lister and Bahn; UCMP]. By around 3 million years ago, their descendants, including the widely distributed southern mammoth (Mammuthus meridionalis), had ranged across the Sinai Peninsula into southern Eurasia. Gradually, they spread west to the British Isles and east to Siberia, but whether they crossed into the New World 1.8 million years ago remains a matter of debate. With the exception of their sloping backs, twisting tusks and overall size -- around 13 feet (4 meters) tall and weighing 8-10 tons -- southern mammoths would have much resembled modern elephants. They fed on the leaves, fruit and bark of trees and exerted a strong influence on forests, stripping bark, knocking down trees and opening up habitat for other grazers [sources: BBC; Lister and Bahn; Mueller; Poinar; UCMP].

Around 750,000 years ago, M.meridionalis was succeeded by the largest mammoth of all, the steppe mammoth (Mammuthus trogontherii), which stood 14 feet (4.3 meters) and weighed at least 10 tons. It may have originated in northeastern Eurasia around 2.0-1.5 million year ago, and was the probable ancestor of the woolly mammoth. It sported smallish ears and tail, and a bit of a shaggy coat. Primarily a grazer, it also supplemented its diet with trees and shrubs [sources: Lister and Bahn; Poinar].

The comparatively smaller woolly mammoth, established around 400,000 years ago, likely resulted from specializations suited for the chill of Siberia, and it was from this Russian icebox that botanist Mikhail Adams recovered the first woolly mammoth carcass in 1806 [sources: Lister and Bahn; Mueller]. But the species eventually spread as far as modern Ireland and, starting 125,000 years ago, crossed the Bering Strait and continued across Canada to the eastern coast [sources: Mueller; Poinar; UCMP]. Another New World species, the Columbian mammoth (Mammuthus columbi), lived at the same time, feeding on a mosaic of parklands and open woods in what is today the U.S. and Mexico. It likely evolved from steppe mammoths that arrived there 1.5 million years ago [sources: Lister and Bahn; Poinar].

The mammoth stock was highly adaptable to the fluctuations in climate that characterized the Pleistocene. Yet, within the brief period spanning 14,000-10,000 years ago, they and most other large mammal species in the Northern Hemisphere died out [source: Mueller]. Why?

Lyuba: Fresh from the Icebox

On May 15, 2007, a nomadic tribesman in Russia's Yamal Peninsula found the fully intact carcass of a baby mammoth, the best-preserved prehistoric mammal ever found. At 33.5 inches (85 centimeters) high, the calf is roughly the size of a large dog, although water loss means that at 110 pounds (50 kilograms) it weighs half of what it did in life. Lyuba was a lucky find. She was buried quickly after death and, once exposed, was recovered before scavengers could take more than few nibbles [source: Lister and Bahn].

Paleontologists have advanced several theories to explain mammoths' rapid disappearance at the end of the last ice age, including meteors, diseases, climate change and human hunting. Evidence for meteor strikes has failed to materialize. As for human- or dog-borne diseases, experts say that it's hard to imagine a bug that could kill such a wide range of animals and only affect the large ones [sources: Lister and Bahn; UCMP]. That leaves climate and hunting.

As far as we know, mammoths could not live in areas akin to today's steppes, deserts, savannas or tropical forests, but were confined to the mix of plants peculiar to the mammoth steppe and parkland biomes. According to the climate hypothesis, that specialization may have doomed them to isolation and starvation. As the climate shift melted glaciers and raised sea levels, continents shrank and wetter conditions prevailed. Ill-adapted to such conditions, mammoth food sources dwindled, and mammoth populations declined with them [sources: Lister and Bahn; Mueller; Saey; Willerslev et al. ].

Like the disease hypothesis, the overkill hypothesis emphasizes the fact that mammoths' shockingly fast decline coincides with the generally accepted arrival of humans in North America 13,300-12,800 years ago. It argues that big-game hunters, wielding spears with fluted, hafted Clovis points, hunted mammoths to extinction. Clovis points have been found with mammoth bones, and we know that humans used mammoth furs, meat and ivory. Moreover, we have found that both Neanderthals and Stone Age humans constructed buildings from mammoth bone [sources: Bower; Demay, Péan and Patou-Mathis].

But many questions remain. Given that many humans could have survived on a single mammoth, especially aided by natural refrigeration, and that early humans venerated the beasts in cave art, it's possible they treated mammoths with the reverence and restraint that Native Americans used toward buffalo [source: MGP]. Either way, hunter-gatherers likely had a varied diet and relied on small to medium game for meat, so how often they actually hunted mammoths (versus scavenging their remains) is unclear [sources: AMNH; Guthrie ; Lister and Bahn].

Ultimately, the limitations of large mammals like mammoths, with their low birth rates and vast need for sustenance, might well have hastened their end, worsening the effects of isolation, habitat loss and predation, leaving only their dwarf descendants, cut off from the mainland on scattered islands, to carry on for another 6,000 years [sources: AMNH; Bower; Lister and Bahn; Nikolskiy and Pitulko].

To Clone or Not to Clone

While DNA's fragility and limited shelf life make cloning dinosaurs impossible, we could theoretically clone a mammoth or breed one through in vitro fertilization (IVF). Cloning, which would involve scooping the nucleus out of an elephant ovum, replacing it with a nucleus recovered from a frozen mammoth carcass, and then implanting it in a female elephant's uterus, would attempt to produce a true woolly mammoth. IVF, which would involve fertilizing an elephant egg with a mammoth sperm, would produce a hybrid that, assuming it produced viable offspring, would require repeated breeding to achieve near-pure mammoth-ness. Both approaches entail complex ethical and practical concerns [sources: Lister and Bahn; Poinar; San Diego Zoo].

Author's Note: How Woolly Mammoths Worked

Although the Pleistocene, with its climate wobbles and pulses of globe-spanning glaciation, might strike us as a fundamentally different sort of world than the one in which we live, the modern world is governed by the same forces and elements as the paleo. Now, as then, solar energy powers a complex, self-regulating climatological and ecological system that, though resilient, can rapidly collapse when pushed past a tipping point.

Whether mammoths were killed by hunters, by climate-driven starvation or some combination of the two is a question of much concern to their living cousins, the elephants, who once thundered across vast swaths of land and who today face human-driven habitat loss and poaching. The problem with tipping points is that they can move fast, have far-reaching impacts and quickly become virtually irreversible. The problem with allowing elephants to die, beyond the obvious tragedy, is that they are a keystone species in their ecosystems, potentially a kind of living tipping point. Their movements and activities create habitat for other animals and natural firebreaks, and their dung feeds numerous species, spreads seeds and provides soil nutrients. When an animal like that dies out, tipping point or not, it sends thunderous impacts throughout the ecosystem.

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