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NOVA | scienceNOW | Mammoth Mystery: A Mammoth Waste of TIme (non-Flash) | PBS
Dung
When it comes to figuring out all you can about an extinct
mammoth and its world from its remains, there's nothing
quite like a good piece of poop. It may not look like much
to you or me, but to a paleoecologist it's a priceless gem.
Such a specialist can hardly wait to get his hands on it, to
ferret out all its long-held secrets. In this feature, have a
look at all the primeval goodies that scientists have
teased from the dung at left, and what those leftovers
have revealed about the mammoth as well as its diet,
habitat, even the climate in which it lived 22,000 years
ago.
Mammoth
The dung was packed within the intestine of this frozen
woolly mammoth. It is known as the Yukagir mammoth
for the Siberian village near where it was found in 2002.
The mammoth's permafrost tomb preserved its head,
tusks, front legs, and parts of its stomach and intestinal
tract. From its bones and enormous tusks, the scientists
who rushed to the site (including mammoth experts Dick
Mol, left, and Larry Agenbroad) guessed that the
mammoth was an old male that when alive stood over
nine feet tall at the shoulder and weighed four to five
tons. From the dung ball, they learned heaps more.
Grass
The main component of the Yukagir's final meal was
grass, including these stems from the Poaceae family.
Remarkably, like many of the dung's floral remains, the
stems have retained their color and shape ever since the
mammoth tore them from the tundra roughly 22,500
years ago. (Radiocarbon dating supplied his estimated
age.) Earlier studies had shown that grasses, sedges, and
rushes comprised the bulk of the diet of Siberian woolly
mammoths during the Pleistocene ice ages, so this
discovery came as no surprise. But this was only the most
obvious finding.
Seeds
The stool held grass seeds as well, including this seed
from a species identified as Poa cf. arctica. (The "cf."
means "confer" and indicates that the primordial species
resembles a still-living species but is not confirmed to be
the same.) To identify such "macrofossils," or visible
parts, the international team that analyzed the dung
boiled bits of poop, sieved the remains, floated them in a
petri dish full of water, and studied them under a
stereomicroscope. Such seeds and other floral bits
enabled them to "flesh out" the mammoth's ice-age
environment.
Moss
For microfossils and other largely invisible stuff, the team
relied on methods with mouthful names like thermally
assisted hydrolysis and polymerase-chain-reaction
amplification. One such tiny ingredient in the poop was
mineral dust (seen here, in gray, coating a piece of
moss). Wind would have lifted this dust from eroded
patches of ground and covered plants with it; when the
mammoth ate the plants, he took in these minerals as
well. The presence in the giant's gut of mosses such as
this one showed that his surroundings were not all dry
grassland; moist areas existed there as well.
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Twigs
Another sizeable portion of the mammoth's last supper
was willow. These were not the big, bushy willow trees
common in temperate areas today. Rather, the stems at
left came from a small-leaved dwarf species known as
Salix cf. arctica. The twigs had been broken but not
digested, leaving the scientists wondering whether the
mammoth could possibly have absorbed sufficient
nutrients from his food. The lack of attached leaf stalks on
the twigs also led them to infer that he had died between
two growing seasons.
Leaves
The dung offered up willow leaves as well (left). All were
badly preserved, and none of them was connected to a
twig—further evidence that the mammoth had perished
between growing seasons. The team thinks, in fact, that
the Yukagir mammoth may have eaten and partially
digested dead leaves. Was this because little else was
available at the time of his death? Just how harsh was the
climate at the time? And what season of the year did he
die?
Rings
To help find out, the team sliced thin cross-sections of the
willow twigs. The thickest twig was less than a fifth of an
inch in diameter, yet it bore more than 20 annual rings.
That growth rate is even slower than that of modern Salix
arctica, indicating the mammoth's climate was even more
austere than that of northern Greenland, where S. arctica
lives today. The cross-sections were even clearer as to
season of death: When the mammoth ate the willow, the
first spring vessels of the outermost rings were just
forming—a clear sign that he had died in early spring.
Pollen
Pollen abounded in the dung. The majority of the grains
were of wind-dispersed pollen, such as that of Artemisia,
a type of sage (top pair). The dung also retained small
amounts of insect-carried pollen from a variety of
flowering plants, including Polemonium, commonly known
as Jacob's ladder (bottom pair). The pollen record was
likely influenced by the mammoth's food choices during
his final meal, the team notes, and the pollen probably
integrates several years of plant growth. But one finding
was unequivocal: the total absence of tree pollen. The
mammoth's world was treeless.
Landscape
This is the spot where the mammoth was found. Since the
area remains treeless today, his home may have looked
largely like this. Paleoexperts have given the mammoth's
ancient habitat a name, "mammoth steppe." It was a
cold, arid plain but with moister meadows here and there.
Water was likely available year-round, including snow in
winter and streams or standing water in summer. Several
plant species identified in the dung, including marsh
marigold, require permanent water, and the mammoth
certainly drank from freshwater pools, as indicated by the
green pond algae found in his stool.
Buds
The absence of any trees in his ecosystem marks a
significant change in the usual diet of Siberian woolly
mammoths (Mammuthus primigenius). In all other
Siberian mammoth dung analyzed to date, scientists have
recovered twigs of alder, birch, larch, and spruce.
Mammoths nibbled these trees to get nutrients lacking in
grass. Since no trees of any kind lived in his
neighborhood, the Yukagir mammoth may have
consumed the dwarf willow shrubs (including this bud,
with nascent leaves visible within) to get vitamins lacking
in the meadow grasses.
Dung, Part Two
Still other nutrients came from dung—dung the mammoth
ate. Animal droppings may have supplemented his daily
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NOVA | scienceNOW | Mammoth Mystery: A Mammoth Waste of TIme (non-Flash) | PBS
intake of grasses and other vegetation (here, a moss
spore structure). The team recovered fruit bodies of a
dung-inhabiting fungus that only develops at least a week
after manure is exposed to air, which the mammoth's own
poop never was. The swallowed stool was probably
mammoth dung, in fact. Among living mammals,
elephants (along with hyraxes and manatees) are unique
in having no bile acids—and none were found in the feces
of the mammoth, a close relative of the elephant.
Fate
In the end, the team was unable to determine his cause
of death. (Here, one of his front legs in situ.) His molars
were heavily worn, another possible indication that he
was malnourished. The added stress of a severe winter
may have sealed his fate. As Dutch scientist Bas van Geel
and his 15 coauthors write in the 2008 paper on which
this feature is based, "the start of the growing season
might have come too late for this animal. Lying down in a
sheltered hollow, he died, and became covered with a
thick mud layer that ... subsequently froze and preserved
part of him."
© | Created July 2008
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