Chapter 5
Lost Serengetis 2: Australia and North
America
While I was writing this chapter, I heard the
presenter of a TV show about Australian wildlife tell his
viewers that “before man arrived in Australia, the kangaroo
had no enemies.”
Nothing could be further from the truth. When the first humans
arrived in Australia somewhere in the neighborhood of fifty
thousand years ago, kangaroos were in fact being preyed on
by a marsupial “lion” called Thylacoleo carnifex.
Until recently, it was thought that Thylacoleo was
a leopard-sized animal, but evidence marshaled by Stephen
Wroe of the University of New South Wales suggests that might
have been closer in size to a female lion or tiger. Barring
the discovery of a painting or engraving of Thylacoleo,
we’ll never know what kind of markings it had.
Thylacoleo was more of a “rat-bear”
than a cat – the animal’s body was stocky and
muscular rather than lithe. Two big incisor teeth pressed
against each other in a rodent-like way in front of each of
its jaws to form a kind of “beak” for seizing
its prey. Behind the remaining incisors – which were
small – lay huge premolars which had developed into
long carnassials or “meat cutting” blades. The
front ends of the upper carnassials ended in a pair of low
“summits” that could, at a quick glance, look
like the canine teeth which were absent or undeveloped in
this animal. The teeth situated behind the carnassials were
also small. The toes of this big marsupial predator were equipped
with claws, two of which, situated on powerful opposing “thumbs,”
were retractable.
Thylacoleo may not have been particularly cat-like,
but the wolf-sized marsupial predator Thylacinus cynocephalus
was astonishingly and faithfully dog-like. Named “Tasmanian
wolf” because of this resemblance, Thylacinus
was only “Tasmanian” in the sense that a somewhat
dwarfed, coyote-sized version of this animal survived on the
island of Tasmania until it was exterminated in the nineteen-thirties
by the British colonists who had exterminated the island’s
original human inhabitants during the previous century. Thylacinus
had, along with the “Tasmanian” devil Sarcophilus
harrisi, become extinct on the Australian mainland about
3,500 years ago, soon after the dingo, a placental or “real”
dog, was brought to Australia by humans (long after the first
wave of human immigration). By that time, however, Tasmania,
which had, like New Guinea, been joined to Pleistocene Australia,
had already been cut off from Australia by the post-glacial
rise in the sea level, so the dingo (whose competition Thylacinus
could not, apparently, survive) couldn’t make it there.
Film footage of Thylacinus, taken in a zoo in the early thirties,
shows an animal which looked like, and trotted like, a dog.
Given the fact that “real” wolves are much more
closely related to sheep (or to whales or bats, for that matter)
than they are to this marsupial “wolf,” the shape
and arrangement of their 42 teeth is remarkably similar to
that of Thylacinus’ 46. Among the few obvious
details which betrayed the fact that Thylacinus was
completely unrelated to the dog family to which it bore such
a remarkable resemblance, were a tail which was thicker at
its base than the tails of “real” dogs, and jaws
which could open much wider. Thylacinus’ “pups”
were carried in a backward-facing pouch. The hind end of the
animal’s back, including the thick base of its tail,
was covered with about twenty dark, parallel stripes. Because
of these stripes, some people have taken to referring to Thylacinus
as the Tasmanian “tiger,” but that name obscures
the animal’s remarkable evolutionary convergence with
the dog family.
The extermination of Thylacinus has left only three
small marsupial predators in Australia: the terrier-sized
“Tasmanian” devil, and several mongoose-like “quolls”
in the genus Dasyures.
* * *
Australia’s extinct “wolves,” “lions”
(and a 90 lb. carnivorous “rat-kangaroo” called
Proleopus oscillans) represented only that subcontinent’s
medium-sized predators. Its largest flesh-eaters were all
reptiles. One of the most remarkable of these, was a huge
monitor lizard called Megalania prisca. Megalania
was considerably bigger than its surviving relative, the “Komodo
dragon” which can grow up to 10 feet long, and inhabits
a few Indonesian islands near Australia’s northern coast.
Other big reptilian predators living in Australia when humans
first arrived there were the outsized “python”
Wonambi, and a long-legged crocodile called Quinkana.
The length of the latter’s legs, and fact that its tail
was rounded in cross-section rather than flat-sided like the
tails of water-dwelling crocodiles, suggest that Quinkana
lived and hunted on land. Australia also had several species
of water-dwelling crocodile, of which two have survived. The
larger of these two survivors, Crocodylus porosus,
which occasionally reaches eighteen feet in length, is presently
the world’s largest reptile.
These big reptilian predators would certainly have killed
kangaroos, but they would also have focused their efforts
on larger prey, like Australia’s marsupial “rhinos.”
Those “rhinos” were members of the “Diprotodonid”
group, one of whose genera, Diprotodon, consisted
of two or more species that were as big or bigger than a black
rhinoceros. Australia’s biggest predators would also
have targeted a buffalo-sized marsupial called Zygomaturus,
and the very strange Palorchestes, a one-ton marsupial
“ground sloth” which could balance on its powerful
tail and hind limbs like a kangaroo while reaching up with
the huge, curved claws on its forelimbs to pull trees and
branches into the reach of what was possibly a short, tapir-like
trunk.
The mammalian and reptilian predators we’ve been talking
about would also have preyed on seven species of “giant
short-faced” kangaroos which disappeared along with
the “rhino,” “buffalo,” and “ground-sloth”
analogs I’ve just mentioned. Eight large species of
“ordinary” kangaroos, and five large wombat species
were also exterminated or dwarfed – possibly by the mechanism
we discussed in Chapter 1.
Add to this fanciful collection of extinct giants a family
of horned tortoises in the genus Meiolania, whose
largest species reached a weight of 500 lb. Include with them,
too, a list of extinct birds which contains, inter alia, two
flamingo species, a pelican, one or more giant eagle species,
flightless cuckoos, flightless pilot birds, a giant “mallee
fowl,” and the 450 lb. Genyornis newtoni “ostrich,”
and you can begin to get an idea of the enormous impoverishment
the Australian fauna has experienced in what Paul Martin refers
to “near time” – i.e. the last fifty thousand
years.
* * *
In the year 2001, a study initiated by Tim Flannery and Richard
Roberts, and based on a dating technique known as “optically
stimulated luminescence,” singled out the millennium
between 46,000 and 47,000 years ago as the time when many
species of Australian megafauna died out abruptly over a wide
area of that island-continent.
These findings are in broad agreement with the results of
a 1999 study by Gifford Miller of the University of Colorado,
who used another dating technique – Amino Acid Racemisation
– to establish that the youngest egg-shell fragments
of the giant Genyornis “ostrich,” are
between 45,000 and 55,000 years old.
Fire played a very different role in the ecology of Australia
after humans reached that island continent. Whether they do
so by accident, or to signal other groups, or to help their
hunting or stimulate fresh plant growth, humans start plenty
of fires. The result was that, relatively soon after the arrival
of our species in Northern Australia, dry forests dominated
by Araucaria trees were supplanted by plant communities dominated
by eucalypts, which “rely” on fire to help them
compete against plants which are more vulnerable to it than
they are. Using sophisticated “pre-treatment”
strategies for removing contaminants in his samples, Chris
Turney of Queen’s University in Belfast pushed the horizon
of the radiocarbon method back from forty thousand to sixty
thousand years, to establish that an abrupt increase in burning,
and an accompanying change in vegetation, had taken place
in Queensland sometime between 45,000 and 55,000 years ago.
The dating of archeological material from Arnhem land, on
the other side of the Gulf of Carpentaria, under the direction
of the late Professor Rhys M. Jones of the Australian National
University, suggests, however, that humans had been present
in that area as long as 60,000 years ago.
* * *
While Australia’s extinct megafauna disappeared on
the edge of the 40 thousand-year “window” in which
radiocarbon dating is effective, the New World’s “Serengetis”
of big animals and birds became extinct well inside that window – near
the start, to be more precise, of the “Younger Dryas”
cold phase some 12,870 “calendar,” or 11,200 “radiocarbon”
years ago.
Let’s talk briefly – before we return to the issue
of when North America’s megafaunal extinction took place – about
why the radiocarbon date I’ve mentioned in the preceding
paragraph is so far out of step with the calendar or “real”
date it represents.
Radiocarbon dating is based on the assumption that the amount
of C14 in the atmosphere remains constant. That assumption
doesn’t hold in the real world. Variations in the Earth’s
magnetic field, and in cosmic background radiation, affect
the rate at which C14 is being “manufactured”
in the atmosphere. The big, back-and-forth lurches in temperature
that took place near the end of the last glaciation muddied
the picture further, by causing sudden and relatively large
variations in the ratio of C12 to C14 in the atmosphere. Those
variations make time, as measured by radiocarbon dating, appear
to speed up, slow down and even run backward for brief intervals.
We’re dependent, therefore, on data gleaned from lake
sediments, annual precipitation layers in ancient ice, tree-ring
sequences and other dating methods to produce “calibrated”
or “calendar” dates from the radiocarbon results.
All the dates mentioned in this book are, unless I’ve
indicated otherwise, expressed in calibrated or calendar rather
than in radiocarbon years.
* * *
Although the New World’s “Serengetis” disappeared,
as we’ve just seen, well within the radiocarbon dating
window, many of their members lack the kind of radiometric
records that are needed to calculate the dates of their last
appearances with any degree of precision. Reliable radiometric
histories are only available for some 15 of the approximately
35 genera of mammals weighing over 100 lb. which North America
lost near the end of the Pleistocene. Those measurements tell
us that those 15 genera all became extinct between 11,400
and 10,800 radiocarbon years – i.e. between 13,000 and
12,400 calendar years – before the present.
Some of the remaining 20 genera may have became extinct before
or after that 600-year-long spate of more or less securely-dated
extinctions, but the picture that emerges is, nevertheless,
one in which North America loses a megafauna which was much
richer, as I’ve said, than that of present-day Africa,
in something like a thousand years – a millisecond of geological
time.
The fact that somewhere between 30 and 70 million bison were
living on the prairies of North America in the early nineteenth
century demonstrates the fact of this catastrophic impoverishment
rather than casting doubt upon it: Bison bison could never
have become as plentiful as it was in the 1840s while it was
still sharing the prairies of the “American Serengeti”
with a dozen other large herbivore species (including its
relative Bison latifrons). The real Serengeti contains,
for instance, a great many wildebeest (1.4 million of them
still live there), but the entire, Africa-wide population
of the blue wildebeest (the species that lives on the Serengeti)
could never have come near to the Nineteenth-century abundance
of Bison bison. This is so because blue wildebeests
have always had to share the resources of the African veld
with relatives like black wildebeests, hartebeests, topis,
tsessabies and blesboks, and a host of unrelated grass-eaters
ranging from elephants through white rhinoceroses to oryxes.
The population of the one surviving American bison species,
artificially boosted by the extermination of most of America’s
big animals between thirteen and twelve thousand years ago,
was further inflated after the fifteenth century A.D., when
a large proportion of North America’s human population
was wiped out by the introduction of smallpox and other Eurasian
diseases. The enormous bison herds of the mid-nineteenth century
were, therefore, (in the words of Colin Tudge’s Time
Before History) “an artifact – like a rash
of ragwort on a bombsite.”
* * *
When humans first entered North America, at least one cheetah
species, Miracinonyx trumanii was living there. (Two
older American cheetah species, M. studeri, and
M. inexpectata had probably drifted into “natural”
extinction – i. e. extinction not caused by our species
– by that time.) The American cheetahs probably focused
their predatory efforts on the pronghorn and forked-horn “antelope”
species that were America’s equivalent of Africa’s
gazelles, because the only surviving member of the pronghorn/four-horn
group, Antilocapra americana, is still one of the
fastest-running hoofed animals in the world. Evolution would
never have made the enormous investment in the circulatory,
respiratory and muscular-skeletal development required for
that kind of speed without a pressing reason for doing so.
The cat family originated in Eurasia/Africa, but a member
of that family which reached North America in the early Miocene,
probably over the newly-formed Bering land bridge, founded
the cheetah-cougar family in its new homeland.
The idea that the cheetah’s closest living relative
is the cougar or puma may seem surprising at first. The two
species are, after all, widely separated from each other geographically
at present. They’re also widely separated in terms of
human-created classification or “taxonomy.” We’ve
assigned the cheetah, whose adaptation to fast running has
left it with unhooked, dog-like claws that can’t be
fully retracted, into the separate genus Acinonyx
or “unmoving-claw,” while leaving cougars, who
can retract their claws, in the genus Felis together
with other cats who possess this power, like lynxes and house
cats.
The fact that cheetahs and cougars are each other’s
closest relatives becomes obvious, however, on more focused
consideration: both species have small, rounded heads and
long, relatively heavy tails; neither can roar, but both can
chatter in squeaky, bird-like voices. The black “tear
marks” running from the inner corners of the cheetah’s
eyes down to the corners of its mouth, are echoed by prominent
black smudges on the same area of the cougar’s face.
The cheetah’s spots, too, resemble those which adorn
juvenile cougars: they’re solid dots rather than the
very different “rosettes” or “clusters of
spots” displayed by jaguars, leopards, adolescent lions
and many of the smaller cats.
End-Pleistocene North America was inhabited, too, by lions
and jaguars. The former species was similar to, or identical
with the lions which still inhabit Africa and a small part
of India. For reasons we spoke about in Chapter 1, both the
lions and the jaguars were, however, about 25% bigger than
the present-day members of their species.
In addition to the big cat species I’ve just mentioned
– which still exist somewhere on the planet
if not in North America itself – Pleistocene North America
was inhabited by two large felids which have become completely,
rather than just locally, extinct: the saber-tooth Smilodon,
and the “scimitar-tooth” Homotherium.
Smilodon was a closely-related descendant of the
Megantereon sabertooth which had lived, (along with
Homotherium and the “dirk-tooth” Dinofelis)
in Africa until some 1.4 million years ago.
In Chapters 12 to 14 of this book, I’ll argue that
sabertooths disappeared from Africa at this early date because
hominids had, by that time, begun to dominate the business
of hunting large prey effectively enough to shut out other
predators that were dependent on such prey. If I’m right
about this, the relatively late arrival of hominids in Europe
would explain why sabertooth cats survived there long after
they had become extinct in Africa. (Megantereon only
disappeared from Europe some 800,000 years ago, while Homotherium
made its last appearance as recently as 25,000 years ago,
when our kind of human, Homo sapiens, was already
taking possession of that continent.) The fact that the hominid
family – in the person of Homo sapiens –
only entered the New World near the end of the Pleistocene,
would explain, too, why Megantereon (in its Smilodon
avatar) and Homotherium survived there until
that very recent time.
The six big-cat species we’ve been talking about shared
end-Pleistocene North America with four dog-like species:
the coyote, the “ordinary” wolf, a more heavily-built
“dire” wolf, and the dhole – a wild dog which
is still found in Asia.
The still-surviving black bear also lived in North America
when humans arrived there, as did the grizzly bear. Although
it’s considerably larger than a lion, the grizzly wasn’t
the biggest predator to inhabit the New World when our species
first arrived there: that position was held by the giant short-faced
bear Arctodus, which was probably the largest land-dwelling
carnivorous mammal ever to exist. “Awesome” became
an overused word toward the end of the Twentieth Century,
but Arctodus, equipped with long legs adapted to
running pursuit, must truly have been an awesome animal. A
fourth bear species, Tremarctos floridanus, was living
in North America when humans first arrived there. Floridanus
was closely allied to (but considerably larger than) Tremarctos
ornatus, the mainly-vegetarian “spectacled bear”
which survives in South America.
Another predator living in end-Pleistocene North America,
was the “cursorial” or running hyena Chasmaporthetes,
which disappeared from Africa at about the same time that
the sabertooths did – about 1.4 million years ago.
* * *
Twenty thousand years ago, this huge assortment of big carnivores
was living off a much larger assortment of big herbivores.
All the still-existing North American species such as moose,
elk, caribou, white-tail and mule deer, musk ox, bison and
wild sheep and goats were present of course, but there were,
in addition, the two other species of bison I mentioned a
few paragraphs back; a woodland musk ox named Bootherium;
a “shrub-ox” called Euceratherium; an
extinct relative of the still-living mountain goat Oreamnos;
a “stilt-legged” deer called Sangamona;
a medium-sized one called Navahoceros; a caribou-like
deer named Torontoceros; a moose-like deer called
Cervalces and a very large moose-variant named Bretzia.
Unglaciated pieces of North America’s northern end were
inhabited, too, by the saiga, an antelope which still survives
in Eurasia.
If we could use a time-machine to travel to the North America
of this time, we’d be able to see, too, the varied suite
of “antilocaprids” i.e. the pronghorn and forked-horn
“antelope” species which I mentioned in connection
with America’s cheetahs. Just as present-day visitors
to East Africa’s game parks might argue about whether
they’re watching Thompson’s gazelle, Grant’s
gazelle, Roberts’ gazelle or Rainey’s gazelle,
we might, on such a time-trip, get into lively discussions
about whether we were looking at Matthew’s pronghorn
(Capromeryx furcifer), the little pronghorn (C.
minor), the Mexican little pronghorn (C. mexicana),
Shuler’s pronghorn (Tetrameryx shuleri), Mooser’s
pronghorn (T. mooseri), Conklin’s pronghorn,
(Stockoceros conklingae) or Quentin’s pronghorn
(S. onusrosagris).
We could get into the same kind of arguments about the camel-llama
suborder Tylopoda which was represented in its North
American homeland by three genera at this time: the genus
Camelops, represented by perhaps three species, and two
llama-like genera called Paleolama and Hemiauchenia,
which may also have contained multiple species.
Three peccary or “New World pig” species still
live in the Americas: the collared peccary (or “javelina”),
the white-lipped peccary, and the recently-discovered Chacoan
peccary Catagonus (which was first identified by
late-Pleistocene sub-fossils in the thirties). During the
late Pleistocene, there were two additional species: a long-nosed,
long-legged peccary called Mylohyus, and a large,
“flat-headed” species called Platygonus compressus.
Platygonus’ remains have been found at about
130 sites throughout North America, and it may well have been
that continent’s commonest medium-sized mammal.
Peccaries and cheetahs were “naturalized” Americans,
i.e. animals that had come to North America early in their
evolutionary history, but the camel-llama suborder Tylopoda,
the “pronghorn” or antilocaprid family, and the
Perissodactyl order (i.e. horses, tapirs, rhinoceroses
and chalicotheres) were North American born and bred.
Rhinoceroses disappeared from their North American homeland
about five million years ago. The disappearance of this and
a great many other animal groups from North America during
the late Miocene was caused by the drop in the planet’s
average temperature which had been taking place throughout
the latter part of that Epoch, and accelerated about five
million years ago. North America was, even after that temperature-drop,
still a warmer continent than it is today, but its rainfall
dropped sufficiently to stimulate the evolution and spread
of grasses, including tough, fibrous “C4” species.
This cooling and drying trend, and the accompanying rise
of grasslands, was a world-wide phenomenon, but it seems to
have brought about a particularly large number of extinctions
in North America. That might have resulted (as I suggest in
the appendix to this book) from the fact that North America
lacked the relatively warm, relatively moist tropical refuges
retained by Africa, Eurasia, and South America. (As we’ve
seen, North America had not yet become joined to South America
when this Miocene cooling took place.)
The early Miocene saw the ending, too, of a relatively long
period of isolation for North America, by starting the periodic
openings of the Bering land bridge which have been going on
ever since that time. This let in successive waves of Eurasian
invaders such as proboscideans, bovids, cervids and felids
which may have compounded the difficulties which climatic
and vegetational change was causing for North America’s
“autochthons” or native species.
Long before the North American rhinoceroses became extinct,
at least one of its members had dispersed into the Old World
(where rhinoceroses have, of course, survived into the present).
That “emigration” took place in the Oligocene
Epoch some thirty million years ago. North America may still
have been connected to Scandinavia via Greenland at that time.
Rhinoceroses could, therefore, have used a “Greenland
bridge,” to get to Eurasia and beyond. (As we’ll
see in Chapter 20, in the appendix to this book, Greenland
literally was a “green land” at that
time.)
While the perissodactyl group lost all of its rhinoceroses
and chalicotheres (more about the latter in Chapter 12) in
North America, some members of its horse and tapir groups
survived.
During the late Pleistocene, three species of tapir lived
in North America – Tapiris veroensis, T. copei,
and T. californicus. Four members of this genus still
exist: three in South and Central America, and one in Malaysia
(which it reached via the Bering Bridge).
Of the twelve genera of equids, or horse-like animals, that
had been in existence at the beginning of the Miocene, only
three survived to the end of that epoch. North America’s
mammalian diversity started growing again, however, in the
later Pliocene and the Pleistocene. During that time, one
of the “horse-like” genera that had survived the
Miocene extinction, Equus, evolved a rich diversity
of species in North America. By the end of the Pleistocene,
Equus was – along with the two other surviving
genera, Hippidion and Onohippidium –
also present in South America.
We can divide the still-existing members of the genus Equus
into
(1) Caballines or “true horses,” which includes
the domestic horse Equus caballus and a wild species
called E. pzewalskii;
(2) Hemionines or Asiatic wild asses which include Kiangs,
Onagers, Kulans and Khurs;
(3) Asinids (the Nubian wild ass Equus asinus asinus,
and the domesticated donkey derived from it, as well as the
Somali wild ass E. a. somalicus); and
(4) Zebrines, which include the large, mule-like Grevy’s
zebra, Burchell’s zebra (divided into three subspecies
including the partly-striped, extinct quagga), and the ass-like
mountain zebra (represented by two subspecies).
Greg McDonald, a vertebrate paleontologist with U.S. National
Park Service, thinks that the “horse” species
abundantly represented in the Hagerman fossil beds in Idaho
where he is stationed, Equus simplicidens, was a
close relative of Grevy’s zebra. It’s widely assumed,
too, that the smallest of the American “horses,”
E. tau, was a “pigmy onager”; that E.
calobates was a “stilt-legged onager”; and
that E. conversidens (whose human-butchered remains
have been discovered in association with Clovis spear-points
on the drained bed of St. Mary’s reservoir in southern
Alberta) was a kind of ass.
I’m fully persuaded that ass-like, zebra-like, onager-like
and/or horse-like characteristics were scattered among the
New World’s diverse equine species. I would have to
be guided, however, through a “multivariate” analysis
of the relevant specimens by someone like my friend James
Brink of the Florisbad Quaternary Institute in Bloemfontein,
who has a special interest in equine paleontology, before
I could presume to affirm or deny that one or another of the
American equine species was identical or close to a particular,
still-living member of the genus Equus.
How many horse-like species were there in the New World at
the end of the Pleistocene? FaunMap, an electronic database
documenting the late Quaternary distribution of mammals in
the United States, developed at the Illinois State Museum
and directed by Russel Graham and Ernest Lundelius, lists
seventeen North American equines. (Let me add uncritically,
though, that the creators of FaunMap, who also list five North
American mammoth species, espouse the “splitting,”
as opposed to the “lumping,” end of taxonomic
thinking.)
Despite its wealth of species, the entire Equus
genus disappeared from the New World at the end of the Pleistocene,
along with the South American equids Hippidion and
Onohippidium. The horses later used by American Indians
were, therefore, the descendants of animals imported from
Europe. Horses were, with that importation, completing a journey
around the planet by returning to the continent on which they’d
originally evolved.
Equid species had been spreading into Eurasia since this
family first arose in North America early in the Age of Mammals
some fifty million years ago. The next-to-last wave of equid
emigration washed into the Old World with the arrival of three-toed
horses or “hipparions” in the late Miocene some
ten or twelve million years ago. Together with the remains
of antelope species found in association with it, the cutmarked
femur of a hipparion, unearthed at Bouri in Ethiopia in the
late 1990s, constitutes proof that the human-like beings we’ll
meet in Chapters 9 and 10 were already using stone tools for
the purpose of butchery in the Late Pliocene, 2.5 million
years ago. As we’ll see in Chapter 12, hipparions became
extinct in Africa about a million years ago.
We mustn’t, of course, imagine that biological traffic
flowed only one way over the Beringian “land bridge”
which Equus and other American groups used to reach
Asia. Many African and Eurasian species crossed it in the
opposite direction to establish themselves in the New World
(and some of those recrossed it thereafter). Old World immigrants
to the New World include bison and other bovids, deer and
cat species, as well as several kinds of elephant. At least
seven elephant-like or “proboscidean” species,
divided into three families, (each of which had evolved in
Africa) were living in the New World when our species first
entered it.
The mammoth family was represented by at least three species.
The Eurasian woolly mammoth Mammuthus premigenius
had settled the northern parts of North America late in the
Pleistocene. One or more waves of mammoths had, however, spilled
into North America near the beginning of the Pleistocene some
1.8 million years ago. The descendants of these “early
arriving” mammoths were, by the end of that Epoch, living
in great numbers in the southern, western and midwestern regions
of that continent. Some paleontologists separate these early-arriving
or “native” mammoths into two or even three species,
Mammuthus columbi, M. imperator and M. jeffersoni,
but the current trend is to place them all into the columbi
taxon.
I’ll follow that trend, and talk about all America’s
“native” mammoths as M. columbi. We’re
prepared, after all, to see all African elephants as members
of the single species Loxodonta africana, even though
they’re a very variable group. L. africana
has a “savanna” subspecies L. africana africana,
and a somewhat smaller and very different-looking “forest”
subspecies, L. a. cyclotes. Some zoologists recognize
the West African pygmy elephant – which is only about
six and a half feet tall at the shoulder – as a separate
species which they would call Loxodonta pumilo, but
most would classify it as an even smaller variant of cyclotes.
Another very small elephant – about the size of the
pygmy elephant – is reported to have occurred until
very recently in Mauritania. At the other extreme, the desert
elephants of the Kaokoveld in Namibia, with a shoulder height
of up to 13 feet, tend to be even taller than “standard”
savanna elephants like those found in the Kruger and Serengeti
National Parks.
Columbian mammoths had probably evolved a comparable radiation
of subspecies by the end of the Pleistocene. These “native”
mammoths may have been relatively hairless, or they could
have been sparsely-haired like Sumatran rhinos. Their tusks
could, as we saw in Chapter 4, grow to an astonishing sixteen
feet in length. (The longest African elephant tusk on record
measured eleven feet, five inches.) Columbian mammoths reached
a larger size than both woolly mammoths and African elephants.
Big African elephants weigh about 12,000 lb, and the biggest
ones reach 15,000 lb. The biggest Columbian mammoths probably
exceeded 20,000 pounds. The smallest Columbian or “native”
mammoth we know of, was, however, even smaller than West Africa’s
“pygmy” elephant. Assigned to the separate species
Mammuthus exilis because of this dramatic size difference,
this animal had become dwarfed after reaching, and living
on, the channel islands off what is now Santa Barbara on the
coast of southern California.
The mastodont family had moved out of Africa/Eurasia into
North America in the late Miocene some 3.5 to 4 million years
ago. By the time humans reached that continent, only one of
its members, Mammut americanus, was living there.
The grinding surface of mastodonts’ cheek teeth consisted,
as we saw in Chapter 4, of breast-like bumps or cones. Those
simple, enamel-covered cones stood in sharp contrast to closely-packed
plates of buried enamel which gave the “loxodont”
cheek-teeth of mammoths their grass-resistant qualities.
While it’s clear, therefore, that M. americanus
had simpler cheek-teeth than mammoths did, it may have had
a relatively complex liver. Specialist browsers are usually
confronted with many more kinds of potentially edible plants
than grazers are, and commonly evolve livers which are sophisticated
enough to detoxify the wide range of the “defense-poisons”
to which this catholic diet exposes them. Livers don’t,
however, fossilize the way teeth do, so we can only speculate
that this may have been the case with M. americanus.
Preserved stomach contents confirm, at any rate, that the
American mastodont was a specialist browser, whose
diet included the twigs and leaves or needles of spruce, pine,
larch and cedar trees. As one might expect, therefore, americanus
was the commonest elephant in the forests of what is today
the eastern United States. It was, however, widely distributed
throughout North America, and its remains have been found
as far south as Honduras. Standing about eight feet tall at
the shoulder, it was about two-thirds as tall as a Columbian
mammoth, but its body was as long or longer than that of the
mammoth. Like those of the premigenius mammoth, the
bodies of American mastodonts were covered with hair.
The third American elephant family, the gomphotheres, had
arrived in North America as long ago as fifteen million years
ago, near the middle of the Miocene Epoch. Gomphotheres could
not, of course, have entered South America at this
early stage, because that continent would only come into contact
with North America just over three million years ago. By the
time humans arrived in the New World, most (if not all) of
the members of the gomphothere family had, however,
become restricted to South America: Cuvieronius hyodon
seems to have lived in the colder, more elevated regions of
that continent, while Stegomastodon waringi and S.
platensis inhabited its warmer, lowland regions.
The cheek-teeth of the gomphotheres were broadly similar
to those of the “breast toothed” mastodont, but
they were covered with a somewhat thicker layer of enamel
whose surface area was increased by “folds” or
“wrinkles.” Stable isotope studies tell us that,
at least in some areas, gomphothere species combined browsing
with grazing. This unspecialized feeding pattern may explain
why gomphotheres had, by the end of the Pleistocene, been
displaced in North America by mastodonts and mammoths (which
were both, as we’ve seen, specialist feeders). If humans
had somehow disappeared off the face of the earth 15,000 years
ago, those two specialists might eventually have displaced
the gompotheres from their South American sanctuary too.
Chapter 6 -
Lost Serengetis 3: North America concluded; South America;
the fact that big animals don't go into oblivion alone.
