Chapter 6
Lost Serengetis 3: North America concluded;
South America; the fact that the extinct megafauna didn’t
go into oblivion alone
I’ve been assuming, thus far, that the
Columbian mammoth was the largest member of the New World’s
megafauna. It’s possible, though, that Steller’s
sea-cow Hydrodamalis gigas, the supergiant dugong
which I mentioned in Chapter 1, could have been even bigger.
Estimates of Hydrodamalis’ weight range between
12,000 and 24,000 lb. This species was, as you may recall
from Chapter 1, exterminated by humans in 1768 – less
than thirty years after members of Vitus Bering’s expedition
discovered it living around the two uninhabited and previously
unknown Komandorskiye islands off the end of the Aleutian
chain. That discovery actually took place as a result of Bering
and his crew being shipwrecked on the larger of those two
islands. Bering was, like many members of his crew, to die
on that island, which was later named for him.
Steller’s sea cow was very much a member of North America’s
Pleistocene fauna. The small population discovered in the
Eighteenth Century by the surviving members of Bering’s
crew, was simply the last remnant of a species that had, before
human hunting had restricted it to its remote northern sanctuary,
extended down to California or Mexico (and down to Japan on
the other side of the Pacific). Daryl Domning, an anatomist
at Howard University, suggests that its northern “sanctuary”
could have been a suboptimal environment for the 1,000 - 2,000
animals which survived there, and that the giant dugongs might
have grown larger in the southerly portions of their range.
(Hydrodamalis was more closely related to dugongs
than manatees – its tail resembled, for instance, the
dolphin-like tail of the former, rather than the rounded,
paddle-like tail of manatees.)
Georg Wilhelm Steller, the Bering expedition’s young
medic and naturalist, left us an excellent description of
Hydrodamalis. Steller’s writings make it clear
that these huge dugongs would probably have been as accessible
to early human hunters as North America’s terrestrial
megafauna was. They lived in very shallow water, and came
so close to the shore that Steller and his companions could
“hit and reach them with sticks” while standing
on dry land. Steller never saw a Hydrodamalis submerging
its body completely. Members of this species typically lay
in the water with their backs protruding, using their curved
front limbs (which terminated in “brushes” formed
by a dense growth of stiff bristles) to “walk on or
pull themselves along” the bottom. Steller also saw
them using those front limbs to scrape seaweed from the rocks
and hold each other while mating. (He concluded, incidentally,
that they were monogamous.)
Like its relative the savanna elephant, Steller’s sea
cow was a messy, destructive eater: kelp stalks and pieces
of other sea-weed would float to the surface and wash ashore
in large quantities in where groups of them were feeding.
For some reason, Steller often came upon those feeding parties
at places where streams flowed into the ocean. Did these animals
need, one wonders, to drink fresh water?
After living on the meat of cormorants and seals for several
months, Steller and the other survivors of the wreck of Bering’s
ship, devised a way of slaughtering a few of these monsters:
thirty to forty men would stand on the shore at high tide,
holding one end of a long, stout rope. Another party would
row the wrecked ship’s “jolly boat” up to
the selected animal, and thrust a large metal hook, attached
to the other end of that rope, into its flesh. The shore party
would then start pulling on the rope, while the men in the
boat would harass the hooked animal to the point of exhaustion,
making it bleed copiously by stabbing it with large knives
and bayonets.
While this battle was taking place, the animal’s companions
would, Steller noted, make unavailing efforts to help it.
The shore party would then pull the animal against the side
and hold it there until the falling tide beached its enormous
body, enabling them to cut strips of meat and fat off it.
“We noticed,” Steller tells us, “not without
amazement, that a male approached his mate, who was lying
on the beach, for two consecutive days, as if to find out
what had happened to her.”
Steller and his party may not have had the energy needed
to build a seaworthy vessel out of the wreckage of their ship,
and make it back to Kamchatka, if they had not gained access
to the palatable, beef-like flesh, and the aromatic oil, of
these giants. That oil would, Steller tells us, became “as
pleasantly yellow as the best Dutch butter” after it
had been left in the sun for a few days. Back on Kamchatka,
he and his party spread the world about the Komandorskiye
Islands and their tasty “sea cows.” As Steller
saw it, the animals were present around those islands “...in
such large numbers that, in each year, all the inhabitants
of Kamchatka’s east coast could obtain an abundant supply
of meat and fat from them.” Hydrodamalis would,
as we’ve seen, be completely wiped out in less than
thirty years after this pronouncement.
I can’t imagine what the impact of a manatee or dugong
ten to twenty times bigger than any of the living species
might have been. I remember how surprised I was when I saw
my first member of this group – an Antillean manatee
– surfacing near my boat in a jungle river in South
America. I’d vaguely imagined manatees to be as big
as large otters, but this animal, ten feet or more in length,
and probably over a thousand pounds in weight, was the size
of a beluga whale. Hydrodamalis was, as we’ve
seen, the size of a big killer whale. I find myself regretting
the fact that my species discovered this marvelous creature
– or rather rediscovered it – as early as 1741.
We had, after all, developed the awareness required to prevent
ourselves from exterminating animals like the white rhinoceros
and the American bison by the late nineteenth century. If
we had, therefore, come upon the last Hydrodamalis
population just a hundred years later, I tell myself, we might
have been able to restrain ourselves from wiping it out, and
even managed to return it, eventually, to the Big Sur, like
we’ve returned the white rhinoceros to the Kruger Park.
The sobering reality of my species’ relationship with
the Sirenian order is, however, that, even here in second
millennium of the Common Era, the population levels of its
four living species (three manatees and one dugong) are dropping
steeply under our destructive impact.
* * *
South America had, like Australia, been an island continent
until it joined up with North America some three and a quarter
million years ago. It had originally gained that island status
by separating from Antarctica some thirty million years before
the present. (Australia had broken away from the other end
of Antarctica about ten million years earlier.)
After South America went its own way, many of its plants
and animals still had close relatives in Antarctica (which
had remained a temperate, forested continent until at least
twenty million years ago). South America’s plants and
animals also retained close connections with those of Australia.
As we’ll see in Chapter 20, South America and Australia
still share closely-related plants, invertebrates, fishes,
amphibians and reptiles. Marsupial mammals still live in South
America as they do, of course, in Australia. (One of the South
American marsupials, the “Virginia” opossum, has
very successfully invaded North America.) South America was,
therefore, a kind of “almost-Australia.” In addition
to its marsupials, however, it also had placental or “eutherian”
mammals (i.e. members of the group that humans, bats and whales
belong to).
Marsupials and eutherians had divided South America between
them in an unexpected way – eutherians filled most of
the continent’s plant-eating niches, while the marsupials
were, in the main, flesh eaters. One of the marsupial flesh
eaters – a member of the so-called “borhyeanid”
family – developed a cat-like skull and “saber”
teeth that bore an extraordinary similarity to those of the
eutherian sabertooth Smilodon.
South America’s marsupials were not, however, that
continent’s only flesh-eaters. They competed with a
variety of “phororhacoid” bird species, the largest
of which, Titanis, was a ten-foot tall, 350 lb. monster
with a huge head equipped with a fifteen-inch-long hooked
beak. Titanis was probably able to kill horse-sized prey.
“Never before or since,” E. O. Wilson tells us,
in his Diversity of Life
have mammals faced anything like
the phororhacoids, except during their earliest evolution
in the Age of Dinosaurs. In South America Titanis and its
relatives must have been serious rivals to the borhyeanids
and other carnivorous marsupials. Since anatomists consider
birds as a whole to be direct descendants of dinosaurs...the
phororhacoids might be called the final echo of the ruling
reptiles.
All the marsupial predators and almost all of the phororhacoid
bird species were driven into extinction soon after big cats
and other North American predators entered South America as
a result of the land connection that arose between the North
and South America approximately 3.25 million years ago. (The
entry of North American species into South America, and vice
versa, that resulted from this connection is sometimes referred
to as the “Great American Biotic Interchange”
or “GABI.”) A few vertebrae, two cheek bones,
and some wing and foot bones found in two-million-year-old
sediments in Northern Florida, show that at least one of the
phororhacoids – Titanis itself, no less, –
had not only survived the GABI, but actually gone on to invade,
and establish itself in, the territory of the supposedly “superior”
North American predators.
On the basis of a single toe-bone found in Texas, John Baskin
of Texas A&M argues that Titanis walleri was
still living in North America at the end of the Pleistocene.
I don’t regard Baskin’s conjecture as an improbable
one. We know that Titanis was living in Florida near
the beginning of the Pleistocene. We know, too, that, at least
as far as mammalian extinction was concerned, “...the
entire Pleistocene before the terminal Wisconsinian was,”
in John Alroy’s words, “a period of relative tranquility.”
While it’s no doubt possible that Titanis
survived the turmoil of the GABI only to drift into extinction
sometime during that period of “relative tranquility,”
it seems far more likely that it disappeared in the same “terminal
Wisconsinian” cataclysm which destroyed so many other
species of megafauna.
If Titanis did survive to the end of the Pleistocene,
then it’s very likely that humans met up with it. That
would have been the closest thing our species could have experienced
to a confrontation with a living dinosaur.
* * *
The diversity of South America’s eutherian mammals
rivaled that of any of the Earth’s other continents.
The entirely extinct magnorder Meridiungulata, which was comprised
of the orders Notoungulata, Litopterna, Astropotheria, Pyrotheria,
and Xenungulata, contained a great many species that echoed
the shapes of animals that were, like horses, hippos and pigs,
familiar to us, and a great many others with forms that we
would consider unlikely and outlandish. (Elephants and giraffes
might, of course, also seem like unlikely creatures to people
who weren’t familiar with them.)
Almost all the members of this lost Meridiungulate magnorder
disappeared in the GABI. A few genera of notoungulates (which
included the rhinoceros-sized Toxodon), and one of
the litopterns, (the llama-shaped Machrauchenia)
are known to have survived that interchange, but these survivors
all disappeared in the end-Pleistocene extinction.
Paleontologists suspect that Machrauchnia may have
had a tapir-like trunk. The animal’s nostrils opened,
however, near the top of the its head – above its eyes
– rather than at the end of that putative “trunk.”
We’ll probably never get a realistic idea of what those
end-Pleistocene notoungulates and litopterns looked like.
“To envision living examples of them,” Paul Martin
writes, “would be like trying to dream up a realistic
picture of a rhinoceros if the entire order of Perissodactyla,
to which horses, zebra, tapir, and various genera of rhinos
belong, were known only from fossil bones.”
Martin goes on to describe those late-surviving meridiungulates
as being “among the most mysterious members of the fauna
of near time, utterly neglected by a public hooked on dinosaurs,
and by Pleistocene paleontologists hooked on mammoths and
mastondonts.” I see this neglect in myself, and catch
myself drifting into a solipsistic delusion that animals so
poorly known to us couldn’t have been entirely real.
But the notoungulates and litopterns which still existed at
the end of the Pleistocene, formed by millions of years of
evolution, were of course every bit as real as elands or red
kangaroos are. It’s highly likely, moreover, that the
first human immigrants to South America experienced their
living reality. Gustavo Martinez of the Universidad del Centro
de la Provincia de Buenos Aires, and his co-workers, have
reported the association of “fish tail” projectile
points with the burnt bones of megamammals in Argentina’s
Buenos Aires Province. The bones in question have been assigned
to several extinct species, including the meridiungulates
Macrauchenia patagonica, and a member of the genus Toxodon.
* * *
One other magnorder of eutherians, viz. the Xenarthrans,
developed in South America, and this group does contain members
which have survived into the present. Those survivors are
classified into the orders Pilosa (“hairy ones”),
and Cingulata (“armored ones”). The Pilosa are
presently represented by five tree-sloth species and by the
giant anteater, while the Cingulata are comprised of eight
genera of armadillos, containing twenty-one species (one of
which has very successfully invaded North America).
Fifteen genera of “ground sloths” were living
in South America at the end of the Pleistocene. These sloths
had, therefore, fared much better against competition from
North America’s megaherbivores than most of South America’s
“autochthons” had. They were not only holding
their own in their South American homeland, but had managed,
in addition, to mount a successful invasion of North America,
where four genera were living at the end of the Pleistocene.
Nine further ground-sloth genera, which had radiated into
eighteen species, lived on islands in the Caribbean (where
they survived for thousands of years after the extinction
of their continental counterparts.)
The biggest of the ground-sloths, African elephant-sized
members of the genera Megatherium and Eremotherium,
could probably reach as high into trees as Columbian mammoths
could. They would have done so by stretching their long “arms”
aloft, while standing upright on a “tripod” consisting
of their massive back legs and their powerful tails. All the
ground-sloth species folded their powerful front claws onto
their “palms” or “wrists” when they
walked, using the knuckles of those “hands” to
make contact with the ground. Ground sloths’ massive
hind feet were not, however, designed to fold in this way
– one family, the Megalonchidae, walked on
the soles of their back feet, while the other families used
the sides of those feet.
The 70 lb. giant anteater Myrmicophagus –
also, as I mentioned, a member of the order Pilosa –
is the nearest thing to a ground sloth which survives on our
planet. It walks, like all the ground sloths did, on the knuckles
of its front feet, and, like the megalonchid ground sloths
did, on the soles of its rear feet
The giant anteater uses the long, stout claws on its front
feet to dig for ants. Ground sloths did not, of course, use
their claws for this particular purpose, but some of the prairie-
and pampas-dwelling species might well have dug for roots
to supplement their diet of shrubs and grasses. Giant anteaters
also stand upright on their back legs, using their tails to
create a “tripod” the way the ground sloths are
thought to have done. One of the reasons why they do this,
is to make their “arms,” “hands” and
claws available for defense. Myrmicophagus is limber
and mobile on its hind legs: it can whip around rapidly to
reach an attacker who’s approaching from behind. Its
claws can be used to rip an assailant, or to hold onto it,
in order to crush it with its powerful “arms.”
I think it’s likely that at least some of the ground
sloth species may have defended themselves in much the same
way that Myrmicophagus does. The ground sloths must,
at any rate, have been able to fend off predators in an effective
way: they survived, after all, in the presence of the sophisticated
North American predators that had supplanted most of South
America’s native meat-eaters. If we bear in mind, in
addition, the fact that some of the ground sloth species which
lived in the shadow of those formidable predators, did not
enjoy a size advantage over them, this argument gains even
more force. North America’s two biggest ground sloths,
the elephant-sized Eremotherium rusconi, and the
rhino-sized Paramylodon harlani, were much bigger,
of course, than their potential predators, but the ox-sized
Jefferson’s ground sloth probably weighed about the
same as the great Arctodus bear. The Shasta ground
sloth, which seems to have reached a weight of only about
350 lb., would have been even smaller, on average, than North
America’s saber cats and lions.
Although they would have offered no defense against “stand-off”
weapons like spears, ground sloths’ claws must have
been formidable weapons. I used to think that the claws of
tree-sloths were relatively passive hooks, which engage branches
in the immobile way a cup-hook holds the handle of a mug.
I found out how wrong this idea was, when, fishing for tarpon
in Suriname in South America, I came upon a three-toed sloth
swimming across the Coesewijne river. Out of curiosity, I
engaged the claws on one of its front legs with the hook of
my fishing gaff. To my surprise, the sloth locked a powerful
grasp onto that hook, and then started climbing, “hand-over-hand,”
up the gaff’s four-foot shaft. That steel shaft was
being clamped so firmly between its claws and the “palms”
of its “hands” that no amount of jerking on my
part could halt the animal’s climb. My boatman had to
hit the sloth disconcertingly hard with a paddle to make it
let go and get on its way.
This experience was also my first acquaintance with the fact
that sloths are good swimmers. Those swimming skills could
help explain the presence in North America of megalonchid
ground sloths several million years before that continent
became physically attached to South America, and the fact
that this family established itself on islands in the Caribbean.
* * *
So much, then, for the “hairy” or “Pilosan”
Xenarthrans. Their “armored” or “Cingulate”
order (which still contains, as we’ve seen, twenty-one
species of armadillo), was represented, in the late Pleistocene,
by several different groups referred to (confusingly) as “giant
armadillos.” The first of these extinct “giant
armadillos,” Dasypus bellus, was very similar
to the living nine-banded armadillo of North America. It may
have been about the same size as South America’s still-living
“giant armadillo” Priodontes giganteus,
a rare animal that can weigh as much as 130 lb.
The members of a small family of armadillo-like “pampatheres”
are also sometimes referred to as “giant armadillos,”
but they were real giants: the only North American representative
of this family, Holmesina septentrionalis, reached
about 600 lb. in weight.
The Glyptodontidae is perhaps the best-known of
the extinct armadillo-like families. Some 18 genera belonging
to it inhabited South America at the end of the Pleistocene.
One genus, Glyptotherium had moved into North America.
Most glyptodont species weighed over a thousand pounds. Protected
by a “shell” or carapace made up of hundreds of
bony polygons bound together by collagen, they must, at first
glance, have looked like enormous tortoises. Their heads and
tails could not, however, retract into their carapaces. The
heads were protected, instead, by bony “helmets,”
and the tails, by rings of armor near their bases, and stiff
bony sheaths on their ends. In at least one of the South American
species, that sheath was tipped by a spiked ball which made
it look like the business-end of a medieval mace.
* * *
South America’s recently-extinct megafauna includes
at least two monkey species which were considerably larger
than any other primate, living or extinct, which has been
found on that continent. Protopithecus brasiliensis
and Caipora hambuiorum, whose fossil remains have
been found in Brazil’s Bahia province, each approached
50 lb. in weight. Eckhard Heymann of the Deutches Primantenzentrum
thinks that these big monkeys may have been at least partially
terrestrial.
Surprisingly, perhaps, the extinct megafauna of the New World
also included rodents. South America is still home to giant
rodents – the capybara Hydrochoerus, with its
“loxodont” teeth which we spoke about in Chapter
4, commonly exceeds 100 lb. in weight. During the Pleistocene,
a larger capybara, Neochoerus pinkneyi, which weighed
150 lb. or more, extended into Florida. Neochoerus
was not, however, the New World’s largest rodent. That
title was held by the 450 lb. giant beaver, Castoroides
ohioensis, which lived only in North America.
In Chapter 1 I wrote that “the spread of the hominid
family out of its African homeland across the rest of the
planet has been faithfully tracked by the disappearance of
giant tortoise species.” The New World was no exception
in this regard. One or more Galapagos-sized tortoise species
(including the so-called “Hesperotestudo”)
disappeared in the end-Pleistocene extinction-spasm, as did
a large relative of the still-existing sliding turtle Trychemys.
The bones and shells of tortoises and terrapins (freshwater
turtles) are, I should add, commonly found in association
with Clovis sites in North America.
* * *
When 73% of the North American and 80% of South American
mammal species weighing over 100 lb. disappeared at the end
of the Pleistocene, at least ten genera of birds in the raptor/scavenger
class followed them into extinction. Among these birds were
an American version of Africa’s marabou stork, several
large “new world” vultures, the large condor Breagyps,
the “American secretary-bird” or “walking
eagle” Wetmoregyps, and several members of
the family Teratorthidea, whose largest species,
the aptly-named Terratornis incredibilis, had a sixteen-foot
wing-span.
Africa’s biggest scavenger/raptor birds are presently
threatened with the same fate as these American giants –
the lappet-faced vulture, with a wing-span of over nine feet,
is declining along with the bigger animals whose carcasses
they are adapted to scavenge. Smaller African vultures like
the griffon, white-backed, hooded and Egyptian species can
and do survive in places where big wild animals have been
exterminated, but the lappet-face, whose powerful bill was
adapted to deal with the skins and tendons of large animals,
fades via scarcity into extinction in such conditions.
When a large animal goes extinct, it doesn’t go into
oblivion alone. Early in the twentieth century Buphagus
africanus, the yellow-billed ox-pecker (called, more
aptly, geelbek renostervoël or “yellow-billed
rhino bird,” in Afrikaans) disappeared from the area
which is now protected as the Kruger Park. That disappearance
followed the extermination or decline of many of the area’s
biggest animals. In contrast to the still-plentiful red-billed
ox-pecker, the yellow-bill has evolved a heavy-duty beak which
may give it an advantage over the red-bill in relation to
the larger species of ticks and flies which live on big mammals
like buffaloes and rhinos. A North American bird that may
have had a similar adaptation followed the megafauna of that
continent into extinction at the end of the Pleistocene: the
thick-billed cowbird, Pyelorhamphus molothroides.
Yellowbilled rhino birds filtered back into Kruger from Zimbabwe
sometime after the middle of the twentieth century and have
now, probably because of the return and/or increase in the
larger herbivores in the area, started building up their numbers
again.
The return of the of the yellowbill is a welcome development,
but the return of the rhino-dependent ticks was, of course,
itself a worthwhile re-enrichment of Kruger’s biodiversity.
The fact that I’m mentioning just one of those returning
ticks – Dermacentor rhinocerinus – means
only the attractive orange markings and interesting shape
of that particular parasite often singles it out for human
attention. Also restored to Kruger by the reintroduction of
rhinos was one of the world’s largest flies, Gyrostigma
pavesii, whose eggs hitch-hiked from Zululand to Kruger
on or in their returning hosts. As Leo Braack, a former director
of scientific research at the Kruger Park, points out, the
pioneers of rhino reintroduction weren’t always conscious
of the host of satellite creatures they were bringing back
to Kruger along with the rhinos:
In one of the transporting crates
a rhino must have defecated whilst still in Zululand. A female
of the large bloodsucking fly Rhinomusca dutoiti laid a last-minute
batch of eggs in the dungpad. The eggs finally hatched in
Kruger, and gave rise to a now-flourishing population widespread
from Pretorius Kop to Mooiplaas.
Even under today’s conditions, when biologists are
more careful about identifying the organisms that can hitch
a ride when large animals are translocated, it would be difficult
or impossible to make a complete inventory of the host of
flies, worms, lice, mites, flukes, fungi, protists and prokaryotes
which live around, on, and in rhinos. We can only guess, therefore,
at the huge number of small species – mainly but not
exclusively invertebrate – that must have followed the
extinct members of the Eurasian, American and Australian megafaunas
into oblivion.
The “secondary” extinctions caused by the disappearance
of those big animals would not, moreover, have been restricted
to organisms which were as directly dependent on them as,
say, Dermacentor ticks or Gyrostigma flies.
Any of the big animals or birds which disappeared from the
“vanished Serengetis” could have been a “keystone”
species whose removal could have led to the extinction of
organisms not connected to them in any obvious way.
In his Diversity of Life Edward Wilson explains,
for instance, that when jaguars and pumas disappeared from
Barro Colorado island in Panama, their prey species, raccoon-like
animals called “coatis,” and large rodents called
“agoutis” and “pacas,” experienced
a huge increase. Because coatis, agouties and pacas feed on
large seeds that fall from the rain-forest canopy, they quickly
reduced the reproductive ability of trees which produce those
large seeds:
Other tree species whose seeds are
too small to be of interest to the animals benefit by the
lessened competition. Their seeds set and their seedlings
flourish, and a larger number of the young trees reach full
height and reproductive size. Over a period of years the composition
of the forest shifts in their favor. It seems inevitable that
the animal species specialized to feed on them also prosper,
the predators that attack these animals increase, the fungi
and bacteria that parasitize the small-seed trees and associated
animals spread, the microscopic animals feeding on the fungi
and bacteria grow denser, predators of these creatures increase,
and so on outward across the food web back and back again
as the ecosystem reverberates from the removal of the keystone
species.
The extinction of the Pleistocene megafauna could, therefore,
have had a significant effect on the diversity of biological
communities that supported them. Like the elephants and big
bovids which still inhabit the jungles of Africa and South
Asia, gomphotheres, ground sloths and toxodons probably created
trails, wallows and clearings in the Amazon basin, maintaining,
possibly, a more varied mosaic of plant communities than we
see there today. The South American rainforest still constitutes,
of course, a staggeringly rich storehouse of biodiversity,
but it seems likely that this diversity must, to some non-trivial
extent, have been greater when the giant herbivores
still formed part of its support.
PART
3
The evolution of hominid inventiveness in Africa was a two-edged
sword: it caused the early extinction of many of Africa's largest
animals, but it also forced that continent's megafauna to evolve
the behavioral defenses against our family which have enabled
a relatively large number of its members to survive into the
present.
