GIANT SLOTHS AND ARMADILLOS.
"Injecta monstris terra dolet suis."
Horace, _Odes_, book iii.
It would have been strange, considering how much we owe to North
America, had the great South American continent not enriched our
knowledge of past forms of life on the globe. But such is not the
case. The honours are, as it were, divided, although it must be
admitted that the North American extinct forms at present known are
far more numerous. There are, however, two or three "Extinct Monsters"
of very great interest which once had a home in South America--in that
strange region of the Pampas, where the naturalist of the present day
finds so much to excite his interest. Of these the present chapter
treats.
The Megatherium[48] (Cuvier) was a gigantic mammal allied to sloths and
ant-eaters, and perhaps to the armadillos. In its skull and teeth this
colossus of the past resembled the sloths, in its limbs and backbone
it resembled the ant-eaters, while in size it surpassed the largest
rhinoceros (Plate XVII.). The famous, but imperfect, specimen at
Madrid was for a long time the principal if not the only source of
information with regard to this extinct genus, and for nearly a
century it remained unique.
[48] Greek--_megas_, great; _therion_, beast.
Later on, however, the zeal and energy of Sir Woodbine Parish, his
late Majesty's _chargé-d'affaires_ at Buenos Ayres, greatly helped to
augment the materials for arriving at a just conclusion with regard
to its proper place in the animal kingdom. According to one writer,
Spain formerly possessed considerable parts of three different
skeletons. The first and most complete is that which is preserved in
the royal cabinet at Madrid. This was sent over in 1789, by the
Marquis of Loreto, Viceroy of Buenos Ayres, with a notice stating that
it was found on the banks of the river Luxan. In 1795 a second
specimen arrived from Lima, and other portions, probably not very
considerable, were in the possession of Father Fernando Scio, to whom
they had been presented by a lady from Paraguay. But two German
doctors, Messrs. Pander and D'Alton, who published in 1821 a beautiful
monograph on the subject, state that they were unable in 1818 to find
any traces of either the Lima specimen or that which had belonged to
Fernando Scio.
The remains collected by Sir Woodbine Parish were discovered in the
river Salado, which runs through the flat alluvial plains (Pampas) to
the south of the city of Buenos Ayres, after a succession of three
unusually dry seasons, "which lowered the waters in an extraordinary
degree, and exposed parts of the pelvis to view as it stood upright in
the bottom of the river."[49]
[49] "Some Account of the Remains of the _Megatherium_ sent to England
from Buenos Ayres, by Woodbine Parish, Jun., Esq., F.R.S.," by Wm.
Clift, Esq., F.R.S., _Geological Transactions_, second series, vol.
iii. p. 437.
[Illustration: Plate XVII.
CAST OF A SKELETON OF MEGATHERIUM AMERICANUM.
Set up in the Natural History Museum.]
This and other parts having been carried to Buenos Ayres by the
country people, were placed at the disposal of Sir Woodbine Parish by
Don Hilario Sosa, the owner of the property on which the bones were
found. A further inquiry was instituted by Sir Woodbine; and on his
application, the governor granted assistance, the result of which was
the discovery of the remains of two other skeletons on his
Excellency's properties, at no great distance from the place where the
first had been found. It was in the year 1832 that Sir Woodbine Parish
sent his valuable collection of bones from Buenos Ayres, and presented
them to the Royal College of Surgeons. These specimens formed the
subject of Mr. Clift's memoir above quoted. But even then the
materials were not complete for a thorough knowledge of the bony
framework of the Megatherium, and it was not till 1845, when more
remains (discovered near Luxan, 1837) reached this country, that
Professor Owen was able to clear up one or two doubtful details. These
were purchased by the trustees of the British Museum, and casts of the
bones were taken. Among the various writings by learned men on the
subject, Professor Owen's masterly description stands pre-eminent;
indeed, he was the only one to solve the riddle, to thoroughly explain
the structure of this giant sloth, and to show how its food was
obtained.[50] Neither Cuvier, nor the German doctors, nor Mr. Clift had
succeeded in so doing.
[50] His views are expounded in his _Memoir on the Megatherium, or
Giant Ground Sloth of America_, 1861, which is beautifully
illustrated. The Royal Society gave £100 (part of a Government grant
of £1000) to enable Professor Owen to carry out this important work.
In the Natural History Museum (Stand O, Gallery No. 2 on plan) is a
cast representing the animal nearly erect, and grasping a tree. This
magnificent cast (see Plate XVII.) represents an animal eighteen feet
in length, and its bones are more massive than those of the elephant.
For instance, the thigh-bone is nearly thrice the thickness of the
same bone in the largest of existing elephants, the circumference
being equal to the entire length. To a comparative anatomist several
striking indications of great strength present themselves; thus, not
only the very forms of the bones themselves mean strength, but their
surfaces, ridges, and crests are everywhere made rough for the firm
attachment of powerful muscles and tendons. In the fore part of the
body the skeleton is _comparatively_ slender, but the hind quarters
show enormous strength and weight combined. The tail, also, is very
powerful and massive. The fore limbs are long, and evidently
constructed for the exertion of great force. How this force was
applied we shall see presently. In both sets of limbs we notice
powerful claws, such as might be used for scratching up the ground
near the roots of a tree, and it was at one time thought that this was
the way in which the creature obtained its leafy food, namely, by
digging up trees by the roots and then devouring the leaves. But
Professor Owen had another explanation.
As in the living sloths and armadillos (edentata[51]), there are no
teeth in the fore part of the jaw. The molar teeth, of which there are
five on each side of the upper jaw, and four in the lower, are hollow
prismatic cylinders, straight, seven to nine inches long, and
implanted in deep sockets. There are no other teeth, but these are
composed of different substances, and so arranged that, as the tooth
wears, the surface always presents a pair of transverse ridges, thus
producing a dental apparatus well suited for grinding up vegetable
food. In the elephants, which live on similar food, the grinding is
effected by great molar teeth, which are replaced by new ones as the
old ones are worn away. In the Megatherium, however, only _one_ set of
teeth was provided; but these, by constant upward growth, and
continual addition of new matter beneath, lasted as long as the animal
lived, and never needed to be renewed.
[51] This word, which means _toothless_, is misleading. All the
edentata, however, agree in having no front, or incisor, teeth.
On looking at the model so skilfully set up at South Kensington, and
especially at the front part of the skull, it will be seen that the
snout and lips must have been somewhat elongated, possibly into a
slight proboscis like that of the tapir. The specimens of the lower
jaw in the wall-case close by show that it was much prolonged and
grooved. This fact must be interpreted to mean that the creature
possessed a long and powerful tongue, aided by which it could, like
the giraffe, strip off the small branches of the trees which it had
broken or bent down within its reach.
A bony shield (or carapace) of a great armadillo was found with one of
the specimens described by Mr. Clift, and Buckland and others thought
it belonged to the Megatherium; but Owen afterwards showed, by most
clear and convincing reasoning from the skeleton, that the Megatherium
could not have been protected as armadillos are, by such a shield (see
p. 190).
[Illustration: Plate XVIII.
GREAT GROUND-SLOTH OF SOUTH AMERICA, MEGATHERIUM AMERICANUM.
Length 18 feet.]
And now we come to the question how it obtained its food. The idea of
digging round trees with its claws in order to uproot them, must be
partly, if not entirely, given up; for Professor Owen has proved, by a
masterly piece of reasoning, that this cumbrous creature, instead of
climbing up trees as modern sloths do, actually pulled down the tree
bodily, or broke it short off above the ground by a _tour de force_,
and, in order to do so, sat up on its huge haunches and tail as on a
tripod, while it grasped the trunk in its long powerful arms!
Marvellous as this may seem, it can be shown that every detail in its
skeleton agrees with the idea. Of course there would be limits to
possibilities in this direction, and the larger trees of the period
must have been proof against any such Samson-like attempts on the part
of the Megatherium; but when the trunk was too big, doubtless it
pulled down some of the lower branches. Plate XVIII. is a restoration,
by our artist, of the South Kensington skeleton.
Speaking of the extinct sloths of South America, Mr. Darwin thus
describes Professor Owen's remarkable discovery: "The habits of these
Megatheroid animals were a complete puzzle to naturalists until
Professor Owen solved the problem with remarkable ingenuity. Their
teeth indicate by their simple structure that these animals ... lived
on vegetable food, and probably on the leaves and small twigs of
trees; their ponderous forms and great strong curved claws seem so
little adapted for locomotion, that some eminent naturalists believed
that, like sloths, to which they are intimately related, they
subsisted by climbing, back downwards, on trees, and feeding on the
leaves. It was a bold, not to say preposterous, idea to conceive even
antediluvian trees with branches strong enough to bear animals as
large as elephants. Professor Owen, with far more probability,
believes that, instead of climbing on trees, they pulled the branches
down to them, and tore up the smaller ones by the roots, and so fed
on the leaves. The colossal breadth and weight of their hinder
quarters, which can hardly be imagined without having been seen,
become, on this view, of obvious service instead of being an
encumbrance; their apparent clumsiness disappears. With their great
tails and huge heels firmly fixed like a tripod in the ground, they
could freely exert the full force of their most powerful arms and
great claws."[52]
[52] _Journal of Researches._
To this we may add Dean Buckland's description,[53] "His entire frame
was an apparatus of colossal mechanism, adapted exactly to the work it
had to do; strong and ponderous in proportion as this work was heavy,
and calculated to be the vehicle of life and enjoyment to a gigantic
race of quadrupeds, which, though they have ceased to be counted among
the living inhabitants of our planet, have, in their fossil bones,
left behind them imperishable monuments of the consummate skill with
which they were constructed. Each limb and fragment of a limb form
coordinate parts of a well-adjusted and perfect whole."
[53] _Bridgewater Treatise._
After reading these descriptions, it is not difficult to form a mental
picture of the great beast laying siege to a tree, and to conceive the
massive frame of the Megatherium convulsed with the mighty wrestling,
every vibrating fibre reacting upon its bony attachment with the force
of a hundred giants; extraordinary must be the strength and
proportions of the tree if, when rocked to and fro, to right and left,
in such an embrace, it can long withstand the efforts of its
assailant. It yields, the roots fly up, the earth is scattered wide
upon the surrounding foliage, and the tree comes down with a
thundering crash, cracking and snapping the great boughs like glass.
Then the coveted food is within reach, and the giant reaps the reward
of his Herculean labours.
Sir Woodbine Parish thought that the Megatherium fed on the Agave, or
American aloe.
Another form of extinct sloth found in the same region is the
Mylodon. Though of smaller size, it was much bigger than any living
sloth, and attained a length of eleven feet. It has the same general
structure, but the head and jaws are somewhat different, and more like
the recent forms. A nearly perfect and original skeleton of Mylodon
gracilis has been set up beside its huge relative's cast in the same
gallery at the Natural History Museum. The crowns of its molar teeth
are flat instead of being ridged; hence its name, which signified
"mill-toothed."
Yet another was the Scelidotherium[54] with its long limbs. Darwin
obtained an almost entire skeleton of one of these. It was as large as
a polar bear. Speaking of his discovery, he says, "The beds containing
the fossil skeletons consist of stratified gravel and reddish mud; a
proof that the elevation of the land has been inconsiderable since the
great quadrupeds wandered over the surrounding plains, and the
external features of the country were then very nearly the same as
now. The number of the remains of these quadrupeds embedded in the
vast estuary deposits which form the Pampas and cover the granitic
rocks of Banda Oriental must be extraordinarily great. I believe a
straight line drawn in any direction through the country would cut
through some skeleton or bones. As far as I am aware, not one of these
animals perished, as was formerly supposed, in the marshes or muddy
river-beds of the present land, but their bones have been exposed by
the streams intersecting the subaqueous deposit in which they were
originally embedded. We may conclude that the whole area of the Pampas
is one wide sepulchre of these extinct gigantic quadrupeds."[55]
[54] Greek--_scelis_, limb; _therion_, beast.
[55] _Journal of Researches._
The genus Scelidotherium comprises a number of species and presents
characters more or less intermediate between Megatherium and some
other genera. The skull is low and elongated, and shows an approach to
that of the modern ant-eater. The feet also are different from those
of Megatherium (see Fig. 50).
[Illustration: Fig. 50.--Skeleton of _Scelidotherium_. (After
Capellini.)]
These monster sloths inhabited South America during the latest
geological period, known as the Pleistocene. During part of that time
North America, as well as Northern Europe and Asia, were invaded by a
great ice-sheet, and an arctic climate prevailed. It is therefore very
probable that while the mammoth and the mastodon were roaming over
North America, giant sloths and armadillos were monarchs of the
southern continent. What cause, or causes, led to the extermination of
the giant sloths and armadillos is still a matter of speculation. One
writer suggests an explanation that seems to deserve consideration.
The southern parts of this great continent are even now subject to
long-continued droughts, sometimes lasting for three years in
succession, and bringing great destruction to cattle. In fact, the
discoveries related above were rendered possible by several successive
dry seasons. It is argued that the upright position of most of the
skeletons found _in situ_ seems to suggest that the creatures must
have been mired in adhesive mud sufficiently firm to uphold the
ponderous bones after the flesh had decayed. A long drought would
bring the creatures from the drained and parched country to the
rivers, reduced by want of rain to slender streams running between
extensive mud-banks; and it is possible that, in their anxious efforts
to reach the water, they may have only sunk deeper and deeper in the
mud until they were engulfed. This idea is strengthened by
information supplied to Mr. Darwin when in these parts (recorded in
his _Journal_). An eye-witness told him that during the _gran seco_,
or great drought, the cattle in herds of thousands rushed into the
Parana, and, being exhausted by hunger and thirst, were unable to
crawl up the muddy banks, and so were drowned.
In the last great drought, from 1830 to 1832, it is probable
(according to calculations made) that the number of animals that died
was over one million and a half. The borders of all the lakes and
streamlets in the province were long afterwards white with their
bones.
In the year 1882 reports were published of the discovery of large
footprints--supposed to be human--in a certain sandstone near Carson,
Nevada, U.S. The locality was the yard of the State prison, and the
tracks were uncovered in quarrying stone for building purposes. Many
different kinds of tracks were found, some of which were made by an
animal allied to the elephant; some resembled those of the horse and
deer; others seem to have been made by a wolf, and yet others by large
birds. Those supposed to have been made by human giants were in six
series, each with alternate right and left tracks. The stride is from
two and a half to over three feet, and each footprint is about
eighteen inches long. Now, those who believed these tracks to be human
must have found it hard to explain how a giant with a foot some
eighteen inches long had a stride no longer than that of an ordinary
man of to-day, to say nothing of the fact that the straddle was
eighteen to nineteen inches! For these and other reasons Professor
Marsh has exploded the idea of their having been made by men, and gave
good reasons to show that they were probably made by a giant sloth,
such as the Mylodon above mentioned, the remains of which have been
discovered in the same strata. They agree in size, in stride, and in
width between the right and left impressions, very closely with the
tracks that a Mylodon would have made, and it seems that those of the
fore feet were afterwards impressed by the hind feet, so that each
track contains two impressions.
The reader who has some knowledge of natural history will not need to
be told that the sloths of the present day, inhabiting the same region
as their gigantic ancestors, are of small size, and live among the
branches of the trees, together with the spider monkeys, howlers, and
other apes. An interesting question to the evolutionist is--How did
the change take place from the old huge and heavy types to the smaller
and agile types of the present day? Can it be possible that the more
difficult and tedious task of pulling down branches and even stems of
trees, in order to devour the leaves, was abandoned for the simpler
method of climbing up and feeding among the branches? It certainly
looks as if a change of this kind had been instituted at some distant
period in the past--distant, that is, to _us_, but not very remote
geologically. The present method seems so much simpler that we need
not be surprised at its adoption, for Nature is ever ready to
encourage and assist those among the children of Life which can hit
upon and adopt new and improved methods, either in obtaining food or
repelling enemies, or other duties imposed upon them. Now, suppose
that, in accordance with the well-known fact that variations in the
offspring of animals are constantly cropping up, some considerably
smaller variety of Megatherium, or Mylodon, or other now extinct type,
appeared on the scene, and, by virtue of its comparative agility,
could climb a tree and feed among the branches instead of pulling them
down: then, as Darwin has so well explained, Nature would seize upon
this accidental variation, and give it an advantage over its more
awkward relations. Its offspring, too, would inherit the same
characteristics, they would adopt the same habits, and, in time, as
"natural selection" further increased these characters, by weeding out
those that were unfit while fostering all those that were neither
large nor clumsy in climbing trees, a new race of sloths would arise.
This new race, it can well be imagined, would in time outstrip the old
race in numbers, for successful races multiply while unsuccessful
ones diminish. Victory is not always to the great and the strong, for
cunning and quickness are often of more service than mere brute
strength; and perhaps the sloths, as we now see them in the Brazilian
forests, have hit upon "a new and original plan" by means of which the
old colossal forms described above have been driven out of the field,
and so exterminated by a process of competition. Such an explanation
would be in thorough harmony with modern teaching, and, as the other
suggestion about long-continued droughts, given on p. 184, may not
appear satisfactory to some of our readers, we offer this theory for
what it may be worth.
A few words about these modern sloths may not be out of place; for we
shall better understand how they have succeeded in the struggle for
existence when we know something of their manner of life; and in some
ways they still resemble their great ancestors.
There are few animals which exhibit in a greater degree what appears
to the careless observer to be _deformity_ than the sloth, and none
that have, on this account, been more maligned by naturalists. Buffon,
and many of the older zoologists, were eloquent upon the supposed
defects of the unfortunate sloth. These writers gravely asserted that
when the sloth ascends a tree, for the purpose of feeding upon its
leaves, it is so lazy that it will not quit its station until every
trace of verdure is devoured. Some of them even went so far as to
assert that when the sloth was compelled, after thus stripping a tree,
to look out for a fresh supply of food, it would not take the trouble
to descend the tree, but just allowed itself to drop from a branch to
the ground. Even Cuvier, who ought to have known better, echoes this
tale, and insinuates that Nature, becoming weary of perfection,
"wished to amuse herself by producing something imperfect and
grotesque," when the sloths were formed; and he proceeds, with great
gravity, to show the "inconvenience of organisation," which, in his
opinion, rendered the sloths unfit for the enjoyment of life.
It is quite true that, on the ground, these animals are about the most
awkward creatures that can well be imagined. Their fore legs are much
longer than their hind ones; all their toes are terminated by very
long curved claws, and the general structure of the animal is such as
to prevent them from walking in the manner of an ordinary quadruped,
for they are compelled to rest on the sides of their hands and feet.
Thus they appear the most helpless of animals, and their only means of
progression consists in hooking their claws to some inequality in the
ground, and thus dragging their bodies painfully along. But in their
natural home, amongst the branches of trees, all these seeming
disadvantages vanish--nay, the very peculiarities of structure which
render the sloths objects of pity on the ground, are found to render
them admirably adapted to their peculiar mode of life. The sloth is a
small animal, rarely more than two feet in length, and covered with
woolly hair--probably a protection against snakes, its only enemies.
It spends nearly the whole of its life in the trees. There, safe from
the prowling animals on the ground below, it hangs like a hammock from
the bough, and even travels along the branches with its body
downwards, using its long claws like grappling-irons.
It looks slothful enough when asleep, for then it resembles a bunch of
rough hair, and a jumble of limbs close together, hanging to a branch;
but when awake it is industrious in its search for nice twigs and
leaves, and moves along with considerable activity. When the
atmosphere is still, the sloth keeps to its tree, feeding on the
leaves and twigs, but when there is wind, and the branches of
neighbouring trees come in contact, the opportunity is seized, and the
animal moves along the forest under the shady cover of the boughs. The
Indians have a saying that "when the wind blows the sloth begins to
crawl;" and the reason is quite evident, for they cannot jump, but can
hang, swing, and crawl suspended.
[Illustration: Plate XIX.
A GIGANTIC ARMADILLO, GLYPTODON ASPER.
From Buenos Ayres. Length 8 feet 7 inches.]
We now pass on to the old gigantic representative of the armadillo,
the Glyptodon.[56] To the eye it resembles more or less an armadillo,
and has a huge cuirass, or large plate of armour, covering the whole
of the body, but allowing the head to show in front, while the legs
come out beneath. Both head and tail were also protected with armour.
The great shield, or carapace, in most of the extinct armadillos, is
composed of long plates of regular shape, closely united at their
edges (sutures) so as to form a solid piece. It is evident, therefore,
that this creature, having no movable bands, as living armadillos
have, could not roll itself up into a ball. The fore feet have thick,
short toes, instead of long ones, such as their modern representatives
have; and from this we may infer that they were not in the habit of
burrowing or of seeking their food underground. The family of
Glyptodonts seem to have been chiefly confined to the continent of
South America, but some species are known to have extended their range
as far as Mexico, and Texas into North America. A good deal of
confusion has arisen with regard to the classification of these
old-fashioned armadillos, on account of the fact that isolated
specimens of their tails have often been found, and these cannot
always be referred to the right carapaces. For example, it should be
pointed out here that the tail represented in Fig. 51 really belongs
to another genus, known as Hoplophorus.[57]
[56] So named by Sir R. Owen, in reference to the sculptured aspect of
the grinding surface of the teeth. Greek--_glupho_, I carve; _odous,
odontos_, tooth.
[57] Greek--_Hoplon_, armour; _phero_, I bear.
In Glyptodon asper (Plate XIX.), the scutes of the carapace had a
beautiful rosette-like sculpture, while the sheath of the tail was
entirely composed of a series of movable rings, ornamented with large
projecting tubercles. The vertebræ of the backbone are almost entirely
fused together into a long tube, and also are joined to the under
surface of the great shield, to which the ribs are united. The
cheek-teeth are sixteen in number, four above and four below on each
side. These are channelled with two broad and deep grooves, which
divide the surface into three distinct lobes. Hence the name of the
animal.
The tessellated carapace of the Glyptodon was at first thought to
belong to the Megatherium, with which the remains were associated, but
Professor Owen clearly demonstrated the impossibility of this idea.
Fig. 51 represents Glyptodon clavipes (Owen) from the Pleistocene
deposits of Buenos Ayres; but the reader will gain a much better idea
of the animal by inspecting the splendid specimen of Glyptodon asper
in the Natural History Museum, near the centre window at the east end
of the Pavilion (Glass-case Q on plan).
Plate XIX. is a restoration of another species by our artist.[58]
[58] This plate is based on a beautiful drawing in a Spanish work,
_Anales del Museo publico Buenos Aires_. G. Burmeister, M.D., Phil. D.
Tomo Segundo.
In the Museum of the Royal College of Surgeons (which the reader is
recommended to visit) there are several most valuable specimens of
these extinct armadillos from South America.
[Illustration: Fig. 51.--Extinct Gigantic Armadillo, _Glyptodon
clavipes_, from Pleistocene deposits, Buenos Ayres. (The tail sheath
here represented probably belongs to another genus, Hoplophorus.)]
Armadillos belong, with sloths and ant-eaters, to the same family of
so-called toothless animals (edentata) with no front teeth, though one
or two forms really are toothless. Those of the present day have their
bony armour divided up into a series of bands, so that they can roll
themselves up, more or less, into balls. They burrow under the ground,
where they get their food to a certain extent, and live a safe life,
protected by their casque of mail. Their only enemies seem to be the
monkeys, and one of the tricks of the young monkeys in the American
forests is, when they find an armadillo away from home, to pull its
tail unmercifully, and try to drag it about. Snakes cannot hurt them.
Mr. Hudson, in his most interesting book, _A Naturalist in La Plata_,
narrates how he watched an armadillo kill a snake and then devour it.
If we examine the anatomy of the armadillo, we shall find that its
bones greatly resemble those of the sloth, but still there are a few
differences. It is a burrowing animal, and therefore requires great
power of scratching and tearing the ground. Why the colossal forms of
armadillo should have become extinct and only small ones survived to
the present time, is one of the many and perplexing problems presented
by the study of extinct animals. One would have thought from its size
and strength that the Glyptodon had been built, like Rome, for
eternity.