Elephant-like mammals both living and extinct are classed together in a
single order bearing the name Proboscidea. Living members of the group
are the elephants, of which the large Indian and African species are
best known. Among prehistoric representatives the most frequently
mentioned in the popular literature of North American animals are the
following:
The American Mastodon, an immigrant from Siberia which ranged over
nearly all of the United States and Canada. It was principally a forest
dweller, rarely found in plains regions, was abundant during the
Pleistocene period and may have been known to the early American
Indians;
The Woolly Mammoth, which was about nine feet tall. It ranged over
British Columbia into the United States and across to the Atlantic,
disappearing in late Pleistocene time;
The Columbian Mammoth, about eleven feet tall, lived in the early half
of the Pleistocene period, ranging over the warmer portions of North
America, including practically all of the United States and much of
Mexico;
The Imperial Mammoth, reaching a height of more than thirteen feet, and
becoming extinct in the Middle Pleistocene. It was a western form,
remains being found from Nebraska to Mexico City.
Originally placed in the genus _Elephas_, the mammoths are referred to
commonly as elephants, though technically they should not be regarded as
such. Recent explorations and researches have added greatly to our
knowledge of these animals but have also caused much confusion with
regard to scientific names, for many new subdivisions of the larger
group are now recognized, and it has become necessary to change some of
the older nomenclature.
[Illustration: A Long-Jawed Mastodont (_Trilophodon phippsi_).
One of the Early American Proboscideans]
The large mammoth exhibited by the Museum bears the impressive name of
_Archidiskodon meridionalis nebrascensis_. Fifty years ago it might have
been identified simply as a specimen of the imperial elephant and in
such case would have received the old name of that species, which was
_Elephas imperator_. But late in the last century it was proposed that
the mammoths be recognized by some other name to distinguish them more
sharply from living elephants. The name suggested for the new genus thus
established was _Archidiskodon_, in recognition of the more archaic or
primitive construction of the enamel plates in the mammoths molar teeth.
The specific name, _meridionalis_, had been given to a kind of mammoth
which is well known from the southern part of Europe, and the Latin
name, signifying “southern,” had been applied to differentiate this
species from the northern or woolly mammoth.
This mammoth, however, had disappeared from southern Europe and for many
years its subsequent history remained a mystery. The late Dr. Henry
Fairfield Osborn had been engaged in an extensive study of the subject,
and when the nearly perfect skeleton from Angus, Nebraska, was brought
to his attention he recognized it as being closely related to
_meridionalis_, and considered it to be a record of the migration of
that species into North America. Because of minor variations from the
typical mammoth of southern Europe he regarded it as a variety or
subspecies which had descended from the latter, and the subspecific
name, _nebrascensis_, was added to take care of this situation, using a
Latinized form of the name of the State in which the skeleton was found.
With the knowledge we now have of these mammoths it becomes apparent
that _Archidiskodon meridionalis nebrascensis_ is an ancestor of the
imperial mammoth, currently known as _Archidiskodon imperator_, and not
identical with it.
This instance is typical of the manner in which prehistoric animals
obtain their names. Although given a Latin form, these technical names
are derived from many languages, and the root words are applied with
reference to anything that happens to appeal to the author as
significant. Consequently there is seldom a name of this kind which may
be translated directly into natural history or science. It is a mistake
to believe that these strange phrases conceal important technical
information which is available only to those who are familiar with dead
and foreign languages. Actually they contain nothing of the sort, and
the most enlightened of the Greeks and Romans could not find it there.
When a name is needed there is none better than the one provided by the
specialist who is skilled in the business of naming things. Some
technical ability is required, to apply the name where it properly
belongs, but technical knowledge is not obtained from such sources.
Names, in any form, have another purpose to serve. There is no magic in
them and there need be no mystery about them.
[Illustration: Molar Tooth of Mammoth
This type of tooth is constructed for long continued use and will
withstand the wear of more abrasive foods. The position of the white
enamel plates is seen in this view of the grinding surface. These
plates extend all the way to the base of the tooth, which is of the
long-crowned variety and not to be destroyed by the wearing away of
a single outside layer of enamel.]
Other specimens in the Museum collection are the long-jawed mastodonts,
so named because of the elongated jaws and protruding chin which is
often mistaken for a tusk. Early members of this group had more cheek
teeth than later types of mastodons, and longer jaws were required for
their accommodation. Some of them had flattened lower tusks which
evidently were used for digging purposes. These are popularly known as
“shovel tuskers.” The more modern American mastodon had shorter jaws
and, like the mammoths and elephants, only one pair of tusks. Both the
long-jawed and short-jawed types are represented by complete skeletons,
and also by tusks, jaws, and teeth of many individuals. The American
mastodons and mastodonts were of about the same size as the smaller
mammoths.
The difference between mastodons and mammoths is most readily recognized
in the structure of the grinding teeth, the molars and pre-molars. In
the mastodon these teeth are of the short-crowned type, while in the
mammoths, as in the modern elephants, they are long-crowned. The
difference between these two types of molars has been described with
reference to horses, and the change from the older to the modern form
may be regarded as coming about in the same general way, through a
series of gradual modifications. In both horse and mammoth the final
development shows internal enamel extending from the grinding surface
nearly to the roots. Otherwise, however, there is almost no resemblance,
for the mammoth tooth is made up of flattened enamel plates, the number
of which is variable for different species. In the jaws of a very young
individual these plates may be seen as separate parts. As the tooth
continues to grow, the plates become cemented together, and when the
ends of the plate are worn down it may be observed that each consists of
a layer of enamel surrounding a flat central core of dentine. The type
of construction is rather more obvious in the mammoth tooth than in that
of a horse, partly because of the larger size, and partly because of the
relative simplicity of construction.
The earlier history of the Proboscidea is not recorded in the rocks of
North America, for the group was of African origin and its migrations
did not extend as far as the New World until middle Cenozoic times. The
mastodons and mammoths were the largest of land animals since the Age of
Reptiles, but their Old World ancestors were not conspicuous because of
their bulk. Many of these ancient forms, even in the earliest stages,
reveal some of the prominent characters that dominate the entire group.
None of them, however, should be regarded as a miniature mammoth or
mastodon, for these highly specialized types were perfected only at a
comparatively recent date, and by a process that works very slowly.
Among the earlier forms there were also some oddities which failed to
survive or to produce a successful branch of the stock such as the
elephants.
[Illustration: Nebraska Mammoth
(_Archidiskodon meridionalis nebrascensis_)]
The earliest known member of the order was _Moeritherium_, an animal of
the size of a tapir, living in Egypt during the late Eocene and early
Oligocene time. At this stage the characteristic specializations leading
to the mastodons and mammoths were apparent but not far advanced. The
proboscis was probably much like the flexible snout of modern tapirs,
for the need of a long trunk had not yet arrived. In upper and lower
jaws the second pair of incisor teeth were becoming large and prominent.
The enormous tusks of the mammoths later developed from the enlargement
of the same pair of upper incisors, and in some of the long-jawed
mastodonts the lower pair also produced large tusks, though frequently
the lower tusks were not prominent.
_Dinotherium_ had downward-growing tusks in the lower jaws, none in the
upper. This genus was fairly common in the Miocene of Europe, Asia, and
Africa. In the tropics it survived throughout the Pliocene and possibly
into the Pleistocene. Some of the species acquired the size of
elephants, but it is apparent that they were not ancestral to any of the
more progressive types. They are to be regarded rather as an offshoot
from the main line of descent.
In 1859 only ten species of the elephant-like mammals were known, and
all were referred to a single genus. At the present time eleven genera
appear to be well founded, and the number of recognized species has
reached a hundred, if it has not already passed that figure. New
discoveries are expected to add to the existing total. With this mass of
material before us we note certain definite trends among the more
progressive types. The increasing weight was accompanied by the
development of strong, upright limbs in which the bones have a columnar
position instead of the angular assembly which prevails among most of
the mammals. As the tusks increased in size there was a shortening of
both skull and neck to bring the weight closer to the point of support.
The front teeth disappeared except the second pair of upper incisors
which remain as tusks in the modern elephant. The cheek teeth present in
the shortened jaws of the mammoth were reduced to one pair at a time in
the upper set and another pair below. From a simple, low-crowned origin
these grinding teeth developed into the more successful high-crowned
pattern with numerous plates of enamel inside. A prehensile upper lip
acquired the length and usefulness of the elephants trunk.
[Illustration: Rancho la Brea Fossils
One of the most unusual of the many animals that have been taken
from the tar pits is the large ground sloth, seen at the left in
this group. Such sloths were very abundant during Pleistocene time,
and some may have lived up to a few thousand years ago.
Archaeologists have found indications that these creatures may have
been hunted by cave-dwelling peoples of the American Southwest.
Other skeletons include the saber-tooth tiger, characterized by the
long curved upper canine teeth which undoubtedly were used for
stabbing and slashing, and the dire wolf, the smaller of the two
which are facing the sloth. The artist’s reconstruction of this
scene also shows the great vulture, Teratornis, which is the largest
known bird of flight.]
Over-specialization in the production of tusks appears to have been the
principal factor in the downfall of the mammoths. The large size of the
animals and the difficulties of finding sufficient food to sustain life
must have been a serious handicap at times, but their ability and
inclination to travel over long distances enabled some of them to find
tolerable living conditions until the end of the Glacial Period. They
are now extinct and the nearest living relatives are the elephants,
somewhat reduced in size of tusks and body but otherwise very similar.
There are many other tribes of mammals whose ancient history is
partially known though broken by periods of time for which there is no
fossil evidence. All have undergone changes in which various forms and
degrees of specialization are featured; this general process is best
revealed by the horses and elephant-like animals which have left a
clearer record. For other groups the story would differ but little
except as to names and specific details.