MASTODONS AND MAMMOTHS
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.
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.
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.
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.
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.