Part 11

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.

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.

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.

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.

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.

THE RANCHO LA BREA FOSSIL PITS

The La Brea tar pits, as they are often called, provide a remarkable record of Pleistocene life in southwestern North America. Scattered over an area of about thirty acres just off Wilshire Boulevard in Los Angeles, these bone deposits were known, as far back as 1875, to contain the remains of prehistoric animals. It was not until 1905, however, that their value was recognized by paleontologists. In that year the University of California began an investigation, and excavations were carried on at intervals by various institutions during the next ten years. A great deal of material was acquired by the Los Angeles Museum of History, Science, and Art, where many skeletons, skulls, and other interesting specimens have been placed on exhibition.

The pits have the form of small craters formed by the seeping of oil from the underlying rocks. The seeps appear to have been active during part of the Pleistocene period but apparently not at the beginning. The oil is rich in asphalt which has served as a preservative for the bones, and owing to its sticky properties has been an effective animal trap for thousands of years.

The fossil beds at present are of oil-soaked earth and sand. In past times there must have been a greater percentage of oil, often concealed by a layer of dust or pools of water. The large number of carnivorous animals found in the deposits suggests that they were attracted by the cries and struggles of creatures wandering carelessly into the asphalt and serving as live bait to keep the traps in continuous operation.

Animals found there include many species still living in the locality, some that have migrated to other territory, and a large number that have become extinct. Among the latter may be mentioned species that differ but slightly from living relatives, others that have left no descendants. Horses, bison, and wolves, though extinct species, were of relatively modern types. On the other hand the large sloths and saber-tooth cats seem rather out of place. True cats are represented by the mountain-lion, bob-cat, and a species of lion which is nearly one-fourth larger than any of the great cats of the Old World. A long-legged camel, with a height of approximately eight feet to the top of the head, was among the native animals of the district. Skunks, weasels, badgers, squirrels, rabbits, bear, deer, and antelope were more or less abundant.

The La Brea group exhibited by the Denver Museum of Natural History includes the following species: horse (Equus occidentalis), bison (Bison antiquus), wolf (Aenocyon dirus), saber tooth (Smilodon californicus), sloth (Mylodon harlani). Horses had entirely disappeared from the North American continent by the time the first white man arrived. Equus occidentalis was one of the several species living during the Pleistocene period, this one apparently being restricted to California and perhaps adjacent states. Bison antiquus was slightly larger than the plains bison of recent times and had it horns set at a characteristic different angle. The species was first described from Kentucky and appears to have had a wide distribution.

The wolves in this group are about the size of timber wolves, but have heavier skulls with less brain capacity, massive teeth especially adapted to biting and crushing large bones, and limbs of rather light construction. They probably assembled in packs where meat was abundant and, hunting in this fashion, were able to attack and overcome the larger ungulates and edentates. To most visitors the large ground sloth is the most interesting animal of the group. This edentate animal is shown at the edge of the pool with one foot stuck in the “tar.”

The edentates are a group of primitive animals with very simple teeth, if any. Teeth are usually lacking in the front part of the mouth, sometimes entirely absent, as among anteaters. Better known living representatives of the group are the tree sloths, armadillos, and anteaters of South America. Ground-sloths were prominent among South American mammals during much of Cenozoic time. During Pliocene and Miocene time there was a marked tendency to large size, and it was principally during these two periods that they appeared in the United States area.

Mylodon was one of the larger North American ground-sloths. Its teeth, without the protective enamel which is present among higher mammals, are restricted to the cheek region, and have the form of simple pegs; instead of being specialized they stand close to the extreme of generalization. The construction of the entire skeleton is massive, suggesting great strength with slow movements. The hands are well developed, provided with stout claws, and must have served the creature well as protection against attacks by predatory neighbors. We have some idea as to what caused the extermination of the ground-sloths in this particular region, but the complete disappearance of such a large and widely distributed group at the close of the Pleistocene period is a mystery that may never be explained.

The saber-tooth cat, sometimes referred to as a tiger, was specialized as a meat eater though hardly as a hunting animal. In the La Brea region its principal food was probably the flesh of the sluggish ground-sloths. The size was equal to that of the African lion, with hind limbs slightly longer and the front legs more powerfully developed. The most remarkable characteristic is to be found in the development of the upper canine teeth and modifications of the skull which were necessary to enable the animal to use these teeth as weapons.

In order to make the “sabers” effective it was necessary to get the lower jaws out of the way, and this was provided for in an unusual type of hinge which enabled the mouth to open wider than is possible in the case of the less specialized carnivores. Judging by all the structural features of the skeleton, Smilodon could not have lived well on small animals, for it was not equipped to capture that kind of prey. It is evident that large mammals were preferred, and that the method of attack was to spring upon the victim and cling there with the powerfully developed fore limbs until the kill was completed by stabbing into a vulnerable spot. That the position of the large sabers near the front of the mouth interfered with normal feeding, is a reasonable conclusion. There are also anatomical features which lead to the belief that this carnivore was a blood sucker, perhaps more than it was meat-eater.

If most of these conclusions are correct we have here another case of over-specialization and a possible explanation of the extinction of two species. Such evidence as we have is far from conclusive, for there is no proof that Rancho La Brea was the last stand of either the saber-tooth or the ground-sloth. Both races were widely distributed and their living conditions could not have been exactly duplicated in other localities. It has been suggested, however, that Smilodon ate the last of Mylodon, and starved soon afterward because it had become unable to partake of other foods. The conjecture is offered for what it is worth, together with the facts on which the story has been based.