# The Geographical Distribution of Animals/Chapter 7

CHAPTER VII.
EXTINCT MAMMALIA OF THE NEW WORLD.
The discoveries of very rich deposits of mammalian remains in various parts of the United States have thrown great light on the relations of the faunas of very distant regions. North America now makes a near approach to Europe in the number and variety of its extinct mammalia, and in no part of the world have such perfect specimens been discovered. In what are called the "Mauvaises terres" of Nebraska (the dried-up mud of an ancient lake), thousands of entire crania and some almost entire skeletons of ancient animals have been found, their teeth absolutely perfect, and altogether more resembling the preparations of the anatomist, than time-worn fossils such as we are accustomed to see in the museums of Europe. Other deposits have been discovered in Oregon, California, Virginia, South Carolina, Texas, and Utah, ranging over all the Tertiary epochs, from Post-Pliocene to Eocene, and furnishing a remarkable picture of the numerous strange mammalia which inhabited the ancient North American continent.
North America—Post-Pliocene Period.
Insectivora.—The only indications of this order yet discovered, consists of a single tooth of some insectivorous animal found in Illinois, but which cannot be referred to any known group.
Carnivora.—These are fairly represented. Two species of Felis as large as a lion; the equally large extinct Trucifelis, found only in Texas; four species of Canis, some of them larger ​than wolves; two species of Galera, a genus now confined to the Neotropical region; two bears, and an extinct genus, Arctodus; an extinct species of racoon (Procyon), and an allied extinct genus, Myxophagus—show, that at a very recent period North America was better supplied with Carnivora than it is now. Remains of the walrus (Trichechus) have also been found as far south as Virginia.
Cetacea.—Three species of dolphins belonging to existing genera, have been found in the Eastern States; and two species of Manatus, or sea-cow, in Florida and South Carolina.
Ungulata.—Six extinct horses (Equus), and one Hipparion; the living South American tapir, and a larger extinct species; a Dicotyles, or peccary, and an allied genus, Platygonus; a species of the South American llamas (Auchenia), and one of a kind of camel, Procamelus; two extinct bisons; a sheep, and two musk-sheep (Ovibos); with three living and one extinct deer (Cervus), show an important increase in its Herbivora.
Proboscidea.—Two elephants and two mastodons, added to this remarkable assemblage of large vegetable-feeding quadrupeds.
Rodentia.—These consist mainly of genera and species still living in North America; the only important exceptions being a species of the South American capybara (Hydrochœrus) in South Carolina; and Praotherium, an extinct form of hare, found in a bone cave in Pennsylvania.
Edentata.—Here we meet with a wonderful assemblage, of six species belonging to four extinct genera, mostly of gigantic size. A species of Megatherium, three of Megalonyx, and one of Mylodon—huge terrestrial sloths as large as the rhinoceros or even as the largest elephants—ranged over the Southern States to Pennsylvania, the latter (Mylodon) going as far as the great lakes and Oregon. Another form, Ereptodon, has been found in the Mississippi Valley.
Marsupialia.—The living American genus of opossums, Didelphys, has been found in deposits of this age in South Carolina.
Remarks on the Post-Pliocene fauna of North America.—The assemblage of animals proved, by these remains, to have ​inhabited North America at a comparatively recent epoch, is most remarkable. In Europe, we found a striking change in the fauna at the same period; but that consisted almost wholly in the presence of animals now inhabiting countries immediately to the north or south. Here we have the appearance of two new assemblages of animals, the one now confined to the Old World—horses, camels, and elephants; the other exclusively of South American type—llamas, tapirs, capybaras, Galera, and gigantic Edentata. The age of the various deposits in which these remains are found is somewhat uncertain, and probably extends over a considerable period of time, inclusive of the Glacial epoch, and perhaps both anterior and subsequent to it. We have here, as in Europe, the presence and apparent co-existence in the same area, of Arctic and Southern forms—the walrus and the manatee—the musk-sheep and the gigantic sloths. Unfortunately, as we shall see, the immediately preceding Pliocene deposits of North America are rather poor in organic remains; yet it can hardly be owing to the imperfection of the record of this period, that not one of the South American types above numerated occurs there, while a considerable number of Old World forms are represented. Neither in the preceding wonderfully rich Miocene or Eocene periods, does any one of these forms occur; or, with the exception of Morotherium, from Pliocene deposits west of the Rocky Mountains, any apparent ancestor of them! We have here unmistakable evidence of an extensive immigration from South into North America, not very long before the beginning of the Glacial epoch. It was an immigration of types altogether new to the country, which spread over all the southern and central portions of it, and established themselves sufficiently to leave abundance of remains in the few detached localities where they have been discovered. How such large yet defenceless animals as tapirs and great terrestrial sloths, could have made their way into a country abounding in large felines equal in size and destructiveness to the lion and the tiger, with numerous wolves and bears of the largest size, is a great mystery. But it is nevertheless certain that they did so; and the fact that no such ​migration had occurred for countless preceding ages, proves that some great barrier to the entrance of terrestrial mammalia which had previously existed, must for a time have been removed. We must defer further discussion of this subject till we have examined the relations of the existing faunas of North and South America.
Tertiary Period.
When we get to remains of the Tertiary age, especially those of the Miocene and Eocene epochs, we meet with so many interesting and connected types, and such curious relations with living forms in Europe, that it will be clearer to trace the history of each order and family throughout the Tertiary period, instead of considering each of the subdivisions of that period separately.
It will be well however first to note the few American Post-Pliocene or living genera that are found in the Pliocene beds. These consist of several species of Canis, from the size of a fox to that of a large wolf; a Felis as large as a tiger; an Otter (Lutra); several species of Hipparion; a peccary (Dicotyles); a deer (Cervus); several species of Procamelus; a mastodon; an elephant; and a beaver (Castor). It thus appears that out of nearly forty genera found in the Post-Pliocene deposits, only ten are found in the preceding Pliocene period. About twelve additional genera, however, appear there, as we shall see in going over the various orders.
Primates.—Among the vast number of extinct mammalia discovered in the Tertiary deposits of North America, no example of this order had been recognized up to 1872, when the discovery of more perfect remains showed, that a number of small animals of obscure affinities from the Lower Eocene of Wyoming, were really allied to the lemurs and perhaps also to the marmosets, the lowest form of American monkeys, but having a larger number of teeth than either. A number of other remains of small animals from the same formation, previously supposed to be allied to the Ungulata, are now shown to ​belong to the Primates; so that no less than twelve genera of these animals are recognized by Mr. Marsh, who classes them in two families—Limnotheridæ, comprising the genera Limnotherium, (which had larger canine teeth), Thinolestes, Telmatolestes, Mesacodon, Bathrodon, and Antiacodon of Marsh, with Notharctos, Hipposyus, Microsyops, and Palæacodon previously described by Leidy;—and Lemuravidæ, consisting of the genera Lemuravus (Marsh) and Hyopsodus (Leidy). The animals of the latter family were most allied to existing lemurs, but were a more generalized form, Lemuravus having forty-four teeth, the greatest number known in the order. These numerous forms ranged from the size of a small squirrel to that of a racoon. It is especially interesting to find these peculiar lemuroid forms in America, just when a lemur has been discovered of about the same age in Europe; and as the American forms are said to show an affinity with the South American marmosets, while the European animal is most allied to a West African group, we have evidently not yet got back far enough to find the primeval or ancestral type from which all the Primates sprang.
About the same time, in the succeeding Miocene formation, true monkeys were discovered. Mr. Marsh describes Laopithecus as an animal nearly the size of the largest South American monkeys, and allied both to the Cebidæ and the Eocene Limnotheridæ. Mr. Cope has described Menotherium from the Miocene of Colorado, as a lemuroid animal, the size of a cat, and perhaps allied to Limnotherium. More Miocene remains will, no doubt, be discovered, by which we shall be enabled to trace the origin of some of the existing forms of South American monkeys; and perhaps help to decide the question (now in dispute among anatomists) whether the lemurs are really Primates, or form an altogether distinct and isolated order of mammalia.
Insectivora.—This order is represented by comparatively few forms in the tertiary beds, and these are all very different from existing types. In the Upper Miocene of Dakota are found remains indicating two extinct genera, Lepictis and Ictops. In the Miocene of Colorado, Professor Cope has recently discovered four new genera, Isacis; allied to the preceding, but as large as a ​Mephitis or skunk; Herpetotherium, near the moles; Embasis, more allied to the shrews; and Dommina, of uncertain affinities. Two others have been found in the Eocene of Wyoming; Amomys, having some resemblance to hedgehogs and to the Eastern Tupaia; and Washakius, of doubtful affinities.
Far back in the Triassic coal of North Carolina has been found the jaw of a small mammal (Dromotherium), the teeth of which somewhat resemble those of the Australian Myrmecobius, and may belong either to the Insectivora or Marsupials; if indeed, at that early period these orders were differentiated.
Carnivora.—The most ancient forms of this order are some remains found in the Middle Eocene of Wyoming, and others recently described by Professor Cope (1875) from the Eocene of New Mexico, of perhaps earlier date. The former consist of three genera, Patriofelis, Uintacyon, and Sinopa,—animals of large size but which cannot be classed in any existing family; and two others, Mesonyx and Synoplotherium, believed by Mr. Cope to be allied to Hyænodon. The latter consist of four genera,— Oxyæna, consisting of several species, some as large as a jaguar, was allied to Hyænodon and Pterodon; Pachyæna, allied to the last; Prototomus, allied to Amphicyon and the Viverridæ; and Limnocyon, a civet-like carnivore with resemblances to the Canidæ.
In the Miocene formations we find the Feline type well developed. The wonderful Machairodus, which in Europe lived down to Post-Pliocene times, is found in the Upper Miocene of Dakota; and perfect crania have been discovered, showing that the chin was lengthened downwards to receive and protect the enormous canines. Dinyctis was allied both to Machairodus and to the weasels. Three new genera have been lately described by Professor Cope from the Miocene of Colorado,—Bunælurus, with characters of both cats and weasels; Daptophilus, allied to Dinyctis; and Hoplophoneus, more allied to Machairodus. The Canidæ are represented by Amphicyon, which occurs in deposits of the same age in Europe; and by Canis, four species of which genus are recorded by Professor Cope from the Miocene of Colorado, and it also occurs in the Pliocene. The Hyænodon is represented by three species in the Miocene of Dakota and Colorado. It occurs ​also in the European Miocene and Upper Eocene formations, and constitutes a distinct family Hyænodontidæ, allied, according to Dr. Leidy, to wolves, cats, hyænas and weasels. The Ursidæ are represented by only one species of an extinct genus, Leptarchus, from the Pliocene of Nebraska. From the Pliocene of Colorado, Prof. Cope has recently described Tomarctos, as a "short-faced type of dog;" well as species of Canis and Martes.
Ungulata.—The animals belonging to this order being usually of large size and accustomed to feed and travel in herds, are liable to wholesale destruction by floods, bogs, precipices, drought or hunger. It is for these reasons, probably, that their remains are almost always more numerous than those of other orders of mammalia. In America they are especially abundant; and the number of new and intermediate types about whose position there is much difference of opinion among Palæontologists, renders it very difficult to give a connected summary of them with any approach to systematic accuracy.
Beginning with the Perissodactyla, or odd-toed ungulates, we find the Equine animals remarkably numerous and interesting. The true horses of the genus Equus, so abundant in the Post-Pliocene formations, are represented in the Pliocene by several ancestral forms. The most nearly allied to Equus is Pliohippus, consisting of animals about the size of an ass, with the lateral toes not externally developed, but with some differences of dentition. Next come Protohippus and Hipparion, in which the lateral toes are developed but are small and functionless. Then we have the allied genera, Anchippus, Merychippus, and Hyohippus, related to the European Hippotherium, which were all still smaller animals, Protohippus being only 2½ feet high. In the older deposits we come to a series of forms, still unmistakably equine, but with three or more toes used for locomotion and with numerous differentiations in form, proportions, and dentition. These constitute the family Anchitheridæ. In the Miocene we have the genera Anchitherium (found also in the European Miocene), Miohippus and Mesohippus, all with three toes on each foot, and about the size of a sheep or large goat. In the Eocene of ​Utah and Wyoming, we get a step further back, several species having been discovered about the size of a fox with four toes in front and three behind. These form the genus Orohippus, and are the oldest ancestral horse known. Prof. Marsh points out the remarkably perfect series of forms in America, which, beginning with this minute ancient type, is gradually modified by gaining increased size, increased speed by concentration of the limb-bones, elongation of the head and neck, the canine teeth decreased in size, the molars becoming longer and being coated with cement—till we at last come to animals hardly distinguishable, specifically, from the living horse.
Allied to these, are a series of forms showing a transition to the tapirs, and to the Palæotherium of the European Eocene. In the Pliocene we have Parahippus; in the Miocene Lophiodon, found in the same formation and in the Eocene of Europe, and allied to the tapir; and in the Eocene, Palæosyops, as large as a rhinoceros, which had large canines and was allied to the tapir and Palæotherium; Limnohyus, forming the type of a family Limnohyidæ, which included the last genus and some others mentioned further on; and Hyrachyus, allied to Lophiodon, and to Hyracodon an extinct form of rhinoceros. Besides these we have Lophiotherium (also from the Eocene of Europe); Diplacodon allied to Limnohyus, but with affinities to modern Perissodactyla and nearly as large as a rhinoceros; and Colonoceras, also belonging to the Limnohyidæ, an animal which was the size of a sheep, and had divergent protuberances or horns on its nose. A remarkable genus, Bathmodon, lately described by Professor Cope, and of which five species have been found in the Eocene of New Mexico and Wyoming, is believed to form the type of a new family, having some affinity to Palæosyops and to the extinct Brontotheridæ. It had large canine tusks but no horns.
The Rhinocerotidæ are represented in America by the genus Rhinoceros in the Pliocene and Miocene, and by Aceratherium and Hyracodon in the Miocene. Both the latter were hornless, and Hyracodon was allied to the Eocene Hyrachyus, one of the Lophiodontidæ. In the Eocene and Miocene deposits of Utah, and Oregon, several remarkable extinct rhinoceroses have been ​recently discovered, forming the genus Diceratherium. These had a pair of nasal horns placed side by side on the snout, not behind each other as in existing two-horned rhinoceroses, the rest of their skeleton resembling the hornless Aceratherium. They were of rather small size.
Next to these extinct rhinoceroses come the Brontotheridæ, an extraordinary family of large mammalia, some of which exceeded in bulk the largest living rhinoceros. They had four toes to the front and three to the hind feet, with a pair of large divergent horns on the front of the head, in both sexes. Professor Marsh and Dr. Leidy have described four genera, Brontotherium, Titanotherium, Megacerops, and Anisacodon, distinguished by peculiarities of dentition. Though most nearly allied to the rhinoceroses, they show some affinity for the gigantic Dinocerata of the Eocene to be noticed further on. Professor Cope has since described another genus, Symborodon, from the Miocene of Colorado, with no less than seven species, one nearly the size of an elephant. He thinks they had a short tapir-like proboscis. The species differ greatly in the form of the cranium and development of the horn-bearing processes.
We commence the Artiodactyla, or even-toed Ungulates, with the hog tribe. These are represented by species of peccaries, (Dicotyles) from the Pliocene of Nebraska and Oregon; and by an allied form Thinohyus, very like Dicotyles, but having an additional premolar tooth and a much smaller brain-cavity. From the Miocene are three allied genera, Nanohyus, Leptochœrus, and Perchœrus. Professor Cope, however, thinks Leptochœrus may be Lemuroid, and allied to Menotherium. The Anthracotheridæ, a family which connects the Hippopotamidæ and Ruminants, and which occurs in the Miocene of Europe and India, are represented in America by the genus Hyopotamus from the Miocene of Dakota, and Elotherium from the Miocene of Oregon and the Eocene of Wyoming; the latter genus being sometimes classed with the preceding family, and lately placed by Professor Marsh, in the new order, Tillodontia. Professor Cope has since described three other genera from the Eocene of New ​Mexico: Meniscotherium, having resemblances to Palæosyops, Hyopotamus, and the Limnotheridæ; Phenacodus, the size of a hog, of doubtful position, but perhaps near Elotherium; and Achænodon, as large as a cow, but more hog-like than the preceding. Another new genus from the Miocene of Colorado—Pelonax—is said by Professor Cope to come between Elotherium and Hippopotamus.
The Camelidæ are very abundant, and form one of the most striking features of the ancient fauna of America. Procamelus, Homocamelus, and Megalomeryx, are extinct genera found in the Pliocene formation; the first very closely allied to the Old World camel, the last smaller and more sheep-like. In the Miocene two other genera occur, Pœbrotherium and Protomeryx, the former allied to both the camel and the llama.
Deer are represented by a single species of Cervus in the Pliocene, while two extinct genera, Leptomeryx and Merycodus, are found in the Miocene deposits, the latter indicating a transition between camels and deer. Two other genera, Hypisodus and Hypertragulus, of very small size, are said by Professor Cope to be allied to the Tragulidæ and to Leptomeryx.
The Bovidæ, or hollow-horned ruminants, are only represented in the Newer Pliocene by a single species of an extinct genus, Casoryx, said to be intermediate between antelopes and deer.
We now come to an exclusively American family, the Oreodontidæ, which consisted of small animals termed by Dr. Leidy, "ruminating hogs," and which had some general structural resemblances to deer and camels. They abounded in North America during the Pliocene, and especially during the Miocene epoch, no less than six genera and twenty species having been discovered. Merychus contains the Pliocene forms; while Oreodon, Eporeodon, Merychochœrus, Leptauchenia, and Agriochœrus are Miocene. The last genus extends back into the Eocene period, and shows affinity to the European Anoplotheridæ of the same epoch.
Proboscidea.—The Elephantidæ are only represented in America by one species of Mastodon and one of Elephas, in the Newer Pliocene deposits. In the Older Pliocene, Miocene, ​and Upper Eocene, no remains of this order have been found; and in 1869, Dr. Leidy remarked on the small average size of the extinct North American mammalia, which were almost all smaller than their living analogues. Since then, however, wonderful discoveries have been made in deposits of Middle Eocene age in Wyoming and Colorado, of a group of huge animals not only rivalling the elephants in size, but of so remarkable and peculiar a structure as to require the formation of a new order of mammals—Dinocerata—for their reception.
This order consists of animals with generalised Ungulate and Proboscidean affinities. The lower jaw resembles that of the hippopotamus; they had five toes on the anterior feet and four on the posterior; three pairs of horns, the first pair on the top of the head, large and perhaps palmated, the second pair above the eyes, while the third and smallest stood out sideways on the snout. They had enormous upper canines, of which the roots entered the middle horn cores, no upper incisors, and small molars. Professor Marsh believes that they had no trunk. The remains discovered indicate four genera, Dinoceras (3 sp.), Tinoceras (2 sp.), Uintatherium (1 sp.), and Eobasileus (2 sp.). Many other names have been given to fragments of these animals, and even those here given may not be all distinct.
Another new order, Tillodontia, recently established by Professor Marsh, is perhaps yet more remarkable in a zoological point of view, since it combines the characters of Carnivora, Ungulata, and Rodents. These animals have been formed into two families, Tillotheridæ and Stylinodontidæ; and three genera, Tillotherium, Anchippodus, and Stylinodontia. All are from the Eocene of Wyoming and New Jersey. Perhaps to these must be added Elotherium from the Miocene of Dakota, the other forms being all Eocene. They were mostly animals of small size, between that of the capybara and tapir. The skull resembled in form that of a bear; the molar teeth were of Ungulate type, and the incisors like those of a Rodent; but the skeleton was more that of the Ursidæ, the feet being plantigrade. Professor Cope has since described three new genera from the Eocene of New Mexico, Ectoganus, Calamodon, and Esthonyx, comprising ​seven species allied to Tillotherium and Anchippodus, and having also relations, as Professor Cope believes, with the South American Toxodontidæ.
Rodentia.—This order is represented in the Pliocene by a beaver, a porcupine, and an American mouse (Hesperomys), all extinct species of living genera, the Hystrix being an Old World type; and Professor Cope has recently described Panolax, a new genus of hares from the Pliocene of New Mexico. The Miocene deposits have furnished an extinct genus allied to the hares—Palæolagus; one of the squirrel family—Ischyromys; a small extinct form of beaver—Palæocastor; and an extinct mouse—Eumys. The Eocene strata of Wyoming have lately furnished two extinct forms of squirrel, Paramys and Sciuravus; and another of the Muridæ (or mouse family), Mysops.
Cetacea.—Numerous remains of dolphins and whales, belonging to no less than twelve genera, mostly extinct, have been found in the Miocene deposits of the Atlantic and Gulf States, from New Jersey to South Carolina and Louisiana; while seven genera of the extinct family, Zeuglodontidæ, have been found in Miocene and Eocene beds of the same districts. Some remains associated with these are doubtfully referred to the Seal family (Phocidæ) among the Carnivora.
Edentata.—Till quite recently no remains of this order have occurred in any North American deposits below the Post-Pliocene; but in 1874 Prof. Marsh described some remains allied to Megalonyx and Mylodon, from the Pliocene beds of California and Idaho, and forming a new genus, Morotherium. As these remains have only occurred to the west of the Rocky Mountains, and in Pliocene deposits whose exact age is not ascertained, they hardly affect the remarkable absence of this group from the whole of the exceedingly rich Tertiary deposits in all other parts of North America.
General Relations of the extinct Tertiary Mammalia of North America and Europe.—Having now given a sketch of the extinct Mammalia which inhabited Europe and North America during the Tertiary period, we are enabled by comparing them, ​to ascertain their relations to each other, and to see how far they elucidate the problem of the birth-place and subsequent migrations of the several families and genera. We have already pointed out the remarkable features of the Quaternary (or Post-Pliocene) fauna of North America, and now proceed to discuss that of the various Tertiary periods, which is closely connected with the extinct fauna of Europe.
The Tertiary Mammalia of North America at present described belong to from eighty to one hundred genera, while those of Europe are nearly double that number; yet only eighteen genera are common to the two faunas, and of these eight are living and belong chiefly to the Pliocene period. Taking first, the genera which in America do not go back beyond the Pliocene period (ten in number), we find that eight of them in Europe go back to the Upper Miocene. These are Felis, Pseudælurus, Hipparion, Cervus, Mastodon, Elephas (in India), Castor and Hystrix; while another, Canis, goes back to the Upper Eocene and the tenth, Equus, confined to the newer Pliocene or perhaps to the Post-Pliocene in America, extends back to the older Pliocene in Europe. Of the seven European genera which are confined to the Miocene period in America, three, Hyænodon, Anchitherium, and Lophiodon go back to the Eocene in Europe; three others, Machairodus, Rhinoceros, and Aceratherium, are also of Miocene age in Europe; Amphicyon goes back to the Lower Miocene of Europe. Lophiotherium belongs to the Eocene of both countries.
If we turn now to families instead of genera, we find that the same general rule prevails. Mustelidæ (weasels), Ursidæ (bears), true Equidæ (horses), and Bovidæ (oxen &c.), go no further back in America than the Pliocene, while they all go back to the Miocene in Europe. Suidæ (swine) and Anoplotheridæ (extinct) are found in the American Miocene and in the European Eocene. Anchitheridæ (extinct) reach the Upper Eocene in America, while in Europe they range through Upper, Middle, and Lower Eocene. Cervidæ (deer) alone are Miocene in both countries. There remain two families in which America has the preeminence. Camelidæ (camels) were wonderfully developed in ​the American Pliocene and Miocene periods, abounding in genera and species; whereas in Europe the group only exists in the Post-Pliocene or Lower Pliocene, with one Upper Miocene species of Camelus in N. India. The Anthracotheridæ (extinct), found only in the Upper Miocene of France and India, reach even the Lower Eocene in America.
These facts may be due, in part, to a want of strict co-ordination between the Tertiary deposits of Europe and North America,—in part to the imperfection of the record in the latter country. Yet it does not seem probable that they are altogether due South America and well marked differences to imperfect knowledge; yet we find such important families as the Civets, Hyænas, Giraffes, and Hippopotami absent from America, with the Weasels, and Antelopes almost so; while America possesses almost all the Camelidæ, two peculiar orders, Dinocerata and Tillodontia, and four remarkably peculiar families, Limnotheridæ, Lemuravidæ, Oreodontidæ and Brontotheridæ. If then the facts at present known represent approximately the real time-relations of the groups in question on the two continents, they render it probable that weasels, bears, true horses, swine, oxen, sheep and antelopes, originated on the Old World continent, and were transmitted to America during some part of the Miocene period; while camels originated in the New World, and somewhere about the same time passed over to Europe. Of the extinct families common to the two hemispheres, the Anthracotheridæ alone seem to have had an American origin. Of the genera common to the two countries, almost all seem to have had a European origin, the only genera of equal date being the two rhinoceroses and three Anchitheridæ; but if the Brontotheridæ are allied to the Rhinocerotidæ, these latter may have originated in America, although now an exclusively Old World type. These conclusions are not improbable when we consider the much greater size of the Old World continents, extending far into the tropics and probably ​always more or less united to the tropical areas; while the evidence of the extinct mammalia themselves shows, that South America has been for the most part isolated from the northern continent, and did not take part in the development of its characteristic Tertiary fauna.
Before speculating further on this subject, it will be well to lay before our readers a summary of South American palæontology, after which we shall be in a better position to draw correct inferences from the whole body of the evidence.
South America.
Unfortunately, our knowledge of the interesting fossil fauna of this continent, is almost wholly confined to the Post-Pliocene and Pliocene periods. A few remains have been discovered in deposits believed to be of Eocene age, but nothing whatever representing the vast intervening period, so rich in peculiar forms of animal life both in North America and Europe.
Fauna of the Brazilian caves.—What we know of the Post-Pliocene period is chiefly due to the long-continued researches of Dr. Lund in the caves of Central Brazil, mostly situated in a district near the head waters of the San Francisco river in the Province of Minas Geraes. The caves are formed in limestone rocks, and are so numerous that Dr. Lund visited thousands, but only sixty contained bones in any quantity. These caves have a floor of reddish earth, often crowded with bones. In one experiment, half a cubic foot of this earth contained jaws of 400 opossums, 2,000 mice, besides remains of bats, porcupines and small birds. In another trial, the whole of the earth in a cavern was carried out for examination, amounting to 6,552 firkins; and, from a calculation made by measured samples, it was estimated to contain nearly seven millions of jaw-bones of cavies, opossums, porcupines, and mice, besides small birds, lizards, and frogs. This immense accumulation is believed to have been formed from the bodies of animals brought into the cavern by owls; and, as these are unsocial birds, the quantity found implies an ​immense lapse of time, probably some thousands of years. More than 100 species of Mammalia, in all, were obtained in these caves. Some were living species or closely allied to such; but the majority were extinct, and a considerable number, about one-fourth, belonged to extinct genera, or genera not now inhabiting South America. Stone implements and human remains were found in several of the caves with extinct animals. The following enumeration of these remains is from the corrected list of M. Gervais.
Primates.—Extinct species of Cebus, Callithrix, and Jacchus—South American genera of monkeys; with an extinct genus, Protopithecus—an animal of large size but belonging to the American family Cebidæ.
Chiroptera.—Species belonging to the South American Phyllostomidæ, and to two South American genera of other families.
Carnivora.—Five species of Felis, some allied to living animals, others extinct; a species of the widespread extinct genus Machairodus; and a small species referred to Cynælurus, the genus containing the hunting leopard now found only in Africa and India. Canidæ are represented by Canis and Icticyon (a living Brazilian species of the latter genus), and the extinct genus Speothos. Mustelidæ are represented by extinct species of the South American genera Mephitis and Galictis. Procyonidæ, by a species of Nasua. Ursidæ, by Arctotherium, a genus closely resembling, if not identical with, that containing the "spectacled bear" of Chili.
Ungulata.—Equus, Tapirus, Dicotyles, Auchenia, Cervus, Leptotherium, and Antilope, are the cave-genera of this order. Equus and Antelope are particularly interesting, as representing groups forming no part of existing South American zoology; while the presence also of Leptotherium, an extinct genus of antelopes, shows that the group was fairly represented in South America at this comparatively recent period.
Proboscidea.—A species of Mastodon, found also in the Pliocene of La Plata, represents this order.
Rodentia.—These abound. Dasyprocta, Cælogenys, Cavia, Kerodon, all living genera of Caviidæ, are represented by ​extinct species. Cercolabes, the 'tree porcupine' (Cercolabidæ) has two species, one as large as a peccary; Myopotamus, Loncheres, Carterodon, are existing genera of spiny rats (Echimyidæ); and there are two extinct genera of the same family, Lonchophorus and Phyllomys. Lagostomus (Chinchillidæ), the viscacha of the Pampas, is represented by an extinct species. There is also an extinct species of Lepus; several species of Hesperomys and Oxymycterus; and a large Arvicola, a genus not living in South America.
Edentata.—These, which constitute the great feature of the existing South American fauna, were still more abundant and varied in the Cave period, and it is remarkable that most of them are extinct genera. The armadillos are alone represented by living forms, Dasypus, and Xenurus; Eurydon and Heterodon, are extinct genera of the same family, as well as Chlamydotherium—huge armadillos the size of a tapir or rhinoceros, and Pachytherium, which was nearly as large. The ant-eaters are represented only by Glossotherium, an extinct form allied to Myrmecophaga and Manis. The sloths were more numerous, being represented by the extinct genera Cælodon, Sphenodon and Ochotherium, the last of large size. The huge terrestrial sloths—Megatheridæ, also abounded; there being species of Megatherium and Megalonyx, as well as the allied Scelidotherium, supposed to have some affinity for the African Orycteropus.
Marsupials.—No new forms of these appear, but numerous species of Didelphys, all closely allied to opossums still living in South America.
The preceding sketch of the wonderful cave fauna of Central Brazil, is sufficient to show that it represents, in the main, a period of great antiquity. Not only are almost the whole of the species extinct, but there are twenty extinct genera, and three others not now inhabitants of South America. The fact that so few remains of the living animals of the country are found in these caves, indicates that some change of physical conditions has occurred since they were the receptacles of so many of the larger animals; and the presence of many extinct genera of ​large size, especially among the Edentata and American families of Rodents, are additional proofs of a very high antiquity. Yet many of these cave animals are closely allied to those which are found in North America in the Post-Pliocene deposits only, so that we have no reason to suppose the cave-fauna to be of much earlier date. But the great amount of organic change it implies, must give us an enlarged idea of the vast periods of time, as measured by years, which are included in this, the most recent of all geological epochs.
Pliocene Period of Temperate South America.—We have now to consider the numerous remains of extinct animals found in various deposits in the Pampas, and in Patagonia, and a few in Bolivia. The age of these is uncertain; but as they are very similar to the cave-fauna, though containing a somewhat larger proportion of extinct genera and some very remarkable new forms, they cannot be very much older, and are perhaps best referred at present to the newer portion of the Pliocene formation.
Carnivora.—The genus Machairodus or sabre-toothed tigers, represents the Felidæ. There are several species of wolves (Canis); a weasel (Mustela); two bears of the Brazilian cave-genus Arctotherium; and the extinct European genus Hyænarctos.
Ungulata.—There are two species of Equus, found in the Pampas, Chili, and Bolivia; two of Macrauchenia, an extraordinary extinct group allied to the tapir and Palæotherium, but with the long neck, and general size of a camel. A second species found on the highlands of Bolivia is much smaller.
A more recent discovery, in Patagonia, is the almost perfect series of teeth of a large animal named Homalodontotherium; and which is believed by Professor Flower, who has described it, to have been allied to Rhinoceros, and still more to the Miocene Hyracodon from North America; and also to present some resemblances to Macrauchenia, and though much more remotely, to the curious genus Nesodon mentioned further on.
The Artiodactyla, or even-toed Ungulates, are represented by a species of Dicotyles, or peccary, found in the deposits of the ​Pampas; by Auchenia, or llama, of which three extinct species inhabited Bolivia, in which country two allied but extinct genera, Palæolama and Camelotherium, have also been found. Three species of deer (Cervus), from the Pampas deposits, complete the list of Pliocene Ungulates.
Proboscidea.—The cave species of Mastodon is found also in the Pampas deposits, and another in the Andes of Chili and Bolivia.
Rodents.—These are not so numerous as in the caves. There are species of the existing genera, Kerodon and Cavia (Caviidæ); Lagostomus (Chinchillidæ); Ctenomys (Octodontidæ); Lepus (hare); Hesperomys and Oxymycterus (Muridæ); Arvicola, a genus not living in South America; and an extinct genus, Cardiodus. There is also a remarkable extinct form, Typotherium, larger than the capybara, and having affinities to Edentates and Ungulates. Three species have been found in the Pampas deposits.
Edentata.—These are as abundant and remarkable as in the cave deposits. Scelidotherium, Megatherium, Megalonyx, Glossotherium and Dasypus, have already been noticed as from the Brazilian caves. We have here, in addition, the huge Mylodon allied to the Megatherium, and the allied genera—Gnathopsis and Lestodon. We then come to the huge extinct armadillos, Glyptodon and Schistopleurum, the former consisting of numerous species, some of which were as large as an elephant. Another genus, Eutatus, is allied to the living three-banded armadillos; and a species of the existing genus Euphractus has been found in Bolivia.
Toxodontidæ.—There remain a number of huge animals rivalling the Megatherium in size, and forming the genera Toxodon and Nesodon, but whose position is doubtful. Several species have been found in the deposits of the Pampas and Patagonia. They are allied at once to Ungulates, Rodents, Edentates, and the aquatic Sirenia, in so puzzling a manner that it is impossible to determine to what order they belong, or whether they require a new order to be formed for their reception. Some are believed to date back to the Miocene period, and they indicate what strange forms may still be discovered, should any ​productive deposits be found in South America of middle Tertiary age.
Pliocene Mammalia of the Antilles.—These may be noticed here, as they are of special interest, proving the connection of the larger West Indian Islands with the Continent some time in the later Tertiary period. They consist of remains of two large animals belonging to the South American Chinchillidæ, found in cave deposits in the island of Anguilla, and forming two new genera, Amblyrhiza and Loxomylus; and remain allied to Megalonyx from Cuba, which have been named Megalocnus and Myomorphus.
Eocene fauna of South America.—The few remains yet discovered in the Tertiary deposits of the Pampas which are believed to be of Eocene age, are exceedingly interesting, because they show us another change in the scenery of the great drama of life; there being apparently a considerable resemblance, at this epoch, between South America and Europe. They consist of a large extinct feline animal, Eutemnodus; of Palæotherium and Anoplotherium, the well-known extinct Ungulates of the European Tertiaries, and which have never been found in North America; and of three genera of Rodents,—Theridomys, allied to Echimys, and found also in the Eocene and Miocene of France; Megamys, allied to the living Capromys of the Antilles, and also to Palæomys, an extinct form of the French Miocene; and a very large animal referred to Arvicola, a genus found also in the Pliocene deposits of South America, and abundant in the northern hemisphere. No Edentates have been found.
The resemblances of this fauna to that of Europe rather than to any part of America, are so strong, that they can hardly be accidental. We greatly want, however, more information on this point, as well as some corresponding evidences as to the condition of West and South Africa about the same epoch, before we can venture to speculate on their bearing as regards the early migrations of organic forms.
General Remarks on the Extinct Mammalian Fauna of the Old ​and New Worlds.—Leaving the more special applications of palæontological evidence to be made after discussing the relations of the existing fauna of the several regions, we propose here to indicate briefly, some of the more general deductions from the evidence which has now been laid before our readers.
The first, and perhaps the most startling fact brought out by our systematic review, is the very recent and almost universal change that has taken place in the character of the fauna, over all the areas we have been considering; a change which seems to be altogether unprecedented in the past history of the same countries as revealed by the geological record. In Europe, in North America, and in South America, we have evidence that a very similar change occurred about the same time. In all three we find, in the most recent deposits—cave-earths, peat-bogs, and gravels—the remains of a whole series of large animals, which have since become wholly extinct or only survive in far-distant lands. In Europe, the great Irish elk, the Machairodus and cave-lion, the rhinoceros, hippopotamus, and elephant;—in North America, equally large felines, horses and tapirs larger than any now living, a llama as large as a camel, great mastodons and elephants, and abundance of huge megatheroid animals of almost equal size;—in South America these same megatheroids in greater variety, numerous huge armadillos, a mastodon, large horses and tapirs, large porcupines, two forms of antelope, numerous bears and felines, including a Machairodus, and a large monkey,—have all become extinct since the deposition of the most recent of the fossil-bearing strata. This is certainly not a great while ago, geologically; and it is almost certain that this great organic revolution, implying physical changes of such vast proportions that they must have been due to causes of adequate intensity and proportionate range, has taken place since man lived on the earth. This is proved to have been the case in Europe, and is supported by much evidence both as regards North and South America.
It is clear that so complete and sudden a change in the higher forms of life, does not represent the normal state of things. Species and genera have not, at all times, become so rapidly extinct. The time occupied by the "Recent period," that is the ​time since these changes took place is, geologically, minute. The time of the whole of the Post-Pliocene period, as measured by the amount of physical and general organic change known to have taken place, is exceedingly small when compared with the duration of the Pliocene period, and still smaller, probably, as compared with the Miocene. Yet during these two periods we meet with no such break in the continuity of the forms of life, no such radical change in the character of the fauna (though the number of specific and generic changes may be as great) as we find in passing from the Post-Pliocene to recent times. For example, in Central Europe numerous hyænas, rhinoceroses, and antelopes, with the great Machairodus, continued from Miocene all through Pliocene into Post-Pliocene times; while hippopotami and elephants continued to live through a good part of the Pliocene and Post-Pliocene periods,—and then all suddenly became extinct or left the country. In North America there has been more movement of the fauna in all the periods; but we have similar great felines, horses, mastodons, and elephants, in the Pliocene and Post-Pliocene periods, while Rhinoceros is common to the Miocene and Pliocene, and camels range continuously from Miocene, through Pliocene, to Post-Pliocene times;—when all alike became extinct. Even in South America the evidence is, as far as it goes, all the same way. We find Machairodus, Equus, Mastodon, Megatherium, Scelidotherium, Megalonyx, and numerous gigantic armadillos, alike in the caves and in the stratified tertiary deposits of the Pampas;—yet all have since passed away.
It is clear, therefore, that we are now in an altogether exceptional period of the earth's history. We live in a zoologically impoverished world, from which all the hugest, and fiercest, and strangest forms have recently disappeared; and it is, no doubt, a much better world for us now they have gone. Yet it is surely a marvellous fact, and one that has hardly been sufficiently dwelt upon, this sudden dying out of so many large mammalia, not in one place only but over half the land surface of the globe. We cannot but believe that there must have been some physical cause for this great change; and it must have been a cause capable of acting almost simultaneously over large ​portions of the earth's surface, and one which, as far as the Tertiary period at least is concerned, was of an exceptional character. Such a cause exists in the great and recent physical change known as "the Glacial epoch." We have proof in both Europe and North America, that just about the time these large animals were disappearing, all the northern parts of these continents were wrapped in a mantle of ice; and we have every reason to believe that the presence of this large quantity of ice (known to have been thousands of feet if not some miles in thickness) must have acted in various ways to have produced alterations of level of the ocean as well as vast local floods, which would have combined with the excessive cold to destroy animal life. There is great difference of opinion among geologists and physicists as to the extent, nature, and duration of the Glacial epoch. Some believe it to have prevailed alternately in the northern and southern hemispheres; others that it was simultaneous in both. Some think there was a succession of cold periods, each lasting many thousands of years, but with intercalated warm periods of equal duration; others deny that there is any evidence of such changes, and maintain that the Glacial epoch was one continuous period of arctic conditions in the temperate zones, with some fluctuations perhaps but with no regular alternations of warm periods. Some believe in a huge ice-cap covering the whole northern hemisphere from the pole to near 50° north latitude in the eastern, and 40° in the western hemisphere; while others impute the observed effects either to glaciers from local centres, or to floating icebergs of vast size passing over the surface during a period of submersion.
Without venturing to decide which of these various theories will be ultimately proved to be correct, we may state, that there is an increasing belief among geologists in the long duration of this ice-period, and the vast extent and great thickness attained by the ice-sheet. One of the most recent, and not the least able, of the writers on this question (Mr. Belt) shows strong reasons for adopting the view that the ice-period was simultaneous in both hemispheres; and he calculates that the vast amount of water abstracted from the ocean and locked up ​in mountains of ice around the two poles, would lower the general level of the ocean about 2,000 feet. This would be equivalent to a general elevation of the land to the same amount, and would thus tend to intensify the cold; and this elevation may enable us to understand the recent discoveries of signs of glacial action at moderate elevations in Central America and Brazil, far within the tropics. At the same time, the weight of ice piled up in the north would cause the land surface to sink there, perhaps unequally, according to the varying nature of the interior crust of the earth; and since the weight has been removed land would rise again, still somewhat irregularly; and thus the phenomena of raised beds of arctic shells in temperate latitudes, are explained.
Now, it is evident, that the phenomena we have been considering—of the recent changes of the mammalian fauna in Europe, North America, South Temperate America, and the highlands of Brazil—are such as might be explained by the most extreme views as to the extent and vastness of the ice-sheet, and especially as to its simultaneous occurrence in the northern and southern hemispheres; and where two such completely independent sets of facts are found to combine harmoniously, and supplement each other on a particular hypothesis, the evidence in favour of that hypothesis is greatly strengthened. An objection that will occur to zoologists, may here be noticed. If the Glacial epoch extended over so much of the temperate and even parts of the tropical zone, and led to the extinction of so many forms of life even within the tropics, how is it that so much of the purely tropical fauna of South America has maintained itself, and that there are still such a vast number of forms, both of mammalia, birds, reptiles, and insects, that seem organized for an exclusive existence in tropical forests? Now Mr. Belt's theory, of the subsidence of the ocean to the extent of about 2,000 feet, supplies an answer to this objection; for we should thus have a tract of lowland of an average width of some hundreds of miles, added to the whole east coast of Central and South America. This tract would, no doubt, become covered with forests as it was slowly formed, would enjoy a perfectly ​tropical climate, and would thus afford an ample area for the continued existence and development of the typical South American fauna; even had glaciers descended in places so low as what is now the level of the sea, which, however, there is no reason to believe they ever did. It is probable too, that this low tract, which all round the Gulf of Mexico would be of considerable width, offered that passage for intermigration between North and South America, which led to the sudden appearance in the former country in Post-Pliocene times, of the huge Megatheroids from the latter; a migration which took place in opposite directions as we shall presently show.
The birth-place and migrations of some mammalian families and genera.—We have now to consider a few of those cases in which the evidence already at our command, is sufficiently definite and complete, to enable us to pronounce with some confidence as to the last movements of several important groups of mammalia.
Primates.—The occurrence in North America of numerous forms of Lemuroidea, forming two extinct families, which are believed by American palæontologists to present generalized features of both Lemuridæ and Hapalidæ, while in Europe only Lemurine forms allied to those of Africa have occurred in deposits of the same age (Eocene), renders it possible that the Primates may have originated in America, and sent one branch to South America to form the Hapalidæ and Cebidæ, and another to the Old World, giving rise to the lemurs and true apes. But the fact that apes of a high degree of organization occur in the European Miocene, while in the Eocene, a monkey believed to have relations to the Lemuroids and Cebidæ has also been discovered, make it more probable that the ancestral forms of this order originated in the Old World at a still earlier period. The absence of any early tertiary remains from the tropical parts of the two hemispheres, renders it impossible to arrive at any definite conclusions as to the origin of groups which were, no doubt, always best developed in tropical regions.
Carnivora.—This is a very ancient and wide-spread group, the families and genera of which had an extensive range in very ​early times. The true bears (Ursus) are almost the only important genus that seems to have recently migrated. In Europe it dates back to the Older Pliocene, while in North America it is Post-Pliocene only. Bears, therefore, seem to have passed into America from the Palæarctic region in the latter part of the Pliocene period. They probably came in on the north-west, and passed down the Andes into South America, where one isolated species still exists.
Ungulata.—Horses are very interesting. In Europe they date back under various forms to the Miocene period, and true Equus to the Older Pliocene. In North America they are chiefly Pliocene, true Equus being Post-Pliocene, with perhaps one or two species Newer Pliocene; but numerous ancestral forms date back to the Miocene and Eocene, giving a more perfect "pedigree of the horse" than the European forms, and going back to a more primitive type—Orohippus. In South America, Equus is the only genus, and is Post-Pliocene or at most Newer Pliocene. While, therefore, the ancient progenitors of the Equidæ were common to North America and Europe, in Miocene and even Eocene times, true horses appear to have arisen in the Palæarctic region, to have passed into North America in the latter part of the Pliocene period, and thence to have spread over all suitable districts in South America. They were not, however, able to maintain themselves permanently in their new territory, and all became extinct; while in their birth-place, the Old World, they continue to exist under several varied forms.
True tapirs are an Old World group. They go back to the Lower Miocene in Europe, while in both North and South America they are exclusively Post-Pliocene. They occur in France down to the Newer Pliocene, and must, about that time, have entered America. The land connection by which this and so many other animals passed between the Old and New Worlds in late Tertiary times, was almost certainly in the North Pacific, south of Behring's Straits, where, as will be seen by our general map, there is a large expanse of shallow water, which a moderate elevation would convert into dry land, in a sufficiently temperate latitude.
​The peccary (Dicotyles), now a characteristic South American genus, is a recent immigrant from North America, where it appears to have been developed from ancestral forms of swine dating back to the Miocene period.
Antelopes are an Old World type, but a few of them appear to have entered North, and reached South America in late Pliocene times. Camels, strange to say, are a special North American type, since they abounded in that continent under various ancient forms in the Miocene period. Towards the end of that period they appear to have entered eastern Asia, and developed into the Siberian Merycotherium and the North Indian Camelus, while in the Pliocene age the ancestral llamas entered South America.
Cervidæ are a wide-spread northern type in their generalized form, but true deer (Cervus) are Palæarctic. They abounded in Europe in Miocene times, but only appear in North and South America in the later Pliocene and Post-Pliocene periods.
True oxen (Bovinæ) seem to be an Oriental type (Miocene), while they appear in Europe only late in the Pliocene period, and in America are confined to the Post-Pliocene.
Elephants (Elephantidæ) are an Old World type, abounding in the Miocene period in Europe and India, and first appearing in America in Post-Pliocene or later Pliocene times. Ancestral forms, doubtfully Proboscidean (Dinocerata), existed in North America in the Eocene period, but these became extinct without leaving any direct descendants, unless the Brontotheridæ and rhinoceroses may be so considered.
Marsupials are almost certainly a recent introduction into South and North America from Asia. They existed in Europe in Eocene and Miocene times, and presumably over a considerable part of the Old World; but no trace of them appears in North or South America before the Post-Pliocene period.
Edentata.—These offer a most curious and difficult problem. In South America they abound, and were so much more numerous and varied in the Post-Pliocene and Pliocene, that we may be sure they lived also in the preceding Miocene period. A few living Edentates are scattered over Africa and Asia, and ​they flourished in Europe during the Miocene age—animals as large (in some species) as a rhinoceros, and most allied to living African forms. In North America no trace of Edentata has been found earlier than the Post-Pliocene period, or perhaps the Newer Pliocene on the west coast. Neither is there any trace of them in South America in the Eocene formations; but this may well be owing to our very imperfect knowledge of the forms of that epoch. Their absence from North America is, however, probably real; and we have to account for their presence in the Old World and in South America. Their antiquity is no doubt very great, and the point of divergence of the Old World and South American groups, may take us back to early Eocene, or even to Pre-Eocene times. The distribution of land and sea may then have been very different from what it is now; and to those who would create a continent to account for the migrations of a beetle, nothing would seem more probable than that a South Atlantic continent, then united parts of what are now Africa and South America. There is, however, so much evidence for the general permanence of what are now the great continents and deep oceans, that Professor Huxley's supposition of a considerable extension of land round the borders of the North Pacific Ocean in Mesozoic times, best indicates the probable area in which the Edentate type originated, and thence spread over much of the Old World and South America. But while in the latter country it flourished and increased with little check, in the other great continents it was soon overcome by the competition of higher forms, only leaving a few small-sized representatives in Africa and Asia.