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THE ANCIENT
LIFE-HISTORY
OF THEĀ EARTH

Chapter 19:

THE MIOCENE PERIOD.


The Miocene rocks comprise those Tertiary deposits which contain less than about 35 per cent of existing species of shells (Mollusca), and more than 5 per cent—or those deposits in which the proportion of living shells is less than of extinct species. They are divisible into a Lower Miocene (Oligocene) and an Upper Miocene series.

In Britain, the Miocene rocks are very poorly developed, one of their leading developments being at Bovey Tracy in Devonshire, where there occur sands, clays, and beds of lignite Page 306 or imperfect coal. These strata contain numerous plants, amongst which are Vines, Figs, the Cinnamon-tree, Palms, and many Conifers, especially those belonging to the genus Sequoia (the "Red-Foods"). These Bovey Tracy lignites are of Lower Miocene age, and they are lacustrine in origin. Also of Lower Miocene age are the so-called "Hempstead Beds" of Yarmouth in the Isle of Wight. These attain a thickness of less than 200 feet, and are shown by their numerous fossils to be principally a true marine formation. Lastly, the Duke of Argyll, in 1851, showed that there existed at Ardtun, in the island of Mull, certain Tertiary strata containing numerous remains of plants; and these also are now regarded as belonging to the Lower Miocene.

In France, the Lower Miocene is represented in Auvergne, Cantal, and Velay, by a great thickness of nearly horizontal strata of sands, sandstone, clays, marls, and limestones, the whole of fresh-water origin. The principal fossils of these lacustrine deposits are Mammalia, of which the remains occur in great abundance. In the valley of the Loire occur the typical European deposits of Upper Miocene age. These are known as the "Faluns," from a provincial term applied to shelly sands, employed to spread upon soils which are deficient in lime; and the Upper Miocene is hence sometimes spoken of as the "Falunian" formation. The Faluns occur in scattered patches, which are rarely more than 50 feet in thickness, and consist of sands and marls. The fossils are chiefly marine; but there occur also land and fresh-water shells, together with the remains of numerous Mammals. About 25 per cent of the shells of the Faluns are identical with existing species. The sands, limestones, and marls of the Department of Gers, near the base of the Pyrenees, rendered famous by the number or Mammalian remains exhumed from them by M. Lartet, also belong to the age of the Faluns.

In Switzerland, between the Alps and the Jura, there occurs a great series of Miocene deposits, known collectively as the "Molasse," from the soft nature of a greenish sandstone, which constitutes one of its chief members. It attains a thickness of many thousands of feet, and rises into lofty mountains, some of which—as the Rigi—are more than 6000 feet in height. The middle portion of the Molasse is of marine origin, and is shown by its fossils to be of the age of the Faluns; but the lower and upper portions of the formation are mainly or entirely of fresh-water origin. The Lower Molasse (of Lower Miocene age) has yielded about 500 species of plants, mostly of tropical or sub-tropical forms. The Upper Page 307 Molasse has yielded about the same number of plants, with about 900 species of Insects, such as wood-eating Beetles Water-beetles, White Ants, Dragon-flies, &c.

In Belgium, strata of both Lower and Upper Miocene age are known,—the former (Rupelian Clays) containing numerous marine fossils; whilst the latter (Bolderberg Sands) have yielded numerous shells corresponding with those of the Faluns.

In Austria, Miocene strata are largely developed, marine beds belonging to both the Lower and Upper division of the formation occurring extensively in the Vienna basin. The well-known Brown Coals of Radaboj, in Croatia, with numerous plants and insects, are also of Lower Miocene age.

In Germany, deposits belonging to both the Lower and Upper division of the Miocene formation are extensively developed. To the former belong the marine strata of the Mayence basin, and the marine Rupelian Clay near Berlin; whilst a celebrated group of strata belonging to the Upper Miocene occurs near Epplesheim, in Hesse-Darmstadt, and is well known for the number of its Mammalian remains.

In Greece, at Pikermé, near Athens, there occurs a celebrated deposit of Upper Miocene age, well known to palæontologists through the researches of M. M. Wagner, Roth, and Gaudry upon the numerous Mammalia which it contains. In Italy, also, strata of both Lower and Upper Miocene age are well developed in the neighbourhood of Turin.

In the Siwâlik Hills, in India, at the southern foot of the Himalayas, occurs a series of Upper Miocene strata, which have become widely celebrated through the researches of Dr Falconer and Sir Proby Cautley upon the numerous remains of Mammals and Reptiles which they contain. Beds of corresponding age, with similar fossils, are known to occur in the island of Perim in the Gulf of Cambay.

Lastly, Miocene deposits are found in North America, in New Jersey, Maryland, Virginia, Missouri, California, Oregon, &c., attaining a thickness of 1500 feet or more. They consist principally of clays, sands, and sandstones, sometimes of marine and sometimes of fresh-water origin. Near Richmond, in Virginia, there occurs a remarkable stratum, wrongly called "Infusorial Earth," which is occasionally 30 feet in thickness, and consists almost wholly of the siliceous envelopes of certain low forms of plants (Diatoms), along with the spicules of Sponges and other siliceous organisms (see fig. 16). The White River Group of Hayden occurs in the Upper Missouri region, and is largely exposed over the barren and desolate Page 308 district known as the "Mauvaises Terres." They have a thickness of 1000 feet or more, and contain numerous remains of Mammals. They are of lacustrine origin, and are believed to be of the age of the Lower Miocene. Upon the whole, about from 15 to 30 per cent of the Mollusca of the American Miocene are identical with existing species.

In addition to the regions previously enumerated, Miocene strata are known to be developed in Greenland, Iceland, Spitzbergen, and in other areas of less importance.

The life of the Miocene period is extremely abundant, and, from the nature of the deposits of this age, also extremely varied in its character. The marine beds of the formation have yielded numerous remains of both Vertebrate and Invertebrate sea-animals; whilst the fresh-water deposits contain the skeletons of such shells, fishes, &c., as now inhabit rivers or lakes. Both the marine and the lacustrine beds have been shown to contain an enormous number of plants, the latter more particularly; whilst the Brown Coals of the formation are made up of vegetable matter little altered from its original condition. The remains of air-breathing animals, such as Insects, Reptiles, Birds, and Mammals, are also abundantly found, more especially in the fresh-water beds.

The plants of the Miocene period are extraordinarily numerous, and only some of the general features of the vegetation of this epoch can be indicated here. Our chief sources of information as to the Miocene plants are the Brown Coals of Germany and Austria, the Lower and Upper Molasse of Switzerland, and the Miocene strata of the Arctic regions. The lignites of Austria have yielded very numerous plants, chiefly of a tropical character—one of the most noticeable forms being a Palm of the genus Sabal (fig. 234, B), now found in America. The plants of the Lower Miocene of Switzerland are also mostly of a tropical character, but include several forms now found in North America, such as a Tulip-tree (Liriodendron) and a Cypress (Taxodium). Amongst the more remarkable forms from these beds may be mentioned Fan-Palms (Chamœrops, fig. 234, A), numerous tropical ferns, and two species of Cinnamon. The plant-remains of the Upper Molasse of Switzerland indicate an extraordinarily rank and luxuriant vegetation, composed mainly of plants which now live in warm countries. Among the commoner plants of this formation may be enumerated many species of Maple (Acer), Plane-trees (Platanus fig. 235), Cinnamon-trees (fig. 236), and other members of the Lauraceœ, many species of Proteaccœ (Banksia, Grevillea, &c.), several species of Sarsaparilla (Smilax), Palms, Cypresses, &c.

Page 309 In Britain, the Lower Miocene strata of Bovey Tracy have yielded remains of Ferns, Vines, Fig, Cinnamon, Proteaccœ, &c., along with numerous Conifers. The most abundant of these last is a gigantic pine—the Sequoia Couttsiœ—which is very nearly allied to the huge Sequoia (Wellingtonia) gigantea of California. A nearly-allied form (Sequoia Langsdorffi) has been detected in the leaf-bed of Ardtun, in the Hebrides.

Fig. 234
Fig. 234.—Miocene Palms A, Chamœrops Helvetica; B, Sabal major. Lower Miocene of Switzerland and France.
Fig. 235
Fig. 235.—Platanus aceroides, an Upper Miocene Plane-tree. a, Leaf; b, The core of a bundle of fruits; c, A single fruit.
Fig. 236
Fig. 236.—Cinnamomum polymorphum. a, Leaf; b, Flower. Upper Miocene.

In Greenland, as well as in other parts of the Arctic regions, Miocene strata have been discovered which have yielded a great number of plants, many of which are identical with species found in the European Miocene. Amongst these Page 310 plants are found many trees, such as Conifers, Beeches, Oaks, Maples, Plane-trees, Walnuts, Magnolias, &c., with numerous shrubs, ferns, and other smaller plants. With regard to the Miocene flora of the Arctic regions, Sir Charles Lyell remarks that "more than thirty species of Coniferæ have been found, including several Sequoias (allied to the gigantic Wellingtonia of California), with species of Thujopsis and Salisburia, now peculiar to Japan. There are also beeches, oaks, planes, poplars, maples, walnuts, limes, and even a magnolia, two cones of which have recently been obtained, proving that this splendid evergreen not only lived but ripened its fruit within the Arctic circle. Many of the limes, planes, and oaks were large-leaved species; and both flowers and fruits, besides immense quantities of leaves, are in many cases preserved. Among the shrubs are many evergreens, as Andromeda, and two extinct genera, Daphnogene and M'Clintockia, with fine leathery leaves, together with hazel, blackthorn, holly, logwood, and hawthorn. A species of Zamia (Zimites) grew in the swamps, with Potamogeton, Sparganium, and Menyanthes; while ivy and villes twined around the forest-trees, and broad-leaved ferns grew beneath their shade. Even in Spitzbergen, as far north as lat. 78° 56', no less than ninety-five species of fossil plants have been obtained, including Taxodium of two species, hazel, poplar, alder, beech, plane-tree, and lime. Such a vigorous growth of trees within 12° of the pole, where now a dwarf willow and a few herbaceous plants form the only vegetation, and where the ground is covered with almost perpetual snow and ice, is truly remarkable."

Taking the Miocene flora as a whole, Dr Heer concludes from his study of about 3000 plants contained in the European Miocene alone, that the Miocene plants indicate tropical or sub-tropical conditions, but that there is a striking inter-mixture of forms which are at present found in countries widely removed from one another. It is impossible to state with certainty how many of the Miocene plants belong to existing species, but it appears that the larger number are extinct. According to Heer, the American types of plants are most largely represented in the Miocene flora, next those of Europe and Asia, next those of Africa, and lastly those of Australia. Upon the whole, however, the Miocene flora of Europe is mostly nearly allied to the plants which we now find inhabiting the warmer parts of the United States; and this has led to the suggestion that in Miocene times the Atlantic Ocean was dry land, and that a migration of Page 311 American plants to Europe was thus permitted. This view is borne out by the fact that the Miocene plants of Europe are most nearly allied to the living plants of the eastern or Atlantic seaboard of the United States, and also by the occurrence of a rich Miocene flora in Greenland. As regards Greenland, Dr Heer has determined that the Miocene plants indicate a temperate climate in that country, with a mean annual temperature at least 30° warmer than it is at present.

The present limit of trees is the isothermal which gives the mean temperature of 500 Fahr. in July, or about the parallel of 67° N. latitude. In Miocene times, however, the Limes, Cypresses, and Plane-trees reach the 79th degree of latitude, and the Pines and Poplars must have ranged even further north than this.

The Invertebrate Animals of the Miocene period are very numerous, but they belong for the most part to existing types, and they can only receive scanty consideration here. The little shells of Foraminifera are extremely abundant in some beds, the genera being in many cases such as now flourish abundantly in our seas. The principal forms belong to the genera Textularia (fig. 237), Robulina, Glandulina, Polystomella, Amplistegina, Fig. 237
Fig. 237.—Textularia Meyeriana, greatly enlarged. Miocene Tertiary.
&c. Corals are very abundant, in many instances forming regular "reefs;" but all the more important groups are in existence at the present day. The Red Coral (Corallium), so largely sought after as an ornamental material, appears for the first time in deposits of this age. Amongst the Echinoderms, we meet with Heart-Urchins (Spatangus), Cake-Urchins (Scutella; fig. 238), and various other forms, the majority of which are closely allied to forms now in existence.

Numerous Crabs and Lobsters represent the Crustacea; but the most important of the Miocene Articulate Animals are the Insects. Of these, more than thirteen hundred species have been determined by Dr Heer from the Miocene strata of Switzerland alone. They include almost all the existing orders of insects, such as numerous and varied forms of Beetles (Coleoptera), Forest-bugs (Hemiptera), Ants (Hymenoptera), Flies (Diptera), Termites and Dragon-flies (Neuroptera), Grasshoppers (Orthoptera), and Butterflies (Lepidoptera). Page 312 One of the latter, the well-known Vanessa Pluto of the Brown Coals of Croatia, even exhibits the pattern of the wing, and to some extent its original coloration; whilst the more durably-constructed insects are often in a state of exquisite preservation.

Fig. 238
Fig. 238.—Different views of Scutella subrotunda, a Miocene "Cake-Urchin" from the south of France.

The Mollusca of the Miocene period are very numerous, but call for little special comment. Upon the whole, they are generically very similar to the Shell-fish of the present day; whilst, as before stated, from fifteen to thirty per cent of the species are identical with those now in existence. So far as the European area is concerned, the Molluscs indicate a decidedly hotter climate than the present one, though they have not such a distinctly tropical character as is the case with the Eocene shells. Thus we meet with many Cones, Volutes, Cowries, Olive-shells, Fig-shells, and the like, which are decidedly indicative of a high temperature of the sea. Polyzoans are abundant, and often attain considerable dimensions; whilst Brachiopods, on the other hand, are few in number. Bivalves and Univalves are extremely plentiful; and we meet here with the shells of Winged-Snails (Pteropods), belonging to such existing genera as Hyalea (fig. 239) and Cleodora. Lastly, the Cephalopods are represented both by the chambered shells of Nautili and by the internal skeletons of Cuttle-fishes (Spirulirostra.)

Fig. 239
Fig. 239.—Different views of the shell of Hyalea Orbignyana, a Miocene Pteropod.

The Fishes of the Miocene Period are very abundant but of little special importance. Besides the remains of Bony Fishes, we meet in the marine deposits of this age with numerous pointed teeth belonging to different kinds of Sharks. Some of the genera of these—such as Carcharodon (fig. 241), Oxyrhina (fig. 240), Lamna, and Galeocerdo—are very widely distributed, ranging through Page 313 both the Old and New Worlds; and some of the species attain gigantic dimensions.

Fig. 240
Fig. 240.—Tooth of Oxyrhina xiphodon. Miocene.
Fig. 241
Fig. 241.—Tooth of Carcharodon productus. Miocene.

Amongst the Amphibians we meet with distinctly modern types, such as Frogs (Rana) and Newts or Salamanders. The most celebrated of the latter is the famous Andrias Scheuchzeri (fig. 242), discovered in the year 1725 in the fresh-water Miocene deposits of Œningen, in Switzerland. The skeleton indicates an animal nearly five feet in length; and it was originally described by Scheuchzer, a Swiss physician, in a dissertation published in 1731, as the remains of one of the human beings who were in existence at the time of the Noachian Deluge. Hence he applied to it the name of Homo diluvii testis. In reality, however, as shown by Cuvier, we have here the skeleton of a huge Newt, very closely allied to the Giant Salamander (Menopoma maxima) of Java.

The remains of Reptiles are far from uncommon in the Miocene rocks, consisting principally of Chelonians and Crocodilians. The Land-tortoises (Testudinidœ) make their first appearance during this period. The most remarkable form of this group is the huge Colossochelys Atlas of the Upper Miocene deposits of the Siwâlik Hills in India, described by Dr Falconer and Sir Proby Cautley. Far exceeding any living Tortoise in its dimensions, this enormous animal is estimated as having had a length of about twenty feet, measured from the tip of the snout to the extremity of the tail, and to have stood upwards of seven feet high. All the details of its organisation, however, prove that it must have been "strictly a land animal, with herbivorous habits, and probably of the most inoffensive nature." The accomplished palæontologist just quoted, shows further that some of the traditions of the Hindoos would render it not improbable that this colossal Tortoise had survived into the earlier portion of the human period.

Of the Birds of the Miocene period it is sufficient to remark that though specifically distinct, they belong, so far as known, wholly to existing groups, and therefore present no points of special palæontological interest.

Fig. 242
Fig. 242.—Front portion of the skeleton of Andrias Scheuchzeri, a Giant Salamander from the Miocene Tertiary of Œningen, in Switzerland. Reduced in size.

The Mammals of the Miocene are very numerous, and only Page 314 the more important forms can be here alluded to. Amongst the Marsupials, the Old World still continued to possess species Page 315 of Opossum (Didephys), allied to the existing American forms. The Edentates (Sloths, Armadillos, and Ant-eaters), at the present day mainly South American, are represented by two large European forms. One of these is the large Macrotherium giganteum of the Upper Miocene of Gers in Southern France, which appears to hare been in many respects allied to the existing Scaly Ant-eaters or Pangolins, at the same time that the disproportionately long fore-limbs would indicate that it possessed the climbing habits of the Sloths. The other is the still more gigantic Ancylotherium Pentelici of the Upper Miocene of Pikermé, which seems to have been as large as, or larger than, the Rhinoceros, and which must have been terrestrial in its habits. This conclusion is further borne out by the comparative equality of length which subsists between the fore and hind limbs, and is not affected by the curvature and crookedness of the claws, this latter feature being well marked in such existing terrestrial Edentates as the Great Ant-eater.

The aquatic Sirenians and Cetaceans are represented in Miocene times by various forms of no special importance. Amongst the former, the previously existing genus Halitherium continued to survive, and amongst the latter we meet with remains of Dolphins and of Whales of the "Zeuglodont" family. We may also note here the first appearance of true "Whalebone Whales," two species of which, resembling the living "Right Whale" of Arctic seas, and belonging to the same genus (Balœna), have been detected in the Miocene beds of North America.

The great order of the Ungulates or Hoofed Quadrupeds is very largely developed in strata of Miocene age, various new types of this group making their appearance here for the first time, whilst some of the characteristic genera of the preceding period are still represented under new shapes. Amongst the Odd-toed or "Perissodactyle" Ungulates, we meet for the first time with representatives of the family Rhinoceridœ comprising only the existing Rhinoceroses. In India in the Upper Miocene beds of the Siwâlik Hills, and in North America, several species of Rhinoceros have been detected, agreeing with the existing forms in possessing three toes to each foot, and in having one or two solid fibrous "horns" carried upon the front of the head. On the other hand, the forms of this group which distinguish the Miocene deposits of Europe appear to have been for the most part hornless, and to have resembled the Tapirs in having three-toed hind-feet, but four-toed fore-feet. Page 316 The family of the Tapirs is represented, both in the Old and New Worlds, by species of the genus Lophiodon, some of which were quite diminutive in point of size, whilst others attained the dimensions of a horse. Nearly allied to this family, also, is the singular group of quadrupeds which Marsh has described from the Miocene strata of the United States under the name of Brontotheridœ. These extraordinary animals, typified by Brontotherium (fig. 243) itself, agree with the existing Tapirs of South America and the Indian Archipelago in having the fore-feet four-toed, whilst the hind-feet are three-toed; and a further point of resemblance is found in the fact (as shown by the form of the nasal bones) that the nose was long and flexible, forming a short movable proboscis or trunk, by means of which the animal was enabled to browse on shrubs or trees. They differ, however, from the Tapirs, not only in the apparent presence of a long tail, but also in the possession of a pair of very large "horn-cores," carried upon the nasal bones, indicating that the animal possessed horns of a similar structure to those of the "Hollow-horned" Ruminants (e.g., Sheep and Oxen). Brontotherium gigas is said to be nearly as large as an Elephant, whilst B. Ingens appears to have attained dimensions still more gigantic. The well-known genus Titanotherium of the American Miocene would also appear to belong to this group.

Fig. 243
Fig. 243.—Skull of Brontotherium ingens. Miocene Tertiary, United States. (After Marsh.)

The family of the Horses (Equidœ) appears under various forms in the Miocene, but the most important and best known of these is Hipparion. In this genus the general conformation of the skeleton is extremely similar to that of the existing Horses, and the external appearance of the animal must have been very much the same. The foot of Hipparion, Page 317 however, as has been previously mentioned, differed from that of the Horse in the fact that whilst both possess the middle toe greatly developed and enclosed in a broad hoof, the former, in addition, possessed two lateral toes, which were sufficiently developed to carry hoofs, but were so far rudimentary that they hung idly by the side of the central toe without touching the ground (see fig. 230). In the Horse, on the other hand, these lateral toes, though present, are not only functionally useless, but are concealed beneath the skin. Remains of the Hipparion have been found in various regions in Europe and in India; and from the immense quantities of their bones found in certain localities, it may be safely inferred that these Middle Tertiary ancestors of the Horses lived, like their modern representatives, in great herds, and in open grassy plains or prairies.

Amongst the Even-toed or Artiodactyle Ungulates, we for the first time meet with examples of the Hippopotamus, with its four-toed feet, its massive body, and huge tusk-like lower canine teeth. The Miocene deposits of Europe have not hitherto yielded any remains of Hippopotamus; but several species have been detected in the Upper Miocene of the Siwâlik Hills by Dr Falconer and Sir Proby Cautley. These ancient Indian forms, however, differ from the existing Hippopotamus amphibius of Africa in the fact that they possessed six incisor teeth in each jaw (fig. 244), whereas the latter has only four.

Amongst the other Even-toed Ungulates, the family of the Pigs (Suida) is represented by true Swine (Sus Erymanthius), Peccaries (Dicotyles antiquus), and by forms which, like the great Elotherium of the American Miocene, have no representative at the present day. The Upper Miocene of India has yielded examples of the Camels. Small Musk-deer (Amphitragulus and Dremotherium) are known to have existed in France and Greece; and the true Deer (Cervidœ), with their solid bony antlers, appear for the first time here in the person of species allied to the living Stags (Cervus), accompanied by the extinct genus Dorcatherium. The Giraffes (Camelopardalidœ), now confined to Africa, are known to have lived in India and Greece; and the allied Helladotherium, in some respects intermediate between the Giraffes and the Antelopes, ranged over Southern Europe from Attica to France. The great group of the "Hollow-horned" Ruminants (Cavicornia), lastly, came into existence in the Miocene period; and though the typical families of the Sheep and Oxen are apparently wanting, there are true Antelopes, together with forms which, if systematically referable to the Antilopidœ, nevertheless are more or less clearly transitional between this and the family of the Sheep Page 318 and Goats. Thus the Palœoreas of the Upper Miocene of Greece may be regarded as a genuine Antelope; but the Tragoceras of the same deposit is intermediate in its characters between the typical Antelopes and the Goats.

Fig. 244
Fig. 244.—a, Skull of Hippopotamus Sivalensis, viewed from below, one-eighth of the natural size; b, Molar tooth of the same, showing the surface of the crown, one-half of the natural size: c, Front of the lower jaw of the same, showing the six incisors and the tusk-like canines, one-eighth of the natural size. Upper Miocene, Siwâlik Hills; (After Falconer and Cautley.)

Perhaps the most remarkable, however, of these Miocene Ruminants is the Sivatherium giganteum (fig. 245) of the Siwâlik Hills, in India. In this extraordinary animal there were two pairs of horns, supported by bony "horn-cores," so that there can be no hesitation in referring Sivatherium to the Cavicorn Ruminants. If all these horns had been simple, there would have been no difficulty in considering Sivatherium as simply a gigantic four-horned Antelope, essentially similar to the living Antilope (Tetraceros) quadricornis of India. The hinder pair of horns, however, is not only much larger than the front pair, but each possesses two branches or snags—a peculiarity not to be paralleled amongst any existing Antelope, save the abnormal Prongbuck (Antilocapra) of North America. Dr Murie, however, in an admirable memoir on the structure and relationships Page 319 of Sivatherium, has drawn attention to the fact that the Prongbuck sheds the sheath of its horns annually, and has suggested that this may also have been the case with the extinct form. This conjecture is rendered probable, amongst other reasons, by the fact that no traces of a horny sheath surrounding the horn-cores of the Indian fossil have been as yet detected. Upon the whole, therefore, we may regard the elephantine Sivatherium as being most nearly allied to the Prongbuck of Western America, and thus as belonging to the family of the Antelopes.

Fig. 245
Fig. 245.—Skull of Sivatherium giganteum, reduced in size. Miocene, India. (After Murie.)

It is to the Miocene period, again, to which we must refer the first appearance of the important order of the Elephants and their allies (Proboscideans), all of which are characterised by their elongated trunk-like noses, the possession of five toes to the foot, the absence of canine teeth, the development of two or more of the incisor teeth into long tusks, and the adaptation of the molar teeth to a vegetable diet. Only three generic groups of this order are known-namely, the extinct Deinotherium, the equally extinct Mastodons, and the Elephants; and all these three types are known to have been in existence as Page 320 early as the Miocene period, the first of them being exclusively confined to deposits of this age. Of the three, the genus Deinotherium is much the most abnormal in its characters; so much so, that good authorities regard it as really being one of the Sea-cows (Sirenia)—though this view has been rendered untenable by the discovery of limb-bones which can hardly belong to any other animal, and which are distinctly Proboscidean in type. The most celebrated skull of the Deinothere (fig. 246) is one Fig. 246
Fig. 246.—Skull of Deinotherium giganteum, greatly reduced. From the Upper Micene of Germany.
which was exhumed from the Upper Miocene deposits of Epplesheim, in Hesse-Darmstadt, in the year 1836. This skull was four and a half feet in length, and indicated an animal larger than any existing species of Elephant. The upper jaw is destitute of incisor or canine teeth, but is furnished on each side with five molars, which are opposed to a corresponding series of grinding teeth in the lower jaw. No canines are present in the lower jaw; but the front portion of the jaw is abruptly bent downwards, and carries two huge tusk-like incisor teeth, which are curved downwards and backwards, and the use of which is rather problematical. Not only does the Deinothere occur in Europe, but remains belonging to this genus have also been detected in the Siwâlik Hills, in India.

The true Elephants (Elephas) do not appear to have existed during the Miocene period in Europe, but several species have been detected in the Upper Miocene deposits of the Siwâlik Hills, in India. The fossil forms, though in all cases specifically, and in some cases even sub-generically, distinct, agree with those now in existence in the general conformation of their skeleton, and in the principal characters of their dentition. In all, the canine teeth are wanting in both jaws; and there are no incisor teeth in the lower jaw, whilst there are two incisors in the front of the upper jaw, which are developed into two huge "tusks." There are six molar teeth on each side of both the upper and lower jaw, but only one, or at most a part of two, is in actual use at any given time; and as this becomes worn away, it is pushed forward and replaced by its successor behind it. The molars are of Page 321 very large size, and are each composed of a number of transverse plates of enamel united together by ivory; and by the process of mastication, the teeth become worn down to a flat surface, crossed by the enamel-ridges in varying patterns; These patterns are different in the different species of Elephants, though constant for each; and they constitute one of the most readily available means of separating the fossil forms from one another. Of the seven Miocene Elephants of India, as judged by the characters of the molar, teeth, two are allied to the existing Indian Elephant, one is related to the living African Elephant, and the remaining four are in some respects intermediate between the true Elephants and the Mastodons.

Fig. 247
Fig. 247.—A, Molar tooth of Elephas planifrons, one-third of the natural size, showing the grinding surface—from the Upper Miocene of India; B, Profile view of the last upper molar of Mastodon Sivalensis, one-third of the natural size—from the Upper Miocene of India. (After Falconer.)

The Mastodons, lastly, though quite elephantine in their Page 322 general characters, possess molar teeth which have their crowns furnished with conical eminences or tubercles placed in pairs (fig. 247, B), instead of having the approximately flat surface characteristic of the grinders of the Elephants. As in the latter, there are two upper incisor teeth, which grow permanently during the life of the animal, and which constitute great tusks; but the Mastodons, in addition, often possess two lower incisors, which in some cases likewise grow into small tusks. Three species of Mastodon are known to occur in the Upper Miocene of the Siwâlik Hills of India; and the Miocene deposits of the European area have yielded the remains of four species, of which the best known are the M. Longirostris and the M. Angustidens.

Whilst herbivorous Quadrupeds, as we have seen, were extremely abundant during Miocene times, and often attained gigantic dimensions, Beasts of Prey (Carnivora) were by no means wanting, most of the principal existing families of the order being represented in deposits of this age. Thus, we find aquatic Carnivores belonging to both the living groups of the Seals and Walruses; true Bears are wanting, but their place is filled by the closely-allied genus Amphicyon, of which various species are known; Weasels and Otters were not unknown, and the Hyœnictis and Iditherium of the Upper Miocene of Greece are apparently intermediate between the Civet-cats and the Hyænas; whilst the great Cats of subsequent periods are more than adequately represented by the huge "Sabre-toothed Tiger" (Machairodus), with its immense trenchant and serrated canine teeth.

Amongst the Rodent Mammals, the Miocene rocks have yielded remains of Rabbits, Porcupines (such as the Hystrix primigenius of Greece), Beavers, Mice, Jerboas, Squirrels, and Marmots. All the principal living groups of this order were therefore differentiated in Middle Tertiary times.

The Cheiroptera are represented by small insect-eating Bats; and the order of the Insectivorous Mammals is represented by Moles, Shrew-mice, and Hedgehogs.

Fig. 248
Fig. 248.—Lower jaw of Pliopithcus antiquus. Upper Miocene, France.

Lastly, the Monkeys (Quadrumana) appear to have existed during the Miocene period under a variety of forms, remains of these animals having been found both in Europe and in India; but no member of this order has as yet been detected in the Miocene Tertiary of the North American continent. Amongst the Old World Monkeys of the Miocene, the two most interesting are the Pliopithecus and Dryopithecus of France. The former of these (fig. 248) is supposed to have been most nearly related to the living Semnopitheci of Southern Asia, in Page 323 which case it must have possessed a long tail. The Mesopithecus of the Upper Miocene of Greece is also one of the lower Monkeys as it is most closely allied to the existing Macaques. On the other hand, the Dryopithecus of the French Upper Miocene is referable to the group of the "Anthropoid Apes," and is most nearly related to the Gibbons of the present day, in which the tail is rudimentary and there are no cheek-pouches. Dryopithecus was, also, of large size, equalling Man in stature, and apparently living amongst the trees and feeding upon fruits.

 



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