The Ancient Life History of the Earth Part 24

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. lat.i.tude. In Miocene times, however, the Limes, Cypresses, and Plane-trees reach the 79th degree of lat.i.tude, 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 sh.e.l.ls of _Foraminifera_ are extremely abundant in some beds, the genera being in many cases such as now flourish abundantly in our seas.

The princ.i.p.al forms belong to the genera _Textularia_ (fig. 237), _Robulina, Glandulina, Polystomella, Amplistegina_, &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.

[Ill.u.s.tration: Fig. 237.--_Textularia Meyeriana_, greatly enlarged.

Miocene Tertiary.]

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_), Gra.s.shoppers (_Orthoptera_), and b.u.t.terflies (_Lepidoptera_). 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.

[Ill.u.s.tration: 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 Sh.e.l.l-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 sh.e.l.ls. Thus we meet with many Cones, Volutes, Cowries, Olive-sh.e.l.ls, Fig-sh.e.l.ls, 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 sh.e.l.ls of Winged-Snails (_Pteropods_), belonging to such existing genera as _Hyalea_ (fig. 239) and _Cleodora_. Lastly, the _Cephalopods_ are represented both by the chambered sh.e.l.ls of _Nautili_ and by the internal skeletons of Cuttle-fishes (_Spirulirostra_.)

[Ill.u.s.tration: Fig. 239.--Different views of the sh.e.l.l 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 both the Old and New Worlds; and some of the species attain gigantic dimensions.

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 OEningen, 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 _h.o.m.o 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.

[Ill.u.s.tration: Fig. 240.--Tooth of _Oxyrhina xiphodon_. Miocene.]

[Ill.u.s.tration: Fig. 241.--Tooth of _Carcharodon productus_. Miocene.]

The remains of _Reptiles_ are far from uncommon in the Miocene rocks, consisting princ.i.p.ally of Chelonians and Crocodilians.

The Land-tortoises (_Testudinidoe_) 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 Siwalik 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 palaeontologist 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 palaeontological interest.

The _Mammals_ of the Miocene are very numerous, and only the more important forms can be here alluded to. Amongst the _Marsupials_, the Old World still continued to possess species 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 Pikerme, 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.

[Ill.u.s.tration: Fig. 242.--Front portion of the skeleton of _Andrias Scheuchzeri_, a Giant Salamander from the Miocene Tertiary of Oeningen, in Switzerland. Reduced in size.]

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 (_Baloena_), 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 _Rhinoceridoe_ comprising only the existing Rhinoceroses. In India in the Upper Miocene beds of the Siwalik 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.

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 _Brontotheridoe_. 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 _t.i.tanotherium_ of the American Miocene would also appear to belong to this group.

[Ill.u.s.tration: Fig. 243.--Skull of _Brontotherium ingens_. Miocene Tertiary, United States. (After Marsh.)]

The family of the Horses (_Equidoe_) 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_, 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 quant.i.ties 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 gra.s.sy 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 ma.s.sive 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 Siwalik 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.

[Ill.u.s.tration: 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, Siwalik Hills; (After Falconer and Cautley.)]

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 (_Cervidoe_), 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 (_Camelopardalidoe_), now confined to Africa, are known to have lived in India and Greece; and the allied _h.e.l.ladotherium_, 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 _Antilopidoe_, nevertheless are more or less clearly transitional between this and the family of the Sheep and Goats. Thus the _Paloeoreas_ 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. Perhaps the most remarkable, however, of these Miocene Ruminants is the _Sivatherium giganteum_ (fig.

245) of the Siwalik 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 p.r.o.ngbuck (_Antilocapra_) of North America.

Dr Murie, however, in an admirable memoir on the structure and relationships of _Sivatherium_, has drawn attention to the fact that the p.r.o.ngbuck 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 h.o.r.n.y 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 p.r.o.ngbuck of Western America, and thus as belonging to the family of the Antelopes.

[Ill.u.s.tration: 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 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 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 dest.i.tute 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 Siwalik Hills, in India.

[Ill.u.s.tration: Fig. 246.--Skull of _Deinotherium giganteum_, greatly reduced. From the Upper Micene of Germany.]

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 Siwalik 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 princ.i.p.al characters of their dent.i.tion. 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 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 const.i.tute 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.

[Ill.u.s.tration: 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 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 const.i.tute 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 Siwalik 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 princ.i.p.al 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 _Hyoenictis_ and _Iditherium_ of the Upper Miocene of Greece are apparently intermediate between the Civet-cats and the Hyaenas; 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 princ.i.p.al 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.

[Ill.u.s.tration: 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 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.

CHAPTER XX.

THE PLIOCENE PERIOD.

The highest division of the Tertiary deposits is termed the _Pliocene_ formation, in accordance with the cla.s.sification proposed by Sir Charles Lyell. The Pliocene formations contain from 40 to 95 per cent of existing species of _Mollusca_, the remainders belonging to extinct species. They are divided by Sir Charles Lyell into two divisions, the Older Pliocene and Newer Pliocene.

The Pliocene deposits of Britain occur in Suffolk, and are known by the name of "Crags," this being a local term used for certain sh.e.l.ly sands, which are employed in agriculture. Two of these Crags are referable to the Older Pliocene, viz., the White and Red Crags,--and one belongs to the Newer Pliocene, viz., the Norwich Crag.

The _White or Coralline Crag_ of Suffolk is the oldest of the Pliocene deposits of Britain, and is an exceedingly local formation, occurring in but a single small area, and having a maximum thickness of not more than 50 feet. It consists of soft sands, with occasional intercalations of flaggy limestone. Though of small extent and thickness, the Coralline Crag is of importance from the number of fossils which it contains. The name "Coralline" is a misnomer; since there are few true Corals, and the so-called "Corals" of the formation are really _Polyzoa_, often of very singular forms.

The sh.e.l.ls of the Coralline Crag are mostly such as inhabit the seas of temperate regions; but there occur some forms usually looked upon as indicating a warm climate.

The _Upper_ or _Red Crag_ of Suffolk--like the Coralline Crag--has a limited geographical extent and a small thickness, rarely exceeding 40 feet. It consists of quartzose sands, usually deep red or brown in colour, and charged with numerous fossils.

Altogether more than 200 species of sh.e.l.ls are known from the Red Crag, of which 60 per cent are referable to existing species.