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 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 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 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
(_Chamoerops_, 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
_Lauraceoe_, many species of _Proteaccoe_ (_Banksia, Grevillea_,
&c.), several species of Sarsaparilla (_Smilax_), Palms, Cypresses,
&c.
[Illustration: Fig. 234.--Miocene Palms A, _Chamoerops Helvetica_;
B, _Sabal major_. Lower Miocene of Switzerland and France.]
[Illustration: Fig. 235.--_Platanus aceroides_, an Upper Miocene
Plane-tree. a, Leaf; b, The core of a bundle of fruits; c,
A single fruit.]
[Illustration: Fig. 236.--_Cinnamomum polymorphum_. a, Leaf;
b, Flower. Upper Miocene.]
In Britain, the Lower Miocene strata of Bovey Tracy have yielded
remains of Ferns, Vines, Fig, Cinnamon, _Proteaccoe_, &c., along
with numerous Conifers. The most abundant of these last is a
gigantic pine--the _Sequoia Couttsioe_--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.
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 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 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_, &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.
[Illustration: 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_), Grasshoppers (_Orthoptera_), and Butterflies
(_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.
[Illustration: 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_.)
[Illustration: 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 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 _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.
[Illustration: Fig. 240.--Tooth of _Oxyrhina xiphodon_. Miocene.]
[Illustration: Fig. 241.--Tooth of _Carcharodon productus_. Miocene.]
The remains of _Reptiles_ are far from uncommon in the Miocene
rocks, consisting principally 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 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.
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 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.
[Illustration: 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 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.
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 _Titanotherium_ of the American Miocene would
also appear to belong to this group.
[Illustration: 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
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.
[Illustration: 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.)]
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 _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 _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 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 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.
[Illustration: 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 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.
[Illustration: 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 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
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.
[Illustration: 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 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 _Hyoenictis_
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.
[Illustration: 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.