LIFE OF THE EOCENE PERIOD.
The fossils of the Eocene deposits are so numerous that nothing more can be attempted here than to give a brief and general sketch of the life of the period, special attention being directed to some of the more prominent and interesting types, amongst which—as throughout the Tertiary series—the Mammals hold the first place. It is not uncommon, indeed, to speak of the Tertiary period as a whole under the name of the "Age of Mammals," a title at least as well deserved as that of "Age of Reptiles" applied to the Mesozoic, or "Age of Molluscs" applied to the Palæozoic epoch.
As regards the plants of the Eocene, the chief point to
be noticed is, that the conditions which had already set in with
the commencement of the Upper Cretaceous, are here continued,
and still further enforced. The
Cycads of the Secondary period, if they have not totally
disappeared, are exceedingly rare; and the Conifers,
losing the predominance which they enjoyed in the Mesozoic, are
now relegated to a subordinate though well-defined place in the
terrestrial vegetation. The great majority of the Eocene plants
are referable to the groups of the Angiospermous Exogens and the
Monocotyledons; and the vegetation of the period, upon the whole,
approximates closely to that now existing upon the earth. The
plants of the European Eocene are, however, in the main most
closely allied to forms which are now characteristic of tropical
or sub-tropical regions. Thus, in the London Clay are found
numerous fruits of Palms (Napdites, fig. 213), along with
various other plants,
Fig. 213.—Napadites ellipticus, the fruit of a fossil
Palm. London Clay, Isle of Sheppey.
most of which indicate a warm climate as prevailing in the south
of England at the commencement of the Eocene period. In the Eocene
strata of North America occur numerous plants belonging to existing
types—such as Palms, Conifers, the Magnolia, Cinnamon, Fig.
Dog-wood, Maple, Hickory, Poplar, Plane, &c. Taken as a whole,
the Eocene flora of North America is nearly related to that of
the Miocene strata of Europe, as well as to that now existing
in the American area. We conclude, therefore, that "the forests
of the American Eocene resembled those of the European Miocene,
and even of modern America" (Dana).
As regards the animals of the Eocene period, the
Protozoans are represented by numerous Foraminifera,
which reach here their maximum of development, both as regards
the size of individuals and the number of generic types. Many
of the Eocene Foraminifers are of small size; but even these not
uncommonly form whole rock-masses. Thus, the so-called "Miliolite
Limestone" of the Paris basin, largely used as a building-stone,
is almost wholly composed of the shells of a small species of
Miliola. The most remarkable, however, of the many members
of this group of animals which flourished in Eocene times, are the
"Nummulites" (Nummulina), so called from their resemblance
in shape to coins (Lat. nummus, a coin). The Nummulites are
amongst the largest of all known Foraminifera, sometimes
attaining a size of three inches in circumference; and their
internal structure is very complex (fig. 214).
Many species are
known, and they are particularly characteristic of the Middle and
Upper of these periods—their place being sometimes taken
Fig. 214.—Nummulina lœvigata. Middle Eocene.
by Orbitoides, a form very similar to the Nummulite in
external appearance, but differing in its internal details. In
the Middle Eocene, the remains of Nummulites are found in vast
numbers in a very widely-spread and easily-recognised formation
known as the "Nummulitic Limestone" (fig. 10). According to Sir
Charles Lyell, "the Nummulitic Limestone of the Swiss Alps rises
to more than 10,000 feet above the level of the sea, and attains
here and in other mountain-chains a thickness of several thousand
feet. It may be said to play a far more conspicuous part than
any other Tertiary group in the solid framework of the earth's
crust, whether in Europe, Asia, or Africa. It occurs in Algeria
and Morocco, and has been traced from Egypt, where it was largely
quarried of old for the building of the Pyramids, into Asia Minor,
and across Persia by Bagdad to the mouths of the Indus. It has
been observed not only in Cutch, but in the mountain-ranges which
separate Scinde from Persia, and which form the passes leading
to Cabul; and it has been followed still further eastward into
India, as far as Eastern Bengal and the frontiers of China." The
shells of Nummulites have been found at an elevation of 16,500
feet above the level of the sea in Western Thibet; and the
distinguished and philosophical geologist just quoted, further
remarks, that "when we have once arrived at the conviction that
the Nummulitic formation occupies a middle and upper place in the
Eocene series, we are struck with the comparatively modern date to
which some of the greatest revolutions in the physical geography
of Europe, Asia, and Northern Africa must be referred. All the
mountain-chains—such as the Alps, Pyrenees, Carpathians, and
Himalayas—into the composition of whose central and loftiest
parts the Nummulitic
strata enter bodily, could have had no existence till after the
Middle Eocene period. During that period, the sea prevailed where
these chains now rise; for Nummulites and their accompanying
Testacea were unquestionably inhabitants of salt water."
The Cœlenterates of the Eocene are represented
principally by Corals, mostly of types identical with or
nearly allied to those now in existence. Perhaps the most
characteristic group of these is that of the Turbinolidœ,
comprising a number of simple "cup-corals," which probably lived in
moderately deep water. One of the forms belonging to this family is
here figured (fig. 215). Besides true Corals, the Eocene deposits have
Fig. 215.—Turbinolia sulcata, viewed from one side,
and from above. Eocene.
yielded the remains of the "Sea-pens" (Pennatulidœ) and
the branched skeletons of the "Sea-shrubs" (Gorgontidœ).
The Echinoderms are represented principally by Sea-urchins, and demand nothing more than mention. It is to be observed, however, that the great group of the Sea-lilies (Crinoids) is now verging on extinction, and is but very feebly represented.
Amongst the Mollusca, the Polyzoans and
Brachiopods also require no special mention, beyond the
fact that the latter are greatly reduced in numbers, and belong
principally to the existing genera Terebratula and
Rhynchonella. The Bivalves (Lamellibranchs) and
the Univalves (Gasteropods) are exceedingly numerous, and
almost all the principal existing genera are now represented;
though less than five percent of the Eocene species are
identical with those now living. It is difficult to make any
selection from the many Bivalves which are known in deposits of
this age; but species of Cardita, Crassatella, Leda, Cyrena,
Mactra, Cardium, Psammobia, &c., may be mentioned as very
characteristic. The Caradita planicosta here figured (fig.
216) is not only very abundant in the Middle Eocene, but is very
widely distributed, ranging from Europe to the Pacific coast of
North America. The Univalves of the Eocene are extremely
numerous, and generally beautifully preserved. The majority of them
belong to that great section of the Gasteropods in which the
mouth of the shell is notched or produced into
a canal (when the
shell is said to be "siphonostomatous")—this section including
the carnivorous and most highly-organized groups of the class. Not
Fig. 216.—Cardita planicosta. Middle Eocene.
only is this the case, but a large number of the Eocene Univalves
belong to types which now attain their maximum of development in the
warmer regions of the globe. Thus we find numerous species of Cones
(Conus), Volutes (Voluta), Cowries (Cyprœa,
Fig. 217.—Typhis tubifer, a "siphonostomatous" Univalve.
Eocene.
Fig. 218.—Cyprœa elegans. Eocene.
fig. 218), Olives and Rice-shells (Oliva), Mitre-shells
(Mitra), Trumpet-shells (Triton), Auger-shells
(Terebra), and Fig-shells (Pyrula). Along with these
are many forms of Pleurotoma, Rostellaria, Spindle-shells
(Fusus), Dog-whelks (Nassa), Murices, and
many round-mouthed ("holostomatous") species, belonging to such
genera as Turritella, Nerita, Natica, Scalaria, &c.
The genus Cerithium (fig. 219), most of the living forms
of which are found in warm regions, inhabiting fresh or brackish
waters, undergoes a vast development in the Eocene period, where
it is represented by an immense number of specific forms, some
of which attain very large dimensions. In the Eocene strata of
Fig. 219.—Cerithium hexagonum. Eocene.
the Paris basin alone, nearly one hundred and fifty species of
this genus have been detected. The more strictly fresh-water
deposits of the Eocene period have also yielded numerous remains
of Univalves such as are now proper to rivers and lakes, together
with the shells of true Land-snails. Amongst these may be mentioned
numerous species of Limnœa (fig. 220), Physa
(fig. 221), Melania, Paludina, Planorbis, Helix, Bulimus,
and Cyclostoma (fig. 222).
With regard to the Cephalopods, the chief point to be
noticed is, that all the beautiful and complex forms which peculiarly
characterised the Cretaceous period have here disappeared. We no
longer meet with a single example of the Turrilite, the Baculite,
the Hamite, the Scaphite, or the Ammonite. The only exception
to this statement is the occurrence of one species of Ammonite
Fig. 220.—Limnœa pyramidalis. Eocene.
Fig. 221.—Physa columnaris. Eocene.
Fig. 222.—Cyclostoma Arnoudii. Eocene.
in the so-called "Lignitic Formation" of North America; but the
beds containing this may possibly be rather referable to the
Cretaceous—and this exception does not affect the fact
that the Ammonitidœ, as a family, had become
extinct before the Eocene strata were deposited. The ancient
genus Nautilus still survives, the sole representative
of the once mighty order of the Tetrabranchiate Cephalopods.
In the order of the Dibranchiates, we have a like
phenomenon to observe in the total extinction of the great
family of the "Belemnites." No form referable to this group
has hitherto been found in any Tertiary stratum; but the
internal skeletons of Cuttle-fishes (such as Belosepia)
are not unknown.
Remains of Fishes are very abundant in strata of Eocene
age, especially in certain localities. The most famous depot for
the fossil fishes of this period is the limestone of Monte Bolca,
near Verona, which is interstratified with beds of volcanic ashes,
the whole being referable to the Middle Eocene. The fishes here
seem to have been suddenly destroyed by a volcanic eruption,
and are found in vast numbers. Agassiz has described over one
hundred and thirty species of Fishes from this locality, belonging
to seventy-seven genera. All the species are extinct; but
about one-half of the genera are represented by living
forms. The great majority of the Eocene Fishes belong to the
Fig. 223.—Rhombus minimus, a small fossil Turbot from
the Eocene Tertiary, Monte Bolca.
order of the "Bony Fishes" (Teleosteans), so that in the
main the forms of Fishes characterising the Eocene are similar
to those which predominate in existing seas. In addition to the
above, a few Ganoids and a large number of Placoids
are known to occur in the Eocene rocks. Amongst the latter are
found numerous teeth of true Sharks, such as Otodus (fig.
224) and Carcharodon. The pointed and serrated teeth of the
latter sometimes attain a length of over half a foot, indicating
that these predaceous fishes attained gigantic dimensions; and it
is interesting to note that teeth, in external appearance very
similar to those of the early Tertiary genus Carcharodon,
have been dredged from great depths during the recent expedition
of the Challenger. There also occur not uncommonly the flattened
teeth of Rays (fig. 225), consisting of flat bony pieces placed
close together, and forming "a kind of mosaic pavement on both
the upper and lower jaws" (Owen).
In the class of the Reptiles, the disappearance of the
Fig. 224.—Tooth of Otodus obliquus. Eocene.
Fig. 225.—Flattened dental plates of a Ray (Myliobatis
Edwardsii). Eocene.
characteristic Mesozoic types is as marked a phenomenon as the
introduction of new forms. The Ichthyosaurs, the Plesiosaurs,
the Pterosaurs, and the Mosasaurs of the Mesozoic, find no
representatives in the Eocene Tertiary; and the same is true
of the Deinosaurs, if we except a few remains from the
doubtfully-situated "Lignitic formation" of the United States,
On the other hand, all the modern orders of Reptiles are known to
have existed during the Eocene period. The Chelonians are
represented by true marine Turtles, by "Terrapins"
(Emydidœ), and by "Soft Tortoises"
(Trionycidœ). The order of the Snakes and Serpents
(Ophidia) makes its appearance here, for the first time
under several forms—all of which, however, are referable to
the non-venomous group of the "Constricting Serpents"
(Boidœ). The oldest of these is the Palœophis
toliapicus of the London Clay of Sheppey, first made known to
science by the researches of Professor Owen. The nearly-allied
Palœophis typhœus of the Eocene beds of
Bracklesham appears to have been a Boa-constrictor-like Snake of
about twenty feet in length. Similar Python-like Snakes
(Palœophis, Dinophis, &c.) have been described
from the Eocene deposits of the United States. True Lizards
(Lacertilians) are found in some abundance in the Eocene
deposits,—some being small terrestrial forms, like the
common European lizards of the present day; whilst others equal or
exceed the living Monitors in size. Lastly, the modern order of
the Crocodilia is largely represented in Eocene times, by
species belonging to all the existing genera, together with
others referable to extinct types. As pointed out by Owen, it
is an interesting fact that in the Eocene rocks of the south-west
of England, there occur fossil remains of all the three living
types of Crocodilians—namely, the Gavials, the true
Crocodiles, and the Alligators (fig. 226)—though at the
Fig. 226.—Upper jaw of Alligator. Eocene Tertiary, Isle of
Wight.
present day these forms are all geographically restricted in
their range, and are never associated together.
Almost all the existing orders of Birds, if not all, are
represented in the Eocene deposits by remains often very closely
allied to existing types. Thus, amongst the Swimming Birds
(Natatores) we find examples of forms allied to the living
Pelicans and Mergansers; amongst the Waders (Grallatores)
we have birds resembling the Ibis (the Numenius gypsorum of
the Paris basin); amongst the Running Birds (Cursores) we
meet with the great Gastornis Parisiensis, which equalled
the African Ostrich in height, and the still more gigantic
Dasornis Londinensis; remains of a Partridge represent
the Scratching Birds (Rasores); the American Eocene has
yielded the bones of one of the Climbing Birds (Scansores),
apparently referable to the Woodpeckers; the Protornis
Glarisiensis of the Eocene Schists of Glaris is the oldest
known example of the Perching Birds (Insessores); and
the Birds of Prey (Raptores) are represented by Vultures,
Owls, and Hawks. The toothed Birds of the Upper Cretaceous are no
longer known to exist; but Professor Owen has recently described
from the London Clay the skull of a very remarkable Bird, in
which there is, at any rate, an approximation to the structure of
Ichthyornis and Hesperornis. The bird in question
has been named the Odontopteryx totiapicus, its generic
title being derived from the very remarkable characters of its
jaws. In this singular form (fig. 227) the margins of both jaws
are furnished with tooth-like denticulations, which differ from
true teeth in being actually portions of the bony substance of
Fig. 227.—Skull of Odontopteryx toliapicus restored.
(After Owen.)
the jaw itself, with which they are continuous, and which were
probably encased by extensions of the horny sheath of the bill.
These tooth-like processes are of two sizes, the larger ones
being comparable to canines; and they are all directed forwards,
and have a triangular or compressed conical form. From a careful
consideration of all the discovered remains of this bird, Professor
Owen concludes that "Odontopteryx was a warm-blooded
feathered biped, with wings; and further, that it was web-footed
and a fish-eater, and that in the catching of its slippery prey
it was assisted by this Pterosauroid armature of its jaws." Upon
the whole, Odontopteryx would appear to be most nearly
related to the family of the Geese (Anserinœ) or Ducks
(Anatidœ); but the extension of the bony substance of
the jaws into tooth-like processes is an entirely unique character,
in which it stands quite alone.
The known Mammals of the Mesozoic period, as we have seen, are all of small size; and with one not unequivocal exception, they appear to be referable to the order of the Pouched Quadrupeds (Marsupials), almost the lowest group of the whole class of the Mammalia. In the Eocene rocks, on the other hand, numerous remains of Quadrupeds have been brought to light, representing most of the great Mammalian orders now in existence upon the earth, and in many cases indicating animals of very considerable dimensions. We are, in fact, in a position to assert that the majority of the great groups of Quadrupeds with which we are familiar at the present day were already in existence in the Eocene period, and that their ancient root-stocks were even in this early time separated by most of the fundamental differences of structure which distinguish their living representatives. At the same time, there are some amongst the Eocene quadrupeds which have a "generalised" character, and which may be regarded as structural types standing midway between groups now sharply separated from one another.
The order of the Marsupials—including the existing Kangaroos, Wombats, Opossums, Phalangers, &c.—is poorly represented in deposits of Eocene age. The most celebrated example of this group is the Didelphys gypsorum of the Gypseous beds of Montmartre, near Paris, an Opossum very nearly allied to the living Opossums of North and South America.
No member of the Edenates (Sloths, Ant-eaters, and Armadillos)
has hitherto been detected in any Eocene deposit. The aquatic
order of the Sirenians (Dugongs and Manatees), with their
fish-like bodies and tails, paddle-shaped forelimbs, and wholly
deficient hind-limbs, are represented in strata of this age by
remains of the ancient "Sea-Cows," to which the name of
Halitherium has been applied. Nearly allied to the preceding
is the likewise aquatic order of the Whales and Dolphins
(Cetaceans), in which the body is also fish-like, the
hind-limbs are wanting, the fore-limbs are converted into powerful
"flippers" or swimming-paddles, and the terminal extremity of
the body is furnished with a horizontal, tail-fin. Many existing
Cetaceans (such as the Whalebone Whales) have no true teeth;
but others (Dolphins, Porpoises, Sperm Whales) possess simple
Fig. 228.—Zeuglodon cetoides. A, Molar
tooth of the natural size; B, Vertebra, reduced in size. From the
Middle Eocene of the United States. (After Lyell.)
conical teeth. In strata of Eocene age, however, we find a singular
group of Whales, constituting the genus Zeuglodon (fig. 228),
in which the teeth differed from those of all
existing forms in being of two kinds,—the front ones being
conical incisors, whilst the back teeth or molars have serrated
triangular crowns, and are inserted in the jaw by two roots. Each
molar (fig. 228, A) looks as if it were composed of two separate
teeth united on one side by their crowns; and it is this peculiarity
which is expressed by the generic name (Gr. zeugle, a yoke;
odous, tooth). The best-known species of the genus is
the Zeuglodon cetoides of Owen, which attained a length
of seventy feet. Remains of these gigantic Whales are very common
in the "Jackson Beds" of the Southern United States. So common
are they that, according to Dana, "the large vertebræ, some of
them a foot and a half long and a foot in diameter, were formerly
so abundant over the country, in Alabama, that they were used
for making walls, or were burned to rid the fields of them."
The great and important order of the Hoofed Quadrupeds
(Ungulata) is represented in the Eocene by examples of both
of its two principal sections—namely, those with an uneven
number of toes (one or three) on the foot (Perissodactyle
Ungulates), and those with an even number of toes (two or four)
to each foot (Artiodactyle Ungulates). Amongst the Odd-toed
Ungulates, the living family of the Tapirs (Tapirdœ) is
represented by the genus Coryphodon of Owen. Nearly related
to the preceding are the species of Palœotherium,
which have a historical interest as being amongst the first of the
Tertiary Mammals investigated by the illustrious Cuvier. Several
species of Palœothere are known, varying greatly in
size, the smallest being little bigger than a hare, whilst the
largest must have equalled a good-sized horse in its dimensions. The
species of Palœotherium appear to have agreed with the
existing Tapirs in possessing a lengthened and flexible nose, which
formed a short proboscis or trunk (fig. 229), suitable as an
instrument for stripping off the foliage of trees—the characters
of the molar teeth showing them to have been strictly herbivorous
in their habits. They differ, however, from the Tapirs, amongst
other characters, in the fact that both the fore and the hind feet
possessed three toes each; whereas in the latter there are four
toes on each fore-foot, and the hind-feet alone are three-toed. The
remains of Palœotheria have been found in such abundance
in certain localities as to show that these animals roamed in great
herds over the fertile plains of France and the south of England
during the later portion of the Eocene period. The accompanying
illustration (fig. 229) represents the notion which the great
Cuvier was induced by
his researches to form as to the outward
appearance of Palœotherium magnum. Recent discoveries,
Fig. 229.—Outline of Palœotherium magnum,
restored. Upper Eocene, Europe. (After Cuvier.)
however, have rendered it probable that this restoration is in some
important respects inaccurate. Instead of being bulky, massive,
and more or less resembling the living Tapirs in form, it would
rather appear that Palœotherium magnum was in reality a
slender, graceful, and long-necked animal, more closely resembling
in general figure a Llama, or certain of the Antelopes.
The singular genus Anchitherium forms a kind of transition
between the Palœotheria and the true Horses
(Equidœ). The Horse (fig. 230, D) possesses but one
fully-developed toe to each foot, this being terminated by a single
broad hoof, and representing the middle toe—the
third of the typical five-fingered or five-toed limb of
Quadrupeds in general. In addition, however, to this fully-developed
toe, each foot in the horse carries two rudimentary toes which are
concealed beneath the skin, and are known as the "splint-bones."
These are respectively the second and fourth toes,
in an aborted condition; and the first and fifth toes are wholly
wanting. In Hipparion (fig. 230, C), the foot is essentially
like that of the modern Horses, except that the second and fourth
toes no longer are mere "splint-bones," hidden beneath the skin;
but have now little hoofs, and hang freely, but uselessly, by the
side of the great middle toe, not being sufficiently developed to
reach the ground. In Anchitherium, again (fig. 230, B),
the foot is three-toed, like that of Hipparion; but the
two lateral toes (the second and fourth) are so far
developed that they now reach the ground.
The first digit (thumb or great toe) is still wanting;
as also is the fifth digit (little finger or little toe).
Fig. 230.—Skeleton of the foot in various forms belonging to
the family of the Equidœ. A, Foot of Orohippus,
Eocene; B, Foot of Anchitherium, Upper Eocene and Lower
Miocene; C, Foot of Hipparion, Upper Miocene and Pliocene:
D, Foot of Horse (Equus), Pliocene and Recent. The figures
indicate the numbers of the digits in the typical five-fingered
hand of Mammals. (After Marsh.)
Lastly, the Eocene rocks have yielded in North America the remains
of a small Equine quadruped, to which Marsh has given the name of
Orohippus. In this singular form—which was not larger
than a fox—the foot (fig. 230, A) carries four toes,
all of which are hoofed and touch the ground, but of which the
third toe is still the largest. The first toe
(thumb or great toe) is still wanting; but in this ancient
representative of the Horses, the fifth or "little" toe
appears for the first time. As all the above-mentioned forms
succeed one another in point of time, it may be regarded as
probable that we shall yet be able to point, with some certainty,
to some still older example of the Equidœ, in which
the first digit is developed, and the foot assumes its typical
five-fingered condition.
Passing on to the Even-toed or Artiodactyle Ungulates, no
representative of the Hippotamus seems yet to have existed,
but there are several forms (Chœropotamus, Hyopotamus,
&c.) more or less closely allied to the Pigs (Suida); and
the singular group of the Anoplotheridœ may be regarded
as forming a kind of transition between the Swine and the Ruminants.
The Anoplotheria (fig. 231) were slender in form, the
largest not exceeding a donkey in size, with long tails, and
having the feet terminated by two hoofed toes each, sometimes
with a pair of small accessory hoofs as well. The teeth exhibit
the peculiarity that they are arranged in a continuous series,
without any gap or interval between the molars and the canines;
Fig. 231.—Anoplotherium commune. Eocene Tertiary,
France. (After Cuvier.)
and the back teeth, like those of all the Ungulates, are adapted
for grinding vegetable food, their crowns resembling in form
those of the true Ruminants. The genera Dichobune and
Xiphodon, of the Middle and Upper Eocene, are closely related
to Anoplotherium, but are more slender and deer-like in
form. No example of the great Ruminant group of the Ungulate
Quadrupeds has as yet been detected in deposits of Eocene age.
Whilst true Ruminants appear to be unknown, the Eocene strata
of North America have yielded to the researches of Professor
Marsh examples of an extraordinary group (Dinocerata),
which may be considered as in some respects intermediate between
the Ungulates and the Proboscideans. In Dinoceras itself
(fig. 232) we have a large animal, equal in dimensions to the
living Elephants, which it further resembles in the structure
of the massive limbs, except that there are only four toes to
each foot. The upper jaw was devoid of front teeth, but there
were two very large canine teeth, in the form of tusks directed
perpendicularly downwards; and there was also a series of six small
molars on each. Each upper jaw-bone carried a bony projection, which
was probably of the nature of a "horn-core," and was originally
sheathed in horn. Two similar, but smaller, horn-cores are carried
on the nasal bones; and two much larger projections, also probably
of the nature of horn-cores, were carried upon the forehead. We
may thus infer that Dinoceras possessed three pairs of
horns, all of which resembled the horns of the Sheep and Oxen
in consisting of a central bony "core," surrounded by a horny
sheath. The nose was not prolonged into a proboscis or "trunk,"
as in the existing Elephants; and the tail was short and slender.
Fig. 232.—Skull of Dinoceras mirabilis, greatly
reduced. Eocene, North America. (After Marsh.)
Many forms of the Dinocerata are known; but all these
singular and gigantic quadrupeds appear to have been confined
to the North American continent, and to be restricted to the
Eocene period.
The important order of the Elephants (Proboscidea) is also not known to have come into existence during the Eocene period. On the other hand, the great order of the Beasts of Prey (Carnivora) is represented in Eocene strata by several forms belonging to different types. Thus the Ardocyon presents us with an Eocene Carnivore more or less closely allied to the existing Racoons; the Palœonyctis appears to be related to the recent Civet-cats; the genus Hyœnodon is in some respects comparable to the living Hyænas; and the Canis Parisiensis of the gypsum-bearing beds of Montmartre may perhaps be allied to the Foxes.
The order of the Bats (Cheiroptera) is represented in Eocene
strata of the Paris basin (Gypseous series of Montmartre) by the
Vespertilio Parisiensis (fig. 233), an insect-eating Bat
very similar to some of the existing European forms. Lastly, the
Eocene deposits have yielded more or less satisfactory evidence of
the existence in Europe at this period of examples of the orders
Fig. 233.—Portion of the skeleton of Vespertilio
Parisienis. Eocene Tertiary, France.
of the Gnawing Mammals (Rodentia), the Insect-eating Mammals
(Insectivora), and the Monkeys (Quadrumana).[24]
[Footnote 24: A short list of the more important works relating to the Eocene rocks and fossils will be given after all the Tertiary deposits have been treated of.]
CHAPTER XIX.
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 (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.
In Britain, the Lower Miocene strata of Bovey Tracy have yielded
remains of Ferns, Vines, Fig, Cinnamon, Proteaccœ, &c.,
Fig. 234.—Miocene Palms A, Chamœrops Helvetica; B,
Sabal major. Lower Miocene of Switzerland and France.
along with numerous Conifers. The most abundant of these last is a
gigantic pine—the Sequoia Couttsiœ—which is
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.—Cinnamomum polymorphum. a, Leaf;
b, Flower. Upper Miocene.
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,
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).
One of the latter,
the well-known Vanessa Pluto of the Brown Coals of Croatia,
Fig. 238.—Different views of Scutella subrotunda,
a Miocene "Cake-Urchin" from the south of France.
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.
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
Fig. 239.—Different views of the shell of Hyalea
Orbignyana, a Miocene Pteropod.
Cephalopods are represented both by the chambered shells
of Nautili and by the internal skeletons of Cuttle-fishes
(Spirulirostra.)
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.
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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.
The Mammals of the Miocene are very numerous, and only
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 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.
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.
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
Fig. 243.—Skull of Brontotherium ingens. Miocene
Tertiary, United States. (After Marsh.)
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.
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, 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
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
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.)
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
Fig. 245.—Skull of Sivatherium giganteum, reduced
in size. Miocene, India. (After Murie.)
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.
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
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
very large size, and are each composed of a number of transverse
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.)
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.
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 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.
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,
Fig. 248.—Lower jaw of Pliopithcus antiquus. Upper
Miocene, France.
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.