Atlantic Monthly, Vol. 12, August, 1863, No. 70 by Various

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[Illustration: Fig. 1. An Ichthyosaurus.]

The Ichthyosauri (Figure 1) must have been very large, seven or eight
feet being the ordinary length, while specimens measuring from twenty to
thirty feet are not uncommon. The large head is pointed, like that of
the Porpoise; the jaws contain a number of conical teeth, of reptilian
form and character; the eyeball was very large, as may be seen by the
socket, and it was supported by pieces of bone, such as we find now only
in the eyes of birds of prey and in the bony fishes. The ribs begin at
the neck and continue to the tail, and there is no distinction between
head and neck, as in most Reptiles, but a continuous outline, as in
Fishes. They had four limbs, not divided into fingers, but forming mere
paddles. Yet fingers seem to be hinted at in these paddles, though not
developed, for the bones are in parallel rows, as if to mark what might
be such a division. The back-bones are short, but very high, and the
surfaces of articulation are hollow, conical cavities, as in Fishes,
instead of ball-and-socket joints, as in Reptiles. The ribs are more
complicated than in Vertebrates generally: they consist of several
pieces, and the breast-bone is formed of a number of bones, making
together quite an intricate bony net-work. There is only one living
animal, the Crocodile, characterized by this peculiar structure of the
breast-bone. The Ichthyosaurus is, indeed, one of the most remarkable of
the synthetic types: by the shape of its head one would associate it
with the Porpoises, while by its paddles and its long tail it reminds
one of the whole group of Cetaceans to which the Porpoises belong; by
its crocodilian teeth, its ribs, and its breast-bone, it seems allied to
Reptiles; and by its uniform neck, not distinguished from the body, and
the structure of the backbone, it recalls the Fishes.

[Illustration: Fig. 2. A Plesiosaurus.]

Another most curious member of this group is the Plesiosaurus, odd
Saurian (Figure 2). By its disproportionately long and flexible neck,
and its small, flat head, it unquestionably foreshadows the Serpents,
while by the structure of the backbone, the limbs, and the tail, it is
closely allied with the Ichthyosaurus. Its flappers are, however, more
slender, less clumsy, and were, no doubt, adapted to more rapid motion
than the fins of the Ichthyosaurus, while its tail is shorter in
proportion to the whole length of the animal. It seems probable, from
its general structure, that the Ichthyosaurus moved like a Fish, chiefly
by the flapping of the tail, aided by the fins, while in the
Plesiosaurus the tail must have been much less efficient as a locomotive
organ, and the long, snake-like, flexible neck no doubt rendered the
whole body more agile and rapid in its movements. In comparing the two,
it may be said, that, as a whole, the Ichthyosaurus, though belonging by
its structure to the class of Reptiles, has a closer external
resemblance to the Fishes, while the Plesiosaurus is more decidedly
reptilian in character. If there exists any animal in our waters, not
yet known to naturalists, answering to the descriptions of the
"Sea-Serpent," it must be closely allied to the Plesiosaurus. The
occurrence in the fresh waters of North America of a Fish, the
Lepidosteus, which is closely allied to the fossil Fishes found with the
Plesiosaurus in the Jurassic beds, renders such a supposition probable.

[Illustration: Fig. 3. A Pterodactylus.]

Of all these strange old forms, so singularly uniting features of Fishes
and Reptiles, none has given rise to more discussion than the
Pterodactylus, (Figure 3,) another of the Saurian tribe, associated,
however, with Birds by some naturalists, on account of its large
wing-like appendages. From the extraordinary length of its anterior
limbs, they have generally been described as wings, and the animal is
usually represented as a flying Reptile. But if we consider its whole
structure, this does not seem probable, and I believe it to have been an
essentially aquatic animal, moving after the fashion of the Sea-Turtle.
Its so-called wings resemble in structure the front paddles of the
Sea-Turtles far more than the wings of a Bird; differing from them,
indeed, only by the extraordinary length of the inner toe, while the
outer ones are comparatively much shorter. But, notwithstanding this
difference, the hand of the Pterodactylus is constructed like that of an
aquatic swimming marine Reptile; and I believe, that, if we represent it
with its long neck stretched upon the water, its large head furnished
with powerful, well-armed jaws, ready to dive after the innumerable
smaller animals living in the same ocean, we shall have a more natural
picture of its habits than if we consider it as a flying animal, which
it is generally supposed to have been. It has not the powerful
breast-bone, with the large projecting keel along the middle line, such
as exists in all the flying animals. Its breast-bone, on the contrary,
is thin and flat, like that of the present Sea-Turtle; and if it moved
through the water by the help of its long flappers, as the Sea-Turtle
does now, it could well dispense with that powerful construction of the
breast-bone so essential to all animals which fly through the air.
Again, the powerful teeth, long and conical, placed at considerable
intervals in the jaw, constitute a feature common to all predaceous
aquatic animals, and would seem to have been utterly useless in a flying
animal at that time, since there were no aerial beings of any size to
prey upon. The Dragon-Flies found in the same deposits with the
Pterodactylus were certainly not a game requiring so powerful a battery
of attack.

The Fishes of the Jurassic sea were exceedingly numerous, but were all
of the Ganoid and Selachian tribes. It would weary the reader, were I to
introduce here any detailed description of them, but they were as
numerous and varied as those living in our present waters. There was the
Hybodus, with the marked furrows on the spines and the strong hooks
along their margin,--the huge Chimera, with its long whip, its curved
bone over the back, and its parrot-like bill,--the Lepidotus, with its
large square scales, its large head, its numerous rows of teeth, one
within another, forming a powerful grinding apparatus,--the Microdon,
with its round, flat body, its jaw paved with small grinding teeth,--the
swift Aspidorhynchus, with its long, slender body and massive tail,
enabling it to strike the water powerfully and dart forward with great
rapidity. There were also a host of small Fishes, comparing with those
above mentioned as our Perch, Herring, Smelts, etc., compare with our
larger Fishes; but, whatever their size or form, all the Fishes of those
days had the same hard scales fitting to each other by hooks, instead of
the thin membranous scales overlapping each other at the edge, like the
common Fishes of more modern times. The smaller Fishes, no doubt,
afforded food to the larger ones, and to the aquatic Reptiles. Indeed,
in parts of the intestines of the Ichthyosauri, and in their petrified
excrements, have been found the scales and teeth of these smaller Fishes
perfectly preserved. It is amazing that we can learn so much of the
habits of life of these past creatures, and know even what was the food
of animals existing countless ages before man was created.

There are traces of Mammalia in the Jurassic deposits, but they were of
those inferior kinds known now as Marsupials, and no complete specimens
have yet been found.

The Articulates were largely represented in this epoch. There were
already in the vegetation a number of Gymnosperms, affording more
favorable nourishment for Insects than the forests of earlier times; and
we accordingly find that class in larger numbers than ever before,
though still meagre in comparison with its present representation.
Crustacea were numerous,--those of the Shrimp and Lobster kinds
prevailing, though in some of the Lobsters we have the first advance
towards the highest class of Crustacea in the expansion of the
transverse diameter now so characteristic of the Crabs. Among Mollusks
we have a host of gigantic Ammonites; and the naked Cephalopods, which
were in later times to become the prominent representatives of that
class, already begin to make their appearance. Among Radiates, some of
the higher kinds of Echinoderms, the Ophiurans and Echinolds, take the
place of the Crinoids, and the Acalephian Corals give way to the Astraean
and Meandrina-like types, resembling the Reef-Builders of the present
time.

* * * * *

I have spoken especially of the inhabitants of the Jurassic sea lying
between England and France, because it was there that were first found
the remains of some of the most remarkable and largest Jurassic animals.
But wherever these deposits have been investigated, the remains
contained in them reveal the same organic character, though, of course,
we find the land Reptiles only where there happen to have been marshes,
the aquatic Saurians wherever large estuaries or bays gave them an
opportunity of coming in near shore, so that their bones were preserved
in the accumulations of mud or clay constantly collecting in such
localities,--the Crustacea, Shells, or Sea-Urchins on the old
sea-beaches, the Corals in the neighborhood of coral reefs, and so on.
In short, the distribution of animals then as now was in accordance with
their nature and habits, and we shall seek vainly for them in the
localities where they did not belong.

But when I say that the character of the Jurassic animals is the same, I
mean, that, wherever a Jurassic sea-shore occurs, be it in France,
Germany, England, or elsewhere throughout the world, the Shells,
Crustacea, or other animals found upon it have a special character, and
are not to be confounded by any one thoroughly acquainted with these
fossils with the Shells or Crustacea of any preceding or subsequent
time,--that, where a Jurassic marsh exists, the land Reptiles inhabiting
it are Jurassic, and neither Triassic nor Cretaceous,--that a Jurassic
coral reef is built of Corals belonging as distinctly to the Jurassic
creation as the Corals on the Florida reefs belong to the present
creation,--that, where some Jurassic bay or inlet is disclosed to us
with the Fishes anciently inhabiting it, they are as characteristic of
their time as are the Fishes of Massachusetts Bay now.

And not only so, but, while this unity of creation prevails throughout
the entire epoch as a whole, there is the same variety of geographical
distribution, the same circumscription of faunae within distinct
zooelogical provinces, as at the present time. The Fishes of
Massachusetts Bay are not the same as those of Chesapeake Bay, nor those
of Chesapeake Bay the same as those of Pamlico Sound, nor those of
Pamlico Sound the same as those of the Florida coast. This division of
the surface of the earth into given areas within which certain
combinations of animals and plants are confined is not peculiar to the
present creation, but has prevailed in all times, though with
ever-increasing diversity, as the surface of the earth itself assumed a
greater variety of climatic conditions. D'Orbigny and others were
mistaken in assuming that faunal differences have been introduced only
in the last geological epochs. Besides these adjoining zooelogical faunae,
each epoch is divided, as we have seen, into a number of periods,
occupying successive levels one above another, and differing
specifically from each other in time as zooelogical provinces differ from
each other in space. In short, every epoch is to be looked upon from two
points of view: as a unit, complete in itself, having one character
throughout, and as a stage in the progressive history of the world,
forming part of an organic whole.

* * * * *

As the Jurassic epoch was ushered in by the upheaval of the Jura, so its
close was marked by the upheaval of that system of mountains called the
Cote d'Or. With this latter upheaval began the Cretaceous epoch, which
we will examine with special reference to its subdivision into periods,
since the periods in this epoch have been clearly distinguished, and
investigated with especial care. I have alluded in the preceding article
to the immediate contact of the Jurassic and Cretaceous epochs in
Switzerland, affording peculiar facilities for the direct comparison of
their organic remains. But the Cretaceous deposits are well known, not
only in this inland sea of ancient Switzerland, but in a number of
European basins, in France, in the Pyrenees, on the Mediterranean
shores, and also in Syria, Egypt, India, and Southern Africa, as well as
on our own continent. In all these localities, the Cretaceous remains,
like those of the Jurassic epoch, have one organic character, distinct
and unique. This fact is especially significant, because the contact of
their respective deposits is in many localities so immediate and
continuous that it affords an admirable test for the development-theory.
If this is the true mode of origin of animals, those of the later
Jurassic beds must be the progenitors of those of the earlier Cretaceous
deposits. Let us see now how far this agrees with our knowledge of the
physiological laws of development.

Take first the class of Fishes. We have seen that in the Jurassic
periods there were none of our common Fishes, none corresponding to our
Herring, Pickerel, Mackerel, and the like,--no Fishes, in short, with
thin membranous scales, but that the class was represented exclusively
by those with hard, flint-like scales. In the Cretaceous epoch, however,
we come suddenly upon a horde of Fishes corresponding to our smaller
common Fishes of the Pickerel and Herring tribes, but principally of the
kinds found now in tropical waters; there are none like our Cods,
Haddocks, etc., such as are found at present in the colder seas. The
Fishes of the Jurassic epoch corresponding to our Sharks and Skates and
Gar-Pikes still exist, but in much smaller proportion, while these more
modern kinds are very numerous. Indeed, a classification of the
Cretaceous Fishes would correspond very nearly to one founded on those
now living. Shall we, then, suppose that the large reptilian Fishes of
the Jurassic time began suddenly to lay numerous broods of these
smaller, more modern, scaly Fishes? And shall we account for the
diminution of the previous forms by supposing that in order to give a
fair chance to the new kinds they brought them forth in large numbers,
while they reproduced their own kind less abundantly? According to very
careful estimates, if we accept this view, the progeny of the Jurassic
Fishes must have borne a proportion of about ninety per cent, of
entirely new types to some ten per cent, of those resembling the
parents. One would like a fact or two on which to rest so very
extraordinary a reversal of all known physiological laws of
reproduction, but, unhappily, there is not one.

Still more unaccountable, upon any theory of development according to
ordinary laws of reproduction, are those unique, isolated types limited
to a single epoch, or sometimes even to a single period. There are some
very remarkable instances of this in the Cretaceous deposits. To make my
statement clearer, I will say a word of the sequence of these deposits
and their division into periods.

These Cretaceous beds were at first divided only into three sets, called
the Neocomian, or lower deposits, the Green-Sands, or middle deposits,
and the Chalk, or upper deposits. The Neocomian, the lower division, was
afterwards subdivided into three sets of beds, called the Lower, Middle,
and Upper Neocomian by some geologists, the Valengian, Neocomian, and
Urgonian by others. These three periods are not only traced in immediate
succession, one above another, in the transverse cut before described,
across the mountain of Chaumont, near Neufchatel, but they are also
traced almost on one level along the plain at the foot of the Jura. It
is evident that by some disturbance of the surface the eastern end of
the range was raised slightly, lifting the lower or Valengian deposits
out of the water, so that they remain uncovered, and the next set of
deposits, the Neocomian, is accumulated along their base, while these in
their turn are slightly raised, and the Urgonian beds are accumulated
against them a little lower down. They follow each other from east to
west in a narrower area, just as the Azoic, Silurian, and Devonian
deposits follow each other from north to south in the northern part of
the United States. The Cretaceous deposits have been intimately studied
in various localities by different geologists, and are now subdivided
into at least ten, or it may be fifteen or sixteen distinct periods, as
they stand at present. This is, however, but the beginning of the work;
and the recent investigations of the French geologist, Coquand, indicate
that several of these periods at least are susceptible of further
subdivision. I present here a table enumerating the periods of the
Cretaceous epoch best known at present, in their sequence, because I
want to show how sharply and in how arbitrary a manner, if I may so
express it, new forms are introduced. The names are simply derived from
the localities, or from some circumstances connected with the locality
where each period has been studied.

_Table of Periods in the Cretaceous Epoch._

Maestrichtian } Chalk.
Senonian }

Turonian } Chalk Marl.
Cenomanian }

Albian }
Aptian } Green Sands.
Rhodanian }

Urgonian }
Neocomian } Wealden.
Valengian }

One of the most peculiar and distinct of those unique types alluded to
above is that of the Rudistes, a singular Bivalve, in which the lower
valve is very deep and conical, while the upper valve sets into to it as
into a cup. The subjoined woodcut represents such a Bivalve. These
Rudistes are found suddenly in the Urgonian deposits; there are none in
the two preceding sets of beds; they disappear in the three following
periods, and reappear again in great numbers in the Cenomanian,
Turonian, and Senonian periods, and disappear again in the succeeding
one. These can hardly be missed from any negligence or oversight in the
examination of these deposits, for they are by no means rare. They are
found always in great numbers, occupying crowded beds, like Oysters in
the present time. So numerous are they, where they occur at all, that
the deposits containing them are called by many naturalists the first,
second, third, and fourth _bank_ of Rudistes. Which of the ordinary
Bivalves, then, gave rise to this very remarkable form in the class,
allowed it to die out, and revived it again at various intervals? This
is by no means the only instance of the same kind. There are a number of
types making their appearance suddenly, lasting during one period or
during a succession of periods, and then disappearing forever, while
others, like the Rudistes, come in, vanish, and reappear at a later
time.

[Illustration: Rudistes.]

I am well aware that the advocates of the development-theory do not
state their views as I have here presented them. On the contrary, they
protest against any idea of sudden, violent, abrupt changes, and
maintain that by slow and imperceptible modifications during immense
periods of time these new types have been introduced without involving
any infringement of the ordinary processes of development; and they
account for the entire absence of corroborative facts in the past
history of animals by what they call the "imperfection of the geological
record." Now, while I admit that our knowledge of geology is still very
incomplete, I assert that just where the direct sequence of geological
deposits is needed for this evidence, we have it. The Jurassic beds,
without a single modern scaly Fish, are in immediate contact with the
Cretaceous beds, in which the Fishes of that kind are proportionately
almost as numerous as they are now; and between these two sets of
deposits there is not a trace of any transition or intermediate form to
unite the reptilian Fishes of the Jurassic with the common Fishes of the
Cretaceous times. Again, the Cretaceous beds in which the crowded banks
of Rudistes, so singular and unique in form, first make their
appearance, follow immediately upon those in which all the Bivalves are
of an entirely different character. In short, the deposits of this year
along any sea-coast or at the mouth of any of our rivers do not follow
more directly upon those of last year than do these successive sets of
beds of past ages follow upon each other. In making these statements, I
do not forget the immense length of the geological periods; on the
contrary, I fully accede to it, and believe that it is more likely to
have been underrated than overstated. But let it be increased a
thousand-fold, the fact remains, that these new types occur commonly at
the dividing line where one period joins the next, just on the margin of
both.

For years I have collected daily among some of these deposits, and I
know the Sea-Urchins, Corals, Fishes, Crustacea, and Shells of those old
shores as well as I know those of Nahant Beach, and there is nothing
more striking to a naturalist than the sudden, abrupt changes of species
in passing from one to another. In the second set of Cretaceous beds,
the Neocomian, there is found a little Terebratula (a small Bivalve
Shell) in immense quantities: they may actually be collected by the
bushel. Pass to the Urgonian beds, resting directly upon the Neocomian,
and there is not one to be found, and an entirely new species comes in.
There is a peculiar Spatangus (Sea-Urchin) found throughout the whole
series of beds in which this Terebratula occurs. At the same moment that
you miss the Shell, the Sea-Urchin disappears also, and another takes
its place. Now, admitting for a moment that the later can have grown out
of the earlier forms, I maintain, that, if this be so, the change is
immediate, sudden, without any gradual transitions, and is, therefore,
wholly inconsistent with all our known physiological laws, as well as
with the transmutation-theory.

There is a very singular group of Ammonites in the Cretaceous epoch,
which, were it not for the suddenness of its appearance, might seem
rather to favor the development-theory, from its great variety of
closely allied forms. We have traced the Chambered Shells from the
straight, simple ones of the earliest epochs up to the intricate and
closely coiled forms of the Jurassic epoch. In the so-called Portland
stone, belonging to the upper set of Jurassic beds, there is only one
type of Ammonite; but in the Cretaceous beds, immediately above it,
there set in a number of different genera and distinct species,
including the most fantastic and seemingly abnormal forms. It is as if
the close coil by which these shells had been characterized during the
Middle Age had been suddenly broken up and decomposed into an endless
variety of outlines. Some of these new types still retain the coil, but
the whorls are much less compact than before, as in the Crioceras; in
others, the direction of the coil is so changed as to make a spiral, as
in the Turrilites; or the shell starts with a coil, then proceeds in a
straight line, and changes to a curve again at the other extremity, as
in the Ancyloceras, or in the Scaphites, in which the first coil is
somewhat closer than in the Ancyloceras; or the tendency to a coil is
reduced to a single curve, so as to give the shell the outline of a
horn, as in the Toxoceras; or the coil is entirely lost, and the shell
reduced to its primitive straight form, as in the Baculites, which,
except for their undulating partitions, might be mistaken for the
Orthoceratites of the Silurian and Devonian epochs. I have presented
here but a few species of these extraordinary Cretaceous Ammonites, and,
strange to say, with this breaking-up of the type into a number of
fantastic and often contorted shapes, it disappears. It is singular that
forms so unusual and so contrary to the previous regularity of this
group should accompany its last stage of existence, and seem to shadow
forth by their strange contortions the final dissolution of their type.
When I look upon a collection of these old shells, I can never divest
myself of an impression that the contortions of a death-struggle have
been made the pattern of living types, and with that the whole group has
ended.

[Illustration: Crioceras.]

[Illustration: Turrilites.]

[Illustration: Ancyloceras.]

[Illustration: Scaphites.]

[Illustration: Toxoceras.]

[Illustration: Baculites.]

Now shall we infer that the compact, closely coiled Ammonites of the
Jurassic deposits, while continuing their own kind, brought forth a
variety of other kinds, and so distributed these new organic elements as
to produce a large number of distinct genera and species? I confess that
these ideas are so contrary to all I have learned from Nature in the
course of a long life that I should be forced to renounce completely the
results of my studies in Embryology and Palaeontology before I could
adopt these new views of the origin of species. And while the
distinguished originator of this theory is entitled to our highest
respect for his scientific researches, yet it should not be forgotten
that the most conclusive evidence brought forward by him and his
adherents is of a negative character, drawn from a science in which they
do not pretend to have made personal investigations, that of Geology,
while the proofs they offer us from their own departments of science,
those of Zooelogy and Botany, are derived from observations, still very
incomplete, upon domesticated animals and cultivated plants, which can
never be made a test of the origin of wild species.[11]

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