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ANIMALS OF THE PAST
[Illustration: Phororhacos, a Patagonian Giant of the Miocene.
_From a drawing by Charles R. Knight._]
_Science for Everybody_
ANIMALS OF THE PAST
BY FREDERIC A. LUCAS
_Curator of the Division of Comparative Anatomy,
United States National Museum_
FULLY ILLUSTRATED
NEW YORK
McCLURE, PHILLIPS & CO.
1901
COPYRIGHT, 1900, BY S. S. MCCLURE CO.
1901, BY MCCLURE, PHILLIPS & CO.
PUBLISHED NOVEMBER, 1901.
TABLE OF CONTENTS
INTRODUCTORY AND EXPLANATORY
Use of scientific names, xvi; estimates of age of earth, xvii;
restorations by Mr. Knight, xviii; Works of Reference, xix.
I. FOSSILS, AND HOW THEY ARE FORMED
Definition of fossils, 1; fossils may be indications of animals
or plants, 2; casts and impressions, 3; why fossils are not more
abundant, 4; conditions under which fossils are formed, 5;
enemies of bones, 6; Dinosaurs engulfed in quicksand, 8;
formation of fossils, 9; petrified bodies frauds, 10; natural
casts, 10; leaves, 13; incrustations, 14; destruction of
fossils, 15; references, 17.
II. THE EARLIEST KNOWN VERTEBRATES
Methods of interrogating Nature, 18; thickness of sedimentary
rocks, 20; earliest traces of life, 21; early vertebrates
difficult of preservation, 22; armored fishes, 23; abundance of
early fishes, 25; destruction of fish, 26; carboniferous sharks,
29; known mostly from teeth and spines, 30; references, 32.
III. IMPRESSIONS OF THE PAST
Records of extinct animals, 33; earliest traces of animal life,
34; formation of tracks, 35; tracks in all strata, 36; discovery
of tracks, 37; tracks of Dinosaurs, 39; species named from
tracks, 41; footprints aid in determining attitude of animals,
43; tracks at Carson City, 45; references, 47.
IV. RULERS OF THE ANCIENT SEAS
The Mosasaurs, 49; history of the first known Mosasaur, 50; jaws
of reptiles, 53; extinction of Mosasaurs, 55; the sea-serpent,
56; Zeuglodon, 58; its habits, 59; Koch's Hydrarchus, 61; bones
collected by Mr. Schuchert, 63; abundance of sharks, 64; the
great Carcharodon, 65; arrangement of sharks' teeth, 67;
references, 68.
V. BIRDS OF OLD
Earliest birds, 70; wings, 71; study of young animals, 73; the
curious Hoactzin, 74; first intimation of birds, 76;
Archaeopteryx, 77; birds with teeth, 78; cretaceous birds, 79;
Hesperornis, 80; loss of power of flight, 81; covering of
Hesperornis, 82; attitude of Hesperornis, 83; curious position
of legs, 84; toothed birds disappointing, 85; early development
of birds, 86; eggs of early birds, 87; references, 88.
VI. THE DINOSAURS
Discovery of Dinosaur remains, 90; nearest relatives of
Dinosaurs, 91; relation of birds to reptiles, 92; brain of
Dinosaurs, 93; parallel between Dinosaurs and Marsupials, 95;
the great Brontosaurus, 96; food of Dinosaurs, 97; habits of
Diplodocus, 99; the strange Australian Moloch, 100; combats of
Triceratops, 101; skeleton of Triceratops, 102; Thespesius and
his kin, 104; the carnivorous Ceratosaurus, 106; Stegosaurus,
the plated lizard, 106; preferences, 109.
VII. READING THE RIDDLES OF THE ROCKS
Fossils regarded as sports of nature, 111; qualifications of a
successful collector, 112; chances of collecting, 114;
excavation of fossils, 115; strengthening fossils for shipment,
117; great size of some specimens, 118; the preparation of
fossils, 119; mistakes of anatomists, 120; reconstruction of
Triceratops, 121; distinguishing characters of bones, 122; the
skeleton a problem in mechanics, 124; clothing the bones with
flesh, 127; the covering of animals, 127; outside ornamentation,
129; probabilities in the covering of animals, 130; impressions
of extinct animals, 131; mistaken inferences from bones of
Mammoth, 133; coloring of large land animals, 134; color
markings of young animals, 136; references, 137.
VIII. FEATHERED GIANTS
Legend of the Moa, 139; our knowledge of the Moas, 141; some
Moas wingless, 142; deposits of Moa bones, 143; legend of the
Roc, 144; discovery of AEpyornis, 145; large-sounding names, 146;
eggs of great birds, 147; the Patagonian Phororhacos, 149; the
huge Brontornis, 150; development of giant birds, 153;
distribution of flightless birds, 154; relation between
flightlessness and size, 156; references, 156.
IX. THE ANCESTRY OF THE HORSE
North America in the Eocene age, 160; appearance of early
horses, 163; early domestication of the horse, 165; the toes of
horses, 166; Miocene horses small, 167; evidence of genealogy of
the horse, 170; meaning of abnormalities, 170; changes in the
climate and animals of the West, 174; references, 176.
X. THE MAMMOTH
The story of the killing of the Mammoth, 177; derivation of the
word "mammoth," 178; mistaken ideas as to size of the Mammoth,
179; size of Mammoth and modern elephants, 180; finding of an
entire Mammoth, 182; birthplace of the Mammoth, 184; beliefs
concerning its bones, 185; the range of the animal, 186;
theories concerning the extinction of the Mammoth, 188; Man and
Mammoth, 189; origin of the Alaskan Live Mammoth Story, 190;
traits of the Innuits, 192; an entire Mammoth recently found,
194; references, 195.
XI. THE MASTODON
Differences between Mastodon and Mammoth, 198; affinities of the
Mastodon, 200; vestigial structures, 201; distribution of
American Mastodon, 203; first noticed in North America, 204;
thought to be carnivorous, 206; Koch's Missourium, 208; former
abundance of Mastodons, 209; appearance of the animal, 210; its
size, 211; was man contemporary with Mastodon? 213; the Lenape
stone, 215; legend of the big buffalo, 216; references, 218.
XII. WHY DO ANIMALS BECOME EXTINCT?
Extinction sometimes evolution, 221; over-specialization as a
cause for extinction, 222; extinction sometimes unaccountable,
223; man's capability for harm small in the past, 224; old
theories of great convulsions, 226; changes in nature slow, 227;
the case of Lingula, 228; local extermination, 229; the Moas and
the Great Auk, 232; the case of large animals, 233;
inter-dependence of living beings, 234; coyotes and fruit, 236;
Shaler on the Miocene flora of Europe, 236; man's desire for
knowledge, 238.
INDEX, 243
NOTE ON THE ILLUSTRATIONS
The original drawings, made especially for this book, are by Charles R.
Knight and James M. Gleeson, under the direction of Mr. Knight. The fact
that the originals of these drawings have been presented to and accepted
by the United States National Museum is evidence of their scientific
value. Mr. Knight has been commissioned by the Smithsonian Institution,
the United States National Museum, and the New York Museum of Natural
History, to do their most important pictures of extinct animals. He is
the one modern artist who can picture prehistoric animals with artistic
charm of presentation as well as with full scientific accuracy. In this
instance, the author has personally superintended the artist's work, so
that it is as correct in every respect as present knowledge makes
possible. Of the minor illustrations, some are by Mr. Bruce Horsfall, an
artist attached to the staff of the New York Museum of Natural History,
and all have been drawn with the help of and under the author's
supervision.
LIST OF ILLUSTRATIONS
Fig. Page
Phororhacos, a Patagonian Giant of the Miocene _From a Drawing
by Charles R. Knight_ _Frontispiece_
1. Diplomystus, an Ancient Member of the Shad Family _From the
fish-bed at Green River, Wyoming. From a specimen in the United
States National Museum._ 4
2. Bryozoa, from the Shore of the Devonian Sea that Covered
Eastern New York _From a specimen in Yale University Museum,
prepared by Dr. Beecher._ 10
3. Skeleton of a Radiolarian Very Greatly Enlarged 17
4. Cephalaspis and Loricaria, an Ancient and a Modern Armored
Fish 24
5. Pterichthys, the Wing Fish 32
6. Where a Dinosaur Sat Down 38
7. Footprints of Dinosaurs on the Brownstone of the Connecticut
Valley _From a slab in the museum of Amherst College._ 40
8. The Track of a Three-toed Dinosaur 47
9. A Great Sea Lizard, _Tylosaurus Dyspelor From a drawing by
J. M. Gleeson._ 52
10. Jaw of a Mosasaur, Showing the Joint that Increased the
Swallowing Capacity of that Reptile 54
11. Koch's Hydrarchus. Composed of Portions of the Skeletons of
Several Zeuglodons 62
12. A Tooth of Zeuglodon, One of the "Yoke Teeth," from which it
derives the name 69
13. Archaeopteryx, the Earliest Known Bird _From the specimen in
the Berlin Museum._ 70
14. Nature's Four Methods of Making a Wing: Bat, Pteryodactyl,
Archaeopteryx, and Modern Bird 72
15. Young Hoactzins 75
16. Hesperornis, the Great Toothed Diver _From a drawing by J.
M. Gleeson._ 82
17. Archaeopteryx _As Restored by Mr. Pycraft._ 89
18. Thespesius, a Common Herbivorous Dinosaur of the Cretaceous
_From a drawing by Charles R. Knight._ 90
19. A Hind Leg of the Great Brontosaurus, the Largest of the
Dinosaurs 96
20. A Single Vertebra of Brontosaurus 97
21. Moloch, a Modern Lizard that Surpasses the Stegosaurs in All
but Size _From a drawing by J. M. Gleeson._ 100
22. Skeleton of Triceratops 103
23. The Horned Ceratosaurus, a Carnivorous Dinosaur _From a
drawing by J. M. Gleeson._ 106
24. Stegosaurus, an Armored Dinosaur of the Jurassic _From a
drawing by Charles R. Knight._ 108
25. Skull of Ceratosaurus _From a specimen in the United States
National Museum._ 110
26. Triceratops, He of the Three-horned Face _From a statuette
by Charles R. Knight._ 126
27. A Hint of Buried Treasures 137
28. Relics of the Moa 140
29. Eggs of Feathered Giants, AEpyornis, Ostrich, Moa, Compared
with a Hen's Egg 148
30. Skull of Phororhacos Compared with that of the Race-horse
Lexington 151
31. Leg of a Horse Compared with that of the Giant Moa 152
32. The Three Giants, Phororhacos, Moa, Ostrich 158
33. Skeleton of the Modern Horse and of His Eocene Ancestor 161
34. The Development of the Horse 168
35. The Mammoth _From a drawing by Charles R. Knight._ 176
36. Skeleton of the Mammoth in the Royal Museum of St.
Petersburg 183
37. The Mammoth _As engraved by a Primitive Artist on a Piece of
Mammoth-Tusk._ 196
38. Tooth of Mastodon and of Mammoth 199
39. The Missourium of Koch _From a Tracing of the Figure
Illustrating Koch's Description._ 207
40. The Mastodon _From a drawing by J. M. Gleeson._ 210
41. The Lenape Stone, Reduced 219
_INTRODUCTORY AND EXPLANATORY_
_At the present time the interest in the ancient life of this earth is
greater than ever before, and very considerable sums of money are being
expended to dispatch carefully planned expeditions to various parts of
the world systematically to gather the fossil remains of the animals of
the past. That this interest is not merely confined to a few scientific
men, but is shared by the general public, is shown by the numerous
articles, including many telegrams, in the columns of the daily papers.
The object of this book is to tell some of the interesting facts
concerning a few of the better known or more remarkable of these extinct
inhabitants of the ancient world; also, if possible, to ease the strain
on these venerable animals, caused by stretching them so often beyond
their due proportions._
_The book is admittedly somewhat on the lines of Mr. Hutchinson's
"Extinct Monsters" and "Creatures of Other Days," but it is hoped that
it may be considered with books as with boats, a good plan to build
after a good model. The information scattered through these pages has
been derived from varied sources; some has of necessity been taken from
standard books, a part has been gathered in the course of museum work
and official correspondence; for much, the author is indebted to his
personal friends, and for a part, he is under obligations to friends he
has never met, who have kindly responded to his inquiries. The endeavor
has been conscientiously made to exclude all misinformation; it is,
nevertheless, entirely probable that some mistakes may have crept in,
and due apology for these is hereby made beforehand._
_The author expects to be taken to task for the use of scientific names,
and the reader may perhaps sympathize with the old lady who said that
the discovery of all these strange animals did not surprise her so much
as the fact that anyone should know their names when they were found.
The real trouble is that there are no common names for these animals.
Then, too, people who call for easier names do not stop to reflect
that, in many cases, the scientific names are no harder than others,
simply less familiar, and, when domesticated, they cease to be hard:
witness mammoth, elephant, rhinoceros, giraffe, boa constrictor, all of
which are scientific names. And if, for example, we were to call the
Hyracotherium a Hyrax beast it would not be a name, but a description,
and not a bit more intelligible._
_Again, it is impossible to indicate the period at which these creatures
lived without using the scientific term for it--Jurassic, Eocene,
Pliocene, as the case may be--because there is no other way of doing
it._
_Some readers will doubtless feel disappointed because they are not told
how many years ago these animals lived. The question is often asked--How
long ago did this or that animal live? But when the least estimate puts
the age of the earth at only 10,000,000 years, while the longest makes
it 6,000,000,000, it does seem as if it were hardly worth while to name
any figures. Even when we get well toward the present period we find the
time that has elapsed since the beginning of the Jurassic, when the
Dinosaurs held carnival, variously put at from 15,000,000 to 6,000,000
years; while from the beginning of the Eocene, when the mammals began to
gain the supremacy, until now, the figures vary from 3,000,000 to
5,000,000 years. So the question of age will be left for the reader to
settle to his or her satisfaction._
_The restorations of extinct animals may be considered as giving as
accurate representations of these creatures as it is possible to make;
they were either drawn by Mr. Knight, whose name is guarantee that they
are of the highest quality, or by Mr. Gleeson, with the aid of Mr.
Knight's criticism. That they are infallibly correct is out of the
question; for, as Dr. Woodward writes in the preface to "Extinct
Monsters," "restorations are ever liable to emendation, and the present
... will certainly prove no exception to the rule." As a striking
instance of this, it was found necessary at the last moment to change
the figure of Hesperornis, the original life-like portrait proving to be
incorrect in attitude, a fact that would have long escaped detection but
for the Pan-American Exposition. The connection between the two is
explained on page 76. However, the reader may rest assured that these
restorations are infinitely more nearly correct than many figures of
living animals that have appeared within the last twenty-five years, and
are even now doing duty._
_The endeavor has been made to indicate, at the end of each chapter, the
museums in which the best examples of the animals described may be seen,
and also some book or article in which further information may be
obtained. As this book is intended for the general reader, references to
purely technical articles have, so far as possible, been avoided, and
none in foreign languages mentioned._
_For important works of reference on the subject of paleontology, the
reader may consult "A Manual of Paleontology," by Alleyne Nicholson and
R. Lydekker, a work in two volumes dealing with invertebrates,
vertebrates, and plants, or "A Text-Book of Paleontology," by Karl von
Zittel, English edition, only the first volume of which has so far been
published. An admirable book on the vertebrates is "Outlines of
Vertebrate Paleontology," by Arthur Smith Woodward. It is to be
understood that these are not at all "popular" in their scope, but
intended for students who are already well advanced in the study of
zooelogy._
ANIMALS OF THE PAST I
FOSSILS, AND HOW THEY ARE FORMED
"_How of a thousand snakes each one
Was changed into a coil of stone._"
Fossils are the remains, or even the indications, of animals and plants
that have, through natural agencies, been buried in the earth and
preserved for long periods of time. This may seem a rather meagre
definition, but it is a difficult matter to frame one that will be at
once brief, exact, and comprehensive; fossils are not necessarily the
remains of extinct animals or plants, neither are they, of necessity,
objects that have become petrified or turned into stone.
Bones of the Great Auk and Rytina, which are quite extinct, would hardly
be considered as fossils; while the bones of many species of animals,
still living, would properly come in that category, having long ago been
buried by natural causes and often been changed into stone. And yet it
is not essential for a specimen to have had its animal matter replaced
by some mineral in order that it may be classed as a fossil, for the
Siberian Mammoths, found entombed in ice, are very properly spoken of as
fossils, although the flesh of at least one of these animals was so
fresh that it was eaten. Likewise the mammoth tusks brought to market
are termed fossil-ivory, although differing but little from the tusks of
modern elephants.
Many fossils indeed merit their popular appellation of petrifactions,
because they have been changed into stone by the slow removal of the
animal or vegetable matter present and its replacement by some mineral,
usually silica or some form of lime. But it is necessary to include
'indications of plants or animals' in the above definition because some
of the best fossils may be merely impressions of plants or animals and
no portion of the objects themselves, and yet, as we shall see, some of
our most important information has been gathered from these same
imprints.
Nearly all our knowledge of the plants that flourished in the past is
based on the impressions of their leaves left on the soft mud or smooth
sand that later on hardened into enduring stone. Such, too, are the
trails of creeping and crawling things, casts of the burrows of worms
and the many footprints of the reptiles, great and small, that crept
along the shore or stalked beside the waters of the ancient seas. The
creatures themselves have passed away, their massive bones even are
lost, but the prints of their feet are as plain to-day as when they were
first made.
Many a crustacean, too, is known solely or mostly by the cast of its
shell, the hard parts having completely vanished, and the existence of
birds in some formations is revealed merely by the casts of their eggs;
and these natural casts must be included in the category of fossils.
Impressions of vertebrates may, indeed, be almost as good as actual
skeletons, as in the case of some fishes, where the fine mud in which
they were buried has become changed to a rock, rivalling porcelain in
texture; the bones have either dissolved away or shattered into dust at
the splitting of the rock, but the imprint of each little fin-ray and
every threadlike bone is as clearly defined as it would have been in a
freshly prepared skeleton. So fine, indeed, may have been the mud, and
so quiet for the time being the waters of the ancient sea or lake, that
not only have prints of bones and leaves been found, but those of
feathers and of the skin of some reptiles, and even of such soft and
delicate objects as jelly fishes. But for these we should have little
positive knowledge of the outward appearance of the creatures of the
past, and to them we are occasionally indebted for the solution of some
moot point in their anatomy.
The reader may possibly wonder why it is that fossils are not more
abundant; why, of the vast majority of animals that have dwelt upon the
earth since it became fit for the habitation of living beings, not a
trace remains. This, too, when some objects--the tusks of the Mammoth,
for example--have been sufficiently well preserved to form staple
articles of commerce at the present time, so that the carved handle of
my lady's parasol may have formed part of some animal that flourished at
the very dawn of the human race, and been gazed upon by her
grandfather a thousand times removed. The answer to this query is that,
unless the conditions were such as to preserve at least the hard parts
of any creature from immediate decay, there was small probability of its
becoming fossilized. These conditions are that the objects must be
protected from the air, and, practically, the only way that this happens
in nature is by having them covered with water, or at least buried in
wet ground.
[Illustration: Fig. 1.--Diplomystus, an Ancient Member of the Shad
Family. From the Fishbed at Green River, Wyoming. _From a specimen in
the United States National Museum._]
If an animal dies on dry land, where its bones lie exposed to the
summer's sun and rain and the winter's frost and snow, it does not take
these destructive agencies long to reduce the bones to powder; in the
rare event of a climate devoid of rain, mere changes of temperature, by
producing expansion and contraction, will sooner or later cause a bone
to crack and crumble.
Usually, too, the work of the elements is aided by that of animals and
plants. Every one has seen a dog make way with a pretty good-sized bone,
and the Hyena has still greater capabilities in that line; and ever
since vertebrate life began there have been carnivorous animals of some
kind to play the role of bone-destroyers. Even were there no carnivores,
there were probably then, as now, rats and mice a-plenty, and few
suspect the havoc small rodents may play with a bone for the grease it
contains, or merely for the sake of exercising their teeth. Now and then
we come upon a fossil bone, long since turned into stone, on which are
the marks of the little cutting teeth of field mice, put there long,
long ago, and yet looking as fresh as if made only last week. These
little beasts, however, are indirect rather than direct agents in the
destruction of bones by gnawing off the outer layers, and thus
permitting the more ready entrance of air and water. Plants, as a rule,
begin their work after an object has become partly or entirely buried in
the soil, when the tiny rootlets find their way into fissures, and,
expanding as they grow, act like so many little wedges to force it
asunder.
Thus on dry land there is small opportunity for a bone to become a
fossil; but, if a creature so perishes that its body is swept into the
ocean or one of its estuaries, settles to the muddy bottom of a lake or
is caught on the sandy shoals of some river, the chances are good that
its bones will be preserved. They are poorest in the ocean, for unless
the body drifts far out and settles down in quiet waters, the waves
pound the bones to pieces with stones or scour them away with sand,
while marine worms may pierce them with burrows, or echinoderms cut
holes for their habitations; there are more enemies to a bone than one
might imagine.
Suppose, however, that some animal has sunk in the depths of a quiet
lake, where the wash of the waves upon the shore wears the sand or rock
into mud so fine that it floats out into still water and settles there
as gently as dew upon the grass. Little by little the bones are covered
by a deposit that fills every groove and pore, preserving the mark of
every ridge and furrow; and while this may take long, it is merely a
matter of time and favorable circumstance to bury the bones as deeply as
one might wish. Scarce a reader of these lines but at some time has cast
anchor in some quiet pond and pulled it up, thickly covered with sticky
mud, whose existence would hardly be suspected from the sparkling waters
and pebbly shores. If, instead of a lake, our animal had gone to the
bottom of some estuary into which poured a river turbid with mud, the
process of entombment would have been still more rapid, while, had the
creature been engulfed in quicksand, it would have been the quickest
method of all; and just such accidents did take place in the early days
of the earth as well as now. At least two examples of the great Dinosaur
Thespesius have been found with the bones all in place, the thigh bones
still in their sockets and the ossified tendons running along the
backbone as they did in life. This would hardly have happened had not
the body been surrounded and supported so that every part was held in
place and not crushed, and it is difficult to see any better agency for
this than burial in quicksand.
If such an event as we have been supposing took place in a part of the
globe where the land was gradually sinking--and the crust of the earth
is ever rising and falling--the mud and sand would keep on accumulating
until an enormously thick layer was formed. The lime or silica contained
in the water would tend to cement the particles of mud and grains of
sand into a solid mass, while the process would be aided by the pressure
of the overlying sediment, the heat created by this pressure, and that
derived from the earth beneath. During this process the animal matter of
bones or other objects would disappear and its place be taken by lime or
silica, and thus would be formed a layer of rock containing fossils. The
exact manner in which this replacement is effected and in which the
chemical and mechanical changes occur is very far from being definitely
known--especially as the process of "fossilization" must at times have
been very complicated.
In the case of fossil wood greater changes have taken place than in the
fossilization of bone, for there is not merely an infiltration of the
specimen but a complete replacement of the original vegetable by mineral
matter, the interior of the cells being first filled with silica and
their walls replaced later on. So completely and minutely may this
change occur that under the microscope the very cellular structure of
the wood is visible, and as this varies according to the species, it is
possible, by microscopical examination, to determine the relationship of
trees in cases where nothing but fragments of the trunk remain.
The process of fossilization is at best a slow one, and soft substances
such as flesh, or even horn, decay too rapidly for it to take place, so
that all accounts of petrified bodies, human or otherwise, are either
based on deliberate frauds or are the result of a very erroneous
misinterpretation of facts. That the impression or cast of a body
_might_ be formed in nature, somewhat as casts have been made of those
who perished at Pompeii, is true; but, so far, no authentic case of the
kind has come to light, and the reader is quite justified in
disbelieving any report of "a petrified man."
Natural casts of such hard bodies as shells are common, formed by the
dissolving away of the original shell after it had become enclosed in
mud, or even after this had changed to stone, and the filling up of this
space by the filtering in of water charged with lime or silica, which
is there deposited, often in crystalline form. In this way, too, are
formed casts of eggs of reptiles and birds, so perfect that it is
possible to form a pretty accurate opinion as to the group to which they
belong.
[Illustration: Fig. 2.--Bryozoa from the Shore of the Devonian Sea that
Covered Eastern New York. _From a specimen in Yale University Museum,
prepared by Dr. Beecher._]
Sometimes it happens that shells or other small objects imbedded in
limestone have been dissolved and replaced by silica, and in such cases
it is possible to eat away the enveloping rock with acid and leave the
silicified casts. By this method specimens of shells, corals, and
bryozoans are obtained of almost lace-like delicacy, and as perfect as
if only yesterday gathered at the sea-shore. Casts of the interior of
shells, showing many details of structure, are common, and anyone who
has seen clams dug will understand how they are formed by the entrance
of mud into the empty shell.
Casts of the kernels of nuts are formed in much the same way, and
Professor E. H. Barbour has thus described the probable manner in which
this was done. When the nuts were dropped into the water of the ancient
lake the kernel rotted away, but the shell, being tough and hard, would
probably last for years under favorable circumstances. Throughout the
marls and clays of the Bad Lands (of South Dakota) there is a large
amount of potash. This is dissolved by water, and then acts upon quartz,
carrying it away in solution. This would find its way by infiltration
into the interior of the nut. At the same time with this process,
carrying lime carbonate in solution was going on, so that doubtless the
stone kernels, consisting of pretty nearly equal parts of lime and
silica, were deposited within the nuts. These kernels, of course, became
hard and flinty in time, and capable of resisting almost any amount of
weathering. Not so the organic shell; this eventually would decay away,
and so leave the filling or kernel of chalcedony and lime.[1]
[1] _Right here is the weak spot in Professor Barbour's explanation, and
an illustration of our lack of knowledge. For it is difficult to see why
the more enduring husk should not have become mineralized equally with
the cavity within._
"Fossil leaves" are nothing but fine casts, made in natural moulds, and
all have seen the first stages in their formation as they watched the
leaves sailing to the ground to be covered by mud or sand at the next
rain, or dropping into the water, where sooner or later they sink, as we
may see them at the bottom of any quiet woodland spring.
Impressions of leaves are among the early examples of color-printing,
for they are frequently of a darker, or even different, tint from that
of the surrounding rock, this being caused by the carbonization of
vegetable matter or to its action on iron that may have been present in
the soil or water. Besides complete mineralization, or petrifaction,
there are numerous cases of incomplete or semi-fossilization, where
modern objects, still retaining their phosphate of lime and some animal
matter even, are found buried in rock. This takes place when water
containing carbonate of lime, silica, or sometimes iron, flows over beds
of sand, cementing the grains into solid but not dense rock, and at the
same time penetrating and uniting with it such things as chance to be
buried. In this way was formed the "fossil man" of Guadeloupe, West
Indies, a skeleton of a modern Carib lying in recent concretionary
limestone, together with shells of existing species and fragments of
pottery. In a similar way, too, human remains in parts of Florida have,
through the infiltration of water charged with iron, become partially
converted into limonite iron ore; and yet we know that these bones have
been buried within quite recent times.
Sometimes we hear of springs or waters that "turn things into stone,"
but these tales are quite incorrect. Waters there are, like the
celebrated hot springs of Auvergne, France, containing so much carbonate
of lime in solution that it is readily deposited on objects placed
therein, coating them more or less thickly, according to the length of
time they are allowed to remain. This, however, is merely an
encrustation, not extending into the objects. In a similar way the
precipitation of solid material from waters of this description forms
the porous rock known as tufa, and this often encloses moss, twigs, and
other substances that are in no way to be classed with fossils.
But some streams, flowing over limestone rocks, take up considerable
carbonate of lime, and this may be deposited in water-soaked logs,
replacing more or less of the woody tissue and thus really partially
changing the wood into stone.
The very rocks themselves may consist largely of fossils; chalk, for
example, is mainly made up of the disintegrated shells of simple marine
animals called foraminifers, and the beautiful flint-like "skeletons" of
other small creatures termed radiolarians, minute as they are, have
contributed extensively to the formation of some strata.
Even after an object has become fossilized, it is far from certain that
it will remain in good condition until found, while the chance of its
being found at all is exceedingly small. When we remember that it is
only here and there that nature has made the contents of the rocks
accessible by turning the strata on edge, heaving them into cliffs or
furrowing them with valleys and canyons, we realize what a vast number
of pages of the fossil record must remain not only unread, but unseen.
The wonder is, not that we know so little of the history of the past,
but that we have learned so much, for not only is nature careless in
keeping the records--preserving them mostly in scattered fragments--but
after they have been laid away and sealed up in the rocks they are
subject to many accidents. Some specimens get badly flattened by the
weight of subsequently deposited strata, others are cracked and twisted
by the movements of the rocks during periods of upheaval or subsidence,
and when at last they are brought to the surface, the same sun and rain,
snow and frost, from which they once escaped, are ready to renew the
attack and crumble even the hard stone to fragments. Such, very briefly,
are some of the methods by which fossils may be formed, such are some of
the accidents by which they may be destroyed; but this description must
be taken as a mere outline and as applying mainly to vertebrates, or
backboned animals, since it is with them that we shall have to deal. It
may, however, show why it is that fossils are not more plentiful, why we
have mere hints of the existence of many animals, and why myriads of
creatures may have flourished and passed away without so much as leaving
a trace of their presence behind.
_REFERENCES_
_A very valuable and interesting article by Dr. Charles A. White,
entitled "The Relation of Biology to Geological Investigation," will be
found in the Report of the United States National Museum for 1892. This
comprises a series of essays on the nature and scientific uses of fossil
remains, their origin, relative chronological value and other questions
pertaining to them. The United States National Museum has published a
pamphlet, part K, Bulletin 39, containing directions for collecting and
preparing fossils, by Charles Schuchert; and another, part B, Bulletin
39, collecting recent and fossil plants, by F. H. Knowlton._
[Illustration: Fig. 3.--Skeleton of a Radiolarian Very Greatly
Enlarged.]
II
THE EARLIEST KNOWN VERTEBRATES
"_We are the ancients of the earth
And in the morning of the times._"
There is a universal, and perfectly natural, desire for information,
which in ourselves we term thirst for knowledge and in others call
curiosity, that makes mankind desire to know how everything began and
causes much speculation as to how it all will end. This may take the
form of a wish to know how a millionaire made his first ten cents, or it
may lead to the questions--What is the oldest animal? or, What is the
first known member of the great group of backboned animals at whose head
man has placed himself? and, What did this, our primeval and
many-times-removed ancestor, look like? The question is one that has
ever been full of interest for naturalists, and Nature has been
interrogated in various ways in the hope that she might be persuaded to
yield a satisfactory answer. The most direct way has been that of
tracing back the history of animal life by means of fossil remains, but
beyond a certain point this method cannot go, since, for reasons stated
in various places in these pages, the soft bodies of primitive animals
are not preserved. To supplement this work, the embryologist has studied
the early stages of animals, as their development throws a side-light on
their past history. And, finally, there is the study of the varied forms
of invertebrates, some of which have proved to be like vertebrates in
part of their structure, while others have been revealed as vertebrates
in disguise. So far these various methods have yielded various answers,
or the replies, like those of the Delphic Oracle, have been variously
interpreted so that vertebrates are considered by some to have descended
from the worms, while others have found their beginnings in some animal
allied to the King Crab.
Every student of genealogy knows only too well how difficult a matter it
is to trace a family pedigree back a few centuries, how soon the family
names become changed, the line of descent obscure, and how soon gaps
appear whose filling in requires much patient research. How much more
difficult must it be, then, to trace the pedigree of a race that
extends, not over centuries, but thousands of centuries; how wide must
be some of the gaps, how very different may the founders of the family
be from their descendants! The words old and ancient that we use so
often in speaking of fossils appeal to us somewhat vaguely, for we speak
of the ancient civilizations of Greece and Rome, and call a family old
that can show a pedigree running back four or five hundred years, when
such as these are but affairs of yesterday compared with even recent
fossils.
Perhaps we may better appreciate the meaning of these words by recalling
that, since the dawn of vertebrate life, sufficient of the earth's
surface has been worn away and washed into the sea to form, were the
strata piled directly one upon the other, fifteen or twenty miles of
rock. This, of course, is the sum total of sedimentary rocks, for such a
thickness as this is not to be found at any one locality; because,
during the various ups and downs that this world of ours has met with,
those portions that chanced to be out of water would receive no deposit
of mud or sand, and hence bear no corresponding stratum of rock. The
reader may think that there is a great deal of difference between
fifteen and twenty miles, but this liberal margin is due to the
difficulty of measuring the thickness of the rocks, and in Europe the
sum of the measurable strata is much greater than in North America.
The earliest traces of animal life are found deeper still, beneath
something like eighteen to twenty-five miles of rock, while below this
level are the strata in which dwelt the earliest living things,
organisms so small and simple that no trace of their existence has been
left, and we infer that they were there because any given group starts
in a modest way with small and simple individuals.
At the bottom, then, of twenty miles of rocks the seeker for the
progenitor of the great family of backboned animals finds the scant
remains of fish-like animals that the cautious naturalist, who is much
given to "hedging," terms, not vertebrates, but prevertebrates or the
forerunners of backboned animals. The earliest of these consist of small
bony plates, and traces of a cartilaginous backbone from the Lower
Silurian of Colorado, believed to represent relatives of Chimaera and
species related to those better-known forms Holoptychius and Osteolepis,
which occur in higher strata. There are certainly indications of
vertebrate life, but the remains are so imperfect that little more can
be said regarding them, and this is also true of the small conical teeth
which occur in the Lower Silurian of St. Petersburg, and are thought to
be the teeth of some animal like the lamprey.
A little higher up in the rocks, though not in the scale of life, in the
Lower Old Red Sandstone of England, are found more numerous and better
preserved specimens of another little fish-like creature, rarely if ever
exceeding two inches in length, and also related (probably) to the
hag-fishes and lampreys that live to-day.
These early vertebrates are not only small, but they were cartilaginous,
so that it was essential for their preservation that they should be
buried in soft mud as soon as possible after death. Even if this took
place they were later on submitted to the pressure of some miles of
overlying rock until, in some cases, their remains have been pressed out
thinner than a sheet of paper, and so thoroughly incorporated into the
surrounding stone that it is no easy matter to trace their shadowy
outlines. With such drawbacks as these to contend with, it can scarcely
be wondered at that, while some naturalists believe these little
creatures to be related to the lamprey, others consider that they belong
to a perfectly distinct group of animals, and others still think it
possible that they may be the larval or early stages of larger and
better-developed forms.
Still higher up we come upon the abundant remains of numerous small
fish-like animals, more or less completely clad in bony armor,
indicating that they lived in troublous times when there was literally a
fight for existence and only such as were well armed or well protected
could hope to survive. A parallel case exists to-day in some of the
rivers of South America, where the little cat-fishes would possibly be
eaten out of existence but for the fact that they are covered--some of
them very completely--with plate-armor that enables them to defy their
enemies, or renders them such poor eating as not to be worth the taking.
The arrangement of the plates or scales in the living Loricaria is very
suggestive of the series of bony rings covering the body of the ancient
Cephalaspis, only the latter, so far as we know, had no side-fins; but
the creatures are in no wise related, and the similarity is in
appearance only.
[Illustration: Fig. 4.--Cephalaspis and Loricaria, an Ancient and a
Modern Armored Fish.]
Pterichthys, the wing fish, was another small, quaint, armor-clad
creature, whose fossilized remains were taken for those of a crab, and
once described as belonging to a beetle. Certainly the buckler of this
fish, which is the part most often preserved, with its jointed, bony
arms, looks to the untrained eye far more like some strange crustacean
than a fish, and even naturalists have pictured the animal as crawling
over the bare sands by means of those same arms. These fishes and their
allies were once the dominant type of life, and must have abounded in
favored localities, for in places are great deposits of their protective
shields jumbled together in a confused mass, and, save that they have
hardened into stone, lying just as they were washed up on the ancient
beach ages ago. How abundant they were may be gathered from the fact
that it is believed their bodies helped consolidate portions of the
strata of the English Old Red Sandstone. Says Mr. Hutchinson, speaking
of the Caithness Flagstones, "They owe their peculiar tenacity and
durability to the dead fishes that rotted in their midst while yet they
were only soft mud. For just as a plaster cast boiled in oil becomes
thereby denser and more durable, so the oily and other matter coming
from decomposing fish operated on the surrounding sand or mud so as to
make it more compact."
It may not be easy to explain how it came to pass that fishes dwelling
in salt water, as these undoubtedly did, were thus deposited in great
numbers, but we may now and then see how deposits of fresh-water fishes
may have been formed. When rivers flowing through a stretch of level
country are swollen during the spring floods, they overflow their banks,
often carrying along large numbers of fishes. As the water subsides
these may be caught in shallow pools that soon dry up, leaving the
fishes to perish, and every year the Illinois game association rescues
from the "back waters" quantities of bass that would otherwise be lost.
Mr. F. S. Webster has recorded an instance that came under his
observation in Texas, where thousands of gar pikes, trapped in a lake
formed by an overflow of the Rio Grande, had been, by the drying up of
this lake, penned into a pool about seventy-five feet long by
twenty-five feet wide. The fish were literally packed together like
sardines, layer upon layer, and a shot fired into the pool would set the
entire mass in motion, the larger gars as they dashed about casting the
smaller fry into the air, a score at a time. Mr. Webster estimates that
there must have been not less than 700 or 800 fish in the pool, from a
foot and a half up to seven feet in length, every one of which perished
a little later. In addition to the fish in the pond, hundreds of those
that had died previously lay about in every direction, and one can
readily imagine what a fish-bed this would have made had the occurrence
taken place in the past.
From the better-preserved specimens that do now and then turn up, we are
able to obtain a very exact idea of the construction of the bony cuirass
by which Pterichthys and its American cousin were protected, and to make
a pretty accurate reconstruction of the entire animal. These primitive
fishes had mouths, for eating is a necessity; but these mouths were not
associated with true jaws, for the two do not, as might be supposed,
necessarily go together. Neither did these animals possess hard
backbones, and, while Pterichthys and its relatives had arms or fins,
the hard parts of these were not on the inside but on the outside, so
that the limb was more like the leg of a crab than the fin of a fish;
and this is among the reasons why some naturalists have been led to
conclude that vertebrates may have developed from crustaceans.
Pteraspis, another of these little armored prevertebrates, had a less
complicated covering, and looked very much like a small fish with its
fore parts caught in an elongate clam-shell.
The fishes that we have so far been considering--orphans of the past
they might be termed, as they have no living relatives--were little
fellows; but their immediate successors, preserved in the Devonian
strata, particularly of North America, were the giants of those days,
termed, from their size and presumably fierce appearance, Titantichthys
and Dinichthys, and are related to a fish, _Ceratodus_, still living in
Australia.
We know practically nothing of the external appearance of these fishes,
great and fierce though they may have been, with powerful jaws and
armored heads, for they had no bony skeleton--as if they devoted their
energies to preying upon their neighbors rather than to internal
improvements. They attained a length of ten to eighteen feet, with a
gape, in the large species called Titanichthys, of four feet, and such a
fish might well be capable of devouring anything known to have lived at
that early date.