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of the wide-spread existence of man in an early epoch have multiplied indefinitely, and to-day the

paleontologist traces the history of our race back beyond the iron and bronze ages, through a neolithic or polished-stone age, to a paleolithic or rough-stone age, with confidence born of unequivocal knowledge. And

he looks confidently to the future explorer of the earth's fossil records to extend the history back into vastly

more remote epochs, for it is little doubted that paleolithic man, the most ancient of our recognized progenitors,

is a modern compared to those generations that represented the real childhood of our race.

THE FOSSIL-BEDS OF AMERICA

Coincidently with the discovery of these highly suggestive pages of the geologic story, other still more instructive chapters were being brought to light in America.

It was found that in the Rocky Mountain region,

in strata found in ancient lake beds, records of the tertiary period, or age of mammals, had been made and preserved with fulness not approached in any other region hitherto geologically explored. These records were

made known mainly by Professors Joseph Leidy, O. C. Marsh, and E. D. Cope, working independently, and more recently by numerous younger paleontologists.

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The profusion of vertebrate remains thus brought to

light quite beggars all previous exhibits in point of mere numbers. Professor Marsh, for example, who was first

in the field, found three hundred new tertiary species between the years 1870 and 1876. Meanwhile, in cretaceous strata, he unearthed remains of about two hundred birds with teeth, six hundred pterodactyls,

or flying dragons, some with a spread of wings of twentyfive feet, and one thousand five hundred mosasaurs

of the sea-serpent type, some of them sixty feet or more in length. In a single bed of Jurassic rock, not larger than a good-sized lecture-room, he found the remains

of one hundred and sixty individuals of mammals, representing twenty species and nine genera; while beds

of the same age have yielded three hundred reptiles, varying from the size of a rabbit to sixty or eighty feet in length.

But the chief interest of these fossils from the West is not their number but their nature; for among them are numerous illustrations of just such intermediate types of organisms as must have existed in the past if the succession of life on the globe has been an unbroken

lineal succession. Here are reptiles with bat-like wings, and others with bird-like pelves and legs adapted for bipedal locomotion. Here are birds with teeth, and

other reptilian characters. In short, what with reptilian birds and birdlike reptiles, the gap between

modern reptiles and birds is quite bridged over. In a

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History of Science		133
similar way, various diverse mammalian forms, as the
tapir, the rhinoceros, and the horse, are linked together
by fossil	progenitors. And, most important of all,
Professor	Marsh has discovered a series of mammalian
remains, occurring in successive geological epochs,
which are	held to represent beyond cavil the actual line
of descent of the modern horse; tracing the lineage of
our one-toed species back through two and three toed
forms, to	an ancestor in the eocene or early tertiary
that had four functional toes and the rudiment of a
fifth. This discovery is too interesting and too important
not to be	detailed at length in the words of the

discoverer.

Marsh Describes the Fossil Horse

"It is a well-known fact," says Professor Marsh, "that the Spanish discoverers of America discovered

no horses on this continent, and that the modern horse (Equus caballus, Linn.) was subsequently introduced from the Old World. It is, however, not so generally known that these animals had formerly been abundant here, and that long before, in tertiary time, near

relatives of the horse, and probably his ancestors, existed in the far West in countless numbers and in a

marvellous variety of forms. The remains of equine mammals, now known from the tertiary and quaternary

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deposits of this country, already represent more than double the number of genera and species hitherto found

in the strata of the eastern hemisphere, and hence afford most important aid in tracing out the genealogy

of the horses still existing.

"The animals of this group which lived in America during the three diversions of the tertiary period were especially numerous in the Rocky Mountain regions,

and their remains are well preserved in the old lake basins which then covered so much of that country. The most ancient of these lakes--which extended over

a considerable part of the present territories of Wyoming and Utah--remained so long in eocene times that

the mud and sand, slowly deposited in it, accumulated to more than a mile in vertical thickness. In these deposits vast numbers of tropical animals were entombed, and here the oldest equine remains occur, four species of which have been described. These

belong to the genus Orohippus (Marsh), and are all of a diminutive size, hardly bigger than a fox. The skeletons of these animals resemble that of the horse in

many respects, much more indeed than any other

existing species, but, instead of the single toe on each foot, so characteristic of all modern equines, the various species of Orohippus had four toes before and three behind, all of which reached the ground. The skull,

too, was proportionately shorter, and the orbit was not enclosed behind by a bridge of bone. There were fifty

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four teeth in all, and the premolars were larger than the molars. The crowns of these teeth were very short. The canine teeth were developed in both sexes, and the incisors did not have the "mark" which indicates the age of the modern horse. The radius and ulna were separate, and the latter was entire through the whole length. The tibia and fibula were distinct. In the

forefoot all the digits except the pollex, or first, were well developed. The third digit is the largest, and its close resemblance to that of the horse is clearly marked. The terminal phalanx, or coffin-bone, has a shallow median bone in front, as in many species of this group

in the later tertiary. The fourth digit exceeds the second in size, and the second is much the shortest of all. Its metacarpal bone is considerably curved outward. In the hind-foot of this genus there are but

three digits. The fourth metatarsal is much larger than the second.

"The larger number of equine mammals now known

from the tertiary deposits of this country, and their regular distributions through the subdivisions of this formation, afford a good opportunity to ascertain the probable descent of the modern horse. The American representative of the latter is the extinct Equus fraternus (Leidy), a species almost, if not wholly, identical with the Old World Equus caballus (Linnaeus), to which our recent horse belongs. Huxley

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has traced successfully the later genealogy of the horse through European extinct forms, but the line in America was probably a more direct one, and the record is

more complete. Taking, then, as the extreme of a series, Orohippus agilis (Marsh), from the eocene, and

Equus fraternus (Leidy), from the quaternary, intermediate forms may be intercalated with considerable certainty

from thirty or more well-marked species that

lived in the intervening periods. The natural line of descent would seem to be through the following genera: Orohippus, of the eocene; Miohippus and Anchitherium, of the miocene; Anchippus, Hipparion, Protohippus, Phohippus, of the pliocene; and Equus, quaternary

and recent.

The most marked changes undergone by the successive equine genera are as follows: First, increase in

size; second, increase in speed, through concentration of limb bones; third, elongation of head and neck, and modifications of skull. The eocene Orohippus was the size of a fox. Miohippus and Anchitherium, from the miocene, were about as large as a sheep. Hipparion

and Pliohippus, of the pliocene, equalled the ass in height; while the size of the quaternary Equus was fully up to that of a modern horse.

"The increase of speed was equally well marked, and was a direct result of the gradual formation of the limbs. The latter were slowly concentrated by the

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reduction of their lateral elements and enlargement of the axial bone, until the force exerted by each limb came to act directly through its axis in the

line of motion. This concentration is well seen--e.g., in the fore-limb. There was, first, a change in the scapula and humerus, especially in the latter, which

facilitated motion in one line only; second, an expansion of the radius and reduction of the ulna, until the

former alone remained entire and effective; third, a shortening of all the carpal bones and enlargement of

the median ones, insuring a firmer wrist; fourth, an increase of size of the third digit, at the expense of those

of each side, until the former alone supported the limb.

"Such is, in brief, a general outline of the more marked changes that seemed to have produced in America the highly specialized modern Equus from his

diminutive four-toed predecessor, the eocene Orohippus. The line of descent appears to have been direct,

and the remains now known supply every important intermediate form. It is, of course, impossible to say with certainty through which of the three-toed genera

of the pliocene that lived together the succession came. It is not impossible that the latter species, which appear generically identical, are the descendants of more distinct pliocene types, as the persistent tendency in

all the earlier forms was in the same direction.

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Considering the remarkable development of the group through the tertiary period, and its existence even later, it seems very strange that none of the species should have survived, and that we are indebted for our present horse to the Old World."[7]

PALEONTOLOGY OF EVOLUTION

These and such-like revelations have come to light in

our own time--are, indeed, still being disclosed. Needless to say, no index of any sort now attempts to conceal

them; yet something has been accomplished towards the same end by the publication of the discoveries in Smithsonian bulletins and in technical memoirs of

government surveys. Fortunately, however, the results have been rescued from that partial oblivion by

such interpreters as Professors Huxley and Cope, so the unscientific public has been allowed to gain at

least an inkling of the wonderful progress of paleontology in our generation.

The writings of Huxley in particular epitomize the

record. In 1862 he admitted candidly that the paleontological record as then known, so far as it bears on the

doctrine of progressive development, negatives that doctrine. In 1870 he was able to "soften somewhat

the Brutus-like severity" of his former verdict, and to assert that the results of recent researches seem "to

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leave a clear balance in favor of the doctrine of the evolution of living forms one from another." Six years later, when reviewing the work of Marsh in America and of Gaudry in Pikermi, he declared that, "on the evidence of paleontology, the evolution of

many existing forms of animal life from their predecessors is no longer an hypothesis, but an historical

fact." In 1881 he asserted that the evidence gathered in the previous decade had been so unequivocal that, had the transmutation hypothesis not existed, "the paleontologist would have had to invent it."

Since then the delvers after fossils have piled proof on proof in bewildering profusion. The fossil-beds in the "bad lands" of western America seem inexhaustible. And in the Connecticut River Valley near relatives

of the great reptiles which Professor Marsh and others have found in such profusion in the West left

their tracks on the mud-flats--since turned to sandstone; and a few skeletons also have been found. The

bodies of a race of great reptiles that were the lords of creation of their day have been dissipated to their elements, while the chance indentations of their feet as

they raced along the shores, mere footprints on the sands, have been preserved among the most imperishable of the memory-tablets of the world.

Of the other vertebrate fossils that have been found

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in the eastern portions of America, among the most abundant and interesting are the skeletons of mastodons. Of these one of the largest and most complete is

that which was unearthed in the bed of a drained lake near Newburg, New York, in 1845. This specimen was larger than the existing elephants, and had tusks eleven feet in length. It was mounted and described by Dr.

John C. Warren, of Boston, and has been famous for half a century as the "Warren mastodon."

But to the student of racial development as recorded

by the fossils all these sporadic finds have but incidental interest as compared with the rich Western fossil-

beds to which we have already referred. From records here unearthed, the racial evolution of many mammals has in the past few years been made out in greater or less detail. Professor Cope has traced the ancestry of the camels (which, like the rhinoceroses, hippopotami, and sundry other forms now spoken of as "Old World,"

seem to have had their origin here) with much completeness.

A lemuroid form of mammal, believed to be of the type from which man has descended, has also been

found in these beds. It is thought that the descendants of this creature, and of the other "Old-World"

forms above referred to, found their way to Asia, probably, as suggested by Professor Marsh, across a bridge

at Bering Strait, to continue their evolution on the other hemisphere, becoming extinct in the land of their

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