LESSON XX.

THE EARLY MAMMALS.

“’Tis there the otter dives, the beaver feeds,Where pensive osiers dip their willowy weeds,And there the wild-cat purrs amid her brood,And trains them in the sylvan solitude,To watch the squirrels leap, or mark the minkPaddling the water by the quiet brink.”

“’Tis there the otter dives, the beaver feeds,

Where pensive osiers dip their willowy weeds,

And there the wild-cat purrs amid her brood,

And trains them in the sylvan solitude,

To watch the squirrels leap, or mark the mink

Paddling the water by the quiet brink.”

—Brainard.

COMPANIONS AND FRIENDS.

The last nine lessons have been occupied with brief descriptions of some of the fauna of the first five world-building periods. A knowledge of these early forms of life is not only pleasing in itself, but valuable, as giving us clearer ideas of the past ages, and because the animals and plants that then existed have a close relationship to those of our own day.

The earliest animals described were the foraminifera,from which class we have our most ancient fossils. We might infer from this fact that the foraminifera were the first forms of animal life. But no; even these had predecessors, but of groups from which no fossils remain.

The foraminifera, minute as they were, had shells. There is no doubt that they were preceded in the scale of creation by tiny creatures without shells, creatures that with neither arms nor legs, heads nor stomachs, yet could provide themselves with arms in an emergency, and were all mouth and stomach. Such an animal has been named a proteus from its constant changes of shape, Proteus in the classic fable being a sea-god who was constantly changing his form.

The amœba, or proteus, belonged to the class protozoa, and may be described as a minute drop of a jelly-like substance, never at rest, but ceaselessly changing its shape. Imagine such a particle of jelly held suspended in a glass of water. Now it seems to extend or pour itself out on one side, into what we may call an arm, because it is reaching for an atom of food. This extended portion is drawn back, and whenever it returns into the drop, there the food is received and digested. Therefore we say the amœba is all mouth and all stomach, because it can receive and digest food in any part of its substance.

The earliest of the protozoa was probably a jelly-like drop composed of a single cell. Sometimes a number of these cells, or individuals, clung together in a loosely united mass or community. When a new individual was formed the process was by “budding,” the single cell becoming two, dividingand parting, so that each individual was complete in itself; and which was the new one, and which was the old one, or whether both were part new and part old, certainly they themselves did not know.

Parallel with this group of one-celled jelly-like animals, was a group of one-celled jelly-like plants. Each of these groups stood at the beginning of a great and constantly ascending series; the two groups were different in their nature and in their method of nutrition, yet each so like the other, that it is very difficult to distinguish them. Thus when we consider the dawn of life we must put the shelless protozoa ages back before the busy shell-housed foraminifera.

Yet in so placing the shelless amœbæ we must not fancy them extinct. By no means: in myriad millions they still exist, and have through all the ages, and there is no pond to-day that has not its restless kaleidoscopic representatives of life’s lowest grade.

It was a long, long journey from this formless speck of jelly to the highest grade of life—the mammalian form; and up this long ascent, conducted on a definite plan, life moved without faltering or contradictions. Let us then in our last look at vanished fauna, regard some of the fossil remains of that crowning class of animal life at the head of which stands man—“Time’s noblest offspring and the last.”

Our knowledge of the earliest mammals is very incomplete, and is constantly changing, as the discovery of new beds of fossils shows to us new forms, and supplies new information concerning their relationships. The mammals werelate in their arrival upon the earth. They could afford to wait, for they had come to stay and to possess the kingdom of nature. The first mammals lived in the first age of the Reptilian time. They were nearly the size of large rats or squirrels, and curiously enough their teeth and jawbones are the portions of their bodies which have survived decay to tell their story.

The teeth of mammals differ in construction from the teeth of all other animals, and thus if only one single tooth is found we may be sure that it is a part of a mammalian creature; and, being a mammal, we know certain facts in regard to it, as for instance that it was born alive,[47]and while young was cared for and suckled by its mother. When the teeth are molar, or grinding teeth, we know that the animal lived on grain or herbs—and thus from the formation we may decide that it was a grazing animal; sharp-pointed canine, or dog-like teeth, show a meat-eating animal, a hunting, flesh-seeking creature; worn teeth, teeth with the enamel ground down, tell us that the animal was old. Among the teeth found, some suggest mammals that lived on insects, fruit, and roots, and some teeth found in the ancient rocks are very like those of the kangaroo rat; so that by observing the present animals of this type, we can in general arrive at the habits of these long extinct creatures.

Probably the rat and squirrel families, capable of living on roots and nuts, and small enough to hide in crevices, in decayed trees, and under stumps, where the large reptiles could not follow to destroy them, were the earliest mammalianforms. It is a singular fact that the rocks of the Chalk age, the last era of the time before the last world-building period, have afforded no fossil mammals. This is evidently not because there were no mammals in that age of the world; for the rocks of the succeeding periods have yielded abundant forms of many species, showing that mammals had extended, multiplied, and improved exceedingly. Either the circumstances of the close of this age were not favorable to the preservation of such remains, or there are in the chalk rocks fossils which will yet be found.

In the earlier ages of the present or last building-time, the mammals were not only numerous, but far exceeded in size any now existing. Indeed, it seems that as the type improved the more bulky forms passed away; the higher animals being less unwieldy. Still this suggestion must at once be met by exceptions: for in the case of the horse, as the model improved, the size of the animal constantly increased. The mammals had finally become world-masters, and before them the gigantic reptiles perished. For a time mammals and reptiles of equally stupendous proportions seemed to face each other, but the new type gained the victory over the old.

The mammals, as well as the reptiles, had the faculty of adaptation; they seemed suited to a wide variety of conditions. They fed on fish, flesh, herbs, fruits, and fowl. Some of them had bare tough skins; others wore long scanty hair; others again were clad in fur, or heavy wool. Some of them burrowed in the ground; some lived in caves and dens; some were tree dwellers, or arboreal; others wandered over widesavannahs or in the forests, careless of other shelter than trees or reedy jungles.

Next after the rat-like families came a tribe of insect-eating creatures like the present ant-eaters, but far exceeding them in size, some of them being nearly as large as a rhinoceros. The mylodon was a fruit-eater and so large and strong that it was able to tear down the trees which bore the fruit it coveted; certainly a destructive fashion of fruit-gathering, proving the mylodon much more barbarous than a Saracen.[48]

Meantime, while these mammals flourished on the land there were numerous others in the sea, and these of a very large size, although no fossils have yet shown that the sea-mammals preceded those of the land. The whales and the sirens seem to have appeared many years ago, and have since continued.

Enormous armadillos, covered with mail and very like the tortoise family of reptiles, marched about the woods or sunned themselves upon the shores. When twilight settled over the ancient woods and savannahs the mammals of the air came forth, and bats flew zigzagging about, hunting after insects or little birds.

The bone-caves of the age before man came have abundant bones of mammals; bones which represent the pursuers and the pursued, hunters and hunted,—some the relics of the meat-eating, hunting beasts, and some, the gnawed remains of their prey.

Among the vertebrate vegetable-eating animals we note the elephant, the great woolly elephant now extinct, and themighty mammoth, known only by its remains, yet very well known, because the frozen mud of Siberia has preserved for us the entire animal, even to its eye-balls. We have in another lesson indicated the life history of the horse-like animals which belonged to these successive periods. There were also many families related to the tapirs, deer, bears, and musk-oxen of the present day. In fact the majority of the mammalian forms of the earlier ages have their modified representatives in the present age; while others, as the mastodon and many more, have made way for more modern families and are known only by fossil remains.

The Ice period no doubt made a great change in the fauna of the globe. During its desolation and cold many families of animals perished. Other creatures changed their homes, migrating from the formerly temperate polar regions to the tropics, retreating to warmer latitudes as the ice-sheet advanced. Some of the carnivora especially were capable of resisting the cold by increasing the thickness of their coats; but animals dependent upon a vegetable diet must either perish with the flora of the regions they inhabited, or follow the changed lines of vegetable growth, as the northerly plants perished and vegetation flourished only in the warm southerly lands.

The last of the mammals to appear in the brute creation were the quadrumana or monkey tribe, which hold the highest place in the brute creation.

FOOTNOTES:[47]A later lesson will describe a mammal that comes from an egg![48]The Mohammedan soldiers were forbidden to destroy fruit trees.

[47]A later lesson will describe a mammal that comes from an egg!

[48]The Mohammedan soldiers were forbidden to destroy fruit trees.

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