Animals of Ancient Lands

CHAPTER I.. The First Land Dwellers.

THE FIRST LAND DWELLERS.

In the first book of this series, “Animals of Ancient Seas,” (No. 47) we followed the evolution of animal life from the most primitive one-celled creatures to the fishes, and from the most primitive fishes to those which possessed lung-like organs that enabled them to breathe from air as well as water. The next stage in evolution was the development of feet and legs from the fish fin, and this was accomplished before the end of that geologic period known as the Devonian, or more commonly, as the “Age of Fishes.” True, no actual remains have been found, but one fortunate collector succeeded in getting out a fossil footprint, which is all that is needed to prove the case. This footprint was made by an animal that looked much like the mud puppy, or salamander, of modern streams and lakes, and was related also to the frogs and toads. Like these creatures, he spent the early part of his life in water, breathing with gills, and possessing a more or less fish-like form, while in his maturity he lived at least partly on land, and breathed by means of lungs. This type of development, almost universal among his class, has gained for them the name of Amphibians, or “double livers.”

During those periods which are correctly known as the Mississippian and Pennsylvanian, but which are more commonly grouped under the one name Carboniferous, the amphibians increased in variety, and gave rise to a new and immensely important group of animals, the Reptiles. Since everyone knows the general characters of this group, we shall not take the trouble to define them. The important thing about them, so far as evolution is concerned is that they are capable of living on land throughout their whole lives, not even the eggs having to be deposited in water. This, as can readily be seen, is a very fundamental character, for as long as animals were confined to water during their earliest stages, great progress was quite impossible. Imagine what a state humanity would be in if every child had to begin life in some brook, lake, or pond, and could not emerge from the water until it was fifteen to twenty years old!

Unfortunately for our knowledge of life in the past, fossils of both amphibians and reptiles are by no means common in the Carboniferous systems. It was not until the times of coal deposition were almost past, and great mountains and broad plains were taking the place of shallow seas and sombre swamps, that land dwelling animals became really abundant. This appearance of dry land was not only the cause of the development of the wonderful array of animals that inhabited the Permian world, but also the reason why so few of them are preserved as fossils, for it is only when the bones of animals become buried in water-soaked layers of sediment, or covered by water, that they are readily petrified. An animal that dies and remains exposed to the open air stands very little chance of becoming a fossil; its bones are gnawed by carrion feeders, worn by the wind, and broken up by decay. Thus of the hundreds of thousands, even millions, of buffalo, cattle, antelope, and elk whose carcasses have dotted the plains of this continent in the past half century there remain but a few rotten and frost-split horns and bones. Without question there are, in the muddy banks and bars of rivers, skeletons and parts of skeletons that are undergoing the slow process of petrification, and that will be dug up and treasured in the museums of some future civilization. And just as the record of animal life of today will be but a fragment of that which actually exists, so the record of the great land fauna of the Permian period is but the merest trace of the myriad creatures of that time. It is only in the most exceptional places that great quantities of bones were brought together under conditions favorable to fossilization, and such a district is found in northern Texas.

“When the Appalachian Mountains were raised, an extension of their southern end reached across what are now Arkansas and Oklahoma, terminating in the Wichita Mountains.... North of this range rose a broad upland, reaching from the Rockies to the Appalachians and to the Canadian line on the north; south of the mountains a shallow sea reached nearly to their base, and some great rivers from the mountains and uplands poured their flood waters into the sea and built up a great delta. The remains of animals which haunted the banks of the rivers were swept into them in time of flood and carried out to be deposited in the delta, which covered most of what is now Wichita, Archer, Wilbarger counties in the State of Texas. Naturally, most of the remains which found their way into the streams were already fragmentary, as they had rotted on the banks, and had been torn by predatory animals, but in their course to the sea they were still further disintegrated so that, rolled by the waters and beaten by the waves, they sank to their burial as little more than water-worn fragments; ends of limb bones, isolated vertebrae, and broken skulls, which do little more than tantalize the student with the hints of new forms and new relationships that can not be verified. In some places these water-worn fragments are so thick upon the ground that they literally can be shoveled up by the wagon load. In some instances the bodies of animals found their way unharmed into the water and, distended by the gases of decomposition, floated far and uninjured until they came to rest on some mud flat beyond the reach of sharks or other predatory animals. Such skeletons are preserved entire with most remarkable perfection, but they are exceedingly rare, and it is a fortunate collector who turns up even one in the course of a whole season of search.”

Cacops, a remarkable Permian amphibian.]

Among the most remarkable of the animals found in the stratified rocks of this ancient delta are the amphibians. During the preceding ages, as we have seen, they were the masters of the continental world--the largest and most progressive of land dwellers. But by the time of the Permian they were on the downward road which was to lead them, not to extinction, but to the obscure positions of toads, frogs and salamanders. But this decline did not come at once, and with overwhelming completeness; the early amphibians did not yield tamely to the fate of old age. During the Permian, and the succeeding age, the Triassic, there lived some of the largest and strangest amphibians that the world has known. Some of them returned to the water and developed eel-like bodies with enormous, arrow-like heads; some lived in trees, where their remains have been found by geologists studying coal deposits; others protected themselves by armor and crawled about more or less unmolested, while not a few even went so far as to take refuge in the ground.

The giant among all amphibians was Eryops, of the Permian, with a length of about eight feet. He looked somewhat like an immensely overgrown salamander with flabby sprawling legs that were incapable of lifting his body from the ground except by the greatest effort. His skull was from two to two and a half feet in length, and looked like that of a gigantic frog, the jaws were equipped with sharp, cone-shaped teeth and sharp, powerful tusks. Evidently Eryops held about the same position in Permian swamps of Texas as the alligator does in the Georgia bayous of today, lying near the surface of the water with only its eyes and nostrils exposed until the approach of a victim stirred it to movement.

Sharply contrasted with the giant Eryops, and doubtless often its victim, was the unique Diplocaulus. The head of this amphibian was the form of a rather angular crescent, with strong spines directed to the rear, and protected by heavy armor. The eyes and nostrils were directed straight upward, and situated at the forward end of the skull. The body, remarkably enough, was long, thin, and eel-like, with only rudimentary limb bones, and delicate ribs. Probably the animal spent its entire life in the water, wriggling along and pushing its enormous head before it along the slimy bottom. Perhaps, when attacked from above, Diplocaulus was thrown into a frenzy of energy that lifted his heavy, armored head above the bottom, and thrashed it about in the water, but anything like swimming must have been quite beyond his power.

Diplocaulus, the most bizarre amphibian known.]

But, bizarre though the amphibians of this Permian deposit are, they are exceeded by the reptiles. These creatures, as we have seen, made their appearance in the Pennsylvanian, or late “Carboniferous,” and already, in the very beginning of their history, they showed an astonishing diversity of form and habit. There were reptiles that lived in the water, and reptiles that lived on dry land; reptiles that ate flesh, reptiles that ate plants, and reptiles that ate both. Some of them were extremely primitive, closely resembling their amphibian ancestors, while others were like nothing that has lived either before or since.

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