Part 8 (1/2)
The head is only two feet long, and is, therefore, small out of all proportion to the great body. The neck measures twenty-one feet four inches, and is by far the longest and largest neck known in any animal living or extinct. The back is relatively very short, measuring ten feet eight inches. The vertebrae of the hip measure two feet and three inches. The tail measures from thirty-two to forty feet. We thus obtain, as a moderate estimate of the total length of the animal, sixty-eight to seventy feet. The restored skeleton, published by Mr.
J.B. Hatcher in July, 1901, and partly embodying our results, gave to science the first really accurate knowledge of the length of these animals, which hitherto had been greatly overestimated. The highest point in the body was above the hips; here in fact, was the center of power and motion, because, as observed above, the tail fairly balanced the anterior part of the body.
The restoration by Mr. Knight is drawn from a very careful model made under my direction, in which the proportions of the animal are precisely estimated. It is, I think, accurate--for a restoration--as well as interesting and up-to-date. These restorations are the ”working hypotheses” of our science; they express the present state of our knowledge, and, being subject to modification by future discoveries, are liable to constant change.
By contrast, the second type of giant dinosaur, the _Brontosaurus_, or ”thunder saurian” of Marsh, as shown in the restoration (fig. 22), was far more ma.s.sive in structure and relatively shorter in body. Five more or less complete skeletons are now to be seen in the Yale, American, Carnegie, and Field Columbian museums. In 1898 we discovered in the bluffs, about three miles west of the Bone-Cabin Quarry, the largest of these animals which has yet been found; it was worked out with great care and is now being restored and mounted complete in the American Museum. The thigh-bone is enormous, measuring five feet eight inches in length, and is relatively of greater ma.s.s than that of _Diplodocus_. The neck, chest, hips, and tail are correspondingly ma.s.sive. The neck is relatively shorter, however, measuring eighteen feet, while in _Diplodocus_ it measures over twenty-one feet. The total length of this ma.s.sive specimen is estimated at sixty-three feet, or from six to eight feet less than the largest ”long-limbed”
dinosaur. The height of the skeleton at the hips is fifteen feet.
There is less direct evidence that the ”thunder saurian” had the power of raising its fore quarters in the air than in the case of the ”light-limbed saurian,” because no bend or supporting point in the tail has been distinctly observed.
The third type of giant dinosaur is the less completely known ”chambered saurian,” the _Camarasaurus_ of Cope or _Morosaurus_ of Marsh, an animal more quadrupedal in gait or walking more habitually on all fours, like the great _Cetiosaurus_, or ”whale saurian,”
discovered near Oxford, England. With its shorter tail and heavier fore limbs, it is still less probable that this animal had the power of raising the anterior part of its body from the ground. Of a related type, perhaps, is the largest dinosaur ever found; this is the _Brachiosaurus_, limb-bones of which were discovered in central Colorado in 1901 and are now preserved in the Field Columbian Museum of Chicago. Its thigh-bone is six feet eight inches in length, and its upper arm-bone, or humerus, is even slightly longer.
_Feeding Habits of the Giant Dinosaurs._ We still have to solve one of the most perplexing problems of fossil physiology; how did the very small head, provided with light jaws, slender and spoon-shaped teeth confined to the anterior region, suffice to provide food for these monsters? I have advanced the idea that the food of _Diplodocus_ consisted of some very abundant and nutritious species of water-plant; that the clawed feet were used in uprooting such plants, while the delicate anterior teeth were employed only for drawing them out of the water; that the plants were drawn down the throat in large quant.i.ties without mastication, since there were no grinding or back teeth whatever in this animal. Unfortunately for this theory, it is now found that the front feet were not provided with many claws, there being only a single claw on the inner side. Nevertheless by some such means as this, these enormous animals could have obtained sufficient food in the water to support their great bulk.
_The Carnivorous Dinosaurs._ Mingling with the larger bones in the quarry are the more or less perfect remains of swamp turtles, of dwarf crocodiles, of the entirely different group of plated dinosaurs, or _Stegosauria_, but especially of two entirely distinct kinds of large and small flesh-eating dinosaurs. The latter rounded out and gave variety to the dinosaur society, and there is no doubt that they served the savage but useful purpose, rendered familiar by the doctrine of Malthus, of checking overpopulation. These fierce animals had the same remote ancestry as the giant dinosaurs, but had gradually acquired entirely different habits and appearance.
Far inferior in size, they were superior in agility, exclusively bipedal, with very long, powerful hind limbs, upon which they advanced by running or springing, and with short fore limbs, the exact uses of which are difficult to ascertain. Both hands and feet were provided with powerful tearing claws. On the hind foot is the back claw, so characteristic of the birds, which during the Tria.s.sic period left its faint impression almost everywhere in the famous Connecticut valley imprints of these animals. That the fore limb and hand were of some distinct use is proved by the enormous size of the thumb-claw; while the hand may not have conveyed food to the mouth, it may have served to seize and tear the prey. As to the actual pose in feeding, there can be little doubt as to its general similarity to that of the _Raptores_ among the birds, as suggested to me by Dr. Wortman (see fig. 10); one of the hind feet rested on the prey, the other upon the ground, the body being further balanced or supported by the vertebrae of the tail. The animal was thus in a position to apply its teeth and exert all the power of its very powerful arched back in tearing off its food. That the gristle of the bone or cartilage was very palatable is attested not only by the toothmarks upon these bones, but by many similar markings found in the Bone-Cabin Quarry.
_The Bird-Catching Dinosaur._ Of all the bird-like dinosaurs which have been discovered, none possesses greater similitude to the birds than the gem of the quarry, the little animal about seven feet in length which we have named _Ornitholestes_, or the ”bird-catching dinosaur.” It was a marvel of speed, agility, and delicacy of construction. Externally its bones are simple and solid-looking, but as a matter of fact they are mere sh.e.l.ls, the walls being hardly thicker than paper, the entire interior of the bone having been removed by the action of the same marvelous law of adaptation which sculptured the vertebrae of its huge contemporaries. There is no evidence, however, that these hollow bones were filled with air from the lungs, as in the case of the bones of birds. The foot is bird-like; the hand is still more so; in fact, no dinosaur hand has ever before been found which so closely mimics that of a bird in the great elongation of the first or index-finger, in the abbreviation of the thumb and middle finger, and in the reduction of the ring-finger.
These fingers, with sharp claws, were not strong enough for climbing, and the only special fitness we have been able to imagine is that they were used for the grasping of a light and agile prey (see figs. 17, 18.)
Another reason for the venture of designating this animal as the ”bird-catcher” is that the Jura.s.sic birds (not thus far discovered in America, but known from the _Archaeopteryx_ of Germany) were not so active or such strong fliers as existing birds; in fact, they were not unlike the little dinosaur itself. They were toothed, long-tailed, short-armed, the body was feathered instead of scaled; they rose slowly from the ground. This renders it probable that they were the prey of the smaller pneumatic-built dinosaurs such as the present animal.
This hypothetical bird-catcher seems to have been designed to spring upon a delicately built prey, the structure being the very antipode of that of the large carnivorous dinosaurs. A difficulty in the bird-catching theory, namely, that the teeth are not as sharp as one would expect to find them in a flesh-eater, is somewhat offset by the similarity of the teeth to those of the bird-eating monitor lizards (_Vara.n.u.s_), which are not especially sharp.
_The Great Yield of the Quarry._ Our explorations in the quarry began in the spring of 1898, and have continued ever since during favorable weather. The total area explored at the close of the sixth year was seven thousand two hundred and fifty square feet. Not one of the twelve-foot squares into which the quarry was plotted lacked its covering of bones, and in some cases the bones were two or three deep.
Each year we have expected to come to the end of this great deposit, but it still yields a large return, although we have reason to believe that we have exhausted the richest portions.
We have taken up four hundred and eighty-three parts of animals, some of which may belong to the same individuals. These were packed in two hundred and seventy-five boxes, representing a gross weight of nearly one hundred thousand pounds. Reckoning from the number of thigh-bones, we reach, as a rough estimate of the total, seventy-three animals of the following kinds: giant herbivorous dinosaurs, 44; plated herbivorous dinosaurs, or stegosaurs, 3; iguanodonts or smaller herbivorous dinosaurs, 4; large carnivorous dinosaurs, 6; small carnivorous dinosaurs, 3; crocodiles, 4; turtles, 5. But this represents only a part of the whole deposit, which we know to be of twice the extent already explored, and these figures do not include the bones which were partly washed out and used in the construction of the Bone-Cabin. The grand total would probably include parts of over one hundred giant dinosaurs.
_The Struggle for Existence Among the Dinosaurs._ Never in the whole history of the world as we now know it have there been such remarkable land scenes as were presented when the reign of these t.i.tanic reptiles was at its climax. It was also the prevailing life-picture of England, Germany, South America, and India. We can imagine herds of these creatures from fifty to eighty feet in length, with limbs and gait a.n.a.logous to those of gigantic elephants, but with bodies extending through the long, flexible, and tapering necks into the diminutive heads, and reaching back into the equally long and still more tapering tails. The four or five varieties which existed together were each fitted to some special mode of life; some living more exclusively on land, others for longer periods in the water.
The compet.i.tion for existence was not only with the great carnivorous dinosaurs, but with other kinds of herbivorous dinosaurs (the iguanodonts), which had much smaller bodies to sustain and a much superior tooth mechanism for the taking of food.
The cutting off of this giant dinosaur dynasty was nearly if not quite simultaneous the world over. The explanation which is deducible from similar catastrophes to other large types of animals is that a very large frame, with a limited and specialized set of teeth fitted only to a certain special food, is a dangerous combination of characters.
Such a monster organism is no longer adaptable; any serious change of conditions which would tend to eliminate the special food would also eliminate these great animals as a necessary consequence.
[Ill.u.s.tration: Fig. 46.--Badlands on the Red Deer River in Alberta. This region is the richest known collecting ground for cretacic dinosaurs.]
There is an entirely different cla.s.s of explanations, however, to be considered, which are consistent both with the continued fitness of structure of the giant dinosaurs themselves and with the survival of their especial food; such, for example, as the introduction of a _new enemy_ more deadly even than the great carnivorous dinosaurs. Among such theories the most ingenious is that of the late Professor Cope, who suggested that some of the small, inoffensive, and inconspicuous forms of Jura.s.sic mammals, of the size of the shrew and the hedgehog, contracted the habit of seeking out the nests of these dinosaurs, gnawing through the sh.e.l.ls of their eggs, and thus destroying the young. The appearance, or evolution, of any egg-destroying animals, whether reptiles or mammals, which could attack this great race at such a defenseless point would be rapidly followed by its extinction.
We must accordingly be on the alert for all possible theories of extinction; and these theories themselves will fall under the universal principle of the survival of the fittest until we approximate or actually hit upon the truth.
FOSSIL HUNTING BY BOAT IN CANADA.
_By Barnum Brown._
”How do you know where to look for fossils?” is a common question. In general it may be answered that the surface of North America has been pretty well explored by government surveys and scientific expeditions and the geologic age of the larger areas determined. Most important in determining the geologic sequence of the earth's strata are the fossil remains of animal and plant life. A grouping of distinct species of fossils correlated with stratigraphic characters in the rocks determines these subdivisions. When a collection of fossils is desired to represent a certain period, exploring parties are sent to these known areas. Sometimes however, chance information leads up to most important discoveries, such as resulted from the work of the past two seasons in Alberta, Canada.