Dinosaurs Part 2

THE CARNIVOROUS DINOSAURS, ALLOSAURUS, TYRANNOSAURUS, ORNITHOLESTES, ETC.

SUB-ORDER THEROPODA.

The sharp teeth, compressed and serrated like a palaeolithic spear point, and the powerful sharp-pointed curved claws on the feet, prove the carnivorous habits of these dinosaurs. The well-finished joints, dense texture of the hollow bones and strongly marked muscle-scars indicate that they were active and powerful beasts of prey. They range from small slender animals up to the gigantic _Tyrannosaurus_ equalling the modern elephant in bulk. They were half lizard, half bird in proportions, combining the head, the short neck and small fore limbs and long snaky tail of the lizard with the short, compact body, long powerful hind limbs and three-toed feet of the bird. The skin was probably either naked or covered with h.o.r.n.y scales as in lizards and snakes; at all events it was not armor-plated as in the crocodile.[4]

They walked or ran upon the hind legs; in many of them the fore limbs are quite unfitted for support of the body and must have been used solely in fighting or tearing their prey.

[Ill.u.s.tration: Fig. 10.--Hind Limb of Allosaurus, Dr. J.L. Wortman standing to one side. Dr. Wortman is one of the most notable and successful collectors of fossil vertebrates and was in charge of the Museum's field work in this department from 1891-1898.]

The huge size of some of these Mesozoic beasts of prey finds no parallel among their modern a.n.a.logues. It is only among marine animals that we find predaceous types of such gigantic size. But among the carnivorous dinosaurs we fail to find any indications of aquatic or even amphibious habits. They might indeed wade in the water, but they could hardly be at home in it, for they were clearly not good swimmers. We must suppose that they were dry land animals or at most swamp dwellers.

_Dinosaur Footprints._ The ancestors of the Theropoda appear first in the Tria.s.sic period, already of large size, but less completely bipedal than their successors. Incomplete skeletons have been found in the Tria.s.sic formations of Germany[5] but in this country they are chiefly known from the famous fossil footprints (or "bird-tracks" as they were at first thought to be), found in the flagstone quarries at Turner's Falls on the Connecticut River, in the vicinity of Boonton, New Jersey, and elsewhere. These tracks are the footprints of numerous kinds of dinosaurs, large and small, mostly of the carnivorous group, which lived in that region in the earlier part of the Age of Reptiles, and much has been learned from them as to the habits of the animals that made them. The tracks ascribed to carnivorous dinosaurs run in series with narrow tread, short or long steps, here and there a light impression of tail or forefoot and occasionally the mark of the shank and pelvis when the animal settled back and squatted down to rest a moment. The modern crocodiles when they lift the body off the ground, waddle forward with the short limbs wide apart, and even the lizards which run on their hind legs have a rather wide tread. But these dinosaurs ran like birds, setting one foot nearly in front of the other, so that the prints of right and left feet are nearly in a straight line. This was on account of their greater length of limb, which made it easy for them to swing the foot directly underneath the body at each step like mammals and birds, and thus maintain an even balance, instead of wabbling from side to side as short legged animals are compelled to do.

Of the animals that made these innumerable tracks the actual remains found thus far in this country are exceedingly scanty. Two or three incomplete skeletons of small kinds are in the Yale Museum, of which _Anchisaurus_ is the best known.

_Megalosaurus._ Fragmentary remains of this huge carnivorous dinosaur were found in England nearly a century ago, and the descriptions by Dean Buckland and Sir Richard Owen and the restorations due to the imaginative chisel of Waterhouse Hawkins, have made it familiar to most English readers. Unfortunately it was, and still remains, very imperfectly known. It was very closely related to the American _Allosaurus_ and unquestionably similar in appearance and habits.[6]

ALLOSAURUS.

The following extract is from the American Museum Journal for January 1908.[7]

"Although smaller than its huge contemporary Brontosaurus, this animal is of gigantic proportions being 34 feet 2 inches in length, and 8 feet 3 inches high."

[Ill.u.s.tration: Fig. 11.--MOUNTED SKELETON OF ALLOSAURUS IN THE AMERICAN MUSEUM. _After Osborn_]

_History of the Allosaurus Skeleton._ "This rare and finely preserved skeleton was collected by Mr. F.F. Hubbell in October 1879, in the Como Bluffs near Medicine Bow, Wyoming, the richest locality in America for dinosaur skeletons, and is a part of the great collection of fossil reptiles, amphibians and fishes gathered together by the late Professor E.D. Cope, and presented to the American Museum in 1899 by President Jesup.

"Shortly after the Centennial Exposition (1876) it had been planned that Professor Cope's collection of fossils should form part of a great public museum in Fairmount Park, Philadelphia, the city undertaking the cost of preparing and exhibiting the specimens, an arrangement similar to that existing between the American Museum and the City of New York.[8]

"The plan, however, fell through, and the greater part of this magnificent collection remained in storage in the bas.e.m.e.nt of Memorial Hall in Fairmount Park, for the next twenty years. From time to time Professor Cope removed parts of the collection to his private museum in Pine Street, for purposes of study and scientific description. He seems, however, to have had no idea of the perfection and value of this specimen. In 1899 when the collection was purchased from his executors by Mr. Jesup, the writer went to Philadelphia under the instructions of Professor Osborn, Curator of Fossil Vertebrates, to superintend the packing and removal to the American Museum. At that time the collection made by Hubbell was still in Memorial Hall, and the boxes were piled up just as they came in from the West, never having been unpacked. Professor Cope's a.s.sistant, Mr. Geismar, informed the writer that Hubbell's collection was mostly fragmentary and not of any great value. Mr. Hubbell's letters from the field unfortunately were not preserved, but it is likely that they did not make clear what a splendid find he had made, and as some of his earlier collections had been fragmentary and of no great interest, the rest were supposed to be of the same kind.

"When the Cope Collection was unpacked at the American Museum, this lot of boxes, not thought likely to be of much interest, was left until the last, and not taken in hand until 1902 or 1903. But when this specimen was laid out, it appeared that a treasure had come to light. Although collected by the crude methods of early days, it consisted of the greater part of the skeleton of a single individual, with the bones in wonderfully fine preservation, considering that they had been buried for say eight million years. They were dense black, hard and uncrushed, even better preserved and somewhat more complete than the two fine skeletons of Allosaurus from Bone-Cabin Quarry, the greatest treasures that this famous quarry had supplied. The great carnivorous dinosaurs are much rarer than the herbivorous kinds, and these three skeletons are the most complete that have ever been found.

In all the years of energetic exploration that the late Professor Marsh devoted to searching for dinosaurs in the Jura.s.sic and Cretaceous formations of the West, he did not obtain any skeletons of carnivorous kinds anywhere near as complete as these, and their anatomy was in many respects unknown or conjectural. By comparison of the three Allosaurus skeletons with one another and with other specimens of carnivorous dinosaurs of smaller size in this and other museums, particularly in the National Museum and the Kansas University Museum, we have been able to reconstruct the missing parts of the Cope specimen with very little possibility of serious error."

_Evidence for Combining and Posing this Mount._ "An incomplete specimen of Brontosaurus, found by Doctor Wortman and Professor W.C.

Knight of the American Museum Expedition of 1897, had furnished interesting data as to the food and habits of Allosaurus, which were confirmed by several other fragmentary specimens obtained later in the Bone-Cabin Quarry. In this Brontosaurus skeleton several of the bones, especially the spines of the tail vertebrae, when found in the rock, looked as if they had been scored and bitten off, as though by some carnivorous animal which had either attacked the Brontosaurus when alive, or had feasted upon the carca.s.s. When the Allosaurus jaw was compared with these score marks, it was found to fit them exactly, the s.p.a.cing of the scratches being the same as the s.p.a.cing of the teeth.

Moreover, on taking out the Brontosaurus vertebrae from the quarry, a number of broken off teeth of Allosaurus were found lying beside them.

As no other remains of Allosaurus or any other animal were intermingled with the Brontosaurus skeleton, the most obvious explanation was that these teeth were broken off by an Allosaurus while devouring the Brontosaurus carca.s.s. Many of the bones of other herbivorous dinosaurs found in the Bone-Cabin Quarry were similarly scored and bitten off, and the teeth of Allosaurus were also found close to them.

"With these data at hand the original idea was conceived of combining these two skeletons, both from the same formation and found within a few miles of each other, to represent what must actually have happened to them in the remote Jura.s.sic period, and mount the Allosaurus skeleton standing over the remains of a Brontosaurus in the att.i.tude of feeding upon its carca.s.s. Some modifications were made in the position to suit the exigencies of an open mount, and to accommodate the pose to the particular action; the head of the animal was lifted a little, one hind foot planted upon the carca.s.s, while the other, resting upon the ground bears most of the weight. The fore feet, used in these animals only for fighting or for tearing their prey, not for support, are given characteristic att.i.tudes, and the whole pose represents the Allosaurus devouring the carca.s.s and raising head and fore foot in a threatening manner as though to drive away intruders.

The balance of the various parts was carefully studied and adjusted under direction of the curator. The preparation and mounting of the specimen were done by Mr. Adam Hermann, head preparator, and his a.s.sistants, especially Messrs. Falkenbach and Lang.

[Ill.u.s.tration: Fig. 12.--Restoration of Allosaurus by C.R. Knight.

_After Osborn_]

"As now exhibited in the Dinosaur Hall, this group gives to the imaginative observer a most vivid picture of a characteristic scene in that bygone age, millions of years ago, when reptiles were the lords of creation, and 'Nature, red in tooth and claw' had lost none of her primitive savagery, and the era of brute force and ferocity showed little sign of the gradual amelioration which was to come to pa.s.s in future ages through the predominance of superior intelligence."

_Appearance and Habits of Allosaurus._ A study of the mechanism of the Allosaurus skeleton shows us in the first place that the animal is balanced on the hind limbs, the long heavy tail making an adequate counterpoise for the short compact body and head. The hind limbs are nine feet in length when extended, about equal to the length of the body and neck, and the bones are ma.s.sively proportioned. When the thigh bone is set in its normal position, as indicated by the position of the scars and processes for attachment of the princ.i.p.al muscles (see under Brontosaurus for the method used to determine this), the knee bends forward as in mammals and birds, not outward as in most modern reptiles. The articulations of the foot bones show that the animal rested upon the ends of the metapodials, as birds and many mammals do, not upon the sole of the foot like crocodiles or lizards.

The flat vertebral joints show that the short compact body was not as flexible as the longer body of crocodiles or lizards, in which the articulations are of the ball and socket type showing that in them this region was very flexible. The tail also shows a limited flexibility. It could not be curled or thrown over the back, but projected out behind the animal, swinging from side to side or up and down as much as was needed for balance. The curvature of the ribs shows that the body was narrow and deep, unlike the broad flattened body of the crocodile or the less flattened but still broad body of the lizard. The loose hung jaw, articulated far back, shows by the set of its muscles that it was capable of an enormous gape; while in the skull there is evidence of a limited movement of the upper jaw on the cranial portion, intended probably to a.s.sist in the swallowing of large objects, like the double jointed jaw of a snake.

As to the nature of the skin we have no exact knowledge. We may be sure that it had no bony armor like the crocodile, for remains of any such armor could not fail to be preserved with the skeletons, as it always is in fossil crocodiles or turtles. Perhaps it was scaly like the skin of lizards and snakes, for the h.o.r.n.y scales of the body are not preserved in fossil skeletons of these reptiles. But if so we might expect from the a.n.a.logy of the lizard that the scales of the head would be ossified and preserved in the fossil; and there is nothing of this kind in the Carnivorous Dinosaurs. We can exclude feathers from consideration, for these dinosaurs have no affinities to birds, and there is no evidence for feathers in any dinosaur. Probably the best evidence is that of the Trachodon or duck-billed dinosaur although this animal was but distantly related to the Allosaurus. In Trachodon (see p. 94), we know that the skin bore neither feathers nor overlapping scales but had a curiously patterned mosaic of tiny polygonal plates and was thin and quite flexible. Some such type of skin as this, in default of better evidence, we may ascribe to the Allosaurus.

[Ill.u.s.tration: Fig. 13.--View in the h.e.l.l Creek badlands in central Montana, where the Tyrannosaurus skeleton was found.]

As to its probable habits, it is safe to infer (see p. 33), that it was predaceous, active and powerful, and adapted to terrestrial life.

Its methods of attack and combat must have been more like those of modern reptiles than the more intelligent methods of the mammalian carnivore. The brain cast of Allosaurus indicates a brain of similar type and somewhat inferior grade to that of the modern crocodile or lizard, and far below the bird or mammal in intelligence. The keen sense of smell of the mammal, the keen vision of the bird, the highly developed reasoning power of both, were absent in the dinosaur as in the lizard or crocodile. We may imagine the Allosaurus lying in wait, watching his prey until its near approach stimulates him into a semi-instinctive activity; then a sudden swift rush, a fierce snap of the huge jaws and a savage attack with teeth and claws until the victim is torn in pieces or swallowed whole. But the stealthy, persistent tracking of the cat or weasel tribe, the intelligent generalship of the wolf pack, the well planned attack at the most vulnerable point in the prey, characteristic of all the predaceous mammals, would be quite impossible to the dinosaur. By watching the habits of modern reptiles we may gain a much better idea of his capacities and limitations than if we judge only from the efficiency of his teeth and claws, and forget the inferior intelligence that animated these terrible weapons.

TYRANNOSAURUS.

The "Tyrant Saurian" as Professor Osborn has named him, was the climax of evolution of the giant flesh-eating dinosaurs. It reached a length of forty-seven feet, and in bulk must have equalled the mammoth or the mastodon or the largest living elephants. The ma.s.sive hind limbs, supporting the whole weight of the body, exceeded the limbs of the great proboscideans in bulk, and in a standing position the animal was eighteen to twenty feet high, as against twelve for the largest African elephants or the southern mammoth. The head (see frontispiece) is 4 feet 3 inches long, 3 ft. 4 inches deep, and 2 ft. 9 inches wide; the long deep powerful jaws set with teeth from 3 to 6 inches long and an inch wide. To this powerful armament was added the great sharp claws of the hind feet, and probably the fore feet, curved like those of eagles, but six or eight inches in length.

During ten years explorations in the Western Cretaceous formations, Mr. Brown has secured for the Museum three skeletons of this magnificent dinosaur, incomplete, but finely preserved. The first, found in 1900, included the jaws, a large part of backbone and ribs, and some limb bones. The second included most of skull and jaws, backbone, ribs and pelvis and the hind limbs and feet, but not tail.

The third consisted of a perfect skull and jaws, the backbone, ribs, pelvis and nearly all of the tail, but no limbs. From these three specimens it has been possible to reconstruct the entire skeleton. The exact construction of the fore feet is the only doubtful part. The fore-limb is very small relatively to the huge size of the animal, but probably was constructed much as in the _Allosaurus_ with two or three large curved claws, the inner claw opposing the others.

[Ill.u.s.tration: Fig. 14.--Quarry from which the _Tyrannosaurus_ skeleton was taken. American Museum camp in foreground.]

The missing parts of the two best skeletons have been restored, and with the help of two small models of the skeleton, a group has been made ready for mounting as the central piece of the proposed Cretaceous Dinosaur Hall. One of the skeletons is temporarily placed in the centre of the Quaternary Hall, s.p.a.ce for it in the present Dinosaur Hall being lacking. Following is Professor Osborn's description of the preparation of this group:[9]

"The mounting of these two skeletons presents mechanical problems of very great difficulty. The size and weight of the various parts are enormous. The height of the head in the standing position reaches from 18 to 20 feet above the ground; the knee joint alone reaches 6 feet above the ground. All the bones are ma.s.sive; the pelvis, femur and skull are extremely heavy. Experience with _Brontosaurus_ and with other large dinosaurs proves that it is impossible to design a metallic frame in the right pose in advance of a.s.sembling the parts.

Even a scale restoration model of the animal as a whole does not obviate the difficulty.

"Accordingly in preparing to mount _Tyrannosaurus_ for exhibition a new method has been adopted, namely, to _prepare a scale model of every bone in the skeleton_ and mount this small skeleton with flexible joints and parts so that all studies and experiments as to pose can be made with the models.

"This difficult and delicate undertaking was entrusted to Mr. Erwin Christman of the artistic staff of the Department of Vertebrate Palaeontology of the Museum, who has prepared two very exact models to a one-sixth scale, representing our two skeletons of _Tyrannosaurus rex_, which fortunately are of exactly the same size. A series of three experiments by Mr. Christman on the pose of _Tyrannosaurus_, under the direction of the author and Curator Matthew, were not satisfactory. The advice of Mr. Raymond L. Ditmars, Curator of Reptiles in the New York Zoological Park, was sought and we thus obtained the fourth pose, which is shown in the photographs published herewith.

[Ill.u.s.tration: Fig. 15.--Model of _Tyrannosaurus_ group for the Cretaceous Dinosaur Hall.]

"The fourth pose or study, for the proposed full sized mount, is that of two reptiles of the same size attracted to the same prey. One reptile is crouching over its prey (which is represented by a portion of a skeleton). The object of this depressed pose is to bring the perfectly preserved skull and pelvis very near the ground within easy reach of the visiting observer. The second reptile is advancing, and attains very nearly the full height of the animal. The general effect of this group is the best that can be had and is very realistic, particularly the crouching figure. A fifth study will embody some further changes. The upright figure is not well balanced and will be more effective with the feet closer together, the legs straighter and the body more erect. These reptiles have a series of strong abdominal ribs not shown in the models. The fourth position places the pelvis in an almost impossible position as will be noted from the ischium and pubis.

"The lateral view of this fourth pose represents the animals just prior to the convulsive single spring and tooth grip which distinguishes the combat of reptiles from that of all mammals, according to Mr. Ditmars.

"The rear view of the standing skeleton displays the peculiarly avian structure of the iliac junction with the sacral plate, characteristic of these very highly specialized dinosaurs, also the marked reduction of the upper end of the median metatarsal bone, which formerly was believed to be peculiar to _Ornithomimus_."

This model of the group is on exhibition with the mounted skeleton.

As compared with its predecessor _Allosaurus_, the _Tyrannosaurus_ is much more ma.s.sively proportioned throughout. The skull is more solid, the jaws much deeper and more powerful, the fore limb much smaller, the tail shorter, the hind limb straighter and the foot bones more compacted so that the animal was more strictly "digitigrade,"

approaching the ostriches more closely in this particular.

[Ill.u.s.tration: Fig. 16.--SKELETON OF TYRANNOSAURUS IN COMPARISON WITH HUMAN SKELETON.]

This animal probably reached the maximum of size and of development of teeth and claws of which its type of animal mechanism was capable. Its bulk precluded quickness and agility. It must have been designed to attack and prey upon the ponderous and slow moving Horned and Armored Dinosaurs with which its remains are found, and whose ma.s.sive cuira.s.s and weapons of defense are well matched with its teeth and claws. The momentum of its huge body involved a seemingly slow and lumbering action, an inertia of its movements, difficult to start and difficult to shift or to stop. Such movements are widely different from the agile swiftness which we naturally a.s.sociate with a beast of prey. But an animal which exceeds an average elephant in bulk, no matter what its habits, is compelled by the laws of mechanics to the ponderous movements appropriate to its gigantic size. These movements, directed and controlled by a reptilian brain, must needs be largely automatic and instinctive. We cannot doubt indeed that the Carnivorous Dinosaurs developed, along with their elaborately perfected mechanism for attack, an equally elaborate series of instincts guiding their action to effective purpose; and a complex series of automatic responses to the stimulus afforded by the sight and action of their prey might very well mimic intelligent pursuit and attack, always with certain limits set by the inflexible character of such automatic adjustments.

But no animal as large as _Tyrannosaurus_ could leap or spring upon another, and its slow stride quickening into a swift resistless rush, might well end in unavoidable impalement upon the great horns of _Triceratops_, futile weapons against a small and active enemy, but designed no doubt to meet just such attacks as these. A true picture of these combats of t.i.tans of the ancient world we cannot draw; perhaps we will never be able to reconstruct it. But the above considerations may serve to show how widely it would differ from the pictures based upon any modern a.n.a.logies.

One may well inquire why it is that no such gigantic carnivora have evolved among the mammalian land animals. The largest predaceous quadrupeds living today are the lion and tiger. The bears although some of them are much larger, are not generally carnivorous, except for the polar bear, which is partly aquatic, preying chiefly upon seals and fish. There are indeed carnivorous whales of gigantic size, but no very large land carnivore. There were, it is true, during the Tertiary and Pleistocene, lions and other carnivores considerably larger than the living species. But none of them attained the size of their largest herbivorous contemporaries, or even approached it. Among the dinosaurs on the other hand we find that--setting aside Brontosaurus and its allies as aquatic--the predaceous kinds equalled or exceeded the largest of the herbivorous sorts. The difference is striking, and it does not seem likely that it is merely accidental.

The explanation lies probably in the fact that the large herbivorous mammals are much more intelligent and active, and would be able to use their weapons of defense so as to defy the attacks of relatively slow moving giant beasts of prey, as they do also the more active but less powerful a.s.saults of smaller ones. The elephant or the rhinoceros is in fact practically immune from the attacks of carnivora, and would still be so were the carnivora to increase in size. The large modern carnivora prey upon herbivores of medium or smaller size, which they are active enough to surprise or run down. Carnivora of much larger size would be too slow and heavy in movements to catch small prey, while the larger herbivores by intelligent use of their defensive weapons could still fend them off successfully. In consequence giant carnivores would find no field for action in the Cenozoic world, and hence they have not been evolved.