Dinosaurs Part 4

_Diplodocus._ The _Diplodocus_ nearly equalled the Brontosaurus in bulk and exceeded it in length. A skeleton in the Carnegie Museum at Pittsburgh measures 87 feet in total length; although the mount is composed from several individuals these proportions are probably not far from correct. The skull is smaller and differently shaped and the teeth are of quite different type. In the American Museum of Natural History, a partial skeleton is exhibited in the wall case to the left of the entrance of the Dinosaur Hall, and in an A-case near by are skulls of _Diplodocus_ and _Morosaurus_ and a model of the skull of _Brontosaurus_. The Diplodocus skull is widely different from the other two in size and proportions and in the characters of teeth.

When the first remains of these amphibious Dinosaurs were found in the Oxford Clays of England, they were considered by Richard Owen to be related to the Crocodiles, and named Opisthocoelia. Subsequently the finding of complete skeletons in this country led Cope and Marsh to place them with the true Dinosaurs and the latter named them Sauropoda.[13] Remains of these animals have also been found in India, in German East Africa, in Madagascar, and in South America, so that they were evidently widely distributed. In the Northern world they survived until the Comanchic or Lower Cretaceous Period, but in the southern continents they may have lived on into the Upper Cretaceous or true Cretacic. Some of the remains recently found in German East Africa indicate an animal exceeding either _Brontosaurus_ or _Diplodocus_ in bulk.

[Ill.u.s.tration: Fig. 24.--The Largest Known Dinosaur. Sketch reconstruction of _Brachiosaurus_, from specimens in the Field Museum in Chicago, and the Natural History Museum in Berlin.]

At the date of writing this handbook only preliminary accounts have been given of the marvellous finds made near Tendaguru by the expedition from Berlin. From these it appears that in length of neck and fore limb this East African Dinosaur greatly exceeded either _Brontosaurus_ or _Diplodocus_. The hinder parts of the skeleton however, were relatively small. The proportions and measurements given tally closely with the American _Brachiosaurus_, a gigantic sauropod whose incomplete remains are preserved in the Field Museum in Chicago and to this genus the Berlin authorities now refer their largest and finest skeleton. If the Berlin specimens are correctly referred to _Brachiosaurus_ they indicate an animal somewhat exceeding _Diplodocus_ or _Brontosaurus_ in total bulk but distinguished by much longer fore limbs and an immensely long neck--a giraffe-like wader adapted to take refuge in deeper waters, more out of reach of the fierce carnivores of the land.[14]

FOOTNOTES:

[Footnote 11: The mounted Skeleton of Brontosaurus, by W.D. Matthew, Amer. Mus. Jour. Vol. v, pp. 63-70, figs. 1-5.]

[Footnote 12: Professor Williston makes the following criticism of this theory:

"I cannot agree with this view--the animals _must_ have laid their eggs upon land--for the reason that reptile eggs cannot hatch in water. S.W.W."

But with deference to Williston's high authority I may note that there is no evidence that the Sauropoda were egg-laying reptiles. They, or some of them, may have been viviparous like the Ichthyosaurus.]

[Footnote 13: European palaeontologists, especially Huxley and Seeley in England, had also recognized their true relations.h.i.+ps, and Seeley's term Cetiosauria has precedence over Sauropoda, although the latter is in common use.]

[Footnote 14: It is of interest to observe that in this group of Sauropoda, the Brachiosauridae, the neural spines of the vertebrae are much simpler and narrower than in the Brontosaurus and Diplodocus. The attachments were thus less extensive for the muscles of the back, indicating that these muscles were less powerful. This difference is correlated by Professor Williston with the longer fore limbs of the Brachiosaurus, as signifying that the animal was less able, as indeed he had less need, to rise up upon the hind limbs, in comparison with Diplodocus or Brontosaurus in which the fore limbs were relatively short.]

CHAPTER VI.

THE BEAKED DINOSAURS.

ORDER ORTHOPODA (ORNITHISCHIA OR PREDENTATA.)

The peculiar feature of this group of Dinosaurs is the h.o.r.n.y beak or bill. The bony core sutured to the front of the upper and lower jaws was covered in life by a h.o.r.n.y sheath, as in birds or turtles. But this is not the only feature in which they came nearer to birds than do the other Dinosaurs. The pelvic or hip bones are much more bird-like in many respects, especially the backward direction of the pubic bone, the presence of a prepubis, in the number of vertebrae coossified into a solid sacrum, in the proportions of the ilium and so on. Various features in the anatomy of the head, shoulder-blades and hind limbs are equally suggestive of birds, and it seems probable that the earliest ancestors of the birds were very closely related to the ancestors of this group of Dinosaurs. But the ancestral birds became adapted to flying, the ancestral Predentates to terrestrial life, and in their later development became as widely diversified in form and habits as the warm-blooded quadrupeds which succeeded them in the Age of Mammals.

[Ill.u.s.tration: Fig. 25.--Skulls of Iguanodont and Trachodont Dinosaurs. _Iguanodon_ and _Camptosaurus_ of the Jura.s.sic and Comanchic; _Kritosaurus_ and _Corythosaurus_ of the Middle Cretacic (Belly River); _Saurolophus_ of the late Cretacic (Edmonton); _Trachodon_ of the latest Cretacic (Lance). The Iguanodon is European, the others North American. All 1/25 natural size.]

These Beaked Dinosaurs were, so far as we can tell, all vegetarians.

Unlike the birds, they retained their teeth and in some cases converted them into a grinding apparatus which served the same purpose as the grinders of herbivorous quadrupeds. It is interesting to observe the different way in which this result is attained. In the mammals the teeth, originally more complex in construction and fewer in number, are converted into efficient grinders by infolding and elongation of the crown of each tooth so as to produce on the wearing surface a complex pattern of enamel ridges with softer dentine or cement intervening, making a series of crests and hollows continually renewed during the wear of the tooth. In the reptile the teeth, originally simple in construction but more numerous and continually renewed as they wear down and fall out,[15] are banked up in several close packed rows, the enamel borders and softer dentine giving a wearing surface of alternating crests and hollows continually renewed, and reinforced from time to time, by the addition of new rows of teeth to one side, as the first formed rows wear down to the roots. This is the best ill.u.s.trated in the _Trachodon_ (see fig. 27); the other groups have not so perfect a mechanism.

A. THE IGUANODONTS: IGUANODON, CAMPTOSAURUS.

_Sub-Order Ornithopoda or Iguanodontia._

In the early days of geology, about the middle of the nineteenth century, bones and footprints of huge extinct reptiles were found in the rocks of the Weald in south-eastern England. They were described by Mantell and Owen and shown to pertain to an extinct group of reptiles which Owen called the Dinosauria. So different were these bones from those of any modern reptiles that even the anatomical learning of the great English palaeontologist did not enable him to place them all correctly or reconstruct the true proportions of the animal to which they belonged. With them were found a.s.sociated the bones of the great carnivorous dinosaur _Megalosaurus_; and the weird reconstructions of these animals, based by Waterhouse Hawkins upon the imperfect knowledge and erroneous ideas then prevailing, must be familiar to many of the older readers of this handbook. Life size restorations of these and other extinct animals were erected in the grounds of the Crystal Palace at Sydenham, London, and in Central Park, New York. Those in London still exist, so far as the writer is aware, but the stern mandate of a former mayor of New York ordered the destruction of the Central Park models, not indeed as incorrect scientifically, but as inconsistent with the doctrines of revealed religion, and they were accordingly broken up and thrown into the waters of the Park lake. Small replicas of these early attempts at restoring dinosaurs may still be seen in some of the older museums in this country and abroad.

[Ill.u.s.tration: Fig. 26.--SKELETON OF CAMPTOSAURUS, AN AMERICAN RELATIVE OF THE IGUANODON.]

The real construction of the Iguanodon was gradually built up by later discoveries, and in 1877 an extraordinary find in a coal mine at Bernissart in Belgium brought to light no less than seventeen skeletons more or less complete. These were found in an ancient fissure filled with rocks of Comanchic age, traversing the Carboniferous strata in which the coal seam lay, and with them were skeletons of other extinct reptiles of smaller size. The open fissure had evidently served as a trap into which these ancient giants had fallen, and either killed by the fall or unable to escape from the pit, their remains had been subsequently covered up by sediments and the pit filled in to remain sealed up until the present day. These skeletons, unique in their occurrence and manner of discovery, are the pride of the Brussels Museum of Natural History, and, together with the earlier discoveries, have made the _Iguanodon_ the most familiar type of dinosaur to the people of England and Western Europe.

[Ill.u.s.tration: Fig. 27.--Teeth of the duck-billed dinosaur _Trachodon_. The dental magazine has been removed from the lower jaw and is seen to consist of several close-set rows of numerous small pencil-like teeth which are pushed up from beneath as they wear off at the grinding surface.]

_Camptosaurus._ The American counterpart of the Iguanodons of Europe was the _Camptosaurus_, nearly related and generally similar in proportions but including mostly smaller species, and lacking some of the peculiar features of the Old World genus. In the National Museum at Was.h.i.+ngton, are mounted two skeletons of _Camptosaurus_, a large and a small species, and in the American Museum a skeleton of a small species. It suggests a large kangaroo in size and proportions, but the three-toed feet, with hoof-like claws, the reptilian skull, loosely put together, with lizard-like cheek teeth and turtle beak indicate a near relative of the great _Iguanodon_.

_Thescelosaurus._ The Iguanodont family survived until the close of the Age of Reptiles, with no great change in proportions or characters. Its latest member is _Thescelosaurus_, a contemporary of _Triceratops_. Partial skeletons of this animal are shown in the Dinosaur Hall; a more complete one is in the National Museum.

FOOTNOTES:

[Footnote 15: Trachodont teeth never drop out, they are completely consumed. Only in the Iguanodonts and Ceratopsia are they shed.--B.

Brown.]

CHAPTER VII.

THE BEAKED DINOSAURS (Continued).

B. THE DUCK BILLED DINOSAURS,--TRACHODON, SAUROLOPHUS, ETC.

_Sub-Order Ornithopoda; Family Trachodontidae._

These animals of the Upper Cretaceous are probably descended from the Iguanodonts of an older period. But the long ages that intervened, some millions of years, have brought about various changes in the race, not so much in general proportions as in altering the form and relations of various bones of skull and skeleton and perfecting their adaptation to a somewhat different habit of life, so that they must be regarded as descendants perhaps, but certainly rather distant relatives, of the older group.

We know more about the Trachodonts than any other dinosaurs. For not only are the skeletons more frequently found articulated, but parts of the skin are not uncommonly preserved with them, and in one specimen at least, so much of the skin is preserved that it may fairly be called a "dinosaur mummy." This specimen of _Trachodon_ is in the American Museum, and beside it are two fine mounted skeletons of the largest size. There is also on exhibition a panel mount of a nearly related genus, _Saurolophus_ the skeleton lying as it was found in the rock, and a fine skeleton of a third genus _Corythosaurus_ with the skin partly preserved on both sides of the crushed and flattened body stands beside it. In the _Tyrannosaurus_ group when completed will appear a fourth skeleton of the _Trachodon_. Several skulls and incomplete skeletons on exhibition and other skeletons not yet prepared add to the Museum collection of this group. Trachodon skeletons may also be found in the Museums of New Haven, Was.h.i.+ngton, Frankfurt-on-the-Main, London and Paris, but nowhere a series comparable to that displayed at the American Museum.

THE TRACHODON GROUP.

The following description of the Trachodon group is by Mr. Barnum Brown and first appeared in the American Museum Journal for April 1908:[16]

"This group takes us back in imagination to the Cretaceous period, more than three millions of years ago, when Trachodonts were among the most numerous of the dinosaurs. Two members of the family are represented here as feeding in the marshes that characterized the period, when one is startled by the approach of a carnivorous dinosaur, Tyrannosaurus, their enemy, and rises on tiptoe to look over the surrounding plants and determine the direction from which it is coming. The other Trachodon, unaware of danger, continues peacefully to crop the foliage. Perhaps the erect member of the group had already had unpleasant experiences with hostile beasts, for a bone of its left foot bears three sharp gashes which were made by the teeth of some carnivorous dinosaur.

[Ill.u.s.tration: Fig. 28.--Mounted Skeletons of _Trachodon_ in the American Museum. Height of standing skeleton 16 feet, 10 inches.]

"By thus grouping the skeletons in lifelike att.i.tudes, the relation of the different bones can best be shown, but these of course are only two of the att.i.tudes commonly taken by the creatures during life.

Mechanical and anatomical considerations, especially the long straight shafts of the leg bones, indicate that dinosaurs walked with their limbs straight under the body, rather than in a crawling att.i.tude with the belly close to the ground, as is common among living reptiles.

"Trachodonts lived near the close of the Age of Reptiles in the Upper Cretaceous and had a wide geographical distribution, their remains having been found in New Jersey, Mississippi and Alabama, but more commonly in Wyoming, Montana, and the Dakotas. A suggestion of the great antiquity of these specimens is given by the fact that since the animals died layers of rock aggregating many thousand feet in vertical thickness have been deposited along the Atlantic coast.

"The bones of the erect specimen are but little crushed and a clear conception of the proportions of the animal can best be obtained from this specimen. It will be seen that the Trachodon was shaped somewhat like a kangaroo, with short fore legs, long hind legs, and a long tail. The fore limbs are reduced indeed to about one-sixth the size of the hind limbs and judging from the size and shape of the foot bones the front legs could not have borne much weight. They were probably used in supporting the anterior portion of the body when the creature was feeding, and in aiding it to recover an upright position. The specimen represented as feeding is posed so that the fore legs carry very little of the weight of the body. There are four toes on the front foot but the thumb is greatly reduced and the fifth digit or little finger, is absent." (Subsequent discoveries have shown that the arrangement of the digits made by Marsh and followed in this skeleton is incorrect. It is the first digit that is absent, and the fifth is reduced.)

"The hind legs are ma.s.sive and have three well developed toes ending in broad hoofs. The pelvis is lightly constructed with bones elongated like those of birds. The long deep compressed tail was particularly adapted for locomotion in the water. It may also have served to balance the creature when standing erect on sh.o.r.e. The broad expanded lip of bone known as the fourth trochanter, on the inner posterior face of the femur or thigh bone was for the attachment of powerful tail muscles similar to those which enable the crocodile to move its tail from side to side with such dexterity. This trochanter is absent from the thigh bones of land-inhabiting dinosaurs with short tails, such as _Stegosaurus_ and _Triceratops_. The tail muscles were attached to the vertebrae by numerous rod-like tendons which are preserved in position as fossils on the erect skeleton. Trachodonts are thought to have been expert swimmers. Unlike other dinosaurs their remains are frequently found in rocks that were formed under sea water probably bordering the sh.o.r.es but nevertheless containing typical sea sh.e.l.ls.

"The elaborate dental apparatus is such as to show clearly that Trachodonts were strictly herbivorous creatures. The mouth was expanded to form a broad duck-like bill which during life was covered with a h.o.r.n.y sheath, as in birds and turtles. Each jaw is provided with from 45 to 60 vertical and from 10 to 14 horizontal rows of teeth, so that there were more than 2000 teeth altogether in both jaws.

"Among living saurians, or reptiles, the small South American iguana _Amblyrhynchus_ may be compared in some respects with the Trachodons notwithstanding the difference in size. These modern saurians live in great numbers on the sh.o.r.es of the Galapagos Islands off the coast of Chile. They swim out to sea in shoals and feed exclusively on seaweed which grows on the bottom at some distance from sh.o.r.e. The animal swims with perfect ease and quickness by a serpentine movement of its body and flattened tail, its legs meanwhile being closely pressed to its side and motionless. This is also the method of propulsion of crocodiles when swimming.

"The carnivorous or flesh-eating dinosaurs that lived on land, such as _Allosaurus_ and _Tyrannosaurus_, were protected from foes by their sharp biting teeth, while the land-living herbivorous forms were provided with defensive horns, as in _Triceratops_, sharp spines as in _Stegosaurus_ or were completely armored as in _Ankylosaurus_.