AT the same time as the flying reptiles, the ichthyosaurs and the plesiosaurs, there lived, mainly on land but occasionally in the rivers and lagoons, some of the most remarkable animals the world has ever seen. These were the Dinosaurs, who dominated the world for something like a hundred million years. When we remember that man has been dominant for a mere million or so, we can realize something of the kingship that the dinosaurs enjoyed.
The earliest dinosaurs, evolved from a stem which gave rise both to the crocodiles and to the birds, made their bow in the early Trias.1 Originally they were probably small and leaping creatures, and the most primitive walked habitually upon the hind-legs, using the front merely for feeding or while resting. The bipedal forms are divisible into two kinds, those that lived upon flesh and those that were vegetarians. It is interesting to note that the first dhiosaurs ever discovered and described were these bipedal kinds and that the discoveries were made in England by Englishmen just over a hundred years ago.
The earliest of the bipeds were smallish, hopping or jumping creatures, and while some remained comparatively small throughout the history of the whole group, others became large. Iguanodon, well known from the Wealden rocks of the South of England and from Belgium, was herb-eating, subsisting on the tree fronds. It was about fourteen feet high and over twenty feet long, measured along the backbone. •: The fore-limbs were less stout than the hind and were adapted for grasping, while the thumb was a bony spike, useful for digging off branches from trees as well as in defence or attack. The strong hind-legs supported the body, and the three-toed feet, formed rather like those of birds, have ‘See table, p. 120.
left footprints which are not uncommonly found. The tail was flattened from side to side and may have been used in swimming, an advantage when rapacious carnivores had often to be avoided.
A CREATURE WITH TWO THOUSAND TEETH AMONG the American grass-eating bipeds one of the most notable is Trachodon, a dinosaur similar in general build and appearance to Iguanodon, but having a duck-billed skull and webbed fingers. There is no doubt that Trachodon was adapted as a swimmer. From a mummified skeleton found in the United States, we know the impression of the skin and that it consisted of tuberculated areas1 in a definitely arranged pattern which seems to indicate that the back was darker than the belly.
The jaws of Trachodon are remarkable for the number of teeth, which approached two thousand. All these teeth could not be used at once, but the tooth rows consisted of several lines of compactly arranged teeth which gradually became worn and discarded, while by an imperceptible escalator-like movement the new teeth grew up into position. Apparently these animals lived on horsetails and coarse grass with a high content of silica.
Many forms closely related to Trachodon became very curiously modified in the skull. The growth of the nasal bones seem to have run riot, and bony structures like spikes, helmets, and cockscombs developed, but all were hollow and communicated with the nostrils so that they were perhaps adaptations or consequences of living a good deal in the water.
HOW THE ‘TERRIBLE REPTILE’ LIVED UP TO ITS NAME THE flesh-eating dinosaurs do not appear to have been at all aquatic and contented themselves with life on land. Many of them attained huge size, and with their cruel teeth and rapacious habits justified the name of ‘terrible-reptile ‘which the word dinosaur signifies.
The commonest English and the oldest-known form is Megalosaurus (‘large-reptile ‘) whose remains, generally only fragmentary, have been found in many parts of England as well as abroad. In size these creatures were from ten to about
twenty feet long, with a skull measuring just about twelve inches. The teeth were sharp, flattened from side to side, and the fore and back edges were notched like a saw. The strong hind-legs and three-toed feet suggest a nimble habit on the track of prey. The skin was probably quite unarmoured.
In America a form closely similar to Megalosaurus was living at the same time, but it differed in having a large horn on the nose, from which it has been given the name Ceratosanrus, ‘horned reptile.’
The two-footed flesh-eating forms attained their maximum .in the Cretaceous period, in the guise of the truly terrifying Tyrannosaurus (‘tyrant-reptile ‘). This enormous creature, forty feet from nose to tail end, had a skull four feet long and a mouth full of sabre-like teeth six inches high. The strong hind-legs contrasted markedly with the feeble front limbs with their small but specialised hands. Although this is the largest animal of prey that has ever existed, it must have been an awkward even though a powerful creature. However richly endowed it was physically, it was of low brain power, both quantitatively and qualitatively. Immense and dreadful as it was, it could no doubt easily be defeated by the much smaller mammals of to-day.
FOUR-FOOTED VEGETARIANS, GIGANTIC AND GROTESQUE IT is curious that some time in the Trias, both the grass-eating and the flesh-eating bipeds gave rise to quadrupedal or four-footed forms. These flourished particularly in the Jurassic and Cretaceous periods, and many were gigantic and grotesque. The carnivorous bipeds’ four-footed relatives were huge, unarmoured, water-living vegetarians. In the quiet waters of rivers and estuaries, they lived and moved, feeding upon the floating water-weed. In this environment, safety from enemies was assured, and the placid life was one suited to the encouragement of great size. From all over the world, we know the remains of these amphibious dinosaurs, or Sauropods, which prove them to have attained truly gigantic dimensions. Diplodocus, a well-known American amphibious dinosaur, attained a length of eighty-five feet.
The head of Diplodociis was small and the nostrils were joined in a common opening on top of the head. The teeth were pencil-like and confined to the front of the jaws, so that they formed a kind of rake to pull in the water-weed. The whole skull was only about the size of that of a horse and
looks very inadequate for the long neck, the great elephantine body, and the very long tail.
There is no doubt that, immersed in the waters of lakes, lagoons, and estuaries, these creatures would stand with heads erect, perhaps thirty feet or more from the bottom, and so long as the nostril opening was over the surface of the water, they were not only safe but comfortable, because their burden of flesh was eased by the water’s buoyancy. They probably did not require an immense amount of food, as they were cold-blooded and without the energy requirements of present-day forms. They laid eggs, too, apparently, and laid them on land. For this purpose, therefore, and to change from lagoon to lagoon, they would occasionally leave the water and lumber awkwardly over the land.
In North and South America, in Africa, Australia, India, and in England, other remains have been found. Some forms were taller than, but not quite so long as, Diplodocus, others were somewhat smaller, but all were the nightmarish creations of a ‘lost world,’ creatures of a mechanical complexity that we shall not be likely to see again.
One point of great interest is the fact that these quadruped dinosaurs, both amphibious and armoured, possessed unusual developments in the arrangement of their nerves. While the brain in most of them was ridiculously small and lowly organised, the spinal column in the region of the hip girdle was greatly swollen and formed a kind of second brain. While the brain proper was concerned with sight, smell, hearing, etc., this second brain controlled the movements of the heavy limbs and tail. Despite their complexity in this direction, they were not intelligent creatures, and were totally unfitted for change of environment and alteration of habit. When, therefore, uplift movement of the land, and a consequent draining of lakes, etc., occurred towards the close of the lurassic period, all the sauropods of the northern hemisphere died out.
The four-footed relatives of the grass-eating bipeds were also vegetarians but sought protection from their enemies in armour. The early forms, such as Stegosaurus from America and Scelidosaums in England, had merely rows of plates or scutes upon the back. Some specimens of Stegosaunis (plated-reptile) were over twenty feet long and over five feet high at the hips. Here again there is evidence of slender cerebral organisation, but accessory brains were developed strongly in the spinal cord at the hips and slightly in the shoulder region.
LIVING ‘TANKS’: THE IMPREGNABLE ‘THORNY’ REPTILES OTHER and later forms became armoured like armadillos; they became, in fact, mobile ‘tanks ‘armoured with bone instead of steel. The thick skull, the neck with its protective collar of bone, and the segmented cuirass of bony plates and spikes on the body suggest that when attacked the animal merely lay close to the ground and became an impregnable armoured citadel. Such a specimen, called the ‘thorny reptile ‘or Scolosanrus, is excellently preserved in the British Museum (Natural History). It is about eighteen feet long and walked with bent elbows and knees, keeping the body close to the ground.
There was another kind of armoured dinosaur which, instead of having a plated body, had a bony skull with horns. These Ceratopsia (‘horned-faces ‘) were remarkably rhinoceros-like but were sometimes larger, as much as twenty-five feet long. The earliest dinosaurs of this sort that we know came from the Lower Cretaceous deposits of Mongolia, where nests of eggs and skeletons of young were also discovered. These creatures were small, with a beaked skull and a simple scaffolding of bone from the back of the skull over the neck, to hold the muscles for the heavy jaws.
Gradually, in different geological deposits in North America, we can trace the development of larger types where the simple structure over the neck has become a great bony and protective shield. The climax was obtained in the great Triceratops, with its three-horned head, a horn over each eye and one on the nose. Here the skull alone was six feet long, but it was controlled by a brain smaller than a man’s clenched fist. A birdlike toothless beak was in front of the mouth, and with this the animal cropped the vegetation on the leafy glades near the Cretaceous streams. When attacked, it had only to stand fast with lowered head, so that the attacker was in danger of being impaled on the three-feet long horns.
These then were some of the dinosaurs, kings of all the continents for a hundred million years; yet at the close of the Cretaceous period they were gone, with most of their fellow reptiles of the sea and air, charmed away by an unknown Pied Piper, to lie in their rocky fastness till Man could come and unravel their long story. When they were gone, the world was given over to the few groups of reptiles whose survivors constitute the reptiles of to-day, and to the birds
and mammals which, now unchecked, flourished and evolved to give the dominant faunas of the present.