Not greatly removed in habit or appearance from the Brontosaurus was the Diplodocus, a magnificent specimen of which has been set up in Pittsburg, and a fine replica, owing to the generosity of Mr. Andrew Carnegie, in the Natural History Museum. The Diplodocus, a harmless placid beast, was over eighty feet from the tip of his snout to the end of his enormous tail. It has been calculated that impulses travel along the nerves to the brain at the rate of about twelve yards a second. The rate may have been less in the case of the sluggish Diplodocus, but in any case it would evidently take at least two seconds for a nerve impulse to travel the length of this reptile; so that if any enemy attacked him at the end of his tail it would be two seconds before the Diplodocus would realise the fact, and perhaps four seconds before he could begin to turn round to defend himself. Even larger than these was the tremendous Brachiosaurus, who weighed as much as a steam-engine and whose thigh-bone was nearly eight feet high. These were the largest reptiles ever known, and may be taken as reaching the point when bulk becomes a burden, and as signalising an approach to the limit of evolution in the line of size. Less bulky than these were the Stegosaurs, which were also four-footed. They were curiously armoured, and formed a group of very remarkable creatures found in England and Western America. While they were less gigantic than some of those we have just described, they found compensation in protective plates, spines, and similar modes of defence. A Stegosaurus found in Wyoming was probably the most hideous to look upon; but like his relatives he had an extraordinarily small head and brain, and was a sluggish creature depending on his ugliness and armour for protection. Very likely this small size of the brain of great extinct reptiles had to do with the fact of their ceasing to exist. Animals with bigger and ever-increasing brains outdid them in the struggle for existence.
It has already been noted that the crowding of the land may have led some reptiles to take to the sea. The same influence may have led others to take to the air and thereby escape the monsters of the swamps, jungles, and forests. Whatever the cause, the most striking and wonderful feature of this period was the development of flying reptiles. They had just been seen in the Trias. In the Jurassic they appeared fully developed. They doubtless sprang from some agile hollow-boned saurian, more or less akin to the slender leaping Dinosaurs. Between the ponderous Brontosaurs and the airy Pterodactyls was the most striking of contrasts. At first these bird-like reptiles were small, but later their wings had a spread of as much as twenty feet, veritable flying dragons. They were not adorned with feathers, but like bats had leathery membranes stretched from the fore limbs to the body and to the hind limbs. Their heads were bird-like, and their jaws at first were set with teeth. They had true powers of flight, as is shown by the discovery of their remains in places where they must have been far out at sea when they sank and were buried. Later Pterodactyls had no teeth, and were, perhaps, milder in habits.
Archæopteryx (the earliest known fossil bird), and Compsognathus (a small Dinosaur)
It seems natural to pass from the fossil reptiles to the birds. But as a matter of fact the birds are not very closely related to the Pterodactyls, and seem to have been descended from some other very special form of reptiles, so peculiar as to be considered a distinct class. It may actually have been descended from those reptiles among the Dinosaurs which walked on their hind legs and had only three toes to the foot. The first bird found belongs to Jurassic times; and its skeleton, found in some slate remains at Solenhofen in Bavaria, is now to be seen in the Natural History Museum. There is another one in Berlin. This bird, called the Archæopteryx, was of the size of a large pigeon, had a short head apparently without a beak, and its jaws were armed with teeth. Whereas living birds have the fingers of their "hands" tied together in their wings, this bird has three distinct fingers at the corner of its wings, each armed with a claw. Its legs were like those of living birds, and it had four toes. Its tail was unlike that of any living bird, and like that of a lizard. Whereas the bony part of the tail of living birds is very short and bears the tail feathers set across it fanwise, the Archæopteryx had a long bony tail made up of many bones, and the feathers were set in a series one behind the other till the tail looked like the leaf of a date palm in shape. Strange as this little creature appears it was a genuine bird, for it had these feathers well developed, as the two fossil specimens showed. There are two sets of feathers forming the wings, and the thighs were also covered with feathers.
CHAPTER XXI
THE CHALK PERIOD
Once again the European continent and with it Great Britain began to sink. Great Britain at the beginning of the era which followed the Jurassic system, was joined to France, but south of this barrier was a great fresh-water lake, into which rivers and streams poured from the north and the east. Great forests grew on its borders, forests still crowded with ferns and cycads as in previous ages, but affording scope for pine trees to grow as well. On its borders flourished the giant Iguanodon, a great lizard-like animal which could raise itself on its hind legs and lift a fifteen-foot body so as to feed on the branches of the trees. The Iguanodon is a specially interesting fossil reptile, because it was one of the first to be discovered. The first bones and teeth of the Iguanodon were found seventy years ago by a celebrated and most delightful explorer of the earth's crust, Dr. Gideon Mantell, in the strata known as the Wealden, in Sussex, just below the chalk. Dr. Mantell was only a country practitioner, and when he first produced before the Geological Society his Iguanodon remains, and suggested that they were those of a reptile, some doubt was thrown on this conclusion, because geologists believed from the appearance of the teeth that the animal must be of some other animal family. But Dr. Mantell found that a little lizard living in South America had teeth like those he had discovered in his reptile remains, and he persisted in his view. Many years later a wonderful find was made near Brussels in a coal mine near Bernissart, the skeletons of no fewer than twenty-two huge Iguanodons were found complete and embedded in a fairly soft clay-like rock. The authorities of the Government Museum took charge of the place and most carefully removed the skeletons to Brussels, where the complete skeletons of seven were with enormous difficulty and care removed bit by bit from the rock and set up as entire skeletons in the Brussels Museum, where they may be seen. A replica of one of them is at South Kensington. The fore feet of the Iguanodon had five fingers, but the hind foot was very much like that of a bird, and had only three toes, and the bones of the pelvis or hip girdle were extraordinarily like those of a bird. When Professor Huxley examined the first fragments of the Iguanodon's remains he was inclined to believe them to be those of a gigantic bird; and it is generally believed now that it is from this extraordinary reptile stock that the birds were derived.
But the great lake with all its varied stores was doomed to sink lower and lower, till the great sea overwhelmed England. Another ocean joining it to the east overwhelmed Germany; and the whole of Europe, south of a line drawn through Scotland, Christiania, and Moscow, became sunk under salt water. There were patches standing up here and there—Ireland, Brittany, Cornwall, Spain or a good part of it, Switzerland, part of Italy (and also part of what is now the Western Mediterranean), and most of Turkey and Hungary. But elsewhere marine animals succeeded the reptiles, and the foundations of all the chalk hills and cliffs of modern Europe were laid.
Of what were they made? We may borrow a capital suggestion from Mr. Jerome Harrison, of Birmingham University. "Take," he says, "a piece of chalk and brush it vigorously with a tooth-brush in a glass of water until the liquid looks quite milky. Allow the greater part of the sediment to subside, and then pour away the water and wash the material which has sunk to the bottom of the glass by pouring water on it two or three times. Put the whitish powder which finally remains under a microscope; and examine it with, say, the quarter-inch power, which will magnify about 300 diameters. The greater part of the white powder will then be seen to be composed of the minute shells of creatures called Foraminifera—little specks of jelly-like matter which secrete for themselves a shell or covering from the carbonate of lime dissolved in the sea-water in which they live.