Jurassic

“ In south Russia, the Crimea and Caucasus, Lias and Lower Jurassic rocks are present. In the Alps, the Lower Jurassic rocks are intimately associated with the underlying Triassic formations, and resemble them in consisting largely of reddish limestones and marbles; the ammonites in this region differ in certain respects from those of western and central Europe. The Oxfordian, Callovian, Corallian and Astartian stages are also present. The Upper Jurassic is mainly represented by a uniform series of limestones, with a peculiar and characteristic fauna, to which Oppel gave the name “Tithonian.” ”

“ How the accumulations of all periods may be imagined crashing together into the depths! Silurian gastropods, strange Devonian fishes, enormous Triassic reptiles, the rich and varied shells of the Jurassic, the dinosaurs and primitive birds of Cretaceous, the little early horses of Eocene, and Miocene's camels and mastodons mingling their fossil remnants in a democracy of ruin to defy the eternal ages! ”

“ The Echinoderms are very numerous and abundant fossils in the Jurassic series, and are represented by Sea-lilies, Sea-urchins, Star-fishes, and Brittle-stars. The Crinoids are still common, and some of the limestones of the series are largely composed of the débris of these organisms. Most of the Jurassic forms resemble those with which we are already familiar, in having the body permanently attached to some foreign object by means of a longer or shorter jointed stalk or "column." ”

“ Birds do not appear, so far as their remains are known, until near the close of the Jurassic; whilst Mammals are sparsely represented by Monotremes and Marsupials in the Triassic and Jurassic, becoming more abundant in Cainozoic times, and by the Eutheria (Higher Mammals) from the commencement of the Eocene period. ”

“ The phrase, however, the Age of Reptiles, is a fitting and true description of the greater part of the Mesozoic Era, which lies, like a fertile valley, between the Permian and the Chalk upheavals. From the bleak heights of the Permian period, or—more probably—from its more sheltered regions, in which they have lingered with the ferns and cycads, the reptiles spread out over the earth, as the summer of the Triassic period advances. In the full warmth and luxuriance of the Jurassic they become the most singular and powerful army that ever trod the earth. ”

“ Slowly the land fell further, the sea spread out vast arms of warm water; plants and animals increased. By the Jurassic Period there was marsh again from Norway to Africa and the huge dinosaurs became the masters of the world, living on the islands and peninsulas in the midst of that shallow tropical sea. ”

“ But in the west, along the base of the Rocky Mountains and also in the Arctic area, there were Jurassic seas of large extent, swarming with characteristic animals. At the close of the Jurassic period our continents seem to have been even more extensive than at present. In England and the neighbouring parts of the continent of Europe, according to Lyell, the fresh-water and estuarine beds known as the Wealden have been traced 320 miles from west to east, and 200 miles from north-west to south-east, and their thickness in one part of this area is estimated at no less than 2,000 feet. ”

“ A greater variety of dinosaurs lived during the Jurassic Period than in the Triassic. Both two- and four-footed types were present. The flesh-eaters remained two-footed but increased in size. Antrodemus, perhaps the best known, was much bigger than a kangaroo. The larger plant-eaters weighed from 30 to 40 tons and all were four-footed. The largest land animals, they lived on dry land and in the swamps that formed an important part of the Jurassic landscape. ”

“ This ancient basin, extending from the centre of France into England, is rich in the remains of a number of successive epochs. Around its margin we find the Jurassic deposits, showing that there must have been some changes of level which raised the shores and prevented later accumulations from covering them, while in the centre the Jurassic deposits are concealed by those of the Cretaceous epoch above them, these being also partially hidden under the later Tertiary beds. Let us see, then, what this inland sea has to tell us of the organic world in the Jurassic epoch. ”

“ Its predominant life features are the culmination and the beginning of the decline of reptiles, amphibians, cephalopod mollusks, and cycads, and the advent of marsupial mammals, birds, teleost fishes, and angiospermous plants. The leading events of the long ages of the era we can sketch only in the most summary way.
The Mesozoic comprises three systems,—the Triassic, named from its threefold division in Germany; the Jurassic, which is well displayed in the Jura Mountains; and the Cretaceous, which contains the extensive chalk (Latin, creta) deposits of Europe. ”

“ Several hundred species are found in Jurassic rocks, and by the end of the Cretaceous period most of the insect families now known to us were probably in existence. The record is seriously obscured by the erosion of rocks which so frequently marks the end of a period, also by the small size of the subjects, and by the exceptional conditions required for the production of such delicate fossils. ”

“ Then cartilaginous fishes appear in the Silurian and Devonian, and land-inhabiting vertebrates, amphibia, and reptiles in the Carboniferous and Permian. The development of life goes on in the Mesozoic epoch. The oldest and lowest organized mammals, the marsupials, meet us in the upper Trias. The Jurassic gives us the first birds, curious creatures with teeth in their bills and lizards' tails bearing feathers. ”

“ The plants of the Jurassic period consist principally of Ferns, Cycads, and Conifers—agreeing in this respect, Page 230 therefore, with those of the preceding Triassic formation. The Ferns are very abundant, and belong partly to old and partly to new genera. The Cycads are also very abundant, and, on the whole, constitute the most marked feature of the Jurassic vegetation, many genera of this group being known (Pterophyllum, Otozamites, Zamites, Crossozamia, Williamsonia, Bucklandia, &c.) ”

“ Nothing that we know of in the existing scenery of the globe surpasses the rich vegetation which decorated the continents of the Jurassic period. A temperature still of great elevation, a [239] humid atmosphere, and, we have no reason to doubt, a brilliant sun, promoted the growth of a luxuriant vegetation, such as some of the tropical islands, with their burning temperature and maritime climate, can only give us an idea of, while it recalls some of the Jurassic types of vegetation. ”

“ Regarded as a whole, the Jurassic formation is essentially marine; and though remains of drifted plants, and of insects and other air-breathing animals, are not uncommon, the fossils of the formation are in the main marine. In the Purbeck series of Britain, anticipatory of the great river-deposit of the Wealden, there are fresh-water, brackish-water, and even terrestrial strata, indicating that the floor of the Oolitic ocean was undergoing upheaval, and that the marine conditions which had formerly prevailed were nearly at an end. ”

“ They consist of harder sandstones and limestones interstratified with softer clays and shales. Hence they give rise to a characteristic type of scenery—the more durable beds standing out as long ridges, sometimes even with low cliffs, while the clays underlie the level spaces between.
Jurassic rocks cover a vast area in Central Europe. They rise from under the Cretaceous formations in the north-east of France, whence they range southwards down the valleys of the Saône and Rhone to the Mediterranean. ”

“ As the only air-breathers of paleozoic times were amphibians and reptiles, there must have been, during the time that they reigned supreme,—from the Mississippian to the Jurassic, millions of years,—scores of thousands of their kinds; we know but a few hundreds. Had we records of all that have lived, the major problems would be much easier, the minor ones greatly increased. ”

“ It is an interesting fact that all the Jurassic birds known, both from Europe and America, are land-birds, while all from the Cretaceous are aquatic forms. The four oldest known birds, moreover, differ more widely from each other than do any two recent birds. These facts show that we may hope for most important discoveries in the future, especially from the Triassic, which has as yet furnished no authentic trace of birds. ”

“ Before the Cretaceous period, underground movements had disrupted and irregularly upheaved the Jurassic deposits, and prolonged denudation had worn them away, so that when the Cretaceous formations came to be laid down on the once more subsiding depression, they were spread out with a strong unconformability on everything older than themselves, resting on many successive horizons of the Jurassic system, and passing from these over to the submerged hillsides of the crystalline schists. ”

“ In all these localities, the Cretaceous remains, like those of the Jurassic epoch, have one organic character, distinct and unique. This fact is especially significant, because the contact of their respective deposits is in many localities so immediate and continuous that it affords an admirable test for the development-theory. If this is the true mode of origin of animals, those of the later Jurassic beds must be the progenitors of those of the earlier Cretaceous deposits. ”

“ Fossil footprints have been found in various parts of the world, as in England, Germany, France, and, in our own country, in the Grand Canon of the Colorado, as well as in association with Jurassic dinosaurs in the northwest; but it is in the valley of the Connecticut and in rocks of the same formation in New Jersey that they occur in an abundance and perfection of preservation which is unrivaled elsewhere. ”

“ Their footprints are often very abundant, e.g. Cheirotherium. The reptiles of the Triassic deposits, unlike the amphibians, which are Permian in character, show a closer relationship with Jurassic forms; one of the most interesting facts in the life-history of the group is the development during this period of sea-going forms such as at a later geological period played so prominent a part. ”

“ At Dinosaur National Monument only Morrison rocks of the upper Jurassic Period contain the fossil bones of dinosaurs. After Morrison time, the Cretaceous seas invaded this area. More than 5,000 feet of sandstone, shale, and mudstone were formed from sediments deposited in these seas.
Elsewhere in North America and the rest of the world, the diversity and numbers of dinosaurs actually increased. Entirely new groups evolved and achieved success in the battle for survival. The climax of reptile development seems to have come near the end of Cretaceous time in the Mesozoic Era. ”

“ Nothing could be further from the facts as we find them; we know of not the slightest evidence of the existence of birds before the Jurassic, or perhaps the Triassic, formation;71 while terrestrial animals, as we have just seen, occur in the Carboniferous rocks.
If there were any harmony between the Miltonic account and the circumstantial evidence, we ought to have abundant evidence of the existence of birds in the Carboniferous, the Devonian, and the Silurian rocks. ”

“ The discoveries of Professor Hatcher made in 1900 show that in all probability in like manner the rhinoceros was evolved from a primitive form upon the same theater of zoogenic energy. The most striking objects in the paleontological section, from a popular standpoint, are the huge dinosaurs from the Jurassic beds of Wyoming and Colorado. ”

“ In the American continent Jurassic rocks are not well developed. Marine Lower and Middle Jurassic beds occur on the Pacific coast (California and Oregon) , and in Wyoming, the Dakotas, Colorado, east Mexico and Texas. Above the marine beds in the interior are brackish and fresh-water deposits, the Morrison and Como beds (Atlantosaurus and Baptanodon beds of Marsh) . Later Jurassic rocks are found in northern British Columbia and perhaps in Alaska, Wyoming, Utah, Montana, Colorado, the Dakotas, &c. In California some of the gold-bearing, metamorphic slates are of this age. ”

“ The gigantic Dinosaur, Atlantosaurus montanus, described by the writer in the July number of this Journal, [1] proves to belong to a lower horizon than at first supposed, and is really from the upper Jurassic. ”

“ In the Jurassic period there were no less than six orders of reptiles which independently abandoned terrestrial life and acquired more or less perfect adaptation to sea life. Nature, limited in her resources for adaptation, fashioned so many of these animals in like form that we have learned only recently to distinguish similarities of analogous habit from the similitudes of real kinship. From whatever order of Mammalia or Reptilia an animal may be derived, prolonged aquatic adaptation will model its outer, and finally its inner, structure according to certain advantageous designs. ”

“ The Jurassic dinosaur formations skirt the Rockies and outlying mountain ranges but are often turned up on edge and poorly exposed, or barren of fossils. The richest collecting ground is in the Laramie Plains, between the Rockies and the Laramie range in south-central Wyoming, but important finds have also been made in Colorado and Utah. The Cretaceous Dinosaur formations extend somewhat further out on the plains to the eastward, and the best collecting regions thus far explored are in eastern Wyoming, central Montana and in Alberta, Canada.
The First Discovery of Dinosaurs in the West. ”