United States or South Georgia and the South Sandwich Islands ? Vote for the TOP Country of the Week !
I suppose we may fairly say, from the evidence before us, that there have been two Augustan Ages of big animals in the history of our earth the Jurassic period, which was the zenith of the reptilian type, and the Pliocene, which was the zenith of the colossal terrestrial tertiary mammals.
This cavern occurs in Jurassic limestone, at a slight elevation above the Cure, a small tributary of the Yonne, which last joins the Seine near Fontainebleau about 40 miles south of Paris. The lowest formation in the cavern resembles the "diluvium gris" of Paris, being composed of granitic materials, and like it derived chiefly from the waste of the crystalline rocks of the Morvan.
Originally an archaean sea-bottom rock this stone lay submerged in the ocean until during the Jurassic Period, under the lateral pressure of a cooling earthcrust the table-lands and mountain-chains of Arizona rose from the seas.
These names have, for the present, only a local significance, being derived, like so many of the geological names, from the places where the investigations of the phenomena were first undertaken, but in course of time will, no doubt, apply to all the contemporaneous upheavals, wherever they may be traced, just as we now have Silurian, Devonian, Permian, and Jurassic deposits in America as well as in Europe.
An imperfect intelligence, imperfectly taught, and this is the condition of our finite humanity, will certainly fail to keep all these laws perfectly. Disease is one of the penalties of one of the forms of such failure. Malformed specimens of Crinoids are known from the Triassic and Jurassic deposits.
Every insistence on the close connection of the different strands in the web of life is welcome, but Dr. Wallace does not seem to have learned the facts accurately. There is nothing "puzzling" about the Mesozoic reptilian development; the depression of the land, the moist warmth, and the luscious vegetation of the later Triassic and the Jurassic amply explain it.
But with the fresh upheaval and climatic disturbance at the end of the Jurassic, and during the Cretaceous, they spread northward, and replaced the dying reptiles, as the Angiosperms replaced the dying cycads. When they met the spread of the Angiosperm vegetation they would receive another great stimulus to development. They appear in Europe and North America in the earliest Cretaceous.
Far back before Jurassic times, millions of years ago, before the coming of bony fishes, when the only mammals were tiny nameless creatures, hardly larger than mice; when the great Altantosaurus dinosaurs browsed on the quaint herbage, and Pterodactyls those ravenous bat-winged dragons of the air hovered above the surface of the earth, in this epoch we can imagine a pair of long-tailed, half-winged creatures which skimmed from tree to tree, perhaps giving an occasional flop the beginning of the marvellous flight motions.
The Crocodilians also appear in the later Triassic, abound in the Jurassic, and give way before the later types, the true Crocodiles, in the Cretaceous. They were marine animals with naked skin, a head and neck something like that of the Ichthyosaur, and paddles like those of the Plesiosaur.
As most of the Placentals have not this process, we can, with some probability, recognise the Marsupial from this feature alone. Most of the mammal remains that we have from the Jurassic and Cretaceous deposits are merely lower jaws, and most of the jaws found in the Jurassic deposits at Stonesfield and Purbeck have the peculiar hook-like process that characterises the lower jaw of the Marsupial.
Word Of The Day