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now inhabiting Europe. A butterfly is also well preserved, with all the markings of the wings; and it seems to be a Junonia, a tropical genus, though it may be a Vanessa, which is European, but the fossil most resembles Indian species of Junonia.
The Eocene formations seem to have produced no insect remains ; but they occur again in the Upper Cretaceous at Aix-la-Chapelle, where two butterflies have been found, Cyllo sepulta and Satyrites Reynesii, both belonging to the Satyridæ, and the former to a genus now spread over Africa, India, and Australia.
A little earlier, in the Wealden formation of our own country, numerous insects have been found, principally dragon flies (Libellula, Æshna); aquatic Hemiptera (Velia Hydrometra); crickets cockroaches, and cicadas, of familiar types.
Further back in the Upper Oolite of Bavaria—which produced the wonderful long-tailed bird, Archæopteryx—insects of all orders have been found, including a moth referred to the existing genus Sphinx.
In the Lower Oolite of Oxfordshire many fossil beetles have been found whose affinities are shown by their names : - Buprestidium, Curculionidium, Blapsidium, Melolonthidium, and Prionidium ; a wing of a butterfly has also been found, allied to the Brassolidæ now confined to tropical America, and named Paloontina oolitica.
Still more remote are the insects of the Lias of Gloucestershire, yet they too can be referred to well-known family types— Carabidæ, Melolonthidæ, Telephoridæ, Elateridæ, and Curculionidæ, among beetles; Gryllidæ and Blattidæ among Orthoptera; with Libellula, Agrion, Æshna, Ephemera, and some extinct genera. When we consider that almost the only vertebrata of this period were huge Saurian repliles like the Icthyosaurus, Plesiosaurus, and Dinosaurus, with the flying Pterodactyles ; and that the great mass of our existing genera, and even families, of fish and reptiles had almost certainly not come into existence, we see at once that types of insect-form are, proportionately, far more ancient. At this remote epoch we find the chief family types (the genera of the time of Linnæus) perfectly differentiated
and recognisable. It is only when we go further back still, into the Palæozoic formations, that the insect forms begin to show that generalization of type which renders it impossible to classify them in any existing groups. Yet even in the coal formation of Nova Scotia and Durham, the fossil insects are said by competent entomologists to be “allied to Ephemera,” “near Blatta,” “near Phasmide ;” and in deposits of the same age at Saarbrück near Trèves, a well-preserved wing of a grasshopper or locust has been found, as well as a beetle referred to the Scarabeidæ. More remarkable, however, is the recent discovery in the carboniferous shales of Belgium, of the clearly-defined wing of a large moth (Breyeria borinensis), closely resembling soine of the Saturniidæ ; so that we have now all the chief orders of Insects—including those supposed to be the most highly developed and the most recent-well represented at this very remote epoch. Even the oldest insects, from the Devonian rocks of North America, can mostly be classed as Neuroptera or Myriapoda, but appear to form new families.
We may consider it, therefore, as proved, that many of the larger and more important genera of insects date back to the beginning of the Tertiary period, or perhaps beyond it; but the family types are far older, and must have been differentiated very early in the Secondary period, while some of them perhaps go back to Palæozoic times. The great comparative antiquity of the genera is however the important fact for us, and we shall have occasion often to refer to it, in endeavouring to ascertain the true bearing of the facts of insect distribution, as elucidating or invalidating the conclusions arrived at from a study of the distribution of the higher animals,
ANTIQUITY OF THE GENERA OF LAND AND FRESH-WATER
The remains of land and fresh-water shells are not much more frequent than those of insects. Like them, too, their forms are very stable, continuing unchanged through several geological
periods. In the Pliocene and Miocene formations, most of the shells are very similar to living species, and some are quite identical. In the Eocene we meet with ordinary forms of the genera Helix, Clausilia, Pupa, Bulimus, Glandina, Cyclostoma, Megalostoma, Planorbis, Paludina and Limnæa, some resembling European species, others more like tropical forms. A British Eocene species of Helix is still living in Texas; and in the South of France are found species of the Brazilian sub-genera Megaspira and Anastoma. In the secondary formation no true land shells have been found, but fresh water shells are tolerably abundant, and almost all are still of living forms. In the Wealden (Lower Cretaceous) and Purbeck (Upper Oolite) are found Unio, Melania, Paludina, Planorbis, and Limnoa; while the last named genus occurs even in the Lias.
The notion that land shells were really not in existence during the secondary period is, however, proved to be erroneous by the startling discovery, in the Palæozoic coal measures of Nova Scotia, of two species of Helicidæ, both of living genera—Pupa vetusta, and Zonites priscus. They have been found in the hollow trunk of a Sigillaria, and in great quantities in a bed full of Stigmarian rootlets. The most minute examination detects no important differences of form or of microscopic structure, between these shells and living species of the same genera! These mollusca were the contemporaries of Labyrinthodonts and strange Ganoid fishes, which formed almost the whole vertebrate fauna. This unexpected discovery renders it almost certain, that numbers of other existing genera, of which we have found no traces, lived with these two through the whole secondary period; and we are thus obliged to assume as a probability, that any particular genus has lived through a long succession of geological ages. In estimating the importance of any peculiarities or anomalies in the geographical distribution of land shells as compared with the higher vertebrates, we shall, therefore, have to keep this possible, and even probable high antiquity, constantly in mind.
We have now concluded our sketch of Tertiary Palæontology as a preparation for the intelligent study of the Geographical
Distribution of Land Animals; and however imperfectly the task has been performed, the reader will at all events have been convinced that some such preliminary investigation is an essential and most important part of our work. So much of palæontology is at present tentative and conjectural, that in combining the information derived from numerous writers, many errors of detail must have been made. The main conclusions have, however, been drawn from as large a basis of facts as possible; and although fresh discoveries may show that our views as to the past history of some of the less important genera or families are erroneous, they can hardly invalidate our results to any important degree, either as regards the intercommunications between separate regions in the various geological epochs, or as to the centres from which some of the more important groups have been dispersed.