Prehistoric Plants
Some of the larger and better known plants of past ages are shown as reconstructed by artists. Finer details of the reconstructions often have to be neglected because of uncertainties due to the scattered and fragmentary character of the fossil record.
LEAF IMPRESSIONS Carboniferous Ferns Strap-leaf Conifer (Cordaites) MODERNIZED TYPES Sequoia Cone and foliage Miocene Fossils (Florissant Shales) Maple Willow Eocene palm (Denver Beds) HORSE TAIL RUSHES Restoration (Calamites) Fossils Leaves and Stem CYCADS Restoration Fossil Trunk CLUB MOSSES Restoration (Sigillaria) Fossils Trunk Impressions SCALE TREES Restoration (Lepidodendron) Fossil Leaf scars
Also included among the larger trees were the Cordaites or large-leaved evergreens, tall and slender, seed-bearing but not true conifers as yet. Leaves were strap-shaped or grass-like, the larger ones having a length of six feet and a width of six inches. Trunks were woody, resembling pine, but with a central pith. The flowers were small and resembled catkins in form.
Ferns and fernlike plants were so numerous that the period has been known as an age of ferns. Earlier knowledge of these forests was based on fossils of a fragmentary character from which an accurate association of parts could rarely be obtained. A general relationship with the ferns was apparent, but careful study of additional material has given us a rather different view of Carboniferous plant life and we note a highly diversified array of forms with many suggestions of modern tendencies. The flora as a whole may be regarded as highly specialized for the conditions which prevailed at the time and were not to continue through subsequent periods. Warm temperatures and abundant moisture were essential especially to spore-bearing types, and the cold, arid conditions of the next period put an end to many of the groups, or greatly reduced their prominence.
This could be regarded equally well as an age of insects, for some of these invertebrates acquired the greatest size they have ever had, particularly the dragonflies with a wing-spread of more than two feet in one of the largest fossils so far discovered. Cockroaches numbering upwards of five hundred species have been named. Though large they are hardly to be regarded as giants, lengths of three or four inches being about the limit.
Some of the insect types of today quite evidently existed among the inhabitants of Carboniferous forests, but it is apparent that there were also some antiquated forms which may have descended from the trilobites. Although some authorities regard this as the period in which insects originated, there are others who maintain that definite beginnings are not established so readily on present evidence. Spiders are believed to have made their appearance at this time.
Four-footed vertebrates resembling salamanders were prominent animals of the Carboniferous swamps. At first adapted to a life in water and later to land conditions, they are known as amphibians, the name being based on the ability to live in two different kinds of environment. Common living representatives of this group are the toads and frogs, but these tailless forms are not known among fossils of the Paleozoic era and are almost unknown throughout the Mesozoic. The Age of Amphibians, as we apply that phrase, was definitely not an age of toads and frogs.
These primitive land animals were of different types, ranging from much smaller sizes up to the length of a crocodile. Most of them had short legs, and feet which were suitable for locomotion upon land, but many of the creatures probably spent most of their lives in the water. Tails were usually high and flattened as if for swimming, sometimes long, at other times greatly shortened in proportion to the body. Heads were generally large, jaws long, and mouths wide.
Before the close of the period true reptiles appear, but this race of animals is destined to make a more spectacular advance than the amphibians and will be discussed in connection with Mesozoic life. The amphibians, however, are regarded as being the ancestors of the reptiles as well as the higher quadrupeds which follow them. Although living reptiles are readily distinguished from living amphibians there is a different situation with regard to these primitive forms, for among the fossils it becomes increasingly difficult to separate the two groups as new material is investigated.