The greening of the lands began 100 million years before the Pennsylvanian Period with simple plants without stems, like mosses and liverworts. Then vascular plants, with internal tubes to transport water and nutrients, developed in the form of horsetails, club mosses, and ferns. These seedless plants reproduced from spores, usually a single reproductive cell. Seeds of plants are reproductive cells that have a protective coating. By the time of the Pennsylvanian Period, 320 million years ago, complex plants called gymnosperms (plants with seeds) appeared in the forest of trees that grew to heights of more than 100 feet. The dominant trees of the Pennsylvanian tropical forests were actually giant club mosses, some of which were more than 150 feet tall. There were more than 100 different species of Lepidodendron (which are now extinct) in the Pennsylvanian forests. Today, club mosses are typically less than 5 feet tall. Another giant club moss of this period was Sigillaria. This 100-foot-tall plant had leaves about 3 feet long at the top of the trunk that usually branched only once near the tree top. It's seed-bearing cones were borne on stems that grew directly from the trunk. Sigillaria is easily identified by the vertical ribs on its trunk. Calamities was a giant version of the horsetail. It's leaves are in whorls(circular arrangements about the stem or trunk). These plants grew to heights of 40 feet, whereas today's horsetail, Equisetum, is typically about 3 feet tall. The richest coal deposits on Earth today are the remains of the Pennsylvanian tropical forests. When the fallen, decaying trees of these forests were submerged in swamps and covered in silt, they were well preserved because they were not exposed to oxygen. As layers of rock formed over this action turned the organic matter first into peat and later into coal. Because of the abundance of ferns in the Pennsylvanian Period, this era is often called the " Age Of Ferns". Generally adapted to moist, warn climates, ferns reproduce by means of spores borne on "fertile leaves" of the plant. Some ferns, even those of today, grow to heights of 60 feet.
Insects Adapt To Life On Land :
The earliest fossil evidence of insect life suggests that insects first appeared in the ancient seas, having developed either from crustaceans or from trilobites. Like both crustaceans and trilobites, insects are characterized by an exoskeleton, a structural support surrounding the outsides of their bodies. Insects generally have six jointed legs. Insects were abundant by the start of the Pennsylvanian Period, when insects first developed wings. Primitive version of wings probably permitted only the simplest gliding but soon developed into organs of controlled flight. The giant dragonfly of this period, Meganeuropsis, had wings that more than 2 feet. Insects display of greatest variety of form of any class of animals: more than 13,000 species of fossil insects have been described, more than 8000,000 living species have been indentified, and about 6,000 new species are identified each year. Insects are well adapted to every land and fresh water habitat where food is available. Beetles, dragonflies, mayflies, cockroaches, crickets, grasshoppers, termites, and some species of flies all existed at the time of this re-creation, and many of these were very silimar to today's species. Bees, ants, butterflies, and fleas did not appear until millions of years later. Many species of insects have more than one form: first a larval stage, from, which they undergo metamorphosis into an adult. Metamorphosis, a sudden change in physical form during the development of an animal, first occurred with the advent of winged insects of the Pennsylvanian Period. In general, the larval forms of insects mostly eat and grow. The adult insect insect is essentially the reproductive form; some adults do not even eat, and some, like certain mayflies, live only 20 minutes.
All credit given to the Georgia Fernbank Museum...
No comments:
Post a Comment