Introduction

The fossils of the first tetrapods, early amphibians (Chap. 1), have been found in Upper Devonian strata of the eastern part of Greenland. The flora at that time was surprisingly varied: it included dense growths of increasingly tall club mosses, horsetails, and ferns. The Carboniferous (350 mya) and Permian (270 mya) periods were both warm in the northern hemisphere. In the south, however, a large ice cap developed which covered considerable portions of Gondwanaland (Benton 1996,2004).

Until the Carboniferous period, land plants had been restricted to moist areas around rivers, ponds and lakes: they were by no means large. During the Carboniferous, however, when reptiles first appeared, giant horsetails, ferns, and seed ferns or pteridosperms evolved. Seed ferns resembled true ferns (pteridophytes) in many ways, but had already evolved seeds. They bridged the gulf between ferns and cycads. The latter are palm-like plants and the pteridosperms were more closely related to them than to pteridophytes.

Ferns, tree ferns - which reached to a height of 9-15 m - horsetails and giant club mosses were characteristic of the Carboniferous period. One genus of the club mosses, Sigillaria, grew to ca. 20 m and was one of the main components of the coal forests of the northern hemisphere. Its cones grew directly from the trunk, just below the apex. Spore-bearing ferns predominated in the Early Permian, but by the end of the period they had been largely replaced by gym-nosperms (coniferous trees). This change in the vegetation during the Permian was very pronounced, and marked a transition from the early to the middle phase of plant development. Giant club mosses gradually disappeared, along with many pteridosperms and some of the horsetails, while new types of ferns and ginkgo trees appeared as the climate became drier. In Gondwanaland, ferns of the genus Glossopteris, with long, tongue-shaped leaves and central veins, as well as of Gangamopteris, with leaves from which the central veins were absent, were characteristic of this time.

Was this article helpful?

0 0
Pregnancy And Childbirth

Pregnancy And Childbirth

If Pregnancy Is Something That Frightens You, It's Time To Convert Your Fear Into Joy. Ready To Give Birth To A Child? Is The New Status Hitting Your State Of Mind? Are You Still Scared To Undergo All The Pain That Your Best Friend Underwent Just A Few Days Back? Not Convinced With The Answers Given By The Experts?

Get My Free Ebook


Post a comment