Friday, December 24, 2010


Silurian Period (440-410 mya)

Development of large vertebrates with hard external body coverings.
a) Trilobites 
b) Ammonites
Invasion of land by plants and arthropods.
Evolution of vertebrates with jaws for predation.
Tendency towards increased powers of locomotion in some animal forms;
- Development of external skeleton and muscular systems.


Devonian Period (410-360 mya)

Extensive radiation of fishes with jaws.
Cartilaginous and bony fishes diversified extensively during Devonian period.
They had evolutionary jaws with associated muscles. Reduced body covering. Evolving fins with associated bones and muscles. Fast moving predatory forms were present.
Towards the mid late Devonian period the first appearance of early tetrapods occurred.
They originated from lobe-finned fishes.
Colonization of land.
Fishapods who had both fish-like and amphibian-like qualities came into existence.

Terrestrial Environment in Devonian Period

Cooler Climate.
Development of fresh water basins lakes and swamps.
First appearance of winged insects.
Forests also appeared.
Increased diversity and abundance of plants occurred.
Some plants were about 2 m tall and grew in dense patches.
Arthropods  such as millipedes , scorpions and spiders were the dominant animal group.
Greater diversification and increase of the size of the plants occurred during the late Devonian period.
Giant ferns, horsetails,club mosses and such like plants were present.
Heterosporous plants appeared.

Sources : 
Zoology notes

Extra reading Sources :


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