Question

State the periods within the Paleozoic era that pre-date and follow the Ordovician time period and briefly describe those 2 periods with respect to major aspects of species diversity.

Answer 1

The Paleozoic era contains 6 time periods:Cambrian, Ordovician, Silurian, Devonian, Carboniferous and the Permian time period.

The time period that pre-date and follow the Ordovician time period are Cambrian time period and Silurian time period respectively.

Cambrian time period:

This is the oldest time period of the Paleozoic era which lasts from 541 million years ago to 485 million years. This is the only period which is known to contains largest number of creatures due to an event Cambrian explosion which takes place in this time period. Also this time period is known to contains with the generation of cyanobacteria or blue green algae and also the algae. In this time period most of the vertebrates ( having back bone in their skeleton) have been evolved including the chordates like Humans. The environment of this period contains suitable environment and also ample amount of Oxygen which is the raw factor responsible for such a species diversity in this period.

The event cambrian explosion is considered as the most effective event which results in the high species diversity among all time periods in this time period. It results in the exaggeration of hard -bodied animals and their proliferation which are also fossilized easily. These organisms includes brachiopods which resembles the organisms having outer and jointed skeleton most commonly known as Arthropods.These arthropods are also considered as the ancestors of insects, spiders and crustaceans. The most common arthropods are trilobites which have a peculiar body structure and varies in length from a milimeter to 2 feet. It contains about 17000 species contributing a lot to the species diversity i this time period.

A predator of cambrian period which is shrimp like known as Anomalocaris was found. Five-eyed Opabinia ( a stranger), sponges added to reef habitat are found in this time period. The earliest known primitive chordate is Pikaia gracilens, a wormlike creature who have given traces of notochord which is considered significant for the evolution of chordates.

Silurian Period:

It lasts from 443 to 416 million years ago. This time period is mostly known to be the rejuvenation period of the Earth. Also it is the significant time period for the evolution of fishes, as the jaw less fishes were numerous in number and also the first fresh water fishes and jawed fishes were evolved. Deviation from the chordates also the arthropods like scorpions were the top predators of this time period. Arachnids, fungi centipedes were evolved giving rise to full terrestrial life form. Not only the animals but also the vascular plants were evolved during this time period which are the precursor of all terrestrial plants. The increased sea level has a major role in the species diversity of this time period.

Previous reef-builders such as Bryozoans and  prehistoric sponges known as Stromatoporoids have been evolved in this time period. Many sea creatures like coral reefs and acanthodians, or spiny sharks, evolved more menacing mouths with jaws. These were the first jawed species.Creepy-crawlies were found at this time period.

All these species were varying greatly in their body length as per the species diversity.