Cambrian and Ordovician periods

Cambrian and Ordovician periods - Cambrian and Ordovician...

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Cambrian and Ordovician periods Introduction At the end of the Proterozoic many changes happen to the things inhabiting the ocean at a microscopic at first, but soon explodes into a huge diversity of multi-celled organisms. This introduces the Cambrian period. - Possible multi-cellular organisms before Cambrian period dying at the end of the Proterozoic o Evidence from two fossils found Ediacaran and Doushantuo o Possible ancestors to modern day phyla Sponges, jelly fish - The biodiversity at the beginning of the Cambrian is known as the Cambrian Explosion o At the end of the Cambrian period, mass extinction of most of the animals that came to be in the Cambrian explosion o Still wasn’t considered one of the 5 major extinctions known After the mass extinction of the marine organisms introduced the Ordovician period, another period that mostly dealt with marine organisms, not land - about 30 different body plans of current phyla survive from the extinction o Ancestors of some modern species known Starfish, and relatives First snails Mollusks o Bryozoan colonies form and diversify Feeds using a unique lophophore o Green algal begins to grow on land - Near the end of the Ordovician period, the first of the 5 mass exctinctions occur o Believed to be an ice age causing ocean levels to drop, exposing continental shelves o 50% of generations die o bryozoans and trilobites survive Why do we call it the Cambrian explosion?
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Definitions Acoelomate - A body plan of bilaterally symmetrical animals that lack a body cavity (coelom) between the gut and the body wall. Algal mats - a layer of usually filamentous algae on marine or fresh water soft bottoms Amebocyte - a mobile cell (moving like an amoeba) in the body of invertebrates Archeocyte – (in sponges) a type of amoebocyte capable of developing into other types of cells Assymetric body plan - Characterized by a lack of proportion in the spatial arrangement or placement of parts. Bilateral symmetry body plan - The body plan of animals in which the body can be divided into mirror image right and left halves by a plane passing through the midline of the body. Bivalve - a shell consisting of two asymmetrically rounded halves called valves that are mirror images of each other, joined at one edge by a flexible ligament called the hinge Blastopore - The opening at one end of the archenteron in the gastrula that gives rise to the mouth in protostomes and the anus in deuterostomes. Blastula - The hollow ball of cells that is the result of cleavage divisions in an early embryo. Bryozoa - also known as Ectoprocta or commonly as moss animals, are a phylum of aquatic invertebrate animals. Burgess Shale fossils – fossils of many invertebrates during the Cambrian period Cambrian – really?? Cambrian burrowers – organisms that burrowed underneath the microbial mats
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This note was uploaded on 09/09/2011 for the course BIO 1130 taught by Professor Fenwick during the Fall '08 term at University of Ottawa.

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Cambrian and Ordovician periods - Cambrian and Ordovician...

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