The group I chose to write a report on was the group called Trilobites. The first occurrences I found are different amongst the species. Fossils come, and then go extinct at different times. I also found out that the fossil lineage can drastically change group of organisms. I found that the early occurrences of these organisms were called the biostratigraphic zones, which is understood as worldwide. The Trilobites for the early Paleozoic was mainly Cambrian. The age of Trilobites and dinosaurs showed a pattern of extinction. I found that some of the extinction was cause by external factors such as impacts, volcanism, and floods. And the other parts of extinction were caused by internal factors such as longevity of individuals, population size, and body size. .
.
The Cambrian period occurred about 490-543 million years ago. This was the period when most of the major groups showed up first in the fossil record. This event is known as the Cambrian Explosion. I found that the Vendian strata contained the first and oldest fossils of animals. .
.
The Trilobites are also known for the three lobes which are due to how their bodies are divided into three categories. The first is divided in a central axial lobe, and in the middle comes the two pleural lobes. And lastly, the cephalon, is the head. I found out some trilobites are blind. Trilobites have biramous legs as a form of moving and eating. By using their legs they are able to pass food forward to eat. Some Trilobites also contained a pygiidum which was located at the posterior of the body that looked like a tail. .
Here is a listing of the subgroups: .
Ordovician.
C.
A Sunwaptan.
M Steptoan.
B Marijuman.
R Delamaran.
I Dyeran.
A Montezuman.
N.
Vendian.
While reading some books on Trilobites I discovered that people are more familiar with the Polymerida, which is the greater percentage of all Trilobites. I believe this is about 92% of all Trilobites.