Topics: Ordovician, Biology, Graptolite Pages: 1 (304 words) Published: April 9, 2013

1. Rhabdosomes are tube like colonies of graptolites that were formed from a single individual. They have an overlapping ring structure and they branch out into 1 or more branches. The branches are called stipes and they support tubes or cups called thecae that house individual organisms.

2. Graptolites lived in the oceans; some types of graptolites floated on the surface of the oceans while others lived in deeper water over the self-edge and upper slope and some lived at great depths. Graptolites lived at all levels of the water column and their main food source was plankton. However, we don’t know for sure how graptolites lived because there is not enough information about them to link them to any living organisms.

3. 3-3A. a) Genus: Monograptus b) Order: Graptoloidea 3-3B. a) Genus: Tetragraptus b) Order: Graptoloidea
3-3C. a) Genus: Phyllograptus b) Order: Graptoloidea
3-3D. a) Genus: Dictyonema b) Order: Dendroidea

4. a. If specimens 3-C and 3-D came from the same rock bed, the most precise age of the rock would be lower Ordovician. This is because the specimen in 3-C, Phyllograptus, lived from the lower to middle Ordovician period while the specimen in 3-D, Dictyonema, lived from the Cambrian to the Carbinferous periods. In order for the specimen to be fossilized the rock could not have formed yet and therefore the rock must have formed after the Phyllograptus came into existence. b. The specimen in 3-C would be a better stratigraphic indicator because it lived for a shorter period than the specimen in 3-D.

5. a. The thecal morphology specimen A best represents is hooked monograptid. b. Thecae are tubes or cups and are supported by stipes. The purpose of a theca is to house individual organisms or zooids.
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