Ordovician and Silurian Communities
Ordovician and Silurian Communities
By: Linda Zantout
| Taxon | Count | Life Habit | Complete or Broken | Body or Mold | Period |
| Trepostomes | 2 | Epifaunal Suspension Feeder | Broken | Body | Ordovician |
| Platystropha | 4 | Epifaunal Suspension Feeder | Complete | Mold | Ordovician |
| Homotrypa | 1 | Epifaunal Suspension Feeder | Broken | Mold | Ordovician |
| Batostomella | 3 | Epifaunal Suspension Feeder | Broke | Mold | Ordovician |
| Strophomena | 1 | Epifaunal Suspension Feeder | Broken | Mold | Ordovician |
| Crinoids | 3 | Epifaunal Suspension Feeder | Broken | Body | Ordovician |
| Laptaena | 1 | Epifaunal Suspension Feeder | Broken | Mold | Ordovician |
Data Analysis and Interpretation
1. Depending on the sample size being measured, different sets of individuals will be studied which may lead to different results in measuring species richness. Thus, results regarding species richness are most valid when the sampling sizes are for the most part equated. For example, within the class data we see 20 different types of brachiopods and 17 different types of bryozoa and thus a valid deduction would be that the species richness is higher in brachiopods. However, in a different sample in which the number of individual species in each phylum is added, there are 131 brachiopods and 20y bryozoa. In this sample set, it would be valid to say that the species richness of bryozoa is greater than that of brachiopods.
2.
| Phylum | Genera | Count | Simpson Index |
| Bivalve | Ambonychia |
1 |
0.00212766 |
| Bivalve | Carotidens |
1 |
0.00212766 |
| Brachiopod | Platystrophia |
31 |
0.065957447 |
| Brachiopod | Lepidocyclus |
16 |
0.034042553 |
| Brachiopod | Strophomena |
14 |
0.029787234 |
| Brachiopod | Hypsiptycha |
12 |
0.025531915 |
| Brachiopod | Thaerodonta |
11 |
0.023404255 |
| Brachiopod | Hebertella |
8 |
0.017021277 |
| Brachiopod | Zygospira |
7 |
0.014893617 |
| Brachiopod | Megamyonia |
5 |
0.010638298 |
| Brachiopod | Hesperorthis |
4 |
0.008510638 |
| Brachiopod | Diceromyonia |
3 |
0.006382979 |
| Brachiopod | Hiscobeccus |
3 |
0.006382979 |
| Brachiopod | Rafinesquina |
3 |
0.006382979 |
| Brachiopod | Retrisirostra |
3 |
0.006382979 |
| Brachiopod | Glyptorthis |
2 |
0.004255319 |
| Brachiopod | Leptaena |
2 |
0.004255319 |
| Brachiopod | Rhyncotrema |
2 |
0.004255319 |
| Brachiopod | Sowerbyella |
2 |
0.004255319 |
| Brachiopod | Orbiculoidea |
1 |
0.00212766 |
| Brachiopod | Pentamerus |
1 |
0.00212766 |
| Brachiopod | Reserella |
1 |
0.00212766 |
| Bryozoa | “trepostome” |
83 |
0.176595745 |
| Bryozoa | Batostomella |
36 |
0.076595745 |
| Bryozoa | Homotrypa |
17 |
0.036170213 |
| Bryozoa | Dekayella |
14 |
0.029787234 |
| Bryozoa | Prasapora |
12 |
0.025531915 |
| Bryozoa | Rhombotrypa |
8 |
0.017021277 |
| Bryozoa | Monticulipora |
6 |
0.012765957 |
| Bryozoa | Parvohallopora |
6 |
0.012765957 |
| Bryozoa | Dimesopora |
5 |
0.010638298 |
| Bryozoa | Aspidopora |
4 |
0.008510638 |
| Bryozoa | Fistulipora |
4 |
0.008510638 |
| Bryozoa | Homotrypella |
3 |
0.006382979 |
| Bryozoa | fenestrate |
2 |
0.004255319 |
| Bryozoa | Heterotrypa |
2 |
0.004255319 |
| Bryozoa | Rhimdictya |
2 |
0.004255319 |
| Bryozoa | Dekayia |
2 |
0.004255319 |
| Bryozoa | Batostoma |
1 |
0.00212766 |
| Conularid | Cornulites |
6 |
0.012765957 |
| Coral | Calapoecia |
4 |
0.008510638 |
| Coral | Rugose coral – unid |
3 |
0.006382979 |
| Coral | Favosites |
1 |
0.00212766 |
| Coral | Grewingkia |
1 |
0.00212766 |
| Coral | Protarea |
1 |
0.00212766 |
| Coral | Streptalasma |
3 |
0.006382979 |
| Crinoid | unidentified |
75 |
0.159574468 |
| Monoplacaphoran |
1 |
0.00212766 |
|
| Porifera | Astylospongia |
6 |
0.012765957 |
| Porifera | Hindia |
3 |
0.006382979 |
| Stromatoporoids |
17 |
0.036170213 |
|
| Tentaculitid | Tentaculites |
3 |
0.006382979 |
| Trilobites |
6 |
0.012765957 |
|
| TOTAL |
470 |
1 |
Taphonomy and Life Habits
1. The community seems to be heavily dominated by epifaunal suspension feeders.
2. The fossils can be divided into two sizes: small ones such as the trepostomes and other bryozoans and then bigger ones such as the brachiopods. However amongst each one of these divisions, the sizes are evenly distributed. Also, there are outliers, those that are significantly smaller or bigger, but that is to be expected.
3. What’s missing from the biota is more specimens of coral and porifera and some of cephalopods although they are generally harder to preserve so it makes sense.
4. The mode of preservation was generally mold or cast in that there was an imprint left behind in the rock in which the shape and texture of the shell could be seen. Other than this, there were some that had the body preserved but those were mainly bryozoans, which had hard body parts that were able to withstand the time and preservation.
5. Based on observations, it can be inferred that the organisms resided in a warm shallow marine environment and were deposited and preserved at the bottom in sediments or mud after they died.
6. To a certain extent, the collection does represent the original living community. Of course however, there are a number of species missing due to the fact that they’re usually not preserved well or rare in general but there was a large percentage of brachiopods and bryozoans which is what mostly would have been making up the original living community.
7. The main difference between the Ordovician and Silurian communities is that the organisms of the Ordovician period were all marine organisms whereas the Silurian brought with it the appearance of the first few organisms able to start their way onto land. This makes sense since all the organisms we found were marine based and we were looking in Ordovician beds.
