CNIDARIANS

PALEOECOLOGY

 

Colonial coral growth habits and integration levels

The morphology of coral colonies can be grouped into three broad categories: (i) encrusting forms which are often sheet-like such as this specimen. (ii) massive forms which are domal or hemispherical such as in specimen. (iii) erect forms which are branching or palmate such as this specimen You should return to the coral specimens in the first part of the lab making sure you can place each into one of the three morphologic groups.

Colonial corals nearly always show some level of integration between individual coralites. Such integration is usually reflected in the coral's skeleton by the degree of spetal sharing ranging from completely isolated corallites to those where individual corallite cannot be recognized.

Figure 4 - Colonial Cnidarian Integration Types

From McRoberts (1998)

You should return to the specimens of the earlier part of the lab and make sure you can identify the integration types depicted in Figure above. You should find, for example, that this specimen, is cateniform, this specimen, is cerioid, and this specimen, is meanderoid.

It is important to know that different integration levels were dominant during different periods of geologic time. In fact, given a large enough sample, a rough estimate of gelogic age can be obtained on the relative proportions of various integration levels.

Paleoenvironments

Corals occur as framework organisms in reef environments and as important constituents in level-bottom communities. As a group they are very sensitive to physical and chemical conditions such as fluctuating sea level, turbidity, and salinity. Of all of these factors which may result in differing growth morphology, the overall shape of coral colonies is most responsive to water (= wave + current) energy. However, it should be noted that the morphologic response is quite different when a coral is in a reef setting or in a level bottom setting.

From McRoberts (1998)

Although quite diverse in large-scale morphology and facies relations, reef systems generally conform to the scheme depicted in the accompanying figure . Note that the reef proper (the organic build-up) is quite restricted in size compared to the reef system as a whole. In reef settings, the degree of branching in colonial corals can generally be correlated with water energy. Thus high energy often results in erect, branching and palmate forms, whereas lower water energy levels are generally sites where the encrusting and/or massive forms predominate.

The opposite is generally true for level-bottom settings such as is often found in the Devonian of central New York. Here, greater water energy usually results in encrusting and/or massive morphologies. This is in contrast to lower water energy level bottom environments where branching and ramose morphologies (albeit more delicate than in reefs) predominate.

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