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The AAPG/Datapages Combined Publications Database

AAPG Bulletin

Abstract


Volume: 66 (1982)

Issue: 5. (May)

First Page: 602

Last Page: 603

Title: Significance of Corallite Patterns in Fossil Anthozoan Colonies: ABSTRACT

Author(s): John H. McBride

Article Type: Meeting abstract

Abstract:

Polygonal patterns of corallites in fossil anthozoan colonies have been traditionally explained as a result of close packing arising from space compaction. Such a view envisages polygonal corallite

End_Page 602------------------------------

patterns as "fabricational noise" while ignoring any possible phylogenetic constraints. This study rephrases the question of the adaptational significance of fossil corallite patterns.

The set of all possible two-dimensional mosaics of regular, identical polyhedra consists of triangular, square, and hexagonal nets, and thus represents a simple constructional constraint on pattern in a developing or evolving colony of anthozoan polyps. A regular hexagonal pattern of corallites possesses the utmost possible reduction of surfaces in contact by way of equal-angle triple junctions. This makes a regular hexagonal array to be ideally most efficient. However, most polygonal patterns of corallites deviate from this ideal with a particular pattern often being characteristic of a taxon. For example, a less efficient, irregular pattern may be common for one particular group (e.g., Eridophyllum) but a regular hexagonal array for another (e.g., Hexagonaria). This deviation from i eal form leads to the recognition of a second, phylogenetic constraint on corallite pattern.

The significance, constructional versus phylogenetic, of pattern development can be better understood by also considering the ontogeny of individual corallites in a colony which shows a hexagonal array. Within the continuum of varieties of colony patterns, polygonality first appears in cerioid forms. Transitional phaceloid/cerioid colonies of the Lithostrotionidae demonstrate that corallite centers do not closely approach one another until their margins are actually in apposition. It is at this stage of margin contact that hexagonality is achieved, not at the onset of close packing.

Hexagonality in fossil anthozoans is concluded to have probably first arisen in cerioid colonies as an adaptation to maintain and further a higher level of colony integration.

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Copyright 1997 American Association of Petroleum Geologists