THE FUCTIONAL MORPHOLOGY OF ANTILLOSARCOLITES N.GEN. N.SP

The oolithic grainstones facies of the Cotui Limestone formationis located in southwestern Puerto Rico (Santos, 1999) (Bonilla, 2007).This facies contains complete specimens and fragments of the rudistid bivalves described by Santos (1999) as Antillosarcolites sp. Two complete specimens showing good preservation were studied within a quadrangle of 15m by 10m to determine the functional morphology of Antillosarcolites sp. Many fragments of this rudist were found within the studied quadrangle. The rudist is not found at any other facies within the stratigraphic section area. The Antillosarcolites sp. has a morphology that is classified as recumbent with a coiled shell.The sinistral valve is much smaller than the dextral valve and had probably free movement for feeding. Each specimen studied extended outward forming flanges that act as anchors that help the rudist maintain stability in the substrate. The morphology of the shell and the abundant fragments together with the facts that the rudist is not observed in any other facies of the Cotui Limestone suggest that the Antillosarcolites sp.shell was able to stand normal wave action but probably was not successful during storm waves.

The oolithic grainstone facies in which this rudist is located indicated high-energy, shallow waters, wave dominated environment (Santos 1999). By using the description of the Cotui Limestone provided by Santos (1999) and Bonilla (2007), it was determined that Antillosarcolites sp. may have lived within the shelf edge and was subjected to strong waves and currents. After observing the morphology of the rudist valves it was confirmed that Antillosarcolites sp.had the capacity to thrive in such high energy environment. However, whenstudying the rudist’s mantle cavity oolites were observed within the convex tabulae from every collected sample. This may suggest that even thoughAntillosarcolites sp. was capable of living within the shelf edge it may not have been very resistant to storm waves that may have destroyed the shells. Also, these ooids could have entered the spaces of the mantle cavity after death of the organism.