Produced by the Population Genetics and Evolution class, Furman University

The Ordovician: Stromatoporoids
Stromatoporoids, though once classified as ancient corals or cnidarians, are now considered to be massive, calcareous sponges (Phylum Porifera) occurring first in the Ordovician era. It is due to their calcareous nature that they are so easily preserved as fossils (Kaslev 1999). They come in many shapes, including tabular, encrusting, and arm-shaped. Common features include mamelons, or irregular lumps on the surface of the massive skeleton of the organism, presumably used for expelling water that had been filtered for food (Kentucky Geological Survey 2006). Each mamelon is associated with a channel called an astrorhizum, through which the filtered water flowed. Relatively recent discoveries of modern sponges in Astrosclera with similar structures are what place the stromatoporoids now among Porifera (Collins 1994). Sediment carried with the water would be deposited across the surface of the organism, whose living tissue, much like the corals of today, resided primarily on the outermost layer and grew upwards. Over time, this sediment would encrust both other living objects such as corals and snails, and organic detritus (Kentucky 2006), with layered “colonies” of stromatoporoids that in the later Devonian era have been known to make “reefs” as deep as several hundred meters (Kaslev 1999).

Page by Will Towler
Features of stromatoporoids. From: Kentucky Geological Survey.

Collins A. 2006. Stromatoporoids. University of California Museum of Paleontology. Accessed Feb. 7, 2010.

Kaslev M. 1999. Stromatoporoidea-1. www.palaeos.com. Accessed Feb. 7, 2010.

Kentucky Geological Survey. 2010. Stromatoporoids. Accessed Feb. 7, 2010.