We’re not actually looking at fossils here, but this bivalve-coral-sponge assemblage from the very modern Myrtle Beach in South Carolina is too cool not to share. Jacob Nowell (Wooster ’18) picked it up while on Spring Break this year and donated it to the collections. This is a bit of very worn bivalve shell punctured by clionaid sponge borings and encrusted by a columnar scleractinian coral.
How do we know the shell remnant is from a bivalve? This is what’s left of the hinge region, the thickest part of the shell. We can tell this is a heterodont bivalve, probably of the common genus Mercenaria. The shell material is calcite.
The coral is aragonitic and exquisitely preserved. It did not make the long tumbling journey the bivalve shell did. At its encrusting base you can see that it partially covers some of the sponge borings, showing that it attached after the sponge was at least partly gone. The round structures on the coral are the corallites, each of which housed a coral polyp. The corallites have radiating vertical septa inside in the classic scleractinian manner.
The sponge boring is the star here. This is a side view showing the interconnected galleries and tunnels excavated by a clionaid sponge like Cliona. As a trace fossil this structure would be known as Entobia. It is very common in the fossil record, especially in the Cretaceous and later.
Entobia was named and described by Heinrich Georg Bronn (1800-1862), a German geologist and paleontologist. He had a doctoral degree from the University of Heidelberg, where he then taught as a professor of natural history until his death. He was a visionary scientist who had some interesting pre-Darwinian ideas about life’s history. He didn’t fully accept “Darwinism” at the end of his life, but he made the first translation of On The Origin of Species into German.
Bromley, R.G. 1970. Borings as trace fossils and Entobia cretacea Portlock, as an example. Geological Journal, Special Issue 3: 49–90.
Bronn, H.G. 1838. Lethaea geognostica: oder, Abbildungen und Beschreibung der für die Gebirgs-Formationen bezeichnendsten. E. Schweizerbart’s Verlagshandlung, Stuttgart.
Tapanila, L. 2006. Devonian Entobia borings from Nevada, with a revision of Topsentopsis. Journal of Paleontology 80: 760–767.
Taylor, P.D. and Wilson, M.A. 2003. Palaeoecology and evolution of marine hard substrate communities. Earth-Science Reviews 62: 1-103.
Wilson, M.A. 2007. Macroborings and the evolution of bioerosion, p. 356-367. In: Miller, W. III (ed.), Trace Fossils: Concepts, Problems, Prospects. Elsevier, Amsterdam, 611 pages.
Hi I have vacationed for a number of years at North Myrtle Beach, SC. I have found these sponge borings and corals frequently. This year I collected a number of borings as well as shells with predator holes for a display I will do at the Natural History Society of Maryland (I am a volunteer who is an avid fossil and everything collector-not a professional). I have a partially crushed gastropod from a crab’s predation. My question for you is about the coral. I get that it postdates the shell but is it a modern coral or is it fossil=possibly Pliocene? I have found beach fossils at NMB that date to the Cretaceous (sea urchins-PeeDee Formation) and shark teeth. Miocene/Pliocene shark teeth-megalodon and great white. This year I found a large blister Pearl (1 1/2″) on a piece of quahog shell that could also be fossil (Pliocene) vs modern. The coral’s age I have not been able to resolve. On line i have not yet found enough information to answer this question. Thanks for any information you can provide.
Hi Tom: At this level we just can’t tell if it is a Pliocene or Pleistocene coral. Several species continue from this fossil record into the Recent.