Archive for May 13th, 2012

Wooster’s Fossils of the Week: Intricate networks of tiny holes (clionaid sponge borings)

May 13th, 2012

The most effective agents of marine bioerosion today are among the simplest of animals: clionaid sponges. The traces they make in carbonate substrates are spherical chambers connected by short tunnels, as shown above in a modern example excavated in an oyster shell. The ichnogenus thus created is known as Entobia Bronn, 1838. I’ve become quite familiar with Entobia throughout its range from the Jurassic through the Recent (with an interesting early appearance in the Devonian; see Tapanila, 2006).
The holes in this Cretaceous oyster are the sponge boring Entobia; the cyclostome bryozoan is Voigtopora. This specimen is from the Coon Creek Beds of the Ripley Formation (Upper Cretaceous) near Blue Springs, Mississippi. (This specimen was collected during a 2010 Wooster/Natural History Museum expedition to the Cretaceous and Paleogene of the Deep South.)
This is a modern clam shell showing Entobia and several other hard substrate dwelling organisms (sclerobionts).
Entobia was named and first 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.

References:

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. 1834-1838. Letkaea Geognostica (2 vols., 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.