Wooster’s Fossils of the Week: Demosponge borings in a muricid gastropod from Florida

November 4th, 2016

entobia-snail-2Technically these are “subfossils” since this appears to be an old shell still within the Holocene, although it is possibly eroded out of Pleistocene sediments and then redeposited on a Florida beach. It is a muricid snail eroded enough to erase any specific characters for further identification. It is cool because it is thoroughly bored by clionaid demosponges, producing a beautiful pattern of holes given the ichnological name Entobia Bronn 1838.

entobia-snail-1On the left side of the aperture of this snail shell is a fine reticulate pattern from an encrusting cheilostome bryozoan, also punctured by Entobia. That bryozoan is in a favored place for filter-feeding encrusters on snail shells, so it likely was there during the life of the snail.

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.

Bronn 041616Entobia is common in the fossil record, especially in calcareous rocks and fossils from the Cretaceous on. The ichnotaxon was named (but apparently not described) in 1838 by Heinrich Georg Bronn (1800-1862), a German geologist and paleontologist we’ve met before in this blog. 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.

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. 1838. Lethaea geognostica: oder, Abbildungen und Beschreibung der für die Gebirgs-Formationen bezeichnendsten. E. Schweizerbart’s Verlagshandlung, Stuttgart, 545 pages.

Buatois, L., Wisshak, M., Wilson, M.A. and Mángano, G. 2016. Categories of architectural designs in trace fossils: A measure of ichnodisparity. Earth-Science Reviews (DOI: 10.1016/j.earscirev.2016.08.009).

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.

 

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