Which came first?

Mark Wilson May 27, 2010 8:24 pm

NEW ALBANY, MISSISSIPPI — The Cretaceous oyster above was collected from the Coon Creek Beds of the Ripley Formation (Upper Cretaceous) near Blue Springs, Mississippi.  The holes are borings called Entobia which were produced by clionaid sponges which built a network of connected chambers inside the shell so that they could carry out their filter-feeding with some safety from grazing predators.  The branching white fossil is a cyclostome bryozoan, probably Voigtopora thurni.  Which was present first on the shell, the borings or the bryozoan?  Is there evidence that they were living at the same time?  The largest holes are about two millimeters in diameter.

About Mark Wilson

Mark Wilson is an emeritus Professor of Geology at The College of Wooster. He specializes in invertebrate paleontology, carbonate sedimentology, and stratigraphy. He also is an expert on pseudoscience, especially creationism.
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2 Responses to Which came first?

  1. Micah Risacher says:
    May 28, 2010 at 12:50 pm

    In preparation for my Israel borings I would guess that the sponge came first with the bryozoan following as it avoids the borings by the sponge in almost all cases around the oyster. However in the upper center of the sample the bryozoan bridges the borings in several cases which would suggest it arrived after the sponge had left.

  2. Mark Wilson says:
    May 28, 2010 at 7:55 pm

    Good eyes, Micah! There may be two generations of borings with the bryozoan younger than one and older than the other. I hope we can find similar boring/encruster combinations in the Cretaceous of Israel next week.

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