Callianassid burrows

[Rowboater]

@GeschWhat @Carl It has been cold, but the shrimp (callianassid) coprolite burrows I find have been relatively plentiful (more than decent sized shark teeth) with recent strong north winds and low tides.  One puzzle to me is the variation in diameter of the burrows.  Carl, our expert, believes the coprolites just sank and deposited in burrows (at another site I have found a few steinkerns with similar, sparser deposits. )  All of the burrows I have found on the Rapp beach have been cylindrical, or possibly pieces of cylinders (of course, this could be bias in my collecting, but I examine lots of stuff!)  Usually the coprolite deposits are thicker on one side (the bottom?) of the burrow. 

If the burrows are truly made by the callianassids (Carl says no, others may argue) I expect the coprolites in the big burrows to be bigger than those in the smaller burrows.  I have collected enough to get a tentative answer, but need to align by brightness for comparison  photos (some burrows and coprolites are very light, some are dark).  Here is what I have collected so far:

 

 

 

[Rowboater]

One of the reasons I am looking at this, is I saw this paper on burrows (behind a paywall to me):

 

 

[Hipockets]

My 10x greatgrandfather was a Burrows from Virginia,,,,,,,,,,Jamestown........just saying.

[Coco]

Pics ?

 

Coco

[Carl]

It sure is a puzzler. Here's some of my reasoning. There is little doubt these are callianassid coprolites based on their size, composition, geologic and sedimentological contexts, and detail. Where we find these in NJ we also find burrows that are unambiguously from callianassids as well as abundant claws of the shrimp themselves. There is no conceivable reason to separate these three kinds of fossils when they all agree with the details of their extant relatives. 

 

Now, these cylindrical accumulations you find in VA, and which I've seen elsewhere, including NJ, are very consistently much smaller in diameter than trustworthy specimens of Ophiomorpha. Thus, I suppose they are accumulated in non-Ophiomoprha cavities, possibly smaller burrows of non-callianassid invertebrates. Since the coprolites are so self-similar, they likely would accumulate in drifts because of their hydrodynamically identical form. In fact, I am pretty sure I've seen examples of this in modern settings. In this situation they could easily be transported into cavities and fill them.

[Rowboater]

Hi Carl, @Carl  you're the expert, not my area.  It just seems like the coprolites from the bigger burrows are generally bigger than those from the smallest burrows, although there is not a huge difference   Unfortunately it is difficult to demonstrate by scanner, in that the contrast and brightness seem to emphasize differences in the matrix rather than the coprolites per say (to quantify accurately would need access to an imaging system).  I've wondered if there is a segregation by age, are juveniles more likely to be associated with burrows?  Also you've mentioned the claws before, are these usually found in matrix or are these usually found free like most shark teeth at the beach?  (If so, would have thought I would have found some. I have found crawfish claws (light-weight and colorful) hunting in freshwater creeks.  I have caught mantis shrimp while fishing in NJ, so would assume the claws would be similar, unless they are non-descript?

Anyway, here's an attempt comparing big vs small burrow coprolites.

 

[Rowboater]

@Coco Sorry for  the delay (Christmas).  @GeschWhat had great photos, my scanner is sadly inadequate.

[Carl]

On 12/24/2019 at 1:31 PM, Rowboater said:

Hi Carl, @Carl  you're the expert, not my area.  It just seems like the coprolites from the bigger burrows are generally bigger than those from the smallest burrows, although there is not a huge difference   Unfortunately it is difficult to demonstrate by scanner, in that the contrast and brightness seem to emphasize differences in the matrix rather than the coprolites per say (to quantify accurately would need access to an imaging system).  I've wondered if there is a segregation by age, are juveniles more likely to be associated with burrows?  Also you've mentioned the claws before, are these usually found in matrix or are these usually found free like most shark teeth at the beach?  (If so, would have thought I would have found some. I have found crawfish claws (light-weight and colorful) hunting in freshwater creeks.  I have caught mantis shrimp while fishing in NJ, so would assume the claws would be similar, unless they are non-descript?

Anyway, here's an attempt comparing big vs small burrow coprolites.

 

The claws segments are found both in nodules of matrix and free of any matrix. In NJ they are very dark and shiny. I'm sure if they were there you would not be missing them.