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When faced with a radiodont appendage fossil; How does one effectively determine which slab contains the "part" or "counterpart" ?

 

For reference, here's the holotype Pseudoangustidontus appendage. The first pic, Figure A, is apparently the positive(?) "part" of the fossil. Whilst the second pic, Figure C, is apparently the negative(?) "counterpart".

Like it's easy to tell the difference between an impression/cast, or the actual fossilised remains for hard-bodied specimens like shells, exoskeletons and bone. But for some soft-bodied organisms, it's especially difficult when both slabs seem to preserve both the impressions and the fossilised remains of the organism, as in the case with the Pseudoangustidontus holotype. I've also heard that concavity of the matrix usually helps in identification; but thin and soft-bodied specimens often just leaves a planar imprint, so judging by relief might not be too reliable either. 

 

Any thoughts on this matter?

 

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I think that the terminology is not "descriptive" when referring to these types of fossils.  Just noting that there are two pieces. 

 

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The terms "part" and "counterpart" are only useful when they can distinguish the body fossil from the impression.  If the fossil is truly flat and there is no way to determine what rock contains the actual remains of the organism, perhaps something like "face A" and "face B" would be a more accurate terminology.

 

Don

 

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I see, thanks for the responses! 

 

Weird how a published research paper uses such "vague" terminology (in this specific context) in their description of the fossil. Maybe the difference is a lot more obvious in person? Fossil nomenclature is so confusing at times XD

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1 hour ago, Flaffy said:

I see, thanks for the responses! 

 

Weird how a published research paper uses such "vague" terminology (in this specific context) in their description of the fossil. Maybe the difference is a lot more obvious in person? Fossil nomenclature is so confusing at times XD

Why is it such a big deal?  All that matters is that the authors explicitly state what side they are calling the part and what the counterpart so other researchers will know what rock to look at if they want to verify statements in the paper.  If the two sides are mirror images it is arbitrary which one is chosen for the "part" side.

 

Don

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10 minutes ago, FossilDAWG said:

Why is it such a big deal?  All that matters is that the authors explicitly state what side they are calling the part and what the counterpart so other researchers will know what rock to look at if they want to verify statements in the paper.  If the two sides are mirror images it is arbitrary which one is chosen for the "part" side.

 

Don


No big deal. I personally prefer to collect the positive "part" of a specimen when possible, and just wanted to know if there was reliable method to differentiate between "part" and "counterpart" for flat, soft-bodied fossils. From this convo it seems like there is not, very glad to have that cleared up.

 

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Some workers will explicitly distinguish part and counterpart in the field, with the top piece of rock being the counterpart, and the bottom piece being the part. This is reasonably effective when you are quarrying fossils in shale or laminar limestone like Solnhofen, Bear Gulch, etc. It is harder to do with fossils found in float.

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Seems like it would be just an arbitrary choice. If it were me I would choose the piece with the most detail or most apparent 'body' fossil on it as the 'part', if one side obviously has any more to it than the other, or if one side is on a larger chunk of rock. Otherwise it's purely arbitrary, unless as jdp says you have more context with which to decide.

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It's arbitrary but will be consistent within collections made by a worker at a given site. So, for instance, if you look at Dick Lund's collections of Bear Gulch fishes (across a few museums), he will consistently assign part/counterpart to bottom/top, so if you want to look at, say, taphonomic information, that is recorded directly in the collection data.

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Yes, that makes sense when you know the original orientation. If not I would think it falls to the side that is more complete/larger or has the more important details.

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