Hi everyone.
I'm studying an upper Aptian carbonate succession of NE Spain which has traditionally been considered to be devoid of rudists due to paleoenvironmental stress. I'm not at all familiar with this group, as indeed I haven't come across a single specimen in 4 years of field research.
However, these pictures of one of my reference outcrops, sent to me by a local, show some strangely shaped fossils which I cannot for the life of me identify. All pics are of the same stratigraphic level, which corresponds to a regional discontinuity surface which could have been subaerially exposed for prolonged amounts of time.
What do you see in these pics?
Hello Alvaro,
I´m not a specialist in this group either, but I think they coud be. I´d like to see any thin section or polished slab for being completely sure.
Best regards,
Roi Silva Casal
The third photo seem to represent a rudist, but the other images are no very clear..
Best
The thing on the third image lacks sockets for teeth, and also the preservation of the "shell" with similar-looking inner and outer layers and something different in between isn't very rudist-like. Perhaps that thing is a sponge?
The thing on the third image seems to me as if the original shell had been dissolved and the resulting void had been occupied by neomorphic calcite. The random section of the "thing" is asymmetric, with one part being larger, ornamented with "knobs", and the other being short and smooth. Actually, it reminds me of some kind of "Trigonia" bivalve, but I'm not expert. The junction between the two valves is not seen because it is neomorphic calcite. This is just an impression. For Lower Cretaceous rudists I would ask Jean Pierre Massé. I have no clue on the topic. I think in Barcelona there is also an expert on rudists. They could easily determine whether the fossils in some of these images are rudists or not. Greetings.
Sorry for late response: I've only just seen this post. As others have noted, the preservation of these specimens is not great, so it is difficult to say much about them. However, here are some suggestions (...guesses!):
1. Probably not a rudist: the compressed, elongate triangular ('jamon')shape suggests a pinnid (maybe this is the one Christian commented on?). The lithology looks quite suitable for pinnids.
2. A nice view...
3. I agree with Diego: the cavity left by complete dissolution of the shell has been filled by sparry calcite growing into it from the opposing internal and external mould walls, hence the concentric seam where the prisms have met in the middle. I doubt it's a rudist, as I would have expected to have seen at least a vestige of the calcitic outer shell layer, which tends to remain when the aragonitic inner shell is dissolved, but none is shown. Possibly the thick umbonal tip of another, costulate pinnid, preserved implanted in the sediment?
4. No rudists here - just some burrowing bivalves, including a probable costulate trigonioid.
5. Seems to be an elongate internal mould of a slightly tapering cylindrical shell of some kind (hinted at by the poorly preserved pale lines on either side), but of what I cannot say. I see nothing strictly diagnostic for rudists.
All I can really say is keep looking - y buena suerte!
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