Unidentified Rudist?

[suley78757]

i have found several of these in the austin chalk in travis county, and have tried for weeks to id them...any ideas? the big one is shown with suture marks, the others have been found singly. thanks

[Al Dente]

I don't know what the larger object in the first two photos is but some of the fossils in the third photo look like nautiloid chambers. It is the sediment that filled the chambers after the nautiloid died.

[Carl]

I agree with Al Dente.

[erose]

Hey Suley78757, You brought those into Fossil Fest and we took a shot at them there. I don't know why nautiloid chamber casts did not occur to me then but Al Dente may be correct. There is a common one in the Austin Chalk that is often preserved as just internal casts and often in a distorted form. But I also think that maybe the large piece is something different and possibly a rudist. I think the trick will be to keep looking for similar fossils with more preservation.

And thanks again for coming out to Fossil Fest.

[Plax]

first one looks like Exogyra pseudomorph (if they make them), second one looks just like the chambers (agreeing with Al Dente) we get here in NC in the eocene, first cretaceus ones I've seen loose like that

[truceburner]

I find those nautiloid chamber casts with some regularity in Austin as well.

[RyanNREMTP]

Same here in Waco. I didn't know what they were until now. I always thought some sort of shell but not the part inside of one.

Glad I'm learning here.

[suley78757]

had no idea they might be nautiloid casts. the big one is three of them together. the bottom of it is identical to the single sections. pretty cool! thanks!

[Charles Newsom]

Hi: The first 2 photos could also be Inoceramids. There are some strangely shaped ones to be found that look similar to your photos.

The last photo contains a number of Nautiloid segments. They often disassociate in that manner. If the siphuncle is in the center then they are probably Cymatoceras elegans. If the siphuncle is offset toward the outer edge then it is likely Eutrephoceras campbelli. The C. elegans is quite common in the Austin Chalk. If you find the whole C. elegans nautiloid you will see that the phragmocone is tiny when compared to the enormous living chamber.

[Herb]

The 3rd picture looks like very worn internal casts of Gryphea to me.