Is this a shellfish fossil?

[June P]

I think I’ve posted before in the wrong area…hoping this is reaching y’all:

found this in Bexar County San Antonio, Texas in my neighborhood which is new construction. In this area I’ve found a lot of petrified trees and other types of possible water creatures. I’ll attach those pics since I may have posted them in the wrong discussion area..

this looks like a shell of some sort and has beautiful little crystals in the ‘valleys’ of the sunburst pattern..

[Rockwood]

Shellfish is accurate I suppose, they are mollusks. They aren't like clams though, but free swimming cephalopods. It's a fragment of ammonite shell.

[FranzBernhard]

Could it be a pectinid bivalve?
Franz Bernhard

[JohnJ]

5 minutes ago, FranzBernhard said:

Could it be a pectinid bivalve?
Franz Bernhard

I suspect a partial rudist like Radiolites.

 

Notice the fossil morphology extends beyond a single plane. 

[FranzBernhard]

8 minutes ago, JohnJ said:

I suspect a partial rudist like Radiolites.

Indeed, that could be a possibility! Possibly the upper valve of a radiolitid, not the usual lower valve? I would like to see the cellular structure of a lower valve. Problem is, not all radiolitid lower valves have this cellular structure . Difficult!

Franz Bernhard

[abyssunder]

I agree. It is a rudist fragment (upper or lower valve).

[June P]

Oh my gosh, Y’all! Thanks so much!!!  Now I’m going to look these creatures up!  I love this area of Bexar County Texas. Every time I walk in the old ranch area and dig through the soil, i find myself transported back in time-it’s so humbling and I find myself in a deep state of reverence!