Edwards Formation Rudist Identification

[Heteromorph]

A few weeks after my mother found her most recent cidarid in an Edwards formation check dam, I took a few minutes to swing by the same dam to see for myself what else could be found. Within minutes I dug up a cylindrical fossil that for a few weeks puzzled me due to its resemblance to a belemnite phragmocone. Then on Wednesday night I went to the DPS meeting and afterwards met briefly with Professor Andy Gale and showed him this specimen. He identified it as a rudist and immediately corroborated that with another DPS member familiar with rudists. What confused me is that it doesn't look like any of the other rudists that I have found in the Edwards.

 

So far in my research I have found there to be 4 predominant rudist genera in the Edwards, which are listed in the tags. From pictures online I can't seem to definitively match this fragment to any of them, but it at least resembles some caprinid rudists I have seen online that are not from the Edwards. I know there must be many more rudist genera in the Edwards that I am unaware of, so I am hoping anyone more familiar with rudists than me could at least narrow it down to more than just a likely caprinid.

 

The specimen is 3.75 cm long (Fig. 1), 4.2 cm in diameter at its concave end (Fig. 20), and 4.1 cm in diameter at its flat end (Fig. 22). I really know next to nothing about them so any help is appreciated. If anyone wants to compare this with the many other rudists that I have found from these Edwards dams, see the excessive amount of pictures in this thread.

 

Fig. 1.

 

Fig. 2.

[Heteromorph]

Fig. 3.

 

Fig. 4.

 

Fig. 5.

[Heteromorph]

Fig. 6. Note this more characteristic Edwards rudist (at least to me anyway) stuck to the side of the specimen in question.

 

Fig. 7.

 

Fig. 8.

[Heteromorph]

Fig. 9.

 

Fig. 10.

 

Fig. 11.

[Heteromorph]

Fig. 12.

 

Fig. 13.

 

Fig. 14.

[ynot]

Neet find!

[Heteromorph]

Fig. 15.

 

Fig. 16.

 

Fig. 17.

[Heteromorph]

Fig. 18.

 

Fig. 19.

 

Fig. 20.

[abyssunder]

It looks more like a cephalopod rather than a rudist, maybe a Baculites, in my opinion.

[Heteromorph]

Fig. 21.

 

Fig. 22.

 

Done!

[Heteromorph]

4 minutes ago, abyssunder said:

It looks more like a cephalopod rather than a rudist, maybe a Baculites, in my opinion.

To my knowledge Baculites like ammonites (e.g. Sciponoceras) didn't evolve until the Turonian, whist this is early late Albian. 

[abyssunder]

13 minutes ago, Heteromorph said:

To my knowledge Baculites like ammonites (e.g. Sciponoceras) didn't evolve until the Turonian, whist this is early late Albian. 

I would agree, but baculitids have a range from the Albian to Maastrichtian, at least according to Wikipedia.

[Heteromorph]

8 minutes ago, abyssunder said:

I would agree, but baculitids have a range from the Albian to Maastrichtian, at least according to Wikipedia.

Looking at Fossilworks it appears that you are right. I didn’t realize they ranged down that far. Thanks! 

[FranzBernhard]

It´s a steinkern. 

 

@Heteromorph, I have found hippuritid steinkerns in St. Bartholomä, that look somewhat similar, but not really. And there are obviously no hippuritids in the Edwards formation.

 

@abyssunder, Baculites is a good idea, but shouldn´t they have more complicated suture lines? But maybe the older ones have more simple suture lines.

 

Franz Bernhard

[Heteromorph]

11 hours ago, FranzBernhard said:

Baculites is a good idea, but shouldn´t they have more complicated suture lines? But maybe the older ones have more simple suture lines.

 

Franz Bernhard

All Jurassic-Cretaceous ammonites should have complex sutures unless they have been worn down (although broad generalizations usually get me in trouble, so correct me if I am wrong). The steinkern is in pretty good shape, yet these sutures are so simple that the last time ammonoid’s sutures were this simple was in the Paleozoic. Also notice how, especially in Figs. 15 through 20, that one end is concave. The other end, shown in Fig. 22, is flat, but that is just because that end was sheared flat when it was excavated in the quarry. 

 

It is for these reasons that my first instinct was cephalopod, namely a belemnite phragmocone. The only other cephalopods swimming around the ocean at this time with very simple sutures were the nautiloids, but all the straight, orthoconic ones were extinct and only the planispiral ones remained, so I think I can rule them out. The general look of the specimen reminds me of the belemnites in this and this thread.

 

@JohnJ

@Uncle Siphuncle

@TqB

[Uncle Siphuncle]

Rudists are outside of my wheelhouse.  I've only studied them enough to let them point toward echinoids.  I donated something from the Campanian similar in form to this, but more complete, identified as a back filled burrow.  

[ricardo]

27 minutes ago, Heteromorph said:

All Jurassic-Cretaceous ammonites should have complex sutures unless they have been worn down

 

 

Some Cretaceous ammonites had some how "simple" sutures... looking like "goniatites" sutures with round lobes and round saddles and others like "ceratites" also. E.g. Neolobites and Metengoceras...

[Heteromorph]

8 minutes ago, ricardo said:

 

Some Cretaceous ammonites had simple sutures...

Which specific genera though? All that I have seen are at least somewhat complex, and not just slightly wavy lines like this specimen. I would like to know what examples you have in mind. 

[ricardo]

Not like your specimen 

 

But some genera has more simple sutures. Neolobites looks like a goniatitic suture. 

 

 

ps. Sorry the other post was edit at the moment you was writing yours I supose... mea culpa.

[Heteromorph]

6 minutes ago, ricardo said:

Not like your specimen

 

But some genera has more simple sutures. Neolobites looks like a goniatitic suture. 

Thanks. I didn’t realize there were Cretaceous ammonites like that. I guess my idea of complex sutures was anything from goniatitic and up, but perhaps my idea is not the best definition of complex. 

[ricardo]

4 minutes ago, Heteromorph said:

Thanks. I didn’t realize there were Cretaceous ammonites like that. I guess my idea of complex sutures was anything from goniatites up, but perhaps my idea is not the best definition of complex. 

I believe the mistake was mine. Sometimes my lack of English skills is a problem to understand well some of TFF posts.

 

I will follow this post 

[TqB]

What an interesting specimen! I agree that it looks like a belemnite phragmocone and it's clear from the closeups that it's a steinkern with cephalopod-style chambers, with some of the shell walls still visible.

 

It looks large but, as far as I know, the only belemnites around in the Albian are Neohibolites which seem out of proportion - I don't think they get much more than 3" long and are typically less.

There are some weird belemnites that are mostly phragmocone with hardly any rostrum (diplobelids) but these are all much smaller, less than one inch, and have a much more steeply angled cone.

 

Have you found any belemnite rostra in the same beds?

 

So I'm stuck. Following...

[Heteromorph]

18 minutes ago, TqB said:

What an interesting specimen! I agree that it looks like a belemnite phragmocone and it's clear from the closeups that it's a steinkern with cephalopod-style chambers, with some of the shell walls still visible.

 

It looks large but, as far as I know, the only belemnites around in the Albian are Neohibolites which seem out of proportion - I don't think they get much more than 3" long and are typically less.

There are some weird belemnites that are mostly phragmocone with hardly any rostrum (diplobelids) but these are all much smaller, less than one inch, and have a much more steeply angled cone.

 

Have you found any belemnite rostra in the same beds?

 

So I'm stuck. Following...

Thanks! I have never found any cephalopods in the Edwards until this specimen, and cephalopods in the Edwards are generally quite rare and limited in diversity. As for belemnites, I am not aware of any reports of belemnites coming from the Edwards, or the Fredericksburg group to which it belongs, or any other lower Cretaceous formation in Texas. All of the belemnite occurrences that I know of in Texas are from upper Cretaceous deposits. 

 

In general, Texas is not the place to find belemnites. 

[Tidgy's Dad]

Very interesting find, thread and comments. 

It does look like a cephalopod to me, but no idea how or which one. 

[TqB]

On the other hand, rudists do some fiendish impersonations, like this Shutterstock image which I'd better not copy here...

 

https://www.shutterstock.com/image-photo/rudist-fossil-on-table-1296234763?src=poA0qxEWslQqSQBzPiPD3w-1-1