Bivalve ID

[KimTexan]

I found these a while back at Mineral Wells, TX.

I have been collecting fossils for years, but never bothered to ID any of them. To me it's about the fun of the hunt and discovery. But I'm trying to expand my knowledge of the field and the specimens I've collected.

So I would appreciate any education as to what these are. They're all 2 cm or smaller. I've got more, but I think this is an adiquate sample of what I have to give an ID.

The predominant fossils in the area are crinoids though.

[Fossildude19]

Pretty Brachiopods.   

 

 

@erose  @BobWill @Uncle Siphuncle  @bone2stone

 

 

EDIT: Just came across THIS

[BobWill]

You would have a hard time finding these in the bivalve section of your reference. They are Brachiopods, probably one of the Neospirifer species like N. dunbari.

[westcoast]

Nice brachiopods.  Should be reasonably easy to identify if you have a faunal list from the location or formation.

[Kane]

And just to be mildly helpful here, the difference between bivalve and brachiopod is mostly a matter of symmetry: 

[BobWill]

Good information Kane, thanks. It might also be worth pointing out that brachiopods are in a separate phylum from molluscs and that some bivalves are not symmetrical at all, for example unlike clams most oysters have different shaped valves.

[westcoast]

1 hour ago, BobWill said:

You would have a hard time finding these in the bivalve section of your reference. They are Brachiopods, probably one of the Neospirifer species like N. dunbari.

Some of the brachiopods pictured appear to have the stumps of hinge spines which, with the overall shape, look more like chonetids of some kind.

[Peat Burns]

32 minutes ago, westcoast said:

Some of the brachiopods pictured appear to have the stumps of hinge spines which, with the overall shape, look more like chonetids of some kind.

+1 for chonetid.  Neochonetes maybe?

 

Other possible genera here

[BobWill]

1 hour ago, westcoast said:

Some of the brachiopods pictured appear to have the stumps of hinge spines which, with the overall shape, look more like chonetids of some kind.

Good eye westcoast, Chonetinella verneuilianus is on the faunal list for one site in Mineral Wells.

[KimTexan]

5 hours ago, Kane said:

And just to be mildly helpful here, the difference between bivalve and brachiopod is mostly a matter of symmetry: 

Thank you for the diagram. It is a fairly nice one. I am familiar with this principle.

 

While the general rule is very helpful, from my perspective this example seems only useful if you have both valves. In this case I have no idea what the other half looks like. None of the valves have anything attached. I had assumed some of these pieces were top and some bottom valves. I gather that is not the case. See pic below of back side.

This may be too lengthy to explain to such a novice as I, but where would I begin to reason it out in such an instance without any reference of foreknowledge of the creature? I'm sure a basic education would be a good place to start. How would I know it was a bivalve vs braciopod with only one half? Is there a general rule of thumb?

I wonder if maybe the rule is if it appears symmetrical down the middle (left to right) like these critters, then it's a brachiopod. Surely there are cases where the bottom valve looks the same as the top on brachiopods, what then?

 

I posted one last week when I had both halves thinking it was a bivalve, then was told it was a brachiopod. Then it was finally settled that it was indeed a bivalve, but it really wasn't so clear cut as it would at first appear to be in the little diagram.

I need to work on informing myself quite a bit more to be able to make the distinction without blunder.

[Peat Burns]

@KimTexan, a couple quick "rules of thumb" that may be helpful:

 

The beak (analogous to the umbo of a bivalve) is typically centered on a brachiopod, whereas the umbo of a bivalve is usually (but not always) off center.

 

Not all brachiopods have a fold and sulcus, but if you find a shell with these features (and a centered beak), it is a brachiopod.

 

If in palaeozoic rocks, and you are not sure, assume brachiopod first, as they are typically far more diverse and abundant as compared to bivalves.

 

Maybe others can add more.

[BobWill]

Because of those pesky "exceptions to the rules" the best way to tell the difference is with experience. Over time you will almost always know at first glance. That said, you can look for some particular features found on brahiopods. The pedical valve usually overhangs the brachial valve at the hinge and has a hole where a fleshy foot protruded out to anchor it in the sediment. Yours appear to be the pedical valve but the hole is not always visible. The brachial valve would have been much flatter on yours and many other species but that can vary too. To further confuse the issue some scallops which are bivalves will have one valve rounded and the other flatter and some even have symmetry more like a brachiopod. A good field guide is helpful for learning to make the distinctions. For Texas it's hard to beat Charles Finsley's A Field Guide to Fossils of Texas available at Dallas Paleo meetings or on their website.

[Herb]

they look like Chonetina sp to me

There is a nice book on the Penn. of Texas called "Pennsylvanian Fossils of North Texas" by McKinzie and McLeod, It covers Mineral Wells.

[coled18]

At first, I thought they were a species of Neochonetes similar to what I find here in late Pennsylvanian Kansas. However, I think @Herb is right, these really look like Chonetina. 

[doushantuo]

[doushantuo]

Devonian chonetid spine diversity:

[DPS Ammonite]

Check out the most recent version of Mckinzie's book found on Amazon: "Color Guide to Pennsylvanian Fossils of North Texas". It is pricy but good.

[KimTexan]

20 hours ago, doushantuo said:

This is very helpful. Thank you! It would appear that I have both dorsal and ventral valves among my specimens. Prior to the example you provided I had no clue as to how to tell which was dorsal/ventral, but I am under the perception that I can now, tell, unless I'm corrected.

There are some very subtle variations between the 2 halves. The symmetry appears to be bidirectional. So, I still would have a hard time knowing they were brachiopods without being told.

 

I'm not certain I have the two valves right. Someone correct me if I'm wrong. 

These are the obvious features I see 

Dorsal/brachial valve

1. Single layer edge along the cardinal process edge.

2. The pattern of the little bumps on the interior shell wall is more obvious and dispersed. 

3. Shell deeper and more cupped.

4. Vertical indentation down the center of shell is slightly less pronounced. 

5. No membrane coating noted.

6. Umbo less prominent.

 

Ventral/pedical valve:

1. Double layer edge along the cardinal process edge. Interior set may be teeth.

2. The pattern of the little bumps on the interior shell wall is less obvious and more localized to areas around diductor scars.

3. Shell shallower and more flat.

4. Vertical indentation down the center of shell is more pronounced. 

5. There is a thin membrane coating the interior wall.

6. Umbo slightly more prominent.

 

If I have identified the halves correctly I only have 5 dorsal valves from what I can tell. The remaining 36 are ventral. I'm not certain why that would be, except the ventral/pedical valve is likely to be heavier since more of the fleshy part is attached and would thus be less likely to be swept away by current, also the pedical is more likely to be attached to something. Although I think that would mean it was more likely to be preyed upon as well.

If there are other differences others can see I'd like to hear about them. I'm a complete novice at this so any enlightening thoughts or corrections are eagerly welcomed.

 

The shot below has what I believe are the dorsal valves on the left and the ventral on the right.

 

 

[erose]

One thing to know about "exceptions to the rule", They are all (well maybe 99.99%) bivalves. Brachiopods for all extents and purposes have the consistent left-right symmetry. While bivalves are all over the place. Scallops are close to brachs, especially when the ears are not preserved. But the ears are always asymmetrical proving the rule. Oysters, well they're oysters and just plain obstinate when it comes to shape. And if we throw in Rudists then we will hear a collective moan from those familiar with those TOTAL odd balls. 

 

The other thing you will find here in Texas is that in the older Paleozoic formations brachiopods will outnumber bivalves but in the Cretaceous and younger strata bivalves rule. 

 

There is a great old book on paleontology that I think is still one of the best for getting a handle on the morphology of different groups of animals as well as which ones were around at which times. You can often find it thru used book dealers or even in the odd used book store. 

 

Invertebrate Fossils by Raymond Moore, C. Lalicker, A. Fischer, 1952

 

Easy to read and understand and the best black and white illustrations. You might even find an ID or two using it as it includes many common fossils for various time periods.

[doushantuo]

Moore et al is hopelessly outdated,i think 

Regarding erose's response:

Liow_et_al-2015-Ecology_Letters.pdf

[doushantuo]

None of the specimens I see seem to have epizoan encrustation.

Do others see that too,or is it just me?

Velbel et al(1989,publishers abstract,I highlighted a VERY siginificant part):

 

**Pedicle valves greatly outnumber brachial valves in disarticulated samples of the Upper Ordovician brachiopod Platystrophia ponderosa. Some articulated specimens are compressed (shortened), probably by burial and compaction. The shortening is accommodated by fracturing, which is largely confined to the brachial valve. This preferential fracturing of the brachial valve can account for the observed paucity of whole brachial valves of P. ponderosa in the fossil record and suggests that mechanisms other than differential current transport contribute to valve disproportionation. Discriminating between autochthonous and transported assemblages on the basis of valve ratios may lead to erroneous paleoecological interpretations, because brachial valves could be destroyed preferentially, without significant transport to the burial site. **
 

[doushantuo]

Almost forgot:

I)

 

Fossil Invertebrates, By Boardman, Cheetham And Rowell

Disadvantages of this book: weight & size.Might be extremely hard to get & very pricy

Biased view of yours truly : one of the best,good informative line drawings

II)

[Peat Burns]

24 minutes ago, doushantuo said:

None of the specimens I see seem to have epizoan encrustation.

Do others see that too,or is it just me?

Velbel et al(1989,publishers abstract,I highlighted a VERY siginificant part):

 

**Pedicle valves greatly outnumber brachial valves in disarticulated samples of the Upper Ordovician brachiopod Platystrophia ponderosa. Some articulated specimens are compressed (shortened), probably by burial and compaction. The shortening is accommodated by fracturing, which is largely confined to the brachial valve. This preferential fracturing of the brachial valve can account for the observed paucity of whole brachial valves of P. ponderosa in the fossil record and suggests that mechanisms other than differential current transport contribute to valve disproportionation. Discriminating between autochthonous and transported assemblages on the basis of valve ratios may lead to erroneous paleoecological interpretations, because brachial valves could be destroyed preferentially, without significant transport to the burial site. **
 

Do you mean brachiopods in general or just Platystrophia ponderosa?  

 

In my experience, some species seem to have few if any epizoans, while others are commonly encrusted.  Some suggest that lack of abundant epizoans indicates high energy environments.  But I think that shell surface structure or even benthic life position may also be at play.  I seem to notice that brachiopods with deep plications seem to have less epizoa than more smooth, flattened shells.  That's just currently a subjective observation  (and maybe it has less to do with surface structure and more to do with physics with regard to current manipulation of shells).

[doushantuo]

I meant Kim Texas' specimens,sorry for the confusion

 

[Peat Burns]

1 minute ago, doushantuo said:

I meant Kim Texas' specimens,sorry for the confusion

No,it has been suggestions the plications act as a deterrent to encrustation

Oh, sorry.  I misread your comment. I thought it said "none of the specimens I have seem..." 

 

I need some sleep 

4 minutes ago, doushantuo said:

I meant Kim Texas' specimens,sorry for the confusion

No,it has been suggestions the plications act as a deterrent to encrustation

By the way... Do you have any links to papers on the role of plications in deterring brachiopod encrustation?  

 

I wonder if similar results occur with modern bivalves.