South Texas Upper Cretaceous Crab

[CraigHyatt]

I found several of these specimens near Eagle Pass, Texas. They all seem to have 8 legs, but I have not seen any with large front claws. One of the examples has two dents that might be for antennas or eye stalks. The surrounding rock varies from sandstone to soft shale and clay. These are found in hard sandstone. The only other fossils I've found near this layer look like worm burrows or perhaps coral.

Possible crab specimens (4x)

Other typical fossils from this layer (worm burrows or coral, not sure)

Wide shot of the layers

Edited May 11, 2016 by CraigHyatt

[Fossildude19]

These don'e look like crabs to me, but, I'm not really a crab guy.

Maybe some sort of Rudist?

Interesting, whatever they are.

Hope a local can chime in with some info.

Regards,

[abyssunder]

Very strange. Well-eroded cephalopod maybe ?

[Plax]

looks like your rocks are late cretaceous to eocene in that area but the map is complicated. Your worm burrows or coral look like conglomerate to me but it's hard to tell from the pic. Have seen Eocene sponges that vaguely resemble your crab. If you can get some close ups to show texture it will help us.

[CraigHyatt]

OK. I will get some close ups of the best specimen.

[Auspex]

Fascinating specimens!

Crab would have been my first reaction, but looking closer there is no joint at the bend of the "leg".

I am still puzzling over what it might be,

[abyssunder]

Similar preservation,but different geological time.

[CraigHyatt]

Here are some closeups of my best specimen. I took some through a hand lens using my iPhone.

Unmagnified view.

Views taken through a hand lens.

Inner structure of one "leg" where it was chipped off.

[CraigHyatt]

Fascinating specimens!

Crab would have been my first reaction, but looking closer there is no joint at the bend of the "leg".

I am still puzzling over what it might be,

~.jpg

Good point. If you look at a crab leg the joints are very clearly visible, and there are little spikes all over the leg as in the example I added below.

They could be cephalopods, as abyssunder suggested (and maybe there's a head visible in one of the specimens) but it seems to me that soft parts like tentacles wouldn't fossilize so consistently. That makes me think the "legs" are a solid material like an exoskeleton.

Maybe it's just a Texas Tick.

Circled possible "head" of a cephalopod...

Crab fossil found on the internet showing leg joints.

Edited May 11, 2016 by CraigHyatt

[CraigHyatt]

looks like your rocks are late cretaceous to eocene in that area but the map is complicated. Your worm burrows or coral look like conglomerate to me but it's hard to tell from the pic. Have seen Eocene sponges that vaguely resemble your crab. If you can get some close ups to show texture it will help us.

Thanks, Plax. See magnified photos in the thread.

[tmaier]

I'm going to guess that it is a brachiopod of the Collemataria genus. http://natural-history.uoregon.edu/brachiopod14

[CraigHyatt]

I'm going to guess that it is a brachiopod of the Collemataria genus. http://natural-history.uoregon.edu/brachiopod14

Thanks, tmaier. I think I'll have to find more of them to try and confirm the identity.

[tmaier]

That brach I pointed out is Permian, so try to find associated fossils in that same layer, and try to determine if it is Paleozoic or Cenozoic. Here's another example of that brach... http://www.paleocentral.org/Collection/get/id/2929

[CraigHyatt]

That brach I pointed out is Permian, so try to find associated fossils in that same layer, and try to determine if it is Paleozoic or Cenozoic. Here's another example of that brach... http://www.paleocentral.org/Collection/get/id/2929

OK. If I can find a specimen with more than 4 "legs" on a side, that would help confirm. I will also try to identify the era. The maps for this region say upper cretaceous, but I haven't found many fossils to help confirm the age. Getting the age is my focus at the moment, so if these fossils help with that, it's a big win.

[Uncle Siphuncle]

Craig

You mentioned that you are hunting the Cretaceous strata of your area. The Cretaceous formations of your area all hold ammonites. If you can find even partials, they'll go a long way to pinpointing age of the sediments you are canvassing. Ammonites are used in world wide zonation, so they are very well documented index fossils. Sphenodiscus, Pachydiscus, and possibly Placenticeras are the ones you'd most likely run into in your area, listed here youngest to oldest. I've attached a few photos for reference...be prepared to look for just a flank or keel exposed.

Spheno (narrow cross section with sharp keel esp. in small specimens, generally little or no flank ornamentation)

Pachy (usually a wider cross section with rounded keel, and either smooth or finely ribbed flanks)

Placenticeras (some variation within the genus, but usually a narrow cross section, and a sharp or flattened, narrow keel, flank ornamentation ranging from smooth to tubercled)

[CraigHyatt]

Craig

You mentioned that you are hunting the Cretaceous strata of your area. The Cretaceous formations of your area all hold ammonites. If you can find even partials, they'll go a long way to pinpointing age of the sediments you are canvassing. Ammonites are used in world wide zonation, so they are very well documented index fossils. Sphenodiscus, Pachydiscus, and possibly Placenticeras are the ones you'd most likely run into in your area, listed here youngest to oldest. I've attached a few photos for reference...be prepared to look for just a flank or keel exposed.

Spheno (narrow cross section with sharp keel esp. in small specimens, generally little or no flank ornamentation)

Kes Sphenodiscus pleurisepta 6a Site 417 052310.jpg

Pachy (usually a wider cross section with rounded keel, and either smooth or finely ribbed flanks)

Kco Pachydiscus paulsoni1c Site 349 060207.jpg

Placenticeras (some variation within the genus, but usually a narrow cross section, and a sharp or flattened, narrow keel, flank ornamentation ranging from smooth to tubercled)

Kan Placenticeras Weston 1b Site 496 0213.jpg

Excellent! I will keep an eye out for them. Most of the fossils I see are pretty non-descript. They just look like a bunch of fossilized reddish sticks. I have seen a few small shells, but not many. I know this area was under water, so that makes sense. I'd love to find something definitive like an ammonite to be certain. Thanks!

[Mike from North Queensland]

A photo of the best specimen taken from the side with the clean break would be helpful as it may tell us if the specimen is a bone, infill or shell material.

Mike D

[Plax]

pics of the associated shells would also help

[CraigHyatt]

pics of the associated shells would also help

Will do both when I get back home. Out digging. :-)

[CraigHyatt]

A photo of the best specimen taken from the side with the clean break would be helpful as it may tell us if the specimen is a bone, infill or shell material.

Mike D

Hi Mike,

Here are some magnified photos of breaks.

Top or side view of a segment broken lengthwise, magnified.

End view of a broken segment, magnified.

End view of several broken segments, magnified.

Edited May 13, 2016 by CraigHyatt

[CraigHyatt]

pics of the associated shells would also help

Plax,

Here are some photos of shells and fragments from the nearest layer as well as an overview of the layers.

Layer overview.

[CraigHyatt]

A new specimen of the "crab" (I think). This one isn't so great, but I think I can make out the 4 "legs" on each side. If this is the same guy, it would be great, because I actually dug him out of the ground so I know which layer he's in.

Layer overview.

[CraigHyatt]

Craig

You mentioned that you are hunting the Cretaceous strata of your area. The Cretaceous formations of your area all hold ammonites. If you can find even partials, they'll go a long way to pinpointing age of the sediments you are canvassing. Ammonites are used in world wide zonation, so they are very well documented index fossils. Sphenodiscus, Pachydiscus, and possibly Placenticeras are the ones you'd most likely run into in your area, listed here youngest to oldest. I've attached a few photos for reference...be prepared to look for just a flank or keel exposed.

Spheno (narrow cross section with sharp keel esp. in small specimens, generally little or no flank ornamentation)

Kes Sphenodiscus pleurisepta 6a Site 417 052310.jpg

Pachy (usually a wider cross section with rounded keel, and either smooth or finely ribbed flanks)

Kco Pachydiscus paulsoni1c Site 349 060207.jpg

Placenticeras (some variation within the genus, but usually a narrow cross section, and a sharp or flattened, narrow keel, flank ornamentation ranging from smooth to tubercled)

Kan Placenticeras Weston 1b Site 496 0213.jpg

Uncle,

I haven't found any ammonites, but many circular concretions. Some of these have about the right shape, but no irregularity where an opening would be and no decorations. I can't break these open even with the flat side of a 22 oz hammer. The hammer barely chips them and they ring like steel. Maybe I can get a construction guy to bust one with a front end loader. :-)

I am pretty sure I am seeing some echinoids, though. Unfortunately, these are rough casts in coarse sand. They are dome shaped with a concavity on one side and about 1 cm diameter. Similar to these: https://woostergeologists.scotblogs.wooster.edu/2014/04/27/woosters-fossil-of-the-week-a-helpful-echinoid-from-the-upper-cretaceous-of-Israel/

Pictures of round concretions

[JohnJ]

Craig, I don't see any evidence of ammonites or echinoids in these photos. If you come across parts of them, it will be quite obvious.

Also, none of the other items are "crabs", despite the suggestive shape. It is quite possible that you are seeing interior casts of partial Inoceramus clams. Their parts are common in Upper Cretaceous Texas formations.

[CraigHyatt]

Craig, I don't see any evidence of ammonites or echinoids in these photos. If you come across parts of them, it will be quite obvious.

Also, none of the other items are "crabs", despite the suggestive shape. It is quite possible that you are seeing interior casts of partial Inoceramus clams. Their parts are common in Upper Cretaceous Texas formations.

John,

Thanks so much. As for Inoceramus, I searched online and many of the images absolutely look like what I am seeing. I think you might have nailed it. As for the echinoids, I didn't post any images because the casts are so poor, but if I find any good quality examples, I will post for identification. As for ammonites, I agree none of these concretions are ammonites. If I could manage to break one open, it would certainly be obvious. I am kind of curious what's inside there. :-)

Regards,

Craig

Update: Well, I busted one of the round concretions and there wasn't a dang thing inside it. Highly cathartic, though. :-)

Edited May 13, 2016 by CraigHyatt