Escondido Crocodile

[MarcusFossils]

I think it might be an ammonite shell roll mark.The impression might be skewed because of partial buoyancy

Hats off to you, sir

Edited July 19, 2016 by MarcusFossils

[JohnJ]

You are a genius! I just measured, and the three "lips" (presumably made by the shell opening) are exactly 7.5 cm apart. So, if I dig slightly downhill to the right, I should find an ammonite 2.4 cm diameter. :-)

I rolled an ammonite in soft dough, and it perfectly explains the trace we see. Might not be the exact species of ammonite, but clearly explains the wide marks, the much narrower marks, and the periodic lip mark. Of course, the ammonite I'm using is larger than the one that made the trace.

The trace looks compatible with heteromorphs than the Sphenodiscus I have on hand. Plenty of possible candidates in this overview: https://www.researchgate.net/profile/Jens_Lehmann/publication/281108040_Ammonite_Biostratigraphy_of_the_Cretaceous-An_Overview/links/55eff7ea08ae0af8ee1b4a18.pdf?origin=publication_detail

Strip of soft dough

image.jpeg

Start with lip impression

image.jpeg

Roll wide part of the trace

image.jpeg

Roll narrow part of the trace up to next lip impression

image.jpeg

Maybe...maybe not. If it is, then obviously you would need to only look at ammonites found in that formation. However, they were not the only large shells rolling around at the time. These are good leads, but the other types should be considered, too. Then, again, it could have an entirely different origin. Keep up the research.

[CraigHyatt]

John, what sold me (and not saying it's 100%) was the totality of the evidence.

Pro

a. The precise match of the three traces

b. The precise spacing "lip to lip" to the millimeter

c. The fat .. thin .. lip pattern matches a typical ammonite which is thick on the backside and thin just before the shell mouth.

d. The number and spacing of the flutes is reasonable.

e. Plenty of examples where the opening is "off center".

Con

a. The diameter to width proportions seem questionable. It's roughly 2.4 cm diameter and 1.1 cm wide. That seems too wide.

b. I haven't found an ammonite matching the track.

Based on the "pros" I am pretty confident it's an ammonoid of some sort. Nothing else that I know of matches all the criteria listed.

Edited July 20, 2016 by CraigHyatt

[doushantuo]

Craig ,I like the way you approached the problem the "pre-computer" way,by "analog experimentation" .I'm reminded of the best work of Trueman,Schafer,Muller,Reyment and that group that) publishes every once in a while on neo-ichnological experimentation(using e.g.elephants,would you believe it).The ribbing I noticed (and others too) does tend to make one think of a molluscan originator.

edit:

The originator needn't have been in its original habitat.Think of post-mortem drift,which is extensive in cephalopods. The fact that you didn't find an exact molluscan match in the surrounding sediment

is not too persuasive a counter-argument

Edited July 19, 2016 by doushantuo

[CraigHyatt]

Craig ,I like the way you approached the problem the "pre-computer" way,by "analog experimentation" .I'm reminded of the best work of Trueman,Schafer,Muller,Reyment and that group that) publishes every once in a while on neo-ichnological experimentation(using e.g.elephants,would you believe it).The ribbing I noticed (and others too) does tend to make one think of a molluscan originator.

Paleowilliam posted some 1 inch ammonites a while back. The ribbing looks similar to the tracks. I PM'd him asking for some measurements. I am also planning to dig in the area where I found the trace to see if there are any matching shells.

[doushantuo]

And another thing:if you could prove this,you've got an ichnofossil to (your) name(verb AND noun here),and possibly to publish about

Edited July 19, 2016 by doushantuo

[doushantuo]

some of you might like this one,an ichnological classic:

by Bill Kennedy,no less

http://www.biodiversitylibrary.org/page/36529676#page/233/mode/1up

[DPS Ammonite]

Craig, think WWPD: what would a paleontologist do. First, we need to determine if the trace fossils are impressions of a rolling object/shell or the layer on top that is filling the impressions. I think that these are the layer on top that filled the impressions because the right side of each trace fossil (the lip or opening of a shell) is concave. What do you think? Thinking like a paleontologist, you need to create a model of the object/shell that made the trace fossil. Impress a clay-like substance (such as the material the dentist uses to make impressions of teeth) into one of the trace fossils. Let the impression harden. Then make a cylinder about 2.5cm in diameter out of clay to roll in the hardened impression. If all goes well, the clay should be a model of the object that made the trace fossil. The size and shape of the model's aperture and the ribs should help us determine what type of shell made the trace fossil.

I think that a shell that coiled like a turritella gastropod with ribs would be more likely to roll on the seafloor that the disk shaped Spenodiscus that you demonstrated. See photo for general type of shell that may have made the trace fossil.

Also, for TTF audience, try to recreate Craig's trace fossils by making a rolling impression of shells from the late Cretaceous into clay. Send us a photo of the shell and its impressions to help us decide what type of shell may have made the trace fossils.

[JohnJ]

Maybe...maybe not. If it is, then obviously you would need to only look at ammonites found in that formation. However, they were not the only large shells rolling around at the time. These are good leads, but the other types should be considered, too. Then, again, it could have an entirely different origin. Keep up the research.

...and by "found in that formation", I am making reference to ammonites known to occur in the Escondido Fm., not that you've physically found.

[CraigHyatt]

FYI, I have access to 3D modelling software that can "unroll" a curved model onto a flat surface. I can also get my previous company to print 3D models of shells. I already asked my wife to bring me some alginate so I can preserve the trace in case it gets damaged. She has buckets of it at work.

[CraigHyatt]

...and by "found in that formation", I am making reference to ammonites known to occur in the Escondido Fm., not that you've physically found.

That being said, it can't have rolled *that* far. :-)

[JohnJ]

That being said, it can't have rolled *that* far. :-)

Actually, if it was created by a rolling shell, it could have been eroded into micro pieces back then. I think a rolling shell is a good lead, but far from an exclusive cause.

[DPS Ammonite]

Craig, do you know what the orientation of the trace fossils in the formation was when you collected them? Was the surface that we see at the top?

[CraigHyatt]

Craig, do you know what the orientation of the trace fossils in the formation was when you collected them? Was the surface that we see at the top?

The photo at the top of the post shows how I found it. I pulled out all the surrounding slabs and found nothing that matched it. I could go up the hill and see if it slid down from there. If I can find a match still in the ground, I can get the orientation, but no way to tell otherwise.

Edit: Photos of the back and sides if that helps.

As found. Slab next to black bag.

Edited July 19, 2016 by CraigHyatt

[CraigHyatt]

Actually, if it was created by a rolling shell, it could have been eroded into micro pieces back then. I think a rolling shell is a good lead, but far from an exclusive cause.

I am dying to get back out there and dig some more. What an interesting mystery.

Edit: I think the first thing I'm going to do, as somebody up-thread mentioned, is try to place and orient the slab. I will use the photos I took of the specimen edges and try to match it up to what's in the ground. The thing weighs ~40 lbs. so I'm not lugging it back out there, that's for sure.

Edited July 20, 2016 by CraigHyatt

[doushantuo]

According to Mcnamara & Henderson(1985)diagenesis can cause the disappearance of aragonitic fossils such as ammonites from the stratigraphic record.

Edited July 20, 2016 by doushantuo

[ynot]

Hey hi Graig,

I am just wondering what the age of this rock is?

Tony

[CraigHyatt]

According to Mcnamara & Henderson(1985)diagenesis can cause the disappearance of aragonitic fossils such as ammonites from the stratigraphic record.

[Opens Google translate. Looks for doushantuo dialect.] :-)

I will have to Google the technical terms, but I guess you are saying don't bother looking for the critter that made them tracks. Even so, I am going to give it a shot. I doubt I'll find the source of the tracks, but if I can find the layer those tracks belong to, there's a chance of finding some good stuff.

[CraigHyatt]

Hey hi Graig,

I am just wondering what the age of this rock is?

Tony

I think 80 mya, upper Cretaceous, marine environment. I have found Sphenodiscus sp. in or near the same layer.

[doushantuo]

http://geol.queensu.ca/isotope_lab/pdfs/James%20et%20al%202005%20Arag.pdf

an example aragonite diagenesis

[CraigHyatt]

http://geol.queensu.ca/isotope_lab/pdfs/James%20et%20al%202005%20Arag.pdf

an example aragonite diagenesis

Dumb question: I have found a few specimens with part of the aragonitic shell present, but most are just casts as the specimen shown below. I wonder if it's possible to find the *cast* of an ammonite that created a track, even with the aragonite dissolved away?

I guess it's a moot point because if it left the track while still in the ocean, then the shell would still be in its original form.

Edited July 20, 2016 by CraigHyatt

[DPS Ammonite]

Dumb question: when I pick one of these up off the ground, is it still aragonitic or has its structure been replaced with some other mineral like silicon? So would a fossil like this be destroyed by diagenesis?

image.jpeg

I guess it's a moot point because if it left the track while still in the ocean, then the shell would still be in its original form.T

The original exterior shell of aragonite and /or calcite has dissolved away leaving the hardened sediment that filled the chambers: AKA an internal mold. In many Texas ammonites the septa are preserved as a carbonate. I have yet to see a Texas ammonite replaced by silica. Your fossil might have some septa replaced by carbonate if you cut it open (don't do it).

Edited July 20, 2016 by DPS Ammonite

[ynot]

Dumb question: when I pick one of these up off the ground, is it still aragonitic or has its structure been replaced with some other mineral like silicon?

The calcite in the shell can dissolve completely and be replaced by other minerals, or it can be altered to another mineral without dissolving. It all depends on the conditions after burial. In rare occurrences the original mineral of the shell can be preserved.

Tony

[doushantuo]

what follows is a good piece of Ammo taphonomy in a sequence-stratigraphic context:

http://eprints.sim.ucm.es/23340/1/135_07_Ammonoid_taphonomy.pdf

[CraigHyatt]

@DPSAmmonite: Sorry, I was editing my comment when you replied. Is it still possible I might find a *cast* of the exact ammonite that left a track, even if the aragonitic part dissolved away?