? gastropod

[drbush]

Hi friends , a new fossil i needs yr help , I was yesterday in my favort fossil hunting site and i found this large ? gastropod or ammonite , it is 9 inch wide and 6 high 

what could it be 

[Ludwigia]

I'd guess gastropod as well, but I'd need photos with higher resolution to say for sure.

[izak_]

I agree with Ludwigia 

[RJB]

Thats one big gastropod!

 

RB

[FossilDAWG]

Where is this from? To me it resembles the Ordovician gastropod Maclurites.

 

Don

[drbush]

may this help 

[drbush]

the area is early Jurassic of Saudi Arabia 

[Ludwigia]

Thanks for more photos and approximate stratigraphy. Unfortunately the preservation is so that I can't make out any inner structure, like septal walls or the like. I would lean toward saying that it's a gastropod, although I've never seen anything that large from the Jurassic. The spiral is however very flat, so it could just as well be a weathered down cross section of an ammonite.

[abyssunder]

The planispiral and polygonal look of the specimens make me think they could be gastropods, maybe close to Discohelix (Pentagonodiscus), although they are very large.

 

excerpt from here

[Ludwigia]

This is much too large to be a Discohelix. The problem is, I can't for the life of me think of a gastropod of that size and form in the early Jurassic.

[marguy]

I discovered the subject, the picture made me think of a Caprina cast, but if the Jurassic age is correct, it's not a good idea...

[abyssunder]

How could we know it is or not from the Early Jurassic?

First of all we have to know the geological age of the sediments where the location of the find is, then the name of the formation.

 

picture from here

[Ludwigia]

1 hour ago, abyssunder said:

How could we know it is or not from the Early Jurassic?

First of all we have to know the geological age of the sediments where the location of the find is, then the name of the formation.

 

16 hours ago, drbush said:

the area is early Jurassic of Saudi Arabia 

I'm just going by what the man said.

[KimTexan]

Maybe @Tidgy's Dad would know something since he lives closer to the region. Although I don’t recall how familiar he is with Saudi Arabian geology or fossils.

 

I personally have never seen a gastropod that size in that form. I recall seeing some large gastropods from Israel, but they were of a very different sort, not ones that resembled ammonite shapes. They were more like snails.

[Tidgy's Dad]

8 hours ago, KimTexan said:

Maybe @Tidgy's Dad would know something since he lives closer to the region. Although I don’t recall how familiar he is with Saudi Arabian geology or fossils.

 

I personally have never seen a gastropod that size in that form. I recall seeing some large gastropods from Israel, but they were of a very different sort, not ones that resembled ammonite shapes. They were more like snails.

Thanks for thinking of me, Kim

Though I am more than 7,000 kms away, I did live and work in Saudi for a year. 

Great place, but I never went fossil collecting I'm ashamed to say. 

I saw this thread and quickly hid because I have absolutely no idea. 

It looks like a gastropod but is too big for this period of time compared to any gastropod I've ever seen from the age. 

I would guess at a weathered, cracked ammonite, but I have no reason for saying so other than guesswork. 

Sorry. 

[KimTexan]

24 minutes ago, Tidgy's Dad said:

Thanks for thinking of me, Kim

Though I am more than 7,000 kms away, I did live and work in Saudi for a year. 

Great place, but I never went fossil collecting I'm ashamed to say. 

I saw this thread and quickly hid because I have absolutely no idea. 

It looks like a gastropod but is too big for this period of time compared to any gastropod I've ever seen from the age. 

I would guess at a weathered, cracked ammonite, but I have no reason for saying so other than guesswork. 

Sorry. 

Oops, sorry about that.

No shame in not knowing. I know you’re not close, but merely closer than many of us in North America.

Not going fossil hunting isn’t as bad as me many years ago living in Florida for a year and not going to the beach. I was doing my clinical rotations 60 hours a week, studying every waking hour and working 24 hours every weekend. I had no life other than work and my training. I was so sleep deprived! A few years after I went through the program educators determined it was too much to learn in a year and it is now a 2 year program.

[abyssunder]

Maybe the O.P. could give an answer how he came to this conclusion, then it will be easier to exclude some of the possibilities, I think.

[drbush]

thank you all for the wealth of information , the fossil was found in an area of ohruma formation , Bathonian on top of a small mountain (120 ft) ,on a lower side i found a nautilus. I hope the fig helps .

? could be a withered cephalopod ??

[abyssunder]

The Ohruma formation is Bathonian in age, so it is Middle Jurassic not Lower Jurassic. This rule out any rudists.

[Guguita2104]

This is an odd creature for the Jurassic, indeed...I would have thought that this was a Cretaceous nautiloid or gastropod .

I don't know if this helps...At least I hope so.

"The age of the Dhruma Formation is based primarily on ammonites and nautiloids but supplemented by micropalaeontological and palynological evidence"

"Dhruma lies unconformably on the Early Jurassic (Middle to Late Toarcian) Marrat Formation and is unconformably overlain by the Middle Jurassic (Middle to Late Callovian) Tuwaiq Formation. An allostratigraphic, sequence-based reinterpretation of the originally defined Dhruma now assigns the Atash and Hisyan Members, previously of the uppermost Dhruma Formation, to the overlying Tuwaiq Mountain Formation."

Here it's the link:http://www.searchanddiscovery.com/abstracts/html/2010/geo_bahrain/abstracts/Hughes4.html

Regards,

[Ludwigia]

I'm more and more convinced that this is rather a partial cephalopod than a gastropod. It seems to have lost a lot of the top half, as if erosion has sectioned it off. Unfortunately, the specimen is so damaged and weathered that indicators like rib sculpture or sutures cannot be seen, so I can't even decide if it's an ammonite or a nautilus, let alone guess a genus. How does the other side look? Are any indicators to be seen there or is it just as eroded? A precise stratigraphical position would also help, if possible, since my research has shown that this formation ranges from the Bajocian through the Bathonian up into the Callovian. Link

[abyssunder]

To be honest, I never seen such a big, flat Jurassic (or younger) gastropod to be comparable to the specimen in question, so I think gastropod could be ruled out.

Also, here is a more recent document related to the Dhruma Formation and its diagenetic alterations: Abdelbaset S. El-Sorogy et al. 2017. Microfacies and diagenesis of the Middle Jurassic Dhruma carbonates, southwest Riyadh, Saudi Arabia. Journal of African Earth Sciences 130:125-133