Very Complete Mystery Snail Fossil ID Help!

[ChrisZey]

I found this very complete snail/mollusk looking fossil, it’s the first time I’ve seen the shell and body shape of a snail type organism preserved equally well in a fossil I’ve found- can anyone help tell me what organism it is specifically and from what time period?

I found it in Southampton, Ontario in my rock garden, so I don’t know whether the rocks from the rock garden are from a quarry or the shores of Lake Huron (I would guess they’re from Lake Huron, but I don’t know). Thanks for your help, I’ve been holding onto this for years and always been curious as to what it is!

 

Christian

[Kane]

There may not be enough diagnostic detail to make that determination for these types of gastropod (and more so in cross section without much shell material left), and they do range quite a bit (I've seen them in mostly Devonian deposits, but may also occur in Silurian formations as well). If it could be traced to an in situ area near you, I've provided you with that geological information in your other topic. 

 

The roundness of the rock would make it more a fit for the lake shore and not a quarry (plus I can't quite think of what rock would best suit that purpose of fill near you given that to the south is mostly the salt mine, and to the northeast of you the rock is generally used as flagstone and flooring). 

[ChrisZey]

I understand, thanks for the response! So likely 350-500 million years ago then if it’s from Southampton, based on your response n to my other fossil. Too bad it’s hard to identify specifically with the little shell material, is it purely an imprint of a Gastropod or is it an actual fossilized gastropod that has lost a lot of its shell material?

[Kane]

Given how it was tumbled and weathered, I would say the outline you are seeing is possibly shell material, but the surface has all been tumbled clean.  

[ChrisZey]

Ahh I see, that makes sense. Is there likely to be shell material inside of the rock then, given that it is in the outline? And are there a few Gastropod species that it is more likely to be, given the more simple shape of the shell and imprint of the body and head?

[Kane]

There very well might be, but the nature of the matrix sometimes means any attempt to prep it even with scribes doesn't quite work out most times as the shell may have a firmer bond with the outside matrix than to the steinkern (inside part). Looking at your piece, I'm unsure if it is complete, or an inner whorl of a larger one. I do confess that I know Ontario's Ordovician gastropods better than I do the Devonian or Silurian ones (I tend to rush through them all in search of trilobites  ). 

 

If I was certain this was an index fossil of a formation, that might be much easier for me to pinpoint the literature and get a more definitive ID. What would be equally good is if this appeared in the same rock as another fossil that could be identified (and maybe that one would function as an index fossil, which would more likely direct me to pull up the right faunal list!). The simplicity of the body plan somewhat works against more accurate identification given that I've seen similar morphology ranging from the Ordovician to the Devonian! 

[ChrisZey]

Oh ok, that makes sense- best left to the imagination that there is still shell in there! No problem, trilobites are very interesting so I don’t blame you. 
I’ve relooked at the fossil, and there doesn’t seem to be any other fossils on it, there are a lot of small, thin dark areas that could be smashed shell fragments, but they’re so small and random that it won’t be much help. 
 

I also had a chance to look in more detail at the other, more mysterious boot shaped fossil from my other post, and I noticed that a little piece has broken off, which shows what is underneath. Interestingly, there appears to be four shades of colour- a dark grey on the outside layer, a lighter grey just below it, a beige colour below that, and it’s surrounded by the grey stone. I’ll send a couple close ups because I’m curious what you think of it, if this points more towards it being a fossil covered in stone rather than a concretion. In one of the photos I circled the 4 areas of different shades of colour I talked about. 

[Kane]

If you're ok with taking the risk, you could always take a hammer and split that one open (the gastros are fairly common, so it wouldn't be a big loss until you bumped into another). When rocks like these get weathered by water, a lot of detail goes away with it, but there can be some further fossils inside. It can be tough to tell from the outside what may be the more definitive matrix inside from just looking at the exterior of the rock. I've busted erratics that looked the same as others and the interior can be quite different (and very occasionally with surprises). 

 

As for the other piece, the different colours/shades can likely be attributable to mineral availability and variation. I still wouldn't rule out concretion as sometimes concretions form around fossils (and in your piece we might be privy to seeing a weathered concretion that shows what started the whole layering in the first place!). 

 

But if you want a bit of a fossil bonanza, and you're willing and able to go with a hammer and chisel, you're a 40 minute drive from Formosa. There is a small roadcut just 1-2 km north of the town of Formosa that is full of fossils. 

[ChrisZey]

Good suggestion, that would be interesting to do, how common are these Gastropod fossils where you can see the imprint of the head and antennas like you can on this one? I hadn’t seen one where you see the imprint of the head and antenna, but is that more common than I think?

 

I see, so it points more towards mineral availability than it does towards confirming whether or not it is a fossil, got it! Hmm I’m not sure I follow what you are saying is the specific significance of the weathered concretion- are you saying this weathered concretion could help us see what started the whole layering process, as in it would help us understand what period it is from based on this layering? Or that it gives a hint as to why this layering happened?

Thank you for all your help!

[Kane]

Well, there are no antennae on gastropod shells.  You won't likely ever see the soft-bodied stuff in our rocks (the critter that inhabits the shell, so just shell only as the soft tissue does not preserve outside of a handful of what are called Konservat-Lagerstatte sites where the deposition and preservation conditions were absolutely just right to preserve those details). In terms of commonness, gastropods are definitely common in Ontario rocks, as they could inhabit some fairly turbulent conditions. Think of them as tough survivalists.  

 

In your piece, we might say that the concretion got sheared by erosional forces to permit us access to see what started the whole process as more sediments accrete around whatever the core may be (sometimes it is a sand grain!). 

 

 

[ChrisZey]

Very interesting, so is what looks like the head and antennae on this fossil simply just a fluke of sediment build up? It looks exactly like an imprint of the soft body/head and antennae (I’ll circle it in my picture below). If that’s just a fluke, that’s almost more impressive than a soft tissue imprint haha!
 

Ah that makes sense- so, in layman’s terms, the significance is that this erosion has shown us what started this concretion since it wore it down enough to see the lighter layer below- interesting!

[Kane]

It was indeed a fluke, and nature is a natural trickster on the eyes.  In fact, what you circled may not be part of the gastropod at all if you factor in the angle of the bottom part of the shell which seems more acute rather than continuous. 

[ChrisZey]

No kidding, eh! What are the chances that it formed such a shape that lined up so perfectly to make it look like a snail head! nature (and our eye’s ability to pick up patterns) is crazy. So what formed that snail head and antennae type shape and mild depression in the rock? Is that simply another type of rock that formed in a depression on this part of the rock or is it a different type of fossil underneath?