Placoderm or Onychodontid?

[dinosaur man]

I recently discovered this in the Devonian Onondaga Formation of Ontario and am thinking it’s either a Placoderm or a Onychodontid based off the armour like texture which does not match any coral in the formation, their is also the presence of odd spine like structures.  Any idea if it is one of these species?

    

[Fossildude19]

Pictures are a bit blurry.   

[dinosaur man]

5 minutes ago, Fossildude19 said:

Pictures are a bit blurry.   

I’ll try to get some more, I have a problem with this and a few other posts photos because their small, any ideas on how I could take good photos while magnifying them?  I can’t really use a microscope for this one.  Also thank you for the input.

[Fossildude19]

2 hours ago, dinosaur man said:

I’ll try to get some more, I have a problem with this and a few other posts photos because their small, any ideas on how I could take good photos while magnifying them?  I can’t really use a microscope for this one.  Also thank you for the input.

 

If I use my phone for a photo, I use either a free app called Magnify, or I use a clip on macro lens. Relatively inexpensive. Even cheaper, using a magnifying glass. 

However, the key to clear pictures is stability. Rest your phone or i-pad on a number of books. or a jar/can, to steady it. 

Also, you should take a picture of the entire rock, with a ruler for scale in it, so we can see some contrast. 

Not really seeing anything in the first two pictures. 

 

Contrasted:

 

 

 

 

[Kane]

The last picture is fenestrate bryozoan. The Onondaga in Ontario (particularly around the Wainfleet area) is mostly encrinal and byrozoanal stone with pockets of corals, and is not really known for placoderm material compared to the Onondaga "bone beds" of New York. Better photos might be necessary. 

[dinosaur man]

This is what I was thinking, the part I have labeled as armour resembles that of bony fish.  I was talking to some friends that often fossil hunt in same age formations as I do in New York and they’ve never found anything with this specific texture. @Kane

[dinosaur man]

I was looking for possible candidates for what this could possibly be.  And the scales on this Devonian Lungfish match up to the “armour” on my specimen.

[Kane]

In my opinion, no it doesn’t.

[dinosaur man]

58 minutes ago, Kane said:

In my opinion, no it doesn’t.

Sorry for all the questions tonight but what would you think this is.  The fossils I’ve shown in the last two post caught me off guard as their extremely unusual compared to what I usually find which is why I’m a bit unknowledgeable.  Nonetheless this is a good learning experience.  Also thank you so much for all the information you’ve provided me on both these two and my other posts about this formation.

Edited May 21, 2021 by dinosaur man

[Kane]

It almost seems like the impression of a coral, which wouldn't be out of place for that material. Interestingly enough, not all geological descriptions include Onondaga as a formation, while others do.

 

 

In this example, the author puts the Oriskany as the base of the Devonian in SW Ontario. That would be the reworked sands underneath the Bois Blanc Fm. So in this example, the Onondaga is the name of the group of limestones that include the Amherstburg, Lucas, and Dundee Fms. I know some well logs still refer to it as a formation or just as any of the similar limestones across those formations.

 

What makes the early part of the Mid Devonian so tricky up here is that not only does the lithology differ considerably within a unit/formation without being assigned a distinct member, but there are quite drastic changes in facies laterally. For instance, the Dundee Fm can change depending on where the deposition occurs, and I've seen the listed five facies in person, but laterally some of those may be sandy or armour stone or platy or cherty! If the deposition was nearshore, offshore, carbonate ramp, etc., the lithology and fauna found in there change quite rapidly. 

 

I can show you a typical placoderm spine that I found from the sandier nearshore facies of the Dundee:

 

 

Those spines also occur in the Bois Blanc Fm in some horizons.

 

This would be typical placoderm armour in the Bois Blanc that we kept finding: 

 

 

I think you'll discover our Devonian stratigraphy is a bit messy in Ontario!  Some of the formations are gradational, such as between the Amherstburg and Lucas, making it a real challenge as to where the contact should be. You're probably noticing that sort of messiness in the Dunnville area as it seems to be a confluence of formations. As a recommendation, you're not far from the Wainfleet Conservation Area. Although you are not allowed to collect, have a look at the crinoidal packstones. Those are very similar to the Dundee rocks one can see dumped at the Fanshawe Park dam in northeast London.

[FossilDAWG]

I recall that the Oriskany is/was exposed at only one place in Ontario, a small abandoned quarry (don't recall the exact location).  It had a typical Oriskany sandy lithology and numerous casts of typical Oriskany brachiopods.  At every other place in Ontario it was removed by erosion before the Bois Blanc was deposited.  Also formations are (or they should be) defined based on lithology, so they can be time-transgressive as they follow an invading or receeding sea, for example.  So, local/regional non-deposition, erosion at unconformities, or lithological differences can mean the "stratigraphic column" is different from place to place. 

 

Don

On 5/19/2021 at 9:40 AM, dinosaur man said:

This is what I was thinking, the part I have labeled as armour resembles that of bony fish.  I was talking to some friends that often fossil hunt in same age formations as I do in New York and they’ve never found anything with this specific texture. @Kane

I have no question that this is a coral impression.

 

Don

[Kane]

I've only encountered the Oriskany by accident, and not in situ. It was maybe just one or two examples in a stormwater pond here in London. Some of our lithologies are quite distinctly easy to identify, while others can be a bit of a head-scratcher!  

 

Back before Stauffer's day, the "onondaga limestones" were lumped together as the "corniferous limestone," so the faunal lists get a little confusing. 

 

The Lucas-Dundee contact is a bit clearer on account of measurements of the limestone purity, but the contact between Lucas and Amherstburg is not as clear. It also seems like night and day when comparing the Amherstburg material if it is deposited in either the Michigan or Appalachian basins. 

 

On a related note, I always found reading lithology descriptions a bit amusing and confusing at times: "The X Formation is a thin to massively bedded brown, tan to beige dolostone-limestone with calcareous partings that weather buff grey to brown to beige, with chert nodules that are grey, white to dark grey in parts."  

 

And just to show how the Devonian cake was cut after Hall, Vanuxem, Logan, et al., here's a modification from Stauffer (1915):

 

 

Those temporal divisions are a bit off by today's understanding.

 

All that being said, @dinosaur man, if you are interested in delving into the issues of the Dundee Fm, Birchard's 1990 Master's thesis is a good start:

 

https://macsphere.mcmaster.ca/handle/11375/19595

[FossilDAWG]

1 hour ago, Kane said:

On a related note, I always found reading lithology descriptions a bit amusing and confusing at times: "The X Formation is a thin to massively bedded brown, tan to beige dolostone-limestone with calcareous partings that weather buff grey to brown to beige, with chert nodules that are grey, white to dark grey in parts."

"I know it when I see it."

 

Thanks for the link BTW

Don

[jdp]

Yeah I am pretty sure this is all invert. I see no bone here.

[dinosaur man]

On 5/21/2021 at 11:06 AM, Kane said:

It almost seems like the impression of a coral, which wouldn't be out of place for that material. Interestingly enough, not all geological descriptions include Onondaga as a formation, while others do.

 

 

In this example, the author puts the Oriskany as the base of the Devonian in SW Ontario. That would be the reworked sands underneath the Bois Blanc Fm. So in this example, the Onondaga is the name of the group of limestones that include the Amherstburg, Lucas, and Dundee Fms. I know some well logs still refer to it as a formation or just as any of the similar limestones across those formations.

 

What makes the early part of the Mid Devonian so tricky up here is that not only does the lithology differ considerably within a unit/formation without being assigned a distinct member, but there are quite drastic changes in facies laterally. For instance, the Dundee Fm can change depending on where the deposition occurs, and I've seen the listed five facies in person, but laterally some of those may be sandy or armour stone or platy or cherty! If the deposition was nearshore, offshore, carbonate ramp, etc., the lithology and fauna found in there change quite rapidly. 

 

I can show you a typical placoderm spine that I found from the sandier nearshore facies of the Dundee:

 

 

Those spines also occur in the Bois Blanc Fm in some horizons.

 

This would be typical placoderm armour in the Bois Blanc that we kept finding: 

 

 

I think you'll discover our Devonian stratigraphy is a bit messy in Ontario!  Some of the formations are gradational, such as between the Amherstburg and Lucas, making it a real challenge as to where the contact should be. You're probably noticing that sort of messiness in the Dunnville area as it seems to be a confluence of formations. As a recommendation, you're not far from the Wainfleet Conservation Area. Although you are not allowed to collect, have a look at the crinoidal packstones. Those are very similar to the Dundee rocks one can see dumped at the Fanshawe Park dam in northeast London.

Thank you for all the information, also I’ll have to check out the Dundee one day as I’ve never hunted in it before.

On 5/21/2021 at 11:14 AM, FossilDAWG said:

I recall that the Oriskany is/was exposed at only one place in Ontario, a small abandoned quarry (don't recall the exact location).  It had a typical Oriskany sandy lithology and numerous casts of typical Oriskany brachiopods.  At every other place in Ontario it was removed by erosion before the Bois Blanc was deposited.  Also formations are (or they should be) defined based on lithology, so they can be time-transgressive as they follow an invading or receeding sea, for example.  So, local/regional non-deposition, erosion at unconformities, or lithological differences can mean the "stratigraphic column" is different from place to place. 

 

Don

I have no question that this is a coral impression.

 

Don

Thank you 

On 5/21/2021 at 2:18 PM, jdp said:

Yeah I am pretty sure this is all invert. I see no bone here.

Thank you!