Found this at the Ottawa River?

[dylandreiling]

Was checking out the riverfront in downtown Ottawa and came across this fossil. Any ideas on what I may be? It's Ordovician strata, could It be a headplate from a bony fish species? 

[Kane]

Tough to tell, but perhaps an Isotelus fragment, part of it stuck on the impression?

[dylandreiling]

5 minutes ago, Kane said:

Tough to tell, but perhaps an Isotelus fragment, part of it stuck on the impression?

Could be! I just found the texture and size of it to be a lot different than what I had found before. 

[FossilDAWG]

I agree with Kane, it is almost certainly a somewhat crushed Isotelus pygidium.  The brown shell material is typical of trilobites in the Ottawa limestone formations.  The lack of an obvious axis or segments is indicative of Isotelus or some of the bumastid genera (Bumastus or Failliana), but I get an impression that the part of the edge or "rim" that is preserved flattens out relative to the curvature of the rest of the shell, and that would be typical of Isotelus.  Also Isotelus is probably the most common trilobite there.  Certainly it is not a fish plate, as it 1) has no trace of bony structure or denticles, 2) the cracks are just random cracks produced by flattening/crushing the shell, they do not have the symmetry of sutures between plates, and 3) no placoderm or other fish material has ever been recovered from the Ottawa Ordovician.  Some microscopic fragments of denticles have been recovered from St Joseph Island near Sault St Marie, and also I think from near Quebec City, but you need a microscope to see them.

 

Don

[Kane]

Isotelus tend to be a bit smoother with a few less pronounced features than its "cousin" Pseuogygites. Have a look here: https://en.m.wikipedia.org/wiki/Isotelus

 

 

[dylandreiling]

Thank you @FossilDAWG and @Kane! Looking at it now, definitely looks like an isoletus pygidium. Totally new geologic timescale for me, so still learning the ropes.

 

Dylan