Pygidium?

[Kane]

Another London oddity. While scoping along the Thames River among the usual Devonian-era debris, this caught my eye. At first I thought it was just a spirifer impression, but upon closer examination, it had a kind of border reminiscent of the pygidia I see on Pseudogygites. Obviously, it could not be Devonian if that were the case (the rock would have to travel pretty far some long while ago to be Ordovician in origin). 

 

Would this be another Basidechenella? If so, the pygidium is about 2 cm (~1"). 

 

Or my eyes are playing tricks on me, being rusty after the winter

[FossilDAWG]

Not much left to go on, but I'd be fairly comfortable with Basidechenella.

 

Don

[piranha]

Basidechenella alpenensis is described from the Dundee Limestone.

 

 

[piranha]

Basidechenella planimarginata is also described from the Dundee LS.

 

 

[Kane]

Thanks to you both! That would make two Basidechenella fragments in three days. Scott, I'm a little shy on average sizes, and was curious about that and the morphometric calculation on the full size based on the pygidium I have.

[piranha]

The larger examples I have seen over the years are 2 inches plus.  

 

 

[piranha]

Because of the big size Trypaulites calypso might be a better match as the mystery trilobite.  

Ludvigsen 1979 lists Trypaulites as a Dundee trilobite.  The attached figure is 3 inches plus.

 

Ludvigsen, R. (1979)
Fossils of Ontario - Part 1: The Trilobites.
Royal Ontario Museum Publication, 96 pp.

 

"Although Trypaulites has not yet been reported from Ontario rocks, it is included

here because it occurs in adjoining areas (New York, Ohio, Michigan, Quebec)

in rocks correlative with the Bois Blanc, Amherstburg, and Dundee Formations."

 

 

[Kane]

What luck! Thank you again for helping me out. It would have been more exciting to find a full specimen, but this hopefully bodes well for the rest of the collecting season. 

 

I adore the Ludvigsen text. It is short, and I wish it had more plates, but it makes a handy field guide.

[FossilDAWG]

The Ludvigsen volume is pretty useful, but I wish he or someone would do an updated 2nd edition.  There are a few genera that were not included, and of course new ones have been described from or discovered in Ontario rocks since the first version was published.

 

Don

[Kane]

19 minutes ago, FossilDAWG said:

The Ludvigsen volume is pretty useful, but I wish he or someone would do an updated 2nd edition.  There are a few genera that were not included, and of course new ones have been described from or discovered in Ontario rocks since the first version was published.

 

Don

I definitely agree with that. Relying on a patchwork of papers is not always the most convenient (apart from exceptionally focused study), and a more general roundup in the form of an updated version would certainly come in handy!

 

if I could go back 20 years, I'd probably choose a different academic path

[piranha]

Here is a good paper for Dundee fossils.  Some of the taxonomy has been revised.

 

 

Bassett, C.F. (1935)

Stratigraphy and paleontology of the Dundee Limestone of southeastern Michigan.

Geological Society of America Bulletin, 46(3):425-462