Trilobite Pygidium?

[safossils]

This is from the Rillito river in Tucson. I have it ID'd as a Trilobite Pygidium cross-section, but I was not real sure. I believe this is Pennsylvanian age, but since it's in the river bottom, and away from any outcrops, it could be earlier or later Paleozoic. It is about 1/2 inch long.

Any help appreciated.

Thanks,

Walt

[Auspex]

Paleozoic inverts are not my strength, but I can't think of anything else it could be.

[Napoleon North]

This is from the Rillito river in Tucson. I have it ID'd as a Trilobite Pygidium cross-section, but I was not real sure. I believe this is Pennsylvanian age, but since it's in the river bottom, and away from any outcrops, it could be earlier or later Paleozoic. It is about 1/2 inch long.

Any help appreciated.

Thanks,

Walt

It is at 100% is not pygidium trylobite.

I myself have a lot of them. In our post-glacial sediments are quite frequent.

I have about them the same page. It seems to be one of the most extensive in Poland.

[Guest solius symbiosus]

This is from the Rillito river in Tucson. I have it ID'd as a Trilobite Pygidium cross-section, but I was not real sure. I believe this is Pennsylvanian age, but since it's in the river bottom, and away from any outcrops, it could be earlier or later Paleozoic. It is about 1/2 inch long.

Any help appreciated.

Thanks,

Walt

It is at 100% is not pygidium trylobite.

I myself have a lot of them. In our post-glacial sediments are quite frequent.

???

Are you referring to post-Ord, or post-Dev glaciations? Trilobites died out in the Permian; all but the proetids died out by the end of the Devonian.

If it is a pygidium, it is a ventral??? It appears to be phacopid... not proetid. If so, that would make it pre-Miss.(Caveat: I'm not much on the proetids, maybe someone else will chime in)

[safossils]

It appears to be phacopid... not proetid

Thanks for the replies. This could be Devonian as well, so phacopid would not be out of the question. I found an image on this page that appears to somewhat match in cross section. I think I'll leave the ID as a pygidium.

Again,

Thanks,

Walt

[Napoleon North]

It is at 100% is not pygidium trylobite.

I myself have a lot of them. In our post-glacial sediments are quite frequent.

???

Are you referring to post-Ord, or post-Dev glaciations? Trilobites died out in the Permian; all but the proetids died out by the end of the Devonian.

If it is a pygidium, it is a ventral??? It appears to be phacopid... not proetid. If so, that would make it pre-Miss.(Caveat: I'm not much on the proetids, maybe someone else will chime in)

Good specimens, which I found are from the Silurian or Devonian.Were brought here in the sands of glacial origin from Scandinavia.

[FossilDAWG]

This is from the Rillito river in Tucson. I have it ID'd as a Trilobite Pygidium cross-section, but I was not real sure. I believe this is Pennsylvanian age, but since it's in the river bottom, and away from any outcrops, it could be earlier or later Paleozoic. It is about 1/2 inch long.

Any help appreciated.

Thanks,

Walt

1) Definitely 100% it IS a trilobite pygidium, seen from the ventral side and partially eroded. It looks like it might be one of the Mississippian or Pennsylvanian forms with relatively large pygidia, which were proetids. All the phacopids I know had pygidia that were relatively broad in relation to their length, but I'm no authority on late paleozoic trilobites. When I lived in Tucson I never found trilobites in the Ritillo, but I did find them in the area, such as at the north end of the Tucson mountains, and farther afield in some of the small ranges east of Sierra Vista and in the Chiricahua Mountains near Portal. I found a lot more in the Lake Valley formation in New Mexico. There are bits and pieces of Paleozoic strata around, including some nice Devonian Martin Formation with a silicified coral reef on the north side of Mount Lemmon, Mississippian around Colossal Cave (the name is not exactly truth in advertising), and Permian Concha formation at the southern end of the Tucson Mountains. Any of those could produce a trilovite. I'm not sure how any of those would have ended up in the Ritillo.

Don

[FossilDAWG]

Check out this Griffithides, a Mississippian proetid:

http://images.google.com/imgres?imgurl=htt...l%3Den%26sa%3DG Notice how long the pygidium is compared to its width. Now compare it to a phacopid:

http://images.google.com/imgres?imgurl=htt...l%3Den%26sa%3DG

The pygidium is very broad and short, compared to Griffithides or your specimen.

Don

PS sorry, when you go to the links you may have to scroll down to find and click on the Grffithides and Phacops images.

[safossils]

Yes! I see the difference, the Griffithides is much more elongated. I'll probably be visiting this site again, and this time I'll look for more clues as to the age of the rock. I think it had a lot of Crinoid material which lines up nicely with Mississipian age Escabrosa Limestone sediments....

Many Thanks,

Walt