Tiny Trilobite Pygidium from Pennsylavanian of Western PA.

[Jeffrey P]

I was cleaning up this small Trepospira gastropod I found in 2015 in an exposure of the Ames Limestone in Western Pennsylvania and discovered attached to it is this very, very tiny trilobite pygidium- my first trilobite find of the Pennsylvanian Age.

[ynot]

Nice association!

Congrats on the first!

 

[FossilDudeCO]

Nice find! Congrats!

[Fossil-Hound]

Solid find.

[Ludwigia]

It's really amazing what you find sometimes when you finally get around to cleaning house

[EMP]

Nice find! I'd go with Ditomopyge. 

[RJB]

Ive always loved the gastropods.  Never thought about finding a trilo on one?   Very cool.  Nice find

 

RB

[Jeffrey P]

20 hours ago, ynot said:

Nice association!

Congrats on the first!

 

 

20 hours ago, FossilDudeCO said:

Nice find! Congrats!

 

20 hours ago, jsnrice said:

Solid find.

 

17 hours ago, Ludwigia said:

It's really amazing what you find sometimes when you finally get around to cleaning house

Thanks guys. This was a very fortunate and unexpected find for me.

[Jeffrey P]

12 hours ago, EMP said:

Nice find! I'd go with Ditomopyge. 

Thanks for the ID suggestion. Will have to research the possibilities since this is outside more normal realm.

[piranha]

According to Brezinski 1988, the Ames trilobites are: Ameura missouriensis and Ditomopyge decurtata.

Assuming you have found a partial pygidium, Ditomopyge decurtata would appear to be the best match.

Chow 1951 correlates the Ames LS.  Some trilobites are synonymous and taxonomy has been revised.

 

 

Chow, M.M. (1951)
The Pennsylvanian Mill Creek Limestone in Pennsylvania.
Pennsylvania Geological Survey, Bulletin G26:1-36  LINK

 

Brezinski, D.K. (1988)
Appalachian Carboniferous Trilobites.

Journal of Paleontology, 62(6)934-945

[Jeffrey P]

37 minutes ago, piranha said:

According to Brezinski 1988, the Ames trilobites are: Ameura missouriensis and Ditomopyge decurtata.

Assuming you have found a partial pygidium, Ditomopyge decurtata would appear to be the best match.

Chow 1951 correlates the Ames LS.  Some trilobites are synonymous and taxonomy has been revised.

 

 

Chow, M.M. (1951)
The Pennsylvanian Mill Creek Limestone in Pennsylvania.
Pennsylvania Geological Survey, Bulletin G26:1-36  LINK

 

Brezinski, D.K. (1988)
Appalachian Carboniferous Trilobites.

Journal of Paleontology 62(6)934-945.pdf

 

Thanks Scott for the ID info. You are the most amazing resource.

[piranha]

I found some additional information on the Ames LS.  Note that "Ditomopyge sp." was subsequently assigned to D. decurtata, Brezinski 1988.

 

 

Brezinski, D.K. (1984)
Pennsylvanian trilobites as environmental indicators: an example from the Glenshaw Formation (Missourian-Virgilian) of the Appalachian Basin. pp. 82-87

In: Busch, R.M., & Brezinski, D.K. (eds.)
Stratigraphic analysis of Carboniferous rocks in southwestern Pennsylvania using a hierarchy of transgressive-regressive units.
Guidebook 3, Eastern Section Meeting of the American Association of Petroleum Geologists, Pittsburgh 1984

 

TRILOBITE DISTRIBUTION
Three species of trilobites are found in the Glenshaw strata: Ameura missouriensis, Ditomopyge scitula, and Ditomopyge sp.

Both A. missouriensis and Ditomopyge scitula are found throughout the Glenshaw interval.  Ditomopyge sp. is restricted to the Ames marine unit.

 

Trilobites have been recovered from 38 exposures of marine units from the Glenshaw Formation of western Pennsylvania and eastern Ohio.  Collections from the 38 localities are restricted to, in ascending, the Brush Creek, Pine Creek, Woods Run, and Ames marine intervals.  The trilobites were commonly recovered from similar lithofacies and biofacies from each of the marine intervals.

 

Most commonly, trilobite specimens are present within dark gray to black calcareous shales of the Brush Creek, Woods Run and Ames horizons.  Sixteen of the 38 occurrences (42%) were from the black shale lithology.  This lithology invariably contains a molluscan biofacies with minor numbers of chonetid and productid brachiopods.  As discussed above in the biofacies model, the black shale lithofacies and molluscan-dominated biofacies are both interpreted to be nearshore facies which formed in areas of high clastic input and elevated nutrient concentrations (Brezinski, 1983).

 

The second most common occurrence of trilobites is within the Crurythyris biofacies.  This biofacies is best developed in the regressive deposits of the Ames interval, but is also present in the Brush Creek and Pine Creek intervals.  Eleven of the 38 occurrences (29%) have been noted from this biofacies.

 

Trilobites were also recovered from the chonetid biofacies.  This biofacies is most prevalent in Pine Creek and Ames intervals, but was also noted in the Brush Creek interval.  Only 6 occurrence.s (6%) were noted from this biofacies.  Lithologically, this biofacies is present in thin gray-green calcareous shales to argillaceous limestone, which commonly underlie many of the limestone outcrops.  The lithology and biofacies were formed during the initial stages of transgression of several of the marine episodes, and probably represent a high stress environment at the leading edge of the transgressing sea.

 

The remaining 5 occurrences (13%) were within the limestone lithologies which contain diverse brachiopod and bryozoan faunas (Neospirifer, Punctospirifer, Hustedia, Rhombopora, Stenopora).  This is interpreted as offshore, normal-marine limestone deposited under open-circulation conditions.

 

CONCLUSIONS
Trilobites from the Glenshaw Formation of Pennsylvania and Ohio tend to occur in nearshore or high stress environments, and are commonly associated with eurytopic faunas.  Fifty-eight percent of the trilobite occurrences are in brachiopod dominated biofacies (i.e., Crurythyris biofacies (29%), Chonetid biofacies (16%), offshore biofacies (13%) and their distribution appears to follow Bretsky's (1969) contention that Carboniferous trilobites are indicators of offshore environments.  However, all but the 5 occurrences in the offshore biofacies, or 87%, are within biofacies which can be interpreted as occupying nearshore or high stress settings.  Additionally, the general increase in numbers and number of occurrences of trilobites onshore follows the distribution expected for a eurytopic species and trophic generalist (Valentine, 1972).  In nearshore unstable settings eurytopes abound since there is an abundance of nutrients but a paucity of competitors.  However, in offshore areas resources are more partitioned than in a nearshore environment and competition is greater for available resources. In this setting the trophic generalist is at disadvantage to more specialized trophic types.  Consequently, the generalist does not compete well for available resources and therefore would be present, but less abundant in offshore areas.  The data presented herein suggests that Pennsylvanian trilobites may be used as nearshore or high stressed environmental indicators.