Bivalves or ostracods on this bedding plane

[Bob Clouser]

Hello all. I have been really stumped on these for a long time. They look like small bivalves at first site, but they have odd shapes and some have a long, straight "hinge line"; none have a clear umbo or ornamentation or internal detail. I wonder if they could be ostracods? I found them at an outcrop near Catskill, NY, at a place where you can see the Taconic Unconformity. Specimen came from a big slab of rock detached from the outcrop, and I could not find where it came from. So it's age could be late silurian or middle ordovician. In the microscope, I can tell it's definitely a shell material. Need to do acid test.

 

Any ideas?

Thanks,

Bob

[Archimedes]

I do not believe these are bivalves , some good size ostracods are occasionally found in mass upon a bedding plan in the Ordovician, I think your fossils are ostracods.

[Wrangellian]

Nice piece.. They do mostly have that ostracod shape. Others might chime in with more info.

[doushantuo]

OSTRACODS,with that outline .

Paraparchitids ,geisenids,or kloedenellids,maybe.

Leperditiocopids?

[FossilDAWG]

Leperditia was a large ostracod that is a common fossil in many Ordovician and Silurian formations in New York and Ontario (and elsewhere too).  At some levels it is almost the only body fossil to be found, especially in some very shallow-water deposits.

 

Don

[abyssunder]

" Ostracoda of Leperditicopida-type have been reported to occur in nonmarine, probably fluvial, deposits in the Upper Devonian Cetskill "redbed" magnafacies of New York (Knox,1996; Lundin and Friedman, 1998). Sollenella? sp. was recorded in the Golboa Formation, Upper Middle Devonian, Greene Co., N.Y. in association with a freshwater bivalve Archanodon. " - Frederick M. Swain. 1999. Fossil Nonmarine Ostracoda of the United States: Developments in Palaeontology and Stratigraphy, No.16.

 

" Archanodon catskillensis is a member of the oldest known genus of freshwater bivalves. Although the main occurrences of this species are in New York and Pennsylvania, its burrows are known from the Bellvale Sandstone (Givetian) of northern New Jersey. A. catskillensis has two shell morphs, each of which may be a separate species. A. catskillensis also differs from A. westoni, the other North American Archanodon species. A. catskillensis is the most common macroinvertebrate in non-marine facies of the Devonian Catskill clastic wedge, where it is found in channel fill and overbank deposits. A. catskillensis is an erect, semi-infaunal filter-feeder which often lived in clusters of many individuals. Its life habits thus appear very similar to those of many modern unionoid bivalves. Organic adventitious layers appear to be present in the shell microarchitecture of A. catskillensis. These points, together with its abundance and wide distribution in Catskill rocks, strongly implies that the genus should be included in the bivalve order Unionida. Disparities in shell form among Archanodon species indicate that taxonomic revision of the genus may eventually be necessary. " - Chamberlain & Chamberlain, 2007.pdf

 

Those bivalves are much more larger than the specimens in question which could be very well ostracods.

[doushantuo]

leperd

[Ridgehiker]

Yes, they are ostracods. Neat example.

 

They are difficult to identify without attention to some specific microscopic features. Some of be suggestions above can get you pointed in the right direction.

 

I've never seen a specimen like your one.  Ostracods are fairly common but the death assemblages are usually more of a mishma and not as uniform as yours.  Similar deposits of brachiopods to your ostracod preservation  are usually formed when there had been a sudden event.   When alive the the organisms are  covered  quickly and preserved.  

 

 

[Archimedes]

In the upper Ordovician of south central Tennessee it is not unusual to find these larger ostracods crowded on the surface of a limestone lens. At one occurrence observed, these large Leperditia ostracods were found crowded, with some brachiopods, on the surface of 2 thin limestones for more than 200 ft, noticed while the highway department was cutting a roadcut.

 

11 hours ago, FossilDAWG said:

Leperditia was a large ostracod that is a common fossil in many Ordovician and Silurian formations in New York and Ontario (and elsewhere too).  At some levels it is almost the only body fossil to be found, especially in some very shallow-water deposits.

 

Don

 

[Bob Clouser]

Thanks to everyone for their comments and input. I had never found ostracods before. I'm sure that's what they are.