Saturday, June 27, 2015

Phestia rostellata pelecypod from the Ludlowville formation of New York

On a collecting trip in May I found a specimen of the genus Phestia which I had read about but never found myself. Phestia is a very distinctive shell that looks like a giant comma. One end is rounded while the other sweeps away and narrows nearly to a point. Overall the shell has fine, yet distinct, concentric growth lines as the only decoration. According to Karl Wilson's book "Field Guide to the Devonian Fossil of New York", what I found is called Phestia brevirostra. It looks very similar to Nuculana rostellata (from the Arkona shale) and they could be synonyms or, at the least, close cousins.

I did a little more research into the naming of the species and it appears that Hall originally had a similar form listed as Leda rostellata in "Paleontology of New York", Vol 5, Pt. 1, pg 330, pl 47 and had a Leda brevirostris listed as well (pg 329, pl 47). The difference between the two was that L. rostellata has the elongated valves while L. brevirostris is shorter and less curved. I'm not sure at what point the genus was changed to Phestia as Leda is still valid. To add to the confusion, Conrad created the name Nuculana rostellata in 1841 ( T. A. Conrad. 1841. Fifth annual report on the paleontology of the state of New York. New York Geological Survey, Annual Report 5:25-57) but I can't find a copy of that document which means I'm unable to compare the original descriptions or plates to Hall's from the Paleo. of NY.

To help try and clear up the issue, I posted this specimen and one from Arkona to a couple of Facebook groups. I was fortunate to have Gwen Daley respond in the group "The Devonian Period" and Dan O'Dea respond in the group "The Fossil Forum" both pointing me towards a paper called "Devonian Rocks and Lower and Middle Devonian Pelecypods of Guangxi, China and the Traverse Group of Michigan" and more specifically to Section G - "Systematic Paleontology of the Devonian Pelecypods of Guangxi and Michigan" by John Pojeta Jr., Zhang Renjie , and Yang Zuny. Within that section, on pages 64-65, is a discussion that essentially eliminates the use of Nuculana for Paleozoic pelecypods.

"For many years, Paleozoic opisthogyrate nuculaniform shells with fine external ornament were placed in the genus Nuculana (Link) (=Leda Schumacher)(pl. 3, fig. 10), which they closely resemble in shape (pl. 6; pI. 7, figs. 1-3, 12). McAlester (1962) suggested that the name Nuculana is inappropriate for Paleozoic species; in part, this was because Carboniferous species lack the pallial sinus of living forms. McAlester (1969b, p. N237, N239) limited the name Nuculana to Mesozoic and Cenozoic species and indicated that the name Phestia (Chernyshev) is appropriate for Devonian-Lower Triassic nuculanids that are not yoldiaform."
I've reproduced plate 6 from the paper which illustrates specimens of Phestia rostellata from the Hamilton group of both New York (fig 6-7) and Ontatio (fig 8-10).
In summary, I'm naming the fossil above, which I collected from the Windom shale member of the Moscow Formaiton (Devonian, Givetian stage) in Madison County, New York, and those specimens I've collected from the Arkona shale, and previously called Nuculana rostellata, what I feel is the proper name for both: Phestia rostellata (Conrad 1841) .

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