Pedicle valve
Anterior
Brachial valve
Posterior
Profile
The Keyser formation spans the boundary between the Silurian and Devonian (Pridoli to Lochkovian stage) and thus it is hard to date exactly when a fossil came from. Based on the stratigraphic location of the beds I was searching being closer to the underlying Tolonoway formation (Silurian, Pridoli stage) than the overlying Old Port formation (Devonian, Lochkovian stage), I am betting this fossil came from the very latest Silurian.
Hi Dave,
ReplyDeleteAfter viewing your fossil, I went to an old book titled "The Devonian of Pennsylvania" by Willard 1939. In Plate 1 Keyser Fossils: Willard shows brachiopods that look like yours. They come from the Lower to Middle Keyers: Selinsgrove Junction, Northumberland Co.; Mount Union, Mifflin Co.; and Mexico, Juniata Co. His ID was Spirifer modestus and Spirifer modestus var. plicatus.
That is a good point. I have a copy of that book and I see what you mean. It's been my impression that the genus "Spirifer" was once used as a catch all and it's slowly been parsed into new names. There have not been many studies of the Keyser fauna that I can find (and much of what is out there debates the what era the deposit is from) so I've been equating the fossils I find to known examples. While it may be proper to call the fossil in this post Spirifer modestus based Willards book, I'm not convinced it is a separate genera from Eospirifer as they both look very similar.
ReplyDeleteHi Dave - Sounds like you have a very good Devonian library. Check out "Devonian Paleontology of New York" Linsley (recent publication). In Plate 44 (Lower Devonian Brachiopods) your fossil is shown in pictures 47 to 51 and is given the name "Spirinella modesta" - most likely Willards "Spirifer modestus". These brachs look identical to your fossil. I enjoy your blog. Regards - Jack Kesling
ReplyDeleteAnother good point, Jack, and thank you for suggesting it. I only have a .pdf version of that book as it's out of print and exceedingly hard to find a copy of for a reasonable price. I checked the plate and figures you reference and I have to disagree again. If you look at the width of the shell in figures 47-49 you'll notice that it's much narrower than the shell I illustrate in this post. It looks more akin to an Ambocoelia, Emanuella or Crurispina in my opinion. I checked my copy of the "Devonian Plates" from the Maryland Geological survey (plate LXVIII, fig 17-22) and those figures look very similar to those from the "Devonian Paleontology of New York". In the "Devonian Plates" they are referred to as Spirifer modestus, Hall. "Devonian Plates" was printed in 1913 and "Devonian Paleontology of NY was printed in 1994 and, according to Linsley, borrowed much of the content for the plates from James Hall's original 1847 "Paleontology of NY" or from "Museum Memoirs" by John Clarke. I can't track down whether the Maryland plates are originals or after Hall or Clarke's original drawings but there has been quite a bit or borrowing from previous works to help illustrate the fossils.
ReplyDeleteI appreciate your opinion and your help in trying to ferret out the ID for this shell. - Dave
Jack, You might be onto something... I juct checked my copy of "Brachiopoda of the Keyser Limestone (Silurian-Devonian) of Maryland and Adjacent Areas" by Zeddie Paul Bowen (GSA Memoir 102, 1967) and in it he illustrates a specimen that he calls Howellella modesta. It's shown on plate 6, fig. 21-28 and described on page 47. In the description he lists several species that he is essentially "renaming" such as: Spirifer modesta (Hall 1857), Spirifer modestus (Hall 1859, Maynard 1913, Schwartz 1929, 1939) and Spirifer modestus var. plicatus (Maynard 1913, Schwartz 1929, 1939). I'd not looked at this reference too closely before making this post as the plates do not display the best quality specimens nor do they cover all genera that I have encountered.
ReplyDeleteAnother interesting report I just found on Google "Upper Silurian Brachiopods from Southeastern Alaska" by Edwin Kirk and Thomas Amsden, 1952 USGS, illustrates Howellella specimens (plate 10) and another species called Alaskospira dunbari (plate 7). The authors refer to Spirifer modestus while describing Alaskospira dunbari.
I'm still stumped and more confused now. I'm more convinced that the specimen in my post is not Eospirifer but less sure about what to call it. All this research is good though as it gives me new ideas to think about. I'll likely put a post together from all this with links to the references and scans of the relevant pages. - Dave
Dave, I've looked at two more of my Devonian reference books The first "Pennsylvania Geological Survey 1892" Vol 2 Upper Silurian and Devonian, page 1012. Plate No. VI Lower Helderberg LM shows "Spirifera modesta" - poor photo /drawing, but it looks close to your brachiopod. I also looked at "West Virginia Geological Survey Vol XV Devonian System of West Virginia" This reference has a great fauna reference check list on page 164 which outlines all the fossils coming out of the Keyser LM formation. Although no pictures, they have "Reticularia modesta" and cross reference it as the same as "Spirifer modestus" (it is indicated as a common Keyser brachiopod). In all my references, the only "Eospirifer" brachiopod coming out of the Keyser is "Eospirifer macropleura". I have found this "Eospirifer" in Perry Co. in Keyser LM. They are small in size and do not look like your photo. I really look forward to your further posts on this brachiopod. Jack Kesling
ReplyDeleteJack - You should e-mail me so we can discuss this more: dhayward74(at)gmail.com <-- replace the (at) with @
ReplyDelete