Rafinesquina Alternata Versus Ponderosa

[erose]

So I have all of these various references for identifying brachiopods and one of those that keeps coming up a little sketchy is Rafinesquina alternata (Conrad) versus R. ponderosa (Hall).

In my case I am looking at Cincinnatian specimens from Ohio, Indiana and Kentucky and from the bottom to top, Kope to Drakes, formations.

I certainly have some really big ones that I would on size alone ID as ponderosas. But there are many moderately large to medium-sized specimens that are identical but smaller. I also see a wide degree of variation in the amount of convexity, even among specimens from the same local and strata.

Have any of you tried to parse this out? I believe Hall originally named R. ponderosa for NY state specimens but not sure how "regional" it really is.

[squalicorax]

Looking here http://strata.uga.edu/cincy/fauna/articulata/Rafinesquina.html

Reference: Schwimmer and Sandy, 1996

Schwimmer, B.A., and M.R. Sandy, 1996. Phylum Brachiopoda. In R.M. Feldman and M. Hackathorn (eds.), Fossils of Ohio. Ohio Division of Geological Survey Bulletin 70:210-241.

[Wendell Ricketts]

I've also collected extensively in the U. Ord of OH/KY/IN and I just checked my database: I have 45 specimens of Rafinesquina logged. Except in two cases, I've called them all R. alternata, though it might as well be "R. alternata."

Someone will probably correct me, but my sense is that a number of these genera from the Cincinnatian probably need revising and that no one has looked much at them for a while. For my money, the same goes for the whole Hiscobeccus/Lepidocyclus boondoggle and quite a number of the Platystrophia. Ironically enough, these are probably the most collected invertebrate fossils in the United States.

The only problem with the UGA Stratigraphy site is that it pretty much leads you back to the same publications, esp. the 1948 Dalve work, which is what most amateur collectors use, along with Ohio Fossils, for the IDs, or so I'd wager. In other words, not entirely helpful. I remember, as a young collector, staring for hours at the illos in that old Caster and Dalve Elementary Guide to the Fossils and Strata of the Ordovician in the Vicinity of Cincinnati, Ohio (and in the later revision with contributions by John K. Pope, who was a terrifically generous paleontologist at Miami University in Oxford), and in many cases never being able to understand the distinctions they were making.

You've probably also seen the Dry Dredgers site: http://drydredgers.org/thumb_by_articulate.htm#Rafinesquina. A lot of the brachs they identify as ponderosa, I'd call alternata, so obviously YMMV.

There's also the issue of juvenile specimens. Growth series for a lot of the common U. Ord brachiopods didn't seem to exist, at least not a decade or so ago when I was doing a careful re-examination of all my Ordovician specimens. Here again, someone may correct me and more recent work may have been done. In the meantime, though, size alone seems to be an iffy criterion. Who knows whether you're looking at an R. ponderosa that's only a teenager?

Would you be satisfied with something like "R. ?ponderosa" or "R. ponderosa cf. R. alternata"? It's something I've increasingly done over the years for genera (Conus, e.g.) where I'm quite clear no one in my lifetime is ever going to sort them out and, in the absence of a resident invertebrate paleontologist who is also an expert in the specific era or formation I'm wondering about, neither am I.

Best,

W.

[erose]

Thanks Sqaulicorax, I have Fossils of Ohio and it illustrates R. ponderosa. But it doesn't really get into other species. Years ago I compiled my own list of previously named/described Cincinnatian species. It was pretty close to a 1,200 or more species. Of course many of those are known to be synonymous and the number is probably somewhere between 750 - 1,000. But then again new species still are being found in those abundantly fossiliferous rocks. I have accumulated a fairly extensive library of reference material but this is one of the holes.

Wendell you are right on about how it seems like some of the more common fossils are in need of work. The recent placement of all of the North American Platystrophias into Vinlandostrophia was helpful but Zuykov & Harper didn't look at ALL the species. Steve Holland's web site has all of McEwan's species listed and if ever there was a "splitter" she was it. Holland also lists R. alternata as occurring throughout but declines to list stratigraphic info for R. ponderosa leading me to think he considers it out of date as well.

PS: The Cincinnati Museum Center has many of the early journals describing these fossils now online. They can be a bit daunting to wade through but some of the original work is now available.

And yes I do make use of question marks and confers with (cf.) in my catalog. I'm no paleontologist and consider every ID tentative. I have a notes field in my catalog for each specimen and keep track of what diagnostic feature I found or any other unusual detail I noticed. I also have a field called "ID Reference" and I list the books or papers I used to make the ID. Both of those make it easy to take a second look whenever new material shows up, both specimens and references.

I was just hoping someone else may have some further insight on this. You know, two heads are better than one...

[Shamalama]

I always thought that R. ponderosa were the really large specimens and anything smaller than about 1" was an R. alternata. Are they one in the same? I'd say so unless there is some skeletal feture which can be measured to differentiate between the species. I'm a lumper so I'm in favor of reducing the species.

[Wendell Ricketts]

Hello again, Erose. Thanks for the tip; I've now read the Zuykov & Harper paper. Interesting stuff!

You also got me curious and I did a little more digging about Rafinesquina. Nothing dramatic to report, but wondered if you'd seen Alexander's "Phenotypic Lability of the Brachiopod Rafinesquina alternata (Ordovician) and Its Correlation with the Sedimentologic Regime," J. Paleo, 49, No. 4 (Jul., 1975), pp. 607-618. It doesn't shed any specific light on the ponderosa v. alternata problem, but it's an interesting paper. Anyway, you get the main idea from the title: "phenotypic lability."

What they describe are fairly significant differences in "mean length, perimeter-volume ratio, length-height ratio and alation index" in R. alternata on the basis of the individuals' lifestyle (deep vs. shallow, agitated or muddy vs. calm water), currents, sedimentation rates, and other factors. So the suggestion is that environmental factors had a great deal to do with size and morphology in what Alexander calls a remarkably "plastic" genus.

That, in turn, is at least some basis for speculating that the difference between the ponderosas and the alternatas might at least in part be a question not of separate species but of the living animals' response to their environment. That's kind of neat.

Best,

W.

[Herb]

I believe that R.ponderosa and R.alternata are the same, at least according to R.A.Davis "Cincinnati Fossils". R. ponderosa seems to be the newer name.