Sunday, July 16, 2017

Follow-up: Pipestone National Monument, Scenella, Cylindrocoelia

Here's a little more information on a few enigmas from previous posts, with some additional photos from the University of Minnesota paleontological collections. First up is Pipestone National Monument's "Lingula calumet", then Scenella, and finally Cylindrocoelia minnesotensis.

Pipestone National Monument: "Lingula calumet"

When we checked in with Winchell's Pipestone "fossils" a couple of years ago, I had only a black-and-white sketch and a crop of a printed black and white version of a photo to illustrate "Lingula calumet". On a recent visit to the University of Minnesota paleontological collections, I took some photos of the Pipestone slabs. I did not see UMPC 5555, the holotype of supposed trilobite "Paradoxoides barberi" (although I did find the box and cards, so it's probably there somewhere), but I did see UMPC 5559, the holotype of "Lingula calumet". Actually, I saw several UMPC 5559; it turned out that UMPC 5559 actually consisted of five slabs (so instead of a holotype, I guess it's a syntype series). Furthermore, UMPC 5664 is also listed as including "Lingula calumet", so there were at least seven blocks from the quarry.
 
One of the UMPC 5559 specimens; helpfully, someone in the past marked out some nice examples of "Lingula calumet".

The marking on the upper left of the circled bleb seems to be a fracture, perhaps from extraction of the block (a different UMPC 5559 block than in the previous photo).

With the photos and personal observation in hand, I can add a few things. The illustrations in Winchell's description are broadly similar to the actual objects, but the wrinkles and concentric markings seem exaggerated. I do see what looks like a single ridge around a side of some of the objects, like they were non-rigid things that have been deformed by being pushed in one direction. The objects generally have more or less featureless surfaces. They look like circular, slightly convex pebbles a few mm across. I did not see much in the way of the white "scale" that Winchell mentioned, except perhaps for a sort of chalky residue in one patch of one of the 5559 specimens. This feature is certainly not prevalent, and I cannot rule out that, for example, it is not a remnant of a later deposition of calcium carbonate along a fracture plane. The "scale" does not closely resemble remnants of actual brachiopod shell as seen in Cambrian examples.

A tight crop on a few well-defined blebs with Winchell's white "scale".

What do I think now? Well, I didn't know much about Precambrian life in October 2015 and I haven't improved much since then. Winchell's identification as brachiopods isn't particularly appealing; there are no obvious consistent surficial features to link them to brachiopods, and there's no shell material. As before, they could be anything from little sediment clasts to some kind of unknown organic structure.

Scenella

I have photos of two species assigned to the mysterious Scenella. First, the holotype of Scenella radialis, along with the original illustration to show that they are in fact the same specimen:

UMPC 5535, in the 1890s (Ulrich and Scofield 1897) and the 2010s; the little black bar in the lower right is 1 cm.

Taking into account some differences due to perspective and angle of shot, the illustration and the photo are a pretty good match in terms of the crenulations of the margin. There is, however, one notable difference: 1890s S. radialis has well-defined radial markings, making it look something like a fancy cookie. 2010s S. radialis is quite smooth. Here it is from the side:

In which it still looks quite smooth.

I don't remember seeing any radial features in person, but then again I wasn't looking for them, either. Presumably there should be radial features somewhere, if only because its species name is radialis. The specimen was described as an internal cast in the plate caption. Ulrich and Scofield (1897), who described the species, made the comment that there are five to six lines per 5 mm, and the lines show through the outer shell. How they came to that conclusion is unclear, given they said they had an internal cast and no other specimens are mentioned. Yochelson (1984) includes a photo of a cast of this specimen in the Smithsonian collections, which someone has clearly modified to "improve" the radial markings (which Yochelson also noted). Confusingly, in 1994 Yochelson reported that "the Minnesota specimen of Scenella superba (Billings) figured by Ulrich and Schofield was restored to a large extent with plaster—on which radia lirae were impressed!" Was adding radial markings some kind of inexplicable policy, or did Yochelson conflate the obviously doctored S. radialis cast with S. superba?

Coincidentally, the other species I can present is S. superba. This is not the holotype, nor Ulrich and Scofield's specimen, but a specimen from the Decorah Shale of West St. Paul. I'll let you judge for yourselves how superb it is:

How's that?

Much more ovoid than S. radialis, too.

Frankly, the size is striking. Whatever these scenellids were, they were clearly pretty darn hefty by the standards of the Platteville and Decorah. They seem all out of proportion to the rest of the fauna, like they should really be more like a centimeter across. Yes, I know about the big nautiloids, and the foot-long trilobites, and there were some big snails, I suppose; they weren't super common, either. In a world of cm-scale brachiopods and palm-sized bryozoan colonies and horn corals smaller than fingers, here are these enormous mystery cones doing who-knows-what (probably very slowly, too).

Since we're on the subject of scenellids, I ought to add a few things on taxonomy and relationships. As we saw in the original post, Stauffer and Thiel (1941) reported eight species and one subspecies of Scenella from the Platteville through the Prosser: Scenella affinis, S. a. obsoleta, S. beloitensis, S. compressa, S. magnifica, S. montrealensis, S. obtusa, S. radialis, and S. superba. Since then, authors have been working to restrict Scenella to the Cambrian. Wilson (1951) moved several of the species to the new genus Macroscenella, including S. beloitensis, S. magnifica, S. obtusa, S. radialis, and S. superba, with S. superba as type species (and incidentally, comparison of the UMPC specimen to Wilson's figure of the type of S. superba shows that the Minnesota specimen is either squashed from a naturally circular shape or the species was highly variable). Aside from Wilson (1951), Yochelson (1984) seems to be the only publication to have done much with the Minnesota species assigned to Scenella. Most are based on external molds or internal casts (steinkerns) and are not all that distinctive. Yochelson considered S. affinis, S. affinis obsoleta, and S. compressa as beyond help; was noncommittal on S. beloitensis, S. obtusa, and S. radialis but didn't include them in Macroscenella because the three species had much lower profiles; suggested that S. montrealensis was a small Macroscenella; and was comfortable leaving S. magnifica and S. superba in Macroscenella. Later, Yochelson (1994) returned S. montrealensis to Scenella, so if it is indeed present in the Platteville of Minnesota, both Macroscenella and Scenella would be known from the state.

Knight and Yochelson (1960) and Wahlman (1992) classified Macroscenella in the Monoplacophora, and Sloan and Webers (1987) threw "Scenella" compressa and obtusa that way, too. Yochelson (1984) proposed that Macroscenella was actually a float for a jellyfish-like animal, but walked that back ten years later, suggesting that it was a patellacean gastropod (a limpet, basically) with a thin shell possibly susceptible to deformation without breaking (Yochelson 1994). He could not rule out the float hypothesis, though, or even inarticulate brachiopods (which I know from personal experience can look like just about anything). However, this did not include beloitensis, obtusa, and radialis. In 1984, he suggested that these three species were also impressions of jellyfish-like animals, and did not mention them in 1994, presumably because he did not consider them Macroscenella. They're still out there, I guess.

Cylindrocoelia minnesotensis

Finally, there's our old friend from the sponge post, Cylindrocoelia minnesotensis. The type material (actually a group of specimens) is in the Smithsonian collections, and I haven't seen it, but I did run across a specimen labeled as such in the University of Minnesota collections:

Behold, Cylindrocoelia minnesotensis, in all its glory.

This is UMPC 7709, from the "Galena Shale, base". This translates as the Decorah Shale, and the little orangey sesame-seed things are brassy ooids (brassy ooids being tiny ironstone concretions that show up at discrete horizons in the Decorah). Although it is not the type, I am making the assumption that it looks enough like the actual thing for someone to classify it as C. minnesotensis. If you look at this and think "burrow", I'm not going to say you're wrong—it certainly looks like one to me! Quite how anyone got "sponge" is not obvious. On the other hand, the nautiloid siphuncle thing Sardeson put forward is kind of an odd choice, too, although it's not impossible that multiple kinds of cylindrical things ended up identified as C. minnesotensis over the years.

Literature cited


Knight, J. B., and E. L. Yochelson. 1960. Monoplacophora. Pages I77–I84 in R. C. Moore, editor. Treatise on invertebrate paleontology, volume I. Mollusca 1. Geological Society of America and University of Kansas Press, Lawrence, Kansas.

Sloan, R. E., and G. F. Webers. 1987. Stratigraphic ranges of Middle and Late Ordovician Gastropoda and Monoplacophora of Minnesota. Pages 183–186 in R. E. Sloan, editor. Middle and Late Ordovician lithostratigraphy and biostratigraphy of the Upper Mississippi Valley. Minnesota Geological Survey, St. Paul, Minnesota. Report of Investigations 35.

Stauffer, C. R., and G. A. Thiel. 1941. The Paleozoic and related rocks of southeastern Minnesota. Minnesota Geological Survey, St. Paul, Minnesota. Bulletin 29.

Ulrich, E. O., and W. H. Scofield. 1897. The Lower Silurian Gastropoda of Minnesota. Pages 813–1081 in Ulrich, E., W. Scofield, J. Clarke, and N. H. Winchell. The geology of Minnesota. Minnesota Geological and Natural History Survey, Final Report 3(2). Johnson, Smith & Harrison, state printers, Minneapolis, Minnesota.

Wahlman, G. P. 1992. Middle and Upper Ordovician symmetrical univalved mollusks (Monoplacophora and Bellerophontina) of the Cincinnati Arch region. U.S. Geological Survey, Reston, Virginia. Professional Paper 1066-O.

Wilson, A. E. 1951. Gastropoda and Conularida of the Ottawa Formation of the Ottawa - St. Lawrence Lowland. Geological Survey of Canada, Ottawa, Canada. Bulletin 17.

Yochelson, E. L. 1984. North American Middle Ordovician Scenella and Macroscenella as possible chondrophorine coelenterates. Palaeontographica Americana 54:148–153.

Yochelson, E. L. 1994. Macroscenella (Mollusca) from the Middle Ordovician of Wisconsin: a reinterpretation and reassignment. Journal of Paleontology 68(6):1252–1256.

No comments:

Post a Comment