Uŋčí Makhá Park Revisited, Part 2: Further Fossils

We're now up to the fourth entry in a completely unexpected series on the Platteville–Decorah rocks and fossils of Uŋčí Makhá Park. We've already seen the common fossils from the site, so for this go-round I'm focusing on rarities.

Quick Guide to Fossils at Uŋčí Makhá Park

So I went back to Uŋčí Makhá Park last weekend and spent a couple of hours taking photos of fossils, because it makes such an ideal place to see the upper Platteville fauna. After all, a winter of freezes and thaws may not leave these new exposures looking as nice as they do now. Here's a quick guide to what can be seen there. (Let's see how many photos I can squeeze into one post, and how many species I can misidentify!)

Determining where you are stratigraphically

First of all, I'd just like to reiterate the stratigraphy. Most of the vertical extent is in the Magnolia Member of the Platteville Formation, with the upper part composed of the Carimona Member of the Decorah Shale. I'm thinking more or less the entire extent of the Carimona is exposed, based on thickness; at any rate the next thing up would be the shaly part of the Decorah, and there isn't a trace of it to be seen. I'm suspicious because the difference is just so darn clear, but at this site there is an unmistakable color change between the two units: the Carimona is the upper blue-gray interval and the Magnolia is the light tan-gray interval below. The Deicke K-bentonite is the lower and thicker of the two bentonite gaps in the Carimona. (Note that the Carimona is sometimes supplemented or replaced by landscaping, but this is pretty obvious.) As you walk from south to north, the "floor" goes up stratigraphically, so it's not all one bedding plane but a gently rising series of planes, until by the exit you're close to the color change.

The color change is quite evident here. The Deicke K-bentonite is the cut-in about halfway up the blue-gray Carimona (above the scale bar in the center of the photo).

Here we've gone north, and the floor has risen. The Deicke is still the seam in the middle of the blue-gray rocks.

Rectogloma problematica

What sounds like a kidney disorder, looks kind of like a flattened straight nautiloid possibly with a little curl (or maybe a Devonian Hot Pocket), and remains enigmatic more than a century after its description? It's Rectogloma problematica, which illustrates that even though we're past the Cambrian, the fossil record can still throw some oddballs.

From Van Tuyl and Berckhemer (1914). It's difficult to maintain "natural size" a few generations removed from original illustrations; this is one reason why you should use scale bars instead!

The only reported specimens of Rectogloma problematica were collected by Columbia University students on a field trip to the Delaware Water Gap area. They were found in red shale in the Upper Devonian Catskill Formation in a cut along the Delaware, Lackawanna & Western Railroad near the Henryville station, per Van Tuyl and Berckhemer (1914) ["Henrysville" of their spelling]. The fossils were discovered by Van Tuyl and another student, C. W. Honess, which just goes to show that you should always pay attention on field trips. A couple of the better specimens were collected, and have today made their way into the collections of the American Museum of Natural History (AMNH FI 22377A and B).

The fossils, as illustrated and described by Van Tuyl and Berckhemer (1914) and Conway Morris and Grazhdankin (2005), are a few cm long, roughly rectangular but broader at one end than the other, and have an oval cross-section. They were found oriented vertically, with the wide end pointed up, which as noted by Conway Morris and Grazhdankin (2005) indicates that they are not flattened by compression, but really did have an oval cross-section in life. The broader "sides" are marked with numerous parallel lines 1 to 3 mm apart, each gently arched. Van Tuyl and Berckhemer (1914) described them as "sutures", but they don't go all the way around the fossil. Only one of the two presumed "ends" can be seen in the fossils, so it's not known how the wide end, er, ended. The other end that *can* be seen is also controversial. Van Tuyl and Berckhemer (1914) illustrated a sort of "spit curl" or coil coming off an otherwise rounded termination, but Conway Morris and Grazhdankin (2005) could not confirm this.

Figuring out what Rectogloma problematica is has proven difficult. Van Tuyl and Berckhemer (1914) thought it kind of resembled an abnormal cephalopod, but noted that the incomplete "sutures", lack of a siphuncle, and undivided coil argue against this. (Incidentally, a putative second species, "Rectogloma" zaplensis Turic et al. 1982, did prove to be a nautiloid [Cichowolski 2008].) Knight (1941) noted that it only superficially resembled a gastropod, which is true, but at the same time it's unclear who thought it was a gastropod to start with. Knight instead thought it was more likely a coprolite, which he repeated in 1960 (Knight et al. 1960). While the specimens do indeed appear to be reasonably poop-shaped lumps in basic form, it is rather difficult to produce droppings with smooth sides marked by closely spaced parallel thin features that do not continue all the way around, and a coprolitic identity has been rejected (Häntzschel 1975; Conway Morris and Grazhdankin 2005). Conway Morris and Grazhdankin (2005) did not make any firm classifications; about all they were willing to say was that it may have been "some sort of tube, with a relatively thick wall" of unknown composition. The apparent rarity of Rectogloma fossils and absence of obvious relatives suggest to me that Rectogloma lacked mineralized structures and just lucked out this one time in terms of fossilization. The "sutures" seem more like slits or structural features involved in flexure. Maybe it was some kind of tubular or goblet-like soft-bodied creature, stuck to the sea floor? Or perhaps some kind of fish egg case?

References

Cichowolski, M. 2008. The orthocerid Dawsonoceras? (Nautiloidea) from the Lipeón Formation (Silurian), northwestern Argentina. Ameghiniana 45(4):791–793.

Conway Morris, S., and D. Grazhdankin. 2005. Enigmatic worm-like organisms from the Upper Devonian of New York: an apparent example of Ediacaran-like preservation. Palaeontology 48(2):395–410.

Häntzschel, W. 1975. Treatise on invertebrate paleontology. Part W. Miscellanea. Supplement I. Trace fossils and problematica. Geological Society of America, Boulder, Colorado, and University of Kansas Press, Lawrence, Kansas.

Knight, J. B. 1941. Paleozoic gastropod genotypes. Geological Society of America Special Paper 32.

Knight, J. B., R. L. Batten, E. L. Yochelson, and L. R. Cox. 1960. Supplement. Paleozoic and some Mesozoic caenogastropoda and Opisthobranchia. Pages I310–I331 in R. C. Moore, editor. Treatise on invertebrate paleontology. Part I. Mollusca 1. Geological Society of America, Boulder, Colorado, and University of Kansas Press, Lawrence, Kansas.

Turic, M. A., V. A. Ramos, and J. Oliver Gascón. 1982. "Rectogloma" zaplensis (problemática) de la Formación Lipeón, Provincia de Jujuy, Argentina. Revista del Instituto de Ciencias Geológicas 5.9–14.

Van Tuyl, F. M., and F. Berckhemer. 1914. A problematic fossil from the Catskill Formation. American Journal of Science, 4th series, 38:275–276.

Identifying invertebrate fossils

Pop quiz! (don't worry, it's not for credit)

Romance *and* brachiopods

Here we have an assortment of fossils, tastefully arranged in a holiday-appropriate setting. They're all the typical local Ordovician stuff, but many Paleozoic shallow marine formations will have a lot of the same general things. What are they, and how can you tell?

Enigma of the Day: Rutgersella

Work this week took me to Delaware Water Gap National Recreation Area on the New Jersey–Pennsylvania border, where the Delaware River has taken advantage of geologic weakness to make a shortcut through the Appalachians, and its tributaries descend hundreds of feet in numerous scenic waterfalls.

Like these

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.

One small mystery, and another

Item One: Always pay close attention to your hash slabs

I've recently done some educational events, and I usually bring a few hash slabs. When I'm done, I usually give them a once-over to check for damage incurred from transportation, handling, and so forth (there's a bryozoan that has been breaking on one of the slabs, for one thing). I noticed something unusual on one of the slabs: a small triangular object that on close inspection proved to have interesting surficial markings of fine, gently curved lines running between the long axes of the object. The object is approximately 6.5 mm long by 3 mm wide. What there is of it appears to be either triangular in cross section, or two flaps of material (kind of like a lopsided tent) draped on the matrix. I say this because the tip overlaps a small circular fragment, and because there does not appear to be anything continuing down into the matrix from the two sides that are visible. The lining of the surface does not appear to be segmenting, but looks almost like it defines slightly imbricated sections of the structure. The wide end appears to be open, with the two visible edges slightly overhanging infilling matrix. The edges do not define a flat plane, but curve in slightly where they meet. The sides appear to be flat, making allowance for a slight overall curve and skew to the object. My interpretation is that the structure is a hollow or partially object of triangular cross-section, composed of material that grew in layers from the tip, with the wide end open. The host slab is one of those I collected last spring from the construction pile. It is certainly from the Decorah Shale, and probably came from the lower third or so of the formation, based on geography. Behold (scale bar in mm):

Sponge detective: when faunal lists go bad

I set out to do something simple, really I did. All I wanted to write was an introduction to sponges and a quick description of the forms known from the Twin Cities region. I already had a list of appropriate species, and I knew that most of the original forms weren't actually sponges, which I thought would make things easier. "There's only a couple left, that's not too bad." Then I made the mistake of checking into those leftovers. It turns out that you can never assume a classification for early Paleozoic sponge-like things. There's always room for an argument. In paleontology, the answer to any question always includes "start digging," whether it be rocks or research, and, frankly, isn't some mystery more interesting than a list?