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.