Sunday, February 24, 2019

The many moods of Rauffella

Earlier in February, I attended a Geological Society of Minnesota fossil lab hosted by Jeff Thole and Macalester College. At some point someone brought out a fossil that they weren't familiar with; it looked a lot like the final photo in this post, a light-colored object that resembled loops of cord. What this person had was one of the most characteristic but least scientifically appreciated fossils of the Decorah Shale: the trace fossil Rauffella (specifically R. palmipes, as we'll get to later).

Rauffella has never attracted much attention in the literature, being one of these things people somehow come to know about through osmosis but never feel compelled to discuss scientifically. If you're following the literature, there are really only four substantial publications: Ulrich's original description (Ulrich 1889) of the genus and two species, as sponges (in fact, the name refers to a contemporary sponge paleontologist named Rauff, which is kind of inconvenient as later noted by Sardeson, and also confirms that there are supposed to be two "f"s); Winchell and Schuchert (1895), which has little in the way of new information (reprinting Ulrich's original descriptions) outside of some additional provenance information, but does include new illustrations; Sardeson (1925), the most useful but most difficult to obtain of the lot; and Weiss (1954), confirming Sardeson's worm burrow hypothesis. Sardeson's odd idea about the "fucoid" Camarocladia being stuffed seaweed holdfasts notwithstanding, Sardeson (1925) is quite useful on the topic of Rauffella, and will not leave the reader chasing phantom sponge spicules.

Sardeson seems to have been the first to realize that Rauffella was not a sponge, but a burrow, with surficial markings representing not spicules but marks produced by some feature of the burrower's body (bioglyphs). He suggested worm jaws, and there are indeed worm jaw fossils known from the Decorah, so production by worms seems like a good fit. He did not observe the wall features or spicules reported by Ulrich, although he did observe some potential fecal pellets and a sort of "shaley coating" to the burrows, which he attributed to the limey content of the food and possibly to microbial activity after the burrow was vacated. He reported finding Rauffella "from the top of the sandstone below through the Platteville limestone, and the Decorah shales to the Galena formation". I've only ever seen them in the Decorah, almost invariably as partial specimens eroded out of the shaly beds, but he had a lot more time and material, as evidenced by his remark of examining thousands in the field and several hundred apparently in his collections.

Four ichnospecies have been attributed to Rauffella over the years, although we can dispose of one quickly and another is reportedly very rare:

  • R. filosa Ulrich 1889
  • R.? fucoida Sardeson 1896 (from the St. Peter Sandstone of Fountain, Minnesota)
  • R. palmipes Ulrich 1889
  • R. ulrichana Sardeson 1925

Part of Plate F to Winchell and Schuchert (1895), 16 being R. filosa (somebody making the plates neglected to skooch it over from the edge), 17 and 18 being details of its surface, 19 being R. palmipes, and 20 being details of its surface.

Recycled from the sponge post: Sardeson (1896)'s Rauffella? fucoida.

Also recycled from the sponge post: Sardeson (1925); 1 and 2 are Camarocladia rugosa (I assume from the text, given there is no formal explanation of the plate), 3 is sponge Hindia parva, 4 is Rauffella filosa, 5 and 6 are Rauffella ulrichana, 7 is Rauffella palmipes, and 8 is the true algae Chaetocladus sardesoni.

R.? fucoida is the only non-Decorah species, coming from the St. Peter Sandstone of Fountain, Minnesota. It was described as a branching form also similar to an undescribed species (Camarocladia rugosa, as reported in Sardeson 1925) associated with Licrophycus (=Phycodes). Morphologically, it's fairly different from Rauffella as described by Ulrich. Ulrich, who we already have seen as Sardeson's rival, was not quite so kind in his analysis (Ulrich 1896): "...[W]e do not see why his species fucoida should be referred, even doubtfully, to Rauffella, nor where he gets his information that R. filosa, like his species, 'branched at regular intervals.' The writer has seen over a hundred specimens of R. filosa and not one showing any evidence of branching." Sardeson himself (1925) later concurred that R.? fucoida was not true Rauffella, but was instead basically the same as Camarocladia rugosa from the Decorah, and that both were algal root systems filled in by worms. Two out of three isn't bad. (Following Sardeson's suggestion, we could call this species Camarocladia fucoida, but there hasn't been much of a call for it.)

I don't happen to have a Rauffella? fucoida on me, but this seems to be basically the same thing he illustrated back in 1896, or, for that matter, a branched Camarocladia.

At the same time, Sardeson recognized true Rauffella as worm burrows, with a simple straight or curved form featuring a well-developed "fibrous" or "webbed" surficial texture (R. filosa), a much rarer form with pouching or diverticula, and coarser surface markings (his new R. ulrichana), and a sort of knotted looping burrow bundle (R. palmipes). R. palmipes is definitely the most remarkable, especially with a relatively complete example (see below, or the plates above). Ulrich (1889), under his "sponge" conception, thought that R. palmipes was oriented with the "stem" in the mud and the lobes and loops up in the water column. As a burrow, it's the other way around. The burrow system includes places where the burrower went back over an existing loop, or created new loops (Sardeson 1925). In hindsight, it seems kind of odd to include two such different forms as R. filosa and R. palmipes in the same ichnogenus; R. filosa is just a linear burrow, while R. palmipes is kind of like a Phycodes or Arthrophycus that loops back on itself, even having similar "ribbing" to some Arthrophycus. It might just be taxonomic inertia.

In my experience, R. filosa tends to be found as slightly flattened cylindrical chunks on the order of 1 to 5 cm long (or up to a couple of inches), the cross-section comparable in size to an adult fossil hunter's finger.

Here's a couple of views of a large piece, showing "fibrous" surface texture.

R. palmipes is usually only found as a couple of loops broken from the main structure, but sometimes you get lucky. As Ulrich and Sardeson observed, it doesn't have pronounced "fibrous" surface texture. However, it does have a sort of "ribbed" appearance. The burrower also appears to have been smaller, based on the cross-section.

Typical chunks of R. palmipes: a couple of partial loops with "ribbed" texture (more apparent in the right example than the left, where it is best visible along the curve).

Two views of a much more complete specimen of R. palmipes, showing the overall configuration of loops connecting to a central "stem", as well as the "ribbed" texture (best seen in the long lower loop in the left photo).

I don't stress about identifying Decorah fossils to genus or species, because in many cases the defining characteristics are only apparent under thin section or on the insides of shells (or on the outsides of things that are usually preserved as internal molds), plus most of the names haven't been evaluated for more than 120 years, but there are a few exceptions. If you find yourself in the odd situation where you need to drop a few scientific names for Decorah fossils, here are some of the easier common taxa:

You won't *always* be correct, but you will usually. (Please don't ask for pronunciation help; I invariably put the stress on the wrong syllable.)


Sardeson, F. W. 1896. The Saint Peter Sandstone. Bulletin of the Minnesota Academy of Natural Sciences 4(1):64–88.

Sardeson, F. W. 1914. Characteristics of a corrosion conglomerate. Bulletin of the Geological Society of America 25:265–276.

Sardeson, F. W. 1925. Ordovicic kelp, sponges and sea worms in Minnesota. Pan-American Geologist 43(4):271–286.

Ulrich, E. O. 1889. Preliminary description of new Lower Silurian sponges. The American Geologist 3:233–248.

Ulrich, E. O. 1896. [Review of] The St. Peter Sandstone. The American Geologist 17:390–391.

Weiss, M. P. 1954. Notes on some Middle Ordovician fossils from Minnesota. Journal of Paleontology 28(4):427–429.

Winchell, N. H., and C. Schuchert. 1895. Sponges, graptolites, and corals from the Lower Silurian in Minnesota. Pages 55–95 in L. Lesquereux, C. Schuchert, A. Woodward, E. Ulrich, B. Thomas, and N. H. Winchell. The geology of Minnesota. Minnesota Geological and Natural History Survey, Final Report 3(1). Johnson, Smith & Harrison, state printers, Minneapolis, Minnesota.

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