Sunday, April 29, 2018

Tracking sloths and people at White Sands National Monument

Earlier this week came some of the biggest news concerning National Park Service paleontology in quite some time: the discovery of tracks, including overlapping tracks, of extinct ground sloths and humans at White Sands National Monument, New Mexico. These finds were published in an article by Bustos et al. (2018), which can be accessed here (don't forget the supplement; less technical summary here). It's a pretty darn substantial way of showing humans and extinct sloths as contemporaries, and new evidence on the early history of humans in the Americas and the twilight of the Pleistocene megafauna. About the only ways you could make the tracks more notable would be to have them continue into the end of a hunt, or to have some dateable material that placed them significantly pre-Clovis.

Part of Figure 2 from Bustos et al. (2018). Part B has some faint sloth tracks (when poorly preserved, it can be difficult to distinguish similarly sized human and sloth tracks). Part C shows a "flailing circle" where a sloth appears to have swung its arms at a human. Part E shows a human track inside a much larger sloth track.

Sunday, April 22, 2018

Foerstediscus splendens, a Minnesotan in Washington

Because I was in northern Virginia, I thought I'd visit the National Museum of Natural History. While nosing around the Ocean Hall, I ran into another Minnesotan: the holotype specimen of the edrioasteroid Foerstediscus splendens (Bassler 1936). I couldn't get right up to due to the glass, so the photos aren't the clearest and there's no scale, but it's still a fine specimen, and somewhat larger than I expected following my experience with the minuscule Pyrgocystis (for reference, it's described as 3 cm across, a little more than an inch).

Points to you if you too noted "Middle Ordovician"; with redefinition and redating of the Ordovician, "Late Ordovician" would be more accurate.

Here's a closer view of the specimen. "S. 4079" is the Smithsonian's number; it was originally a University of Minnesota specimen, UMPC 4742a, but it was donated to the Smithsonian (Rice 1990). From my own experience with the UMPC fossils, I think all of the edrioasteroids they had on hand by approximately the mid-1930s went to the Smithsonian at Bassler's request, with the specimens I photographed coming with Sardeson's collections a few years later.

"Edrioasteroid" means "seated star", which is reasonably self-explanatory.

Edrioasteroids are among the rarest fossils from the Decorah and Platteville formations of Minnesota, with their other competition in that category being other echinoderms such as sea stars and cystoids. Seeing as how these fossils are very rare here except in certain places such as the former Johnson Street Quarry, the obvious scenario is that non-crinoid echinoderms only thrived under certain conditions that are poorly represented in the known outcrops of the Platteville and Decorah. (Alternatively, they *were* more common than we know, but they decomposed so completely to their constituent plates that they've been unrecognizable; be that as it may, though, the Platteville/Decorah echinoderm diversity doesn't seem to be as high as in other formations of similar age in the central US.)

Foerstediscus splendens was collected from the Ford Plant (Bassler 1936). Work on the Ford Plant, Ford Bridge, and Ford Dam (Lock and Dam No. 1) in the 1920s made that area a great place for collecting, as discussed in this post. Clinton R. Stauffer named 56 species of microfossils from collections at the bridge (Stauffer 1933, 1935), and August Foerste named the nautiloid Metaspyroceras perlineatum (Foerste 1932) from the vicinity of the plant and dam. F. splendens was found by Irving G. Reimana from the top of the Rhinidictya bed of the Decorah Shale (Bassler 1936), otherwise known as Bed 4 (Sloan 1987), or, a little more informally, the lower third of the Decorah Shale above the Carimona Member. (One of these days I ought to outline the bed divisions.) In more practical terms, Bed 4 is the Decorah you see at Shadow Falls, so the top of Bed 4 would be somewhere at or a little higher than the highest part of the ravine. Strangely, Stauffer and Thiel (1941) attributed Foerstediscus to the underlying Carimona Member, or Bed 3, despite Stauffer presumably being the one who gave Bassler the stratigraphic information in the first place.

Looking east from Minnehaha Park in June 2013, toward the defunct Ford Plant (across Lock and Dam No. 1, aka the Ford Dam).

The closure and dismantling of the Ford Plant over the past few years provide an unusual opportunity to look at current events in a geological frame of mind. The Ford Plant was a fixture of southwestern St. Paul for decades (and it happened to be there because there was a young river gorge carved by a post-glacial waterfall that could be harnessed for hydroelectric power, and because there was once a pure sandy beach that could be turned into auto glass). Its day is now over, though, and soon its former grounds will be rebuilt into something entirely different. Ten thousand years ago, mammoths and giant beavers roamed its grounds. Seventy million years ago it was probably a coastal plain near a sea filled with ammonites and marine reptiles. 454 million years ago edrioasteroids, nautiloids, and other marine invertebrates lived and died in a shallow tropical sea that had submerged the pure sandy beach. Underneath all of it are volcanic rocks more than a billion years old that fill a scar from Michigan to Kansas. Every part of history is made up of what came before it, and shapes what comes after it.


Bassler, R. S. 1936. New species of American Edrioasteroidea. Smithsonian Miscellaneous Collections 95(6).

Foerste, A. F. 1932. Black River and other cephalopods from Minnesota, Wisconsin, Michigan and Ontario (Part 1). Denison University Scientific Laboratories Journal 27:47–137.

Rice, W. F. 1990. Catalog of paleontological type specimens in the Geological Museum, University of Minnesota. Minnesota Geological Survey, St. Paul, Minnesota. Information Circular 33.

Sloan, R. E. 1987. History of study of the Middle and Late Ordovician rocks of the Upper Mississippi Valley. Pages 3–6 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. 1933. Middle Ordovician Polychaeta from Minnesota. Geological Society of America Bulletin 44(6):1173–1218.

Stauffer, C. R. 1935. The conodont fauna of the Decorah Shale (Ordovician). Journal of Paleontology 9(7):596–620.

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

Sunday, April 8, 2018

Phycodes: bundles of burrows

I'm going out of the office again, so, like last year, I'm tossing up a few pictures of something I find interesting, in this case an invertebrate trace fossil called Phycodes (not to be confused with Phycodes the moth). I touched on Phycodes briefly a few years ago, using the image included below:

That pale gray color is characteristic of the Brickyard in Lilydale, for whatever reason(s).

The whole piece looks like this:

"Licrophycus ottawaensis" in older literature.

I collected it on a Geological Society of Minnesota visit back in 2006 and it has since become one of the pieces I like to take to events because it's a great teaching fossil. I ask people what it is and let them explain their choice if they want to, and then I identify it. I get a lot of plant-based guesses (which of course is what a lot of paleontologists and geologists thought this kind of structure was decades ago). What Phycodes really is is an invertebrate trace fossil recording the behavior of some kind of wormy animal probing in the mud for food and returning to a central point. This resulted in splayed bundles of burrows, giving the trace fossil a characteristic root-like or mop-like appearance. It doesn't have quite the oomph of a dinosaur bone, but it looks interesting, it's good for conversation, and worms are more familiar than, say, crinoids.

When space is an issue, I have a more compact specimen.

Phycodes turns up every so often in the Decorah. It's not as common as Rauffella (which has turned up in a half-dozen posts so far), but it certainly makes a striking fossil.

Suitable for framing: this chunk is almost entirely Phycodes, with little matrix, which also makes it more fragile than the first two specimens (too bad, because it's also the best). The individual tubes are a bit smaller in diameter than those of the first two as well.

The makers of Decorah Phycodes differed from the makers of Rauffella in a couple of notable ways: Phycodes-makers were smaller (a few mm in diameter versus finger thickness for many Rauffella) and apparently smoother (no surficial striations in Phycodes).

This piece is one of the group from the construction site last year. I'm not certain what kind of ichnofossil it is. It resembles Phycodes templus, but it's also kind of poorly preserved and it's not clear if the burrows are bundled, so it might not be Phycodes at all. (Another possibility is poorly preserved "Camarocladia".) Note the brassy ooids.