World of Stone

This is part of Devil's Parlor in the Minnesota side of Interstate Park, on the St. Croix River. I was at the park on Saturday for a park geology program, and following work I wandered through the Glacial Gardens section. Interstate Park, as its name suggests, has units in two states, in this case Minnesota and Wisconsin. The two parts are state parks, associated with but not part of St. Croix National Scenic Riverway (the Wisconsin side is also the western trailhead for the Ice Age National Scenic Trail, as well as one of the nine parts of the Ice Age National Scientific Reserve). Interstate Park is known for its glacial landforms, imprinted primarily on Precambrian bedrock.

Crinoids

For the fossil enthusiast in Minnesota, there are few groups with a bigger gap between "what they show in the books" and "what you actually find" than crinoids. The ideal of a crinoid fossil is a long segmented stem or stalk connected to a cup-like structure crowned by a group of delicate feathery arms. The Digital Atlas of Ordovician Life and the UGA Stratigraphy Lab's pages on Cincinnatian fossils have many images of these ideal crinoid fossils, if you're feeling like living vicariously. The reality in Minnesota is a bit more like this:

Of course, they are not always found loose, but you get the idea.

Welcome Waco Mammoth National Monument

July 10, 2015 saw the addition of a new National Park Service unit, Waco Mammoth National Monument. It's the second recent NPS unit to be established for Pleistocene fossils, after Tule Springs Fossil Beds National Monument, and has been a long time germinating. I'll probably have a more detailed post within a few weeks, but here's a quick introduction. 

The noble ostracode

One of the most diverse fossil groups in the Paleozoic rocks of Minnesota is also one of the least familiar to the layperson. This group is the Ostracoda, or "seed shrimp", a class of crustaceans that is still thriving. They owe their lack of familiarity to their diminutive size; they aren't called seed shrimp for nothing. Although found practically anywhere you can rub a couple of water molecules together, they are often more or less invisible to humans because most of them are on the order of 1 mm long. They owe their abundance in the fossil record to their durable shells, being equipped with a pair of valves not unlike a clam. Inside the valves is the tiny crustacean itself, with several pairs of appendages and distinct internal organs. With around 8,000 living species, there's a lot of diversity to go around. Ostracodes (also spelled ostracods) inhabit marine, freshwater, and moist terrestrial settings, are free-swimming or bottom dwellers, and include predators, herbivores, and detritivores. Definite ostracodes appeared during the Ordovician; there are some suspiciously ostracode-like creatures in the Cambrian, such as bradoriids, but they are not currently considered ostracodes. Fossil ostracodes are of particular interest for paleoenvironmental studies (depth, temperature, salinity, etc.) and biostratigraphy. There is one slight drawback to appreciating them as fossils, though: their size. Without a good microscope and the equipment to extract ostracodes, their charms will necessarily be vicarious for most people. Nothing against microfossils (I personally have a fondness for forams, because one of my first projects involved them), but those are just the practical breaks. There is, however, one exception in the rocks of the Twin Cities, a giant among ostracodes, the form commonly known as Eoleperditia fabulites or Leperditia fabulites. This species tops out around a centimeter long and resembles a bean. It can be both common and recognizable in the Platteville Formation.

This is the fabled giant ostracode Eoleperditia (or Leperditia) fabulites, from the University of Minnesota collections.

And here are examples in the wild, in the Platteville Formation (probably Mifflin Member).

Stauffer and Thiel (1941) have their usual list, featuring several dozen species, but it probably won't do much for you unless you have the requisite facilities or are just really good at spotting sesame-seed-sized fossils. Also, there are many publications specifically dedicated to the ostracodes of the Platteville and Decorah, and they're going to be more useful than an uncited faunal list. If you want the true Minnesota Ordovician ostracode experience, a selection of citations includes Ulrich (1890, 1892, 1897), Kay (1934, 1940), Hansen (1951), Cornell (1956), Swain et al. (1961), Swain (1987), Swain and Cornell (1987), and Johnson et al. (1991).

References cited:

Cornell, J. R. 1956. The Ostracoda zones of the Decorah Shale. Thesis. University of Minnesota, Minneapolis, Minnesota.

Hansen, D. L. 1951. Distribution of Ostracoda in the Decorah Shale Formation at St. Paul, Minnesota. Thesis. University of Minnesota, Minneapolis, Minnesota.

Johnson, J. D., L. V. Benolkin, and F. M. Swain. 1991. Ostracoda from the Glenwood Shale (Ordovician-middle Caradocian) of Minnesota. Revista Espanola de Micropaleontologia 23(2):141–152.

Kay, G. M. 1934. Mohawkian Ostracoda: species common to Trenton faunules from the Hull and Decorah Formations. Journal of Paleontology 8(3):328-343.

Kay, G. M. 1940. Ordovician Mohawkian Ostracoda: lower Trenton Decorah fauna. Journal of Paleontology 14(3):234-269.

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

Swain, F. M. 1987. Middle and Upper Ordovician Ostracoda of Minnesota and Iowa. Pages 99–101 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.

Swain, F. M., and J. R. Cornell. 1987. Ostracoda of the superfamilies Drepanellacea, Hollinacea, Leperditellacea, and Healdiacea from the Decorah Shale of Minnesota. Pages 102–130 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.

Swain, F. M., J. R. Cornell, and D. L. Hansen. 1961. Ostracoda of the families Aparchitidae, Aechminidae, Leperditellidae, Drepanellidae, Eurychilinidae and Punctaparchitidae from the Decorah Shale of Minnesota. Journal of Paleontology 35(2):345–372.

Ulrich, E. O. 1890. New and little known American Paleozoic Ostracoda. Journal of the Cincinnati Society of Natural History 13(3):104–137.

Ulrich, E. O. 1892. New Lower Silurian Ostracoda, no. 1. The American Geologist 10(5):263–270.

Ulrich, E. O. 1897. The Lower Silurian Ostracoda of Minnesota. Pages 629–693 in E. Ulrich, 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.

Quaternary paleontology at Channel Islands NP and Mammoth Cave NP

Here's a couple of quick entries on paleontological research going on in the National Parks. In this case, both examples are Quaternary. It's another case of serendipity: I was looking for the first article, and found the second article in the same volume. Neither Channel Islands National Park or Mammoth Cave National Park are slouches paleontologically, but they do get overshadowed. Places like Big Bend National Park, John Day Fossil Beds National Park, and Petrified Forest National Park get a paper or two every year, so it's nice to shine a light on some of the others.

Trilobites

To start it off, this being Father's Day as I write, I shamelessly link to my father's Flickr photostream.  He's got photos of landscapes and landmarks of places in Hawaii, Arizona, Utah, Washington D.C., South Dakota, Virginia, Idaho, Alaska, and Minnesota. I recommend the eagles on Grey Cloud Island.

Where were we? Yes, the majestic trilobite, the three-lobed former denizen of the deep, the oval with antennae, bearer of the first compound eye, shameless vandal of pristine Paleozoic sediment. Trilobites are one of the most famous types of extinct organism, perhaps not on par with certain vertebrates, but certainly the most renowned fossil invertebrates. (In second place, with plenty of daylight intervening, are ammonites. In last place, maybe edrioblastoids? Some kind of echinoderm, probably.) You can find online information on practically any aspect of trilobites you may want to know about, often lovingly illustrated with photos. You'll probably end up at Trilobite.info sooner rather than later. The American Museum of Natural History also has a good guide, with photos of several of the species mentioned below. Wikipedia and the Kansas Geological Survey have detailed entries, and more photo guides particularly relevant to our slice of time can be found at the Atlas of Ordovician Life, the Dry Dredgers, fossilid.info, and University of Georgia pages on the Cincinnatian and Nashville.

Monoclonius recurvicornis, and other things

Serendipity is an unsung force in the universe. I was reminded of the power of random connections when I first saw the skull of Regaliceratops peterhewsi. There, parked slightly behind the eyes, were a pair of small but distinct horn cores. It couldn't have come at a more propitious moment (and I'm not saying that just to work in the word "propitious"), because for various reasons I'd recently been kicking around the idea of posting on another ceratopsid with small but distinct brow horns: "Monoclonius" recurvicornis, one of life's persistent mysteries.