Sunday, July 26, 2020

Decorah craniate brachiopods

One of the more frustrating minor components of the Decorah fauna are the craniate brachiopods. Why are they so frustrating? They're easy to mistake at first glance for all sorts of other fossils (especially when partially buried or partially encrusted), such as:

One of these...

Craniates, in brief, are brachiopods from the "inarticulate" structural wing but the "calcitic" compositional wing. At the Brickyard section, the two most abundant are Acanthocrania setigera and Petrocrania halli, which can be difficult to distinguish in practice (Rice 1987). The phosphatic inarticulate Schizocrania, which does a lot of the same things, is also present but much rarer. Other inarticulates at the Brickyard, from the phosphatic side, include Craniops minor, Pseudolingula eva, and Trematis sp. (Rice 1987). Other species are cited in museum collections; one which I've seen, "Crania" (now Acanthocrania) granulosa, looks suspiciously like the "raspberry cystoids" in this post.

Several more, in situ. A might be a ringer; I'm not sure. B is an overturned shell (note also the tiny pygidium just above and to the right). C is partially encrusted. D shows what happens when a thin piece of rock and a thin shell meet inexperienced preparation from the underside.

Acanthocrania and Petrocrania have thin domed shells with concentric growth rings. Unlike most of the other Decorah brachs, they do not have strong ridges (and, of course, they don't look much like the other brachiopods in a lot of other ways, too). They seem to have been attractive to encrusters; all of the loose specimens I have are covered with bryozoans, and some of them have either tabulate corals or cornulitids growing on them as well. For their part, craniates are noted encrusters of other brachiopods; presumably the unattached specimens in the photos were also originally attached to other brachiopods, becoming dislodged (probably after the death of the craniate).

What do the five rounded domed blobs of bryozoans have in common? If you turn them over, they all have the heart of a brachiopod.

This strophomenid has a craniate encrusting on the lower right, as well as several cornulitids.


Rice, W. F. 1987. The systematics and biostratigraphy of the Brachiopoda of the Decorah Shale at St. Paul, Minnesota. Pages 136–166 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.

Sunday, July 19, 2020

Your Friends The Titanosaurs, part 26: Rinconsaurus, Rocasaurus, and Rukwatitan

And so the procession of titanosaurs continues, this time touching on three small- to medium-sized examples, only two of which are from Patagonia. All three also share relatively complete material compared to many other titanosaurs.

Sunday, July 5, 2020

Fossil Marine Reptiles of the National Park Service

For my annual post summarizing a type of fossils from National Park Service lands, this time around we're going with Mesozoic marine reptiles: ichthyosaurs, plesiosaurs, and mosasaurs. As you might guess, most of the examples come from the rocks of the Western Interior Seaway. This time around, we're only dealing with eleven parks, so there's space for going into more detail. We'll start off with the traditional map, which includes a lovely blue overlay to give you an idea of the extent of shallow seas at their Cretaceous peak:

The outline of the seaway is roughly after Robinson Roberts and Kirschbaum (1995), with a more substantial Mississippi Embayment added and a bit more on the Atlantic Coastal Plain, which I let peter out in New England. No attempt has been made to reconstruct the marine extent on the Pacific coast. Also, Minnesota was improvised after Sloan (1964), due to Robinson Roberts and Kirschbaum (1995) having a text box over the state. Sites mentioned in the post are: 1. Yellowstone National Park; 2. Little Bighorn Battlefield National Monument; 3. Badlands NP; 4. Missouri National Recreational River; 5. Dinosaur NM; 6. Glen Canyon National Recreation Area; 7. Mesa Verde NP; 8. Chaco Culture National Historic Park; 9. Big Bend NP; 10. Wrangell-St. Elias NP and Preserve; 11. Fort Washington Park.

(Also, if you're interested in cave fossils, check out our recently finalized paleontological inventory for Carlsbad Caverns NP!)