|The sweet siren song of the Franconian trilobite.|
Minnesota paleontology and geology, National Park Service paleontology, the Mesozoic, and occasional distractions
Sunday, June 25, 2017
Investigating the rocks of Saint Croix National Scenic Riverway (SACN) is a tougher nut than working in MNRRA. Most of the area where rocks are exposed in MNRRA is part of some kind of park (city, state, regional, county, etc.) and generally accessible to the public. Much of the area with outcrops on the St. Croix is private land, and many of the key localities in the literature are now overgrown, destroyed by construction, or are roadcuts next to busy highways. Determining where you are in the strat column is also more difficult. In MNRRA, it's hard to get mixed up if you can tell sandstone from limestone/dolomite and shale. In SACN, you're dealing with several quartz-rich medium to coarse sandstones that tend to look the same, with some intervening shaly, dolomitic, or finer-grained sandy formations, and in the literature practically every single investigator had their own preferred system of names right up until the 1960s. Finally, in MNRRA there are abundant and diverse fossils in the Platteville and Decorah, while in SACN the special of the day is the BLT (burrows, lophophorates [brachiopods and hyoliths], and trilobites) with a side order of mystery snails, and you have to work for everything but the B.
Sunday, June 18, 2017
When brachiopods ruled the Earth
...well, maybe that's an overstatement, but it's a catchier title than "When brachiopods were dominant marine fauna in parts of cratonic North America", right? Our story today goes back to the latter part of the Cambrian, 500 million years ago or so. The Cambrian Explosion had come and gone, the confetti and stray napkins had been disposed of by various wormy things, and in the absence of thumbs to twiddle, there was nothing much to do until the Ordovician Radiation. Many forms of life got bored of waiting and went extinct, or otherwise died out from less frivolous causes, leaving behind a kind of "blah" marine fauna dominated by brachiopods, trilobites, and conodonts. This stretch of time has been called the "Late Cambrian plateau" or, more ominously, a "dead interval".
|"We are your masters now! Ha ha!"|
Sunday, June 11, 2017
With the recent coverage of Zuul and the Suncor nodosaur, it seems like a good time for another entry on North American armored dinosaurs. We've already visited with Nodosaurus textilis, Stegopelta landerensis, and Hierosaurus sternbergii. Today's star is another species of similar vintage, Hoplitosaurus marshi. Like our other three subjects, Hoplitosaurus was initially described around the turn of the 20th century from a single armor-heavy specimen found in Cretaceous rocks of the American West. Also like the other three, Hoplitosaurus received barely a blurb for its initial description and had to wait for someone else to spare a little more time and ink.
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