Bruce Erickson

This week saw the end of an era in Minnesota paleontology with the passing of Bruce Erickson. Bruce had been the curator of paleontology at the Science Museum of Minnesota from 1959 to 2017, where he was most famous for his work on the Paleocene fossils of Wannagan Creek. Much of his research was on crocodilians (several examples of which were featured in this post), but he also worked on many other topics, including the dinosaurs of the Poison Creek Quarry (Morrison Formation), champsosaurs, and turtles. Examples of many of these fossils can be seen in the paleontology exhibit area of the Science Museum, which includes a Wannagan Creek section (one of the few large Paleocene exhibits you'll find in a museum), several Morrison dinosaurs, and an enormous Triceratops (a composite of two partial skeletons he collected early in his tenure). If you'd like to know more, many of his publications and other paleontological publications from Science Museum collaborators can be downloaded here.

Platteville sea stars and cystoids

It's been a while since I've featured something Ordovician, so here are some photos of some uncommon Platteville Formation echinoderms. I took them a few years back, when I wasn't quite as good at this as I've become. These specimens all come from the Platteville of the Twin Cities, and are in the collections of the Science Museum of Minnesota. In fact, the first example has since been moved out to the exhibits, which is good because it certainly deserves the visibility. It is a specimen of a small stocky early sea star identified as Hudsonaster (Protopalaeaster in older references, not to be confused with Promopalaeaster, another Ordovician sea star but of more conventional appearance).

Here it is, with scale artfully copied from elsewhere in the cropped photo and placed in a more convenient location (mm divisions, one full cm included). A crinoid columnal is visible in the upper left corner.

This was not a very large animal, only about an inch across or so. It's not from the former Johnson Street Quarry, the fabled lost storehouse of Platteville echinoderms in the Twin Cities. Actually, none of the three specimens in this post are from that site. It's possible they're from the Hidden Falls Member, as the Johnson Street specimens were, but I don't have stratigraphic information lower than formation for these specimens, two of which were found on loose slabs.

Another view, taken at closer range and thus a bit sharper, but with no scale.

Hudsonaster was not the only sea star in the Platteville. Urasterella was a larger, more lanky sea star, although since we're talking about the Ordovician of Minnesota, "larger" still isn't enormous by our standards. (It's still pretty big for a non-cephalopod of the Platteville, though.) The specimen is not as complete as the Hudsonaster, but there is one nearly complete arm and most of two others, with the missing sections partially recorded by natural molds.

And I've rather brilliantly arranged to have my reversible transparent ruler wrong-side-out.

From a quick glance of the exteriors, neither Hudsonaster or Urasterella are all that different from sea stars you might see today. Going from the familiar to "what-is-that-and-what-happened-to-it", we have a fossil identified as the rhombiferan cystoid Pleurocystites. Because only one side is visible, I'm not entirely sure if it is Pleurocystites or a close relative (the very similar genus Amecystis is also known from this interval in the Upper Midwest per Kolata et al. 1987), but it's a reasonable identification.

With quarter for scale; the block is also peppered with partial crinoids.

It somewhat resembles a deflated balloon on a string, or some kind of odd fish, and again is not very large. Rhombiferan cystoids were stalked ancestrally, but these pleurocystitids seem to have been using theirs for something else, perhaps on the order of a flagellum. It's not apparent in this specimen, but at the opposite end from the "stalk" were two long appendages that looked like antennae but were actually part of the feeding apparatus (only the bases are visible here). A few formations up, in the lower Prosser Formation, a mass-death assemblage in southern Minnesota yielded dozens of Pleurocystites (Sloan and DesAutels 1987), so whatever they were doing, they were at least briefly successful at it.

Strangely enough, members of a completely different group of echinoderms, the solutan "carpoids", hit upon an astonishingly similar body plan at almost the same time (Kolata et al. 1977). The Prosser bed also includes specimens of these solutan doppelgängers (Sloan and DesAutels 1987). A quick way to tell the two types apart is the "stalk": pleurocystitid "cystoids" have a simple "stalk" of stacked pieces, but the lookalike solutans have complex, "braided" "stalks". (Also, pleurocystitids have two appendages opposite the "stalk" and the lookalikes have one, but those aren't always as easy to see.) The Science Museum has one of these solutan lookalikes, Dendrocystis, on display. The fad for echinoderms that looked like deflated balloons with antennae did not last for either version, with both lineages going extinct long before the end of the Paleozoic.

References

Kolata, D. R., H. L. Strimple, and C. O. Levorson. 1977. Revision of the Ordovician capoid family Iowacystidae. Palaeontology 20(3): 529–557.

Kolata, D. R., J. C. Brower, and T. J. Frest. 1987. Upper Mississippi valley Champlainian and Cincinnatian echinoderms. Pages 179–181 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.

Sloan, R. E., and D. A. DesAutels. 1987. The Wagner Quarry cystoid bed: a study in Prosser (Sherwood) paleoecology. Pages 60–62 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.

Fossil Crocs of the Science Museum

Although the dinosaurs get the most press, the Science Museum of Minnesota's paleontology department has a strongly diversified portfolio of ancient reptiles. In particular, champsosaurs and crocodyliforms (modern crocodilians and their closest extinct relatives) are well-represented in the collections and on exhibit. The Science Museum features mounts of four fossil crocs, each one filling different places in their ecosystems: an apex terrestrial/freshwater croc (Borealosuchus formidabilis), a large estuarine croc with elongate jaws living alongside whales (Gavialosuchus carolinensis), a medium-sized terrestrial/freshwater croc from a dinosaur-dominated setting ("Goniopholis"), and a house-pet-sized terrestrial/freshwater generalist (Wannaganosuchus brachymanus). This diversity shouldn't be too surprising. Crocodylomorphs, with around 225 million years of time on their hands, have done quite a bit of experimentation, including truly marine thalattosuchians and small, terrestrial, occasionally dinosaur-like "sphenosuchians".

Meanwhile, over at the Science Museum

Recently, the Science Museum of Minnesota reconfigured the exhibit space for the paleontology in conjunction with changes to other parts of the floorplan. I don't recall if the previous configuration had been stable all the way back to the 2005 Society of Vertebrate Paleontology meeting (I do know a nice Goniopholis was added around 2010), but where once it had looked like this:

January 2013; watch the space on the left of the Stegosaurus.

Now it looks like this:

That Triceratops wasn't there before...

Two major components, the Morrison dinosaurs and the Wannagan Creek fossils, are still where they had been. The major differences are in the section on the east, with the removal of some visible lab space and some more portable specimens, most notably a sort of "circus ring" of small- to medium-sized Cenozoic animals, mostly mammals.

And a tortoise.

 
In their place are a group of mounts from the Oligocene of coastal South Carolina (transferred from the floor above) and the well-known Science Museum Triceratops, relocated from another part of the floor. A Triceratops going mobile is just not a common occurrence these days, so naturally the event received some local coverage. A few other pieces were also rearranged, including the Xiphactinus lurking behind the Stegosaurus in the first picture above, some of the remaining mammals, the Goniopholis, and your friend and mine Thescelosaurus. Green River Formation fossils also get more prominence.

Triceratops (who also answers to "Fafner") plus overhead pterosaur pal in foreground. The South Carolina mounts are visible in the background by the neon; you can see a whale, pseudodontorn,and sea turtle in the air above the hind end of a mostly obscured croc (next photo).

Estuarine croc Gavialosuchus (or Thecachampsa) carolinensis has an honest face. I was glad that space was made for the South Carolina mounts; many places have Morrison dinosaurs, but you can't see Wannagan Creek and South Carolina fossils just anywhere.

On the one hand, the Triceratops no longer has its niche with the backdrop:

On the other hand, you can now walk around the whole mount, if for example you should want to look at the legs and hips:

Like this, perhaps.

I may cover some of these exhibits in a bit more detail in the coming weeks, given the approaching busy holidays. Till then, though, Allosaurus bids you all adieu: