Sunday, April 16, 2017

Mea culpa and Moabosaurus

I apologize for having been light on the whole "Minnesota" and "invertebrates" part of the blog for this year. Having been doing this for a few years now, the low-hanging fruit is picked, and of course the winter is not the best time to be out and about in the rocks, even if "winter" came with quotation marks instead of snow this year. I'm currently on a short trip to Reston, Virginia, to do some work at the USGS, but I thought I'd at least try to put in something relevant for those topics. Then, of course, there’s a sauropod.

Sunday, April 9, 2017

David Dale Owen and the first geological survey of Minnesota

Although Keating, Featherstonhaugh, and Nicollet made significant contributions to Minnesota geology, the first true geological survey in what is now Minnesota would have to wait until 1847. At this point, the future state was split between Wisconsin Territory and a leftover chunk of Iowa Territory, and with the pending organization of Wisconsin into a state it was actually touch-and-go for a while how the boundaries would fall out. The convergence of St. Croix Valley interests versus the rest of Wisconsin with the old Northwest Territory stipulation that a maximum of five states be made out of the territory, and a dash of underlying slave state versus free state politics, could have led to anything from a super-Wisconsin incorporating much of what is eastern Minnesota to a separate state centered on the St. Croix Valley with Stillwater as the capital (the story can looked at briefly here). Anyway, in 1847 Congress authorized a geological survey in Minnesota and neighboring areas, and appointed David Dale Owen to conduct the work (Hendrickson 1945).

A portrait of Owen, found on p. 206 of Owen (1852).

Sunday, April 2, 2017

The return of "Anatomical terms of location"

Having done a relatively large number of dinosaur-related posts in the past few months, I've found myself running into anatomy and anatomical terms of location (dorsal, lateral, etc.). Given that not everyone knows all about the jargon, parenthetical glosses tend to slow things down, and I had perfectly serviceable glossaries for these subjects on the late Thescelosaurus!, I decided to revisit that information. I've started by putting the anatomical terms of location on their own separate page. Wikipedia has a useful summary as well, but if you aren't a wiki fan, like having the information on hand here, or just like diagrams featuring the excellent Wild Safari Sauropelta, this is for you. Eventually, I plan to put up skeletal anatomy as a page, and probably a geologic time scale as well (or at least a link to one).

Sunday, March 26, 2017

Five minutes with Ornithoscelida

If you are the kind of person who reads a blog like this, you've probably already heard the news about a new analysis (Baron et al. 2017) finding that sauropodomorphs and theropods may not be the closest of evolutionary siblings, as we've long believed. Instead, theropods were paired with ornithischians, and Sauropodomorpha got to pair with the herrerasaurids in the settlement. For the new alliance of bitey (theropod) and beaky (ornithischian) dinosaurs, the authors went back into the mists of time and pulled out Ornithoscelida, a name first proposed by Thomas Henry Huxley for a roughly similar grouping of dinosaurs. There has already been a lot of discussion about the publication, and apart from some criticisms of the exclusion of certain forms and how names were redefined, the tone at this moment is open-minded.

The idea that the relationships of the three major lineages of (non-avian, or "classic") dinosaurs are not what we thought them to be is not far-fetched. The earliest theropods, sauropodomorphs, and ornithischians all had the same grandparents, so to speak. Unsurprisingly these early forms all look kind of similar, had similar lifestyles, and thus are liable to be mixed up by later observers, especially when the observation is happening 230 million years later and the subjects have been reduced to skeletons. (It's a common problem for species near the base of branching lineages to be difficult to place.) Going from (S+T)+O to S+(T+O) does require some rethinking on how and when certain features appeared. It also throws a bit of a kink into the branch-swapping basal saurischians: Eoraptor, herrerasaurids, and friends. Eoraptor had seemed reasonably comfy among the sauropodomorphs and herrerasaurids with the theropods, and here they are switching places.

There is also an interesting question concerning the origin of ornithischians. Historically, Triassic ornithischians have been a problem due to their frustrating insistence on not being there. After a few decades of redating various formations and reassessing a bunch of teeth, we're down to Pisanosaurus (which is itself attracting questions) and Eocursor. Woo-wee. Under the traditional Saurischia–Ornithischia split, there should be more Triassic ornithischians, because of the record of Triassic saurischians. Pairing ornithischians with theropods has the potential to resolve this if it should turn out that ornithischians and theropods actually branched later in the Triassic (which also results in some "theropods" becoming basal ornithoscelidans, but it's not as if current basal theropods haven't been living under taxonomic instability). The results of the current study don't support this, but you never know. (In fact, the authors find that ghost lineages may go back all the way to nearly the beginning of the Triassic, because Nyasasaurus has suddenly started acting like a massospondylid, but then again the rocks it came from may be younger than currently thought.)

At any rate, an injection of controversy is good for the field. Either other studies support the authors, in which case we learned something new, or they don't, in which case the authors got people looking at dinosaur relationships and evolution from new angles, which is also good. In fact, now that I'm thinking about it, it's kind of odd that we have as much consensus as we do. Off the top of my head, for persistent trouble spots we've got Triassic groups and species that can't seem to make up their minds about where they belong, megaraptorans as carnosaurs or coelurosaurs, the knot of undecideds where Dromaeosauridae, Troodontidae, and birds meet, and what to do with various "hypsilophodonts". This doesn't count a few other areas that are questionable because of lack of attention, like the Box of Mystery that is Titanosauria.

All that said, I *am* going to let the issue sit before, say, updating The Compact Thescelosaurus; publications find things all the time that are not supported by later analysis (hey, Phytodinosauria, the hip alternative of the '80s and '90s). Also, redefining Saurischia to hold just sauropodomorphs and herrerasaurs was a mis-step. Just let herrerasaurs into Club Sauropodomorpha, let Saurischia go into dignified retirement, and call it a day.

References:

Baron, M. G., D. B. Norman, and P. M. Barrett. 2017. A new hypothesis of dinosaur relationships and early dinosaur evolution. Nature 543(7646):501–506.

Sunday, March 12, 2017

Xingxiulong

Two dinosaurs were published on February 16, 2017. One of them was Isaberrysaura mollensis, which has gotten a lot of press because it's a weird basal ornithischian with gut contents. The other was Xingxiulong chengi, which hasn't gotten as much attention, although the Wikipedia article is pretty extensive. Xingxiulong is among what we used to call "prosauropods", now known as basal sauropodomorphs. It is represented by most of the skeleton, excepting the tips of the jaws, most of the hands, and the coracoids and sternal elements. It also provides me a half-point on my prediction for "prosauropods", which I'll take because it's been kind of a slow year so far.

Sunday, March 5, 2017

Joseph Nicollet

Judging by place names, Joseph Nicollet must have been a much more popular man than George William Featherstonhaugh. (Or maybe it was just the fact that it took sixteen letters to spell George's name while only taking seven to say it that proved unappealing.) I'm not sure if anyone in Minnesota attached George's name to anything, whereas Nicollet is the namesake for such pieces of geography as Nicollet County, Nicollet Mall, and Nicollet Island. His name was even attached to a ballpark, the long-time home of the old Minneapolis Millers, although probably the adjacent Nicollet Avenue was the main inspiration.

Sunday, February 26, 2017

Subsurface paleontology of Lafayette Square and the Washington Monument

Washington, D.C. is not generally ranked in the first order of fossiliferous areas. It can hardly be considered a bust, though. The "Middle" Cretaceous Potomac Group (due to a tragic geologic oversight, there is no formal Middle Cretaceous) has been reasonably kind for plants; see Fontaine (1889, 1896), Knowlton (1889), Ward (1895), Ward et al. (1905), and Sinnott and Bartlett (1916) for some of the gory details. Something you may notice from that list is that all of those publications are at least a century old. The obvious problem is that Washington is a city first and foremost, so it's not like there are a lot of outcrops for prospecting any more. The Potomac Group has also produced some scrappy dinosaur remains, and anywhere that the Potomac River once flowed is liable to have cobbles with Skolithos tubes, eroded from Cambrian rocks up in the mountains. The classic Potomac Skolithos cobbles are rounded pieces of orangeish quartzite with simple vertical Skolithos burrows, similar to skinny pencils and with a tendency to stand out from the host rock. Washington is also blessed with a profusion of fossiliferous building stone, particularly the inevitable "Indiana Limestone" (Salem Limestone). But I digress. In a city, we cannot come to the outcrop, so the outcrop must come to us. This is where subsurface explorations come in handy. We talked about taking cores from lake sediments a few weeks ago. The subsurface of Washington, like any major city, has been picked at innumerable times, uncovering fossils from places such as just north of the White House and near the Washington Monument.