Sunday, November 19, 2017

Stegomosuchus longipes, the terrestrial croc relative of Massachusetts

If you're the kind of person who reads this blog regularly, you're probably also the kind of person who's got at least one rock laying around. Maybe you've got dozens. Maybe you've got too many. Who am I to judge? The point is you've got rocks. Odds are, though, there isn't a potential type specimen in your yard.

Sunday, November 12, 2017

The first fossils described from Dinosaur National Monument

The first fossils described from Dinosaur National Monument (to the best of my knowledge) were not dinosaurian. They weren't vertebrate. They weren't from the Morrison Formation. They weren't from the Jurassic, or even the Mesozoic. You may not realize it, but the monument has a geologic record extending from the Neoproterozoic to the Quaternary (see for example Untermann and Untermann 1954, Gregson et al. 2010, or Santuci and Kirkland 2010). For this bit of history, we're also going back in geologic time.

Echo Park, at the confluence of the Green and Yampa rivers (NPS/Jacob W. Frank). Why this landmark? Read on!

Sunday, November 5, 2017

Rhabdodontidae

French geologist Philippe Matheron named Rhabdodon priscus in 1869, making it among the oldest dinosaur names still in use. In terms of public interest, Rhabdodon and its close relatives have definitely been late bloomers. From 1869 through the 1990s, we've had a few papers, but the only person who seems to have put much energy into rhabdodontids during that time frame was the inimitable Baron Franz Nopcsa. The fortunes of the group have picked up in the past few decades; several new species have been described since 2000, old species have been reevaluated, and there was even an appearance in a segment of a TV documentary special. (Of course, there were the usual drama-related inaccuracies, and the rhabdodonts had to go in disguise as "dwarf Iguanodon", but at least they were there.) The latest news is a reevaluation of rhabdodontid paleobiology that makes them into something more than stock small ornithopods.

Sunday, October 29, 2017

Halloween: Platteville in disguise

Let's start with a pair of photos, one of typical Platteville Formation fossils and the same for the Decorah Shale:

Welcome to the Ordovician! Hope you like brachiopods!

...or bryozoans and crinoids

No points for guessing which is which. The first photo shows natural molds and casts in the Platteville, while the second shows the well-shredded fossils of the thin limestone beds of the Decorah. Now try this one:

No peeking!

Despite the preservation, this piece is from the Platteville. Specifically, it comes from a bed about halfway up the Mifflin Member. Somehow this bed managed to escape the worst of the heartbreak of dolomitization, at least in a small area. Little glimpses like this show a richer picture of the Platteville fauna than we get from the natural molds and casts. (The tiny crinoid columnals are an interesting touch, as is the relative scarcity of bryozoans.)

They're in there. It's a proper hash.

The strophomenids might be a little smaller, too.

There are also snails, ostracodes, and some elongate triangular things. Some of these are probably small nautiloids, others might be hyoliths.

The example near the center bottom of the photo is one I suspect is a hyolith.

There are a lot of subtleties to the rocks and faunal assemblages once you start looking!

(Also, having found a decent place to see the Glenwood up close, I've added a couple of photos to the old post.)

Sunday, October 22, 2017

Sunday morning Decorah fossils

I've recently made a small collection of Decorah Shale pieces from spoil piles at a construction site. Most of them will go to other people and groups for use in education, but while I've got them I'm certainly going to take the opportunity to photograph them. Incidentally, construction can be a good source of fossils in the Twin Cities, if you don't mind disruption of the original stratigraphic context (which tends to happen anyway with the Decorah around here). Of course, as always, you'll want to ask for permission, and it's advisable to make collections when someone is working there, so you aren't mistaken for a trespasser or other nefarious sort.

Sunday, October 8, 2017

Compact Thescelosaurus Year Two

It's that time of year again, with National Fossil Day just around the corner (Wednesday the 11th) and the anniversary of the original Thescelosaurus just behind us (Saturday the 7th). The Compact Thescelosaurus is up for its second birthday, and this time I have something slightly more ambitious to add than choristoderes, as nice as they are (you may be unsurprised to learn that none of the entries in the "Updates" sheet were specifically for choristoderes). This year the pterosaurs join on their own sheet. The rules of the sheet are the same as for the other taxonomic sheets, except there's one more classification column. As it is, the classification columns are still kind of a kludge, but I haven't figured out a better way to handle the various nested clades.

Had to lie on my back on the Science Museum lobby floor to get that.

Sunday, October 1, 2017

Nanosaurus agilis: the smallest dinosaur you've never heard of (and for good reason)

Many millions of years ago, in a time that we would call the Jurassic and in a place we would call Colorado, small bipedal herbivorous dinosaurs frolicked and otherwise did things appropriate to small bipedal herbivorous dinosaurs. In their time, they died and a very, very few were selected by taphonomy to be fossilized. Of that tiny number, an even smaller subset have happened to be exposed at the surface at the right time and place to be found by a similarly tiny number of human beings who were specifically looking for such things. Having been found, their remains were sent off to be studied by another tiny number of people who had a lot of things on their minds, living in a world that has had little use for small bipedal herbivorous dinosaurs except as props to show off the (speculated) abilities of small bipedal carnivorous dinosaurs. It's not really that surprising that some of them have fallen through the cracks. Then there's Nanosaurus agilis.