Sunday, December 28, 2014

Year-end accounting

Hello, everyone, at the end of 2014 and the beginning of 2015. There isn't a whole lot going on, so I thought I'd check in on a couple of things. First of all, how did Equatorial Minnesota do this year? To the surprise of absolutely no one, the most-read articles were those involving dinosaurs. The champion was "A brief history of dinosaurs on the Internet". Quite astonishingly, the second favorite was... "Fossils of the St. Peter Sandstone". This is not a knock on its quality, or the subject matter, or... well, I suppose it is, after all. The only explanation I can think of is that it is linked somewhere I can't find, perhaps on a forum or class website. A few personal favorites:
"Platteville Follies: a crushed giant rodent from Hidden Falls"
"Where to see metro geology, part 5: Shadow Falls Park"
"Sponge detective: when faunal lists go bad"
"Designasaurus II"
"Thescelosaurus: hello old friend"

Sunday, December 21, 2014

The Glenwood Formation

Beneath the Twin Cities, sandwiched snugly between the crumbling off-white edifice of the St. Peter Sandstone and the proudly jutting gray to tan Platteville Formation, is a gray to brown layer about 3 to 5 feet thick (or about a meter to a meter and a half for our metric friends), composed primarily of shale. This is the Glenwood Formation, sometimes known as the Glenwood Shale (which is a bit of misnomer because of the sand content). Like a fawn or baby bird, it hides from the eye, although we know it must be there, because heavens knows where else we would get adult deer and birds, and the Platteville has yet to collapse onto the St. Peter. The only reliable way to find it is to look for places where both the Platteville and St. Peter are exposed, and then check the area between them. Even then, you might not be able to see it well; for example, at Minnehaha Falls, the Glenwood is so deeply recessed you can't see much at all. The most obvious exposures are at Lock & Dam 1 and Dayton's Bluff.

Friday, December 12, 2014

Brachiopods

Technicalities. Say you've got this thing, it's got two halves to its shell, the halves are called "valves", "bi" is two, "bivalve". Simple, right? Not so fast! There are bivalves, in the simple "it's got two half shells" sense, and then there are bivalves, in the "mollusk that belongs to Class Bivalvia" sense. Why bring this up? Aside from bivalved mollusks, we've also got another group of invertebrates with two half shells that is quite common in the fossil record, with abundant examples in the Decorah and Platteville formations. This group is Brachiopoda.

Friday, November 28, 2014

Thescelosaurus: hello old friend

Thescelosaurus is near and dear to my heart, and Clint Boyd's recent publication on the skull of T. neglectus (Boyd 2014) makes it a good time to ruminate on this animal. Thescelosaurus is one of the most common dinosaur genera from the end of the Cretaceous in North America, and close to a dozen good specimens have at least been mentioned in the literature, to say nothing of the plethora of stray vertebrae, teeth, and limb elements littering the Hell Creek, Lance, Scollard, Frenchman, and other formations. This set of end-Cretaceous formations in western North America is best known for Tyrannosaurus, Triceratops, and the Duckbill Formerly Known As Trachodon/Anatosaurus/Anatotitan (Edmontosaurus annectens), but your standard End-K toybox also comes with Ankylosaurus, Pachycephalosaurus, Torosaurus (depending on where you buy your toys), the original Ornithomimus, this spring's darling Anzu, various nameless dromaeosaurids (perhaps mostly Acheroraptor) and troodontids, and of course Thescelosaurus. Oddly, many of these are among the largest examples of their lineages.

USNM 7757, the type specimen of Thescelosaurus neglectus, as it had been exhibited at the National Museum of National History; we'll see how it looks after the renovation. The neck and skull are reconstructions.

This is more or less how it was found as well, with the neck and skull absent. The right leg was also repositioned (it had been disarticulated from the hip and forming a right angle with the long axis of the body). From Gilmore (1915).

Sunday, November 23, 2014

Paleontology of the Santa Fe Trail

As the note says with my bio, I am a "researcher and writer who has been helping to inventory and catalog the fossil resources of the National Park Service." A lot of the work I've done has been geared around Inventory & Monitoring networks. The I&M program groups parks with significant natural resources into networks based on their geography and the types of natural resources they contain, with geology and paleontology being among these natural resources. We are gearing up to prepare a revised and updated summary for the Southern Plains Network (SOPN), which includes 11 units in Colorado, Kansas, Oklahoma, New Mexico, and Texas. Although the I&M networks have served as the broad framework for a lot of our work, only 270 of the various units of the NPS are included. Granted, most of those that aren't included are usually small urban sites with little paleontological potential (except for fossiliferous building stone, which is more abundant than you might think; you can scarcely go past a large building in Washington, D.C., without finding Salem Limestone, aka Indiana Limestone, or in other words uncounted itty-bitty fragments of Paleozoic marine invertebrates), but it would be foolish to a priori dismiss them. Thus, when I work on a network, I also like to cover the non-network units that are geographically within that network. In the case of the Southern Plains Network, one of those is the Santa Fe National Historic Trail.

Sunday, November 16, 2014

National Park Service military sites and fossils

As of this writing, there are 403 units in the National Park System, although in practice the number of sites with some connection to the NPS is larger: there are many national trails, rivers, heritage areas, and affiliated units that are not included in that total. Of these, 252 are currently known to have some sort of paleontological resource, from the obvious (any unit with "Fossil" in the name, for example) to much more subtle occurrences, such as fossils in building stone at many East Coast units, or one unusual case in which a fossil fish (quite possibly from Fossil Butte National Monument, interestingly enough) is in the collections of Marsh-Billings-Rockefeller National Historical Park because it had been in the holdings of one of the families that had owned the site.

Sunday, November 2, 2014

Out in the fall: the southeastern metro

There is a brief period of time during the fall in the Twin Cities metro after the heat, humidity, insects, and plant growth of the summer have subsided, but before the first significant snowfall has hidden the ground. It usually starts around the middle of October and lasts until about Thanksgiving, depending on temperature and moisture. It's a great time to be outside, if you don't mind the increasing chill, and it gives you one last chance at the rocks. There's one area of bedrock outcrops on the Mississippi before we get to the confluence with the St. Croix, from about Grey Cloud Island and downstream, and we've only really stopped there once, although the rocks are covered here as well. However, there's a reason it hasn't been discussed much: there's not as much to see. If you're down in the area, though, here's the rundown:

Saturday, October 25, 2014

Designasaurus II

The year is 1990. The Yankees are terrible, the Berlin Wall has just fallen, dinosaurs are still walking around without feathers, and this type of introduction is not yet a cliche. Edutainment titles are a firmly established genre, and it is only natural that dinosaurs are represented. Among the prehistoric-centric titles is Designasaurus II, which proves to be fairly durable as these things go...

...And suddenly we wake up, and it is back to 2014 (or, I suppose, later, depending on when you read this), and there have been no floppy disk drives for a decade, and your computer will react as if you tried to command it in Etruscan if you try to play Designasaurus II. However, through the magic of DOSBox, it is possible to bring old bones back to life. Designasaurus II has been reviewed in recent times from the perspective of gamers. How does it fare when viewed from a paleontological perspective, by someone who remembers playing it when it was still fairly new?

Sunday, October 19, 2014

Rostroconchs: Paleozoic taco shells

The Paleozoic was full of invertebrate groups that didn't quite hack it. The kings of extinct invertebrates are, of course, trilobites. The next tier down, widely known to paleontologists, geologists, and fossil collectors, is where we find things like tabulate corals, rugose corals, and eurypterids ("sea scorpions"). Then there are some that linger in obscurity; the aglaspids (Cambrian critters that were something like trilobites with poor-quality horseshoe crab disguises), for example, or cyclocystoids (disc-like echinoderms), which of this writing don't even have a Wikipedia article. Rostroconchs are another group that hangs out near the aglaspid/cyclocystoid end of the scale.

Saturday, October 11, 2014

National Fossil Day 2014

Here in the States, the leaves are turning color, the GSA/SVP conference season is at the doorstep, and National Fossil Day is upon us. This event occurs on the Wednesday of Earth Science Week, fittingly enough, which this year is the 15th. National Fossil Day includes a number of local events across the country, although not all of them are on Wednesday; for example, in the Twin Cities, early readers might be able to catch a fossil and geology event at Coldwater Spring from 9 to noon on Saturday the 11th (and the weather's looking good, too, which is a bonus for mid-October in Minnesota; last year we held a fossil and geology walk the Saturday after National Fossil Day, and just after we finished we had a downpour of ice pellets). If you're unable to get to Coldwater Spring, are busy that day, or would prefer an indoor event, the Science Museum of Minnesota is holding Fossil Day on Saturday the 18th. Of course, there are also plenty of places along the bluffs if you'd just like to spend some time among the fossils in their natural setting before it gets too cold. The flagship events are held in Washington, D.C. In previous years events were held on the National Mall, but because of construction they have been shifted to the National Museum of Natural History. If you're in D.C., I also recommend checking out the building stone as you're walking around; the city has an excellent fossil record on display.

You might think this is an armored dinosaur, but it's actually an aetosaur, a Triassic offshoot of the group that includes crocodilians. The story behind the logo can be found here.

Sunday, October 5, 2014

A brief history of dinosaurs on the Internet

Thescelosaurus appeared on October 7, 1999, under the auspices of a University of St. Thomas student program. 15 years and two changes of address later, it has gone from a shameless imitation of an early version of The Dinosauricon to one of the last sites standing from an earlier epoch in Internet paleontology. 15 years ago, someone interested in dinosaurs would usually hear news first on the Dinosaur Mailing List, and would then find it incorporated into any of a number of personal information sites. Today, that same person may still be a follower of the DML, but they will often hop onto Wikipedia and find the article on the latest new genus, or stop by their favorite blogs, or check the social media chatter. In honor of a site that in all likelihood has outlived most actual thescelosaurs, here's a brief exploration of dinosaur information on the Internet.

Sunday, September 28, 2014

Packrat middens across (parts of) America: update to Tweet et al. 2012

A personal indulgence, but then what isn't with a blog? If you've got your copy of Tweet et al. (2012) handy, you'll see that the body of the paper describes 33 National Park Service units where there has been some reference to packrat middens. Two more were added in proof, and didn't get onto the map. I now have references for packrat middens in five additional NPS units, which will be described below, along with new information for one of the units added in press (City of Rocks National Preserve) and an updated map. There's nothing particularly earth-shaking, mostly anecdotal reports, but there's another geographic outlier in Glacier National Park (which can probably use all the climate proxies it can get). In further good news, the USGS/NOAA packrat midden database can once again be accessed, at http://geochange.er.usgs.gov/midden/.

Sunday, September 21, 2014

Bryozoans

Bryozoans make up one of the "B"s of the Decorah BBC (brachiopods, bryozoans, and crinoids), and may be the most abundant; I have seen rocks that are more or less bryozoan hash. Bryozoans are known colloquially as "moss animals", which is fair enough in terms of some of them encrusting things in the manner of carpets of moss, and also being animals. They are often compared to corals, but are quite different. A coral animal is a sack; food goes in and waste goes out the same passage. Bryozoans have a one-way flow with two holes. Coral animals are much larger than bryozoan animals; for example, for the Ordovician fossils of the Twin Cities, coral apertures typically measure several mm across, while the apertures in bryozoan colonies are sub-mm in scale. Finally, bryozoans have never gone in for the algal symbiont trick like corals have done. Not having symbionts, bryozoans must rely on filter-feeding, which the individual bryozoan animals do via a structure called a lophophore, a sort of ring of tentacles around the mouth. This structure is also found in some soft-bodied marine critters with very poor fossil records and the other "B" of the BBC, the brachiopods, showing that they were related, making up a group called the Lophophorata. Various extinct groups known from "worm tubes", like our old friends the cornulitids, may also have been lophophorates.

Sunday, September 14, 2014

Eousdryosaurus

No doubt you are sick of hearing about giant sauropods, and another post about Spinosaurus would cause headaches, nausea, and vomiting (if not, there's The Bite Stuff, Skeletal Drawing [one and two], The Theropod Database Blog, and Theropoda [one and two], as well as a bevy of news media accounts). What you need is an ornithopod, and fortunately we have one, a dryosaurid known as Eousdryosaurus nanohallucis by way of the Late Jurassic of Portugal. For those of you not fortunate enough to be an initiate (yet), dryosaurids were modestly-sized bipedal herbivores, mostly legs and tail, on the order of 3 or 4 meters long. Like all modestly-sized bipedal herbivores of an ornithischian persuasion that did not include any unusual skeletal features like frills or domeheads, they were once considered hypsilophodonts. Detailed study and the discovery of more "hypsilophodonts" showed that what we now call dryosaurids were more derived ("advanced", for you time-travelers from the past) ornithopods than most of the "hypsilophodonts", and formed a small knot of Middle Jurassic to Early Cretaceous dinosaurs known mostly from leg and pelvic remains. Dryosaurids as a whole are among the most obscure dinosaurs, being small herbivores with no unusual features. If you run across one in popular media, it's probably there to serve as background filler or carnivore chow. They are not to be confused with the considerably more threatening dyrosaurids, extinct crocodilians that lived from the Late Cretaceous to the Eocene. As if in warning of this, the Paleobiology Database currently has "Dryosaurus phosphaticus" (which ought to be Dyrosaurus) as a species of Dryosaurus. Dryosaurus is the flagship dryosaurid, and if you'd like to spend some time in contemplation of it, you can check the Carnegie Museum of Natural History's page on how they remounted their specimen (previously in a panel mount featuring the classic "bipedal dinosaur standing partially upright like a dope"), or Dinosaur National Monument's page.

A more naturalistic stance. NPS photo of the Carnegie's new mount.

Sunday, September 7, 2014

On this occasion of receiving a new giant dinosaur: thinking about dinosaur size estimates

Dinosaur size is something that seems to reduce even otherwise sensible folks to fanboys or fangirls. One of the points that is inevitably addressed in a popular article on a new dinosaur (along with the de rigueur reference to Tyrannosaurus rex) is how big it was. Maybe it was the size of a dog, or a horse, or an elephant. They keep standard elephants in various cities for comparative purposes, just like the old prototype meters. (If a dinosaur is between the size of a dog and about half an elephant, it doesn't get press unless it's got some kind of schtick.) A classic of children's books is "the length of [x number of] school buses". One that seems largely retired is "could look into a [x]-story window". If you are familiar with the nuts and bolts of Wikipedia, and ever go spelunking under the "history" tab of dinosaur articles, you'll find that one of the most common sequences of edits is someone wedging an extra meter or five tons into a size estimate, followed by someone reverting them. You might think that these measurements are pretty darn solid and reliable, for all the passion they inspire. Well...

"Faster than a beer-league softball player! More powerful than the disapproval of your peer group! Longer than the average school bus! Able to look into second-story windows without straining itself!"

Sunday, August 31, 2014

The Amazing Four-Sided Herringboned Ice Cream Cone (with creamy polyp center?)

The farther back you go, the less familiar the lifeforms. Obvious, no? And yet the pattern is not a simple one to one relationship. For example, the Cambrian was a relatively brief time in which the invertebrates collectively decided that "anything goes" and did their darnedest to fulfill that maxim. Many groups didn't hack it and disappeared before the Ordovician. From the Ordovician to the Permian, the shallow seas were filled with bryozoans, brachiopods, and crinoids, with growing numbers of rugose and tabulate corals, mollusks, and fish. The dominant groups of the Paleozoic were greatly reduced or wiped out altogether at the end of the Permian. Almost all of the enigmatic or otherwise difficult-to-classify groups kicked the bucket by the Permian–Triassic extinction, with a few exceptions such as the bellerophont snails (or monoplacophorans), the conodonts, and today's entry, which all persisted into the Triassic for reasons known only to them. The post-Cambrian bryo-brach-crinoid seafloor communities were replaced by Mesozoic communities dominated by mollusks, stony corals, echinoids (sea urchins), and cartilaginous and bony fish. With the end-Cretaceous subtraction of the ammonites, belemnites, certain groups of bivalves, and marine reptiles, and the addition of marine mammals, this becomes the typical modern marine assemblage. Today, many of the extinct Paleozoic groups appear strange, which is a bit unfair because they were just being the best filter feeders/detritivores/algal symbionts they could, and because there are plenty of unusual things alive in the ocean this very instant. Some of them, however, seemingly went out of their way to stand out. One example follows below the fold.

Saturday, August 23, 2014

Corals of the Twin Cities

The Ordovician seas of the Twin Cities would have been unfamiliar in a lot of ways. There were no sharks, no bony fish, no marine mammals, no seabirds. No driftwood bobbed in the water. There were no octopuses or true squids, no lobsters or crabs scuttling about. The kings of the echinoderms were not sea stars, brittle stars, and sea urchins, but crinoids. A diver would see a Lilliputian sea-scape featuring cm-scale brachiopods, profusions of bryozoans, and "forests" of sea lilies, traversed by trilobites. Snails, of course, would provide a common point of reference. "Are there no corals?" you ask, thumbing through your waterproof guidebook as you try to figure out if you have just stepped on an inarticulate brachiopod, a bivalve, or a monoplacophoran. Well, yes, there are corals; it's just they are all representatives of groups that have been extinct since the end of the Permian (that pesky Permian–Triassic extinction).

Sunday, August 17, 2014

Chuanqilong and Tambatitanis

So I finish the Generic History of Dinosaur Paleontology series on July 20th, and four new genera come along. Of course, it's not quantity but quality, and a year with Anzu and Kulindadromeus will be remembered fondly. Every dinosaur should have its day, though, even if they aren't enormous crested caenagnathids or feathered ornithischians. Two of the most recent genera are in freely accessible publications and represent significantly different but still generally overlooked branches of the dinosaurian tree. They are the titanosauriform sauropod Tambatitanis and the ankylosaur Chuanqilong.

Sunday, August 10, 2014

Sponge detective: when faunal lists go bad

I set out to do something simple, really I did. All I wanted to write was an introduction to sponges and a quick description of the forms known from the Twin Cities region. I already had a list of appropriate species, and I knew that most of the original forms weren't actually sponges, which I thought would make things easier. "There's only a couple left, that's not too bad." Then I made the mistake of checking into those leftovers. It turns out that you can never assume a classification for early Paleozoic sponge-like things. There's always room for an argument. In paleontology, the answer to any question always includes "start digging," whether it be rocks or research, and, frankly, isn't some mystery more interesting than a list?

Sunday, August 3, 2014

Where to see metro geology, part 6: odds and ends

And now, to complete, more or less, my other series:

I've already hit most of the best places to see Twin Cities bedrock geology up close, and there isn't really much need to flog this further. So, to wrap up things, I'm collecting a few stray thoughts on other areas. There is one other location that is supremely worthy of its own post, and if you are tuned in to the local fossil-hound scene you can guess exactly what it is, and also why there's not much of a point in discussing it now. Thus, the Brickyard of Lilydale will wait.

Previous entries:
Lock and Dam 1/Ford Bridge area
Minnehaha Regional Park
Coldwater Spring
Fort Snelling State Park
Shadow Falls Park

Sunday, July 27, 2014

Where to see metro geology, part 5: Shadow Falls Park

Having worked the dinosaurs out of my system for a couple of weeks at least, it is time to return to the Twin Cities. Today's location is one of my favorite places. I first visited it when I was an undergrad at the University of St. Thomas around the turn of the century. This may surprise some of you (well, if this is the first post you've read), but the non-scholastic aspects of college life were utterly lost on me. I did some writing and reading, learned how to kind of flail at a guitar in a rhythmic fashion and sing at the same time, and started the world's drabbest-looking website on dinosaurs. It's amazing how these things will occupy you. In my hectic schedule I also found time to spend poking around the network of goat trails along the Mississippi gorge, which is where the subject of this post comes in.

Sunday, July 20, 2014

The generic history of dinosaur paleontology: 1990 to 2014

We come now to the end of this series (previous installments 1699 to 1869, 1870 to 1899, 1900 to 1929, 1930 to 1969, and 1970 to 1989). 1970 to 1989 was the heart of the Dinosaur Renaissance, with its "dinosaur heresies"; as you might guess, when heresies last long enough, they stop being heretical. Funnily enough, for everyone who became interested in dinosaurs after the mid-1980s, the Dinosaur Heresies are a lot closer to the Dinosaur Orthodoxies. You'd have trouble selling a book with that title, though.

Sunday, July 13, 2014

The generic history of dinosaur paleontology: 1970 to 1989

Welcome back! We are nearing the end of this series; for reference, the previous installments are 1699 to 1869 (birth), 1870 to 1899 (Bone Wars), 1900 to 1929 (growth to contraction), and 1930 to 1969 (doldrums). The current period, 1970 to 1989, covers the height of the Dinosaur Renaissance, basically from Deinonychus (1969) to the first edition of The Dinosauria and Jurassic Park (the novel) (1990). The last segment, 1990 to the present, could be broadly considered the Post-Renaissance, the Internet Age, or the Feathered Age of Dinosaurs. If I had to guess, I'd say the transition from Renaissance to the modern era goes from about 1990 to 1996, which includes such milestones as the film version of Jurassic Park (1993) and the appearance of the Dinosaur Mailing List (1994), and ends with the publication of feathered dinosaurs (Sinosauropteryx). Feathers are really the key: before Sinosauropteryx, feathered dinosaurs were the province of just a couple of workers, particularly Gregory Paul. That first description and the discoveries to come changed the game.

Sunday, July 6, 2014

The generic history of dinosaur paleontology: 1930 to 1969

"[O]ne day I was half-stepping, and the lights went out." – B. Dylan
"This is gonna get worse before it gets better." – Chief Wiggum

World War I and the resulting economic turmoil had already kneecapped European dinosaur paleontology in the years leading up to 1930. The market collapse of 1929 and the Great Depression further drove people and resources out of the field. World War II scrambled things again, this time adding wholesale destruction of important collections in bombings of England, France, and Germany. Yet, these all together are not necessarily enough to cripple a science. Changes in attitude that reduced dinosaurs to a sideshow prolonged the deleterious effects of war, lack of new workers, and lack of funding. In the end, dinosaurs had to be rethought for the science to come back, and these movie monsters of the '50s made a triumphal return from seeming death, like any good movie monster.

Sunday, June 29, 2014

"And one minute is a long time", or a reason to listen to Revolution 9

Taking a brief break from the "generic history" series:

If you've gone through a basic geology class at almost any level, you've probably encountered some kind of metaphor for geologic time versus some familiar standard, the objects of which are to give you an idea of the geologic chronology and the scale of deep time, and to impress upon you the rather tiny speck of time occupied by recorded history, Homo sapiens, and so on. The two favorites are the length of a calendar year and the length of a day. If you do not work with geologists and wish to forever establish yourself as eccentric, you should look up one of these and memorize it, and then at appropriate times use that information to excuse yourself from meetings, gatherings, and so forth. "I'd love to come over, but there won't be enough oxygen in the atmosphere at ten." "I am incapable of doing anything until twelve minutes before midnight on December 31." The truth of the matter is you can come up with all sorts of different ways of doing this exercise. All you need is enough of whatever you're converting to geologic time to get decent resolution, and a subject that will hold interest. Geologic time in a mile or kilometer? Sure. Geologic time based on the reigns of Holy Roman Emperors? You could do it, but it probably only appeals to a very select crowd. Why not pop-cultural subjects? A single movie or series of movies could be easily done, and offers the potential for endless irritation by pausing the show and exclaiming that Pangea is rifting apart. How about an album? Well, you're going to want one that goes a little longer than 30 minutes...

Sunday, June 22, 2014

The generic history of dinosaur paleontology: 1900 to 1929

We now turn the page from the 19th century (previous entries here and here). The characters are still colorful (in fact, about the only time the characters aren't colorful is when there aren't any characters), and the stage is expanding, both in terms of geography and in the players. The American Museum of Natural History is in its paleontological ascendancy. Improving logistics are permitting expeditions to go farther afield. With the passing of the previous generation, the bloodlust appears to be under control, but never fear, there are still plenty of driven personalities and nutty ideas. Most of these ideas are beyond the scope of this entry, but if you go through biographies you'll find plenty of strange spiritual theories of evolution and obnoxious racial schemes.

Sunday, June 15, 2014

The generic history of dinosaur paleontology: 1870 to 1899

Following on from the previous post, we end up in the 1870s, departing the formative era of dinosaur paleontology and entering what you could call the "heroic era", of a few larger-than-life individuals performing outsized deeds. It was a time when great finds were being made and great advances being reported, but hardly anyone was playing in the sandbox. Three researchers turn up again and again in the literature from about 1870 to 1900. In alphabetical order, they are Edward Drinker Cope, Othniel Charles Marsh, and Harry Seeley. If you have spent much time reading about dinosaurs, you have probably encountered the first two gentlemen, most likely in the context of the "Bone Wars" that sprang from their stubborn rivalry. Seeley, a British paleontologist, described a number of new genera and species, almost all of which languish in obscurity. His most lasting contribution is instead the division of dinosaurs into saurischians ("lizard-hipped") and ornithischians ("bird-hipped"). Add Seeley's British contemporaries John Hulke and Richard Lydekker, and you've got practically the entire roster of paleontologists working extensively on dinosaurs in this thirty year period.

Sunday, June 1, 2014

The generic history of dinosaur paleontology: 1699 to 1869

A few months ago, not long after I started writing this blog, I thought it might be fun to do a monthly roundup of news in dinosaur paleontology. The month was February, and almost nothing happened. Well, there was a publication on an extension of the geologic range of Polacanthus, which is probably much more interesting to me than to practically anyone else, but that can't really hold a whole month. I might as well just drop the pretense and post on Polacanthus. One day I will be tempted to do so, and it will be a terrible post. Fate has ordained it.

Sunday, May 25, 2014

Where to see metro geology, part 4: Fort Snelling State Park

It seems reasonably fitting for the Memorial Day weekend for the next stop to be at Fort Snelling State Park. Although the fort is certainly best known for its place in the history of Minnesota, it is also an early geological locality of note. Because of this, and because much of the original bedrock has been covered, this post will have a more historical bent.

Sunday, May 18, 2014

Quick notes: 10th Conference on Fossil Resources, Fossil Cycad National Monument

I just got back from the Conference on Fossil Resources (#10, hosted by the South Dakota School of Mines & Technology at Rapid City; I'd like to compliment the organizers on the fine meeting!), so I haven't really had the opportunity to do anything in-depth for the blog. As a consolation prize of sorts, you can follow this link to read the article I presented on Thursday. The citation is at the end (the title is the best part).


A major part of the conference concerned a site represented in the above photograph, a pleasant and picturesque slice of the southern Black Hills once known as Fossil Cycad National Monument. You may notice a distinct lack of fossil cycads (actually, cycadeoids, which are not quite the same thing) or National Monuments in this photo. This is because practically all of the surficial fossils were removed, in large part thanks to the researcher who wanted the site to be a national monument in the first place. My supervisor and sometimes coauthor Vince Santucci wrote a new history of the site for the conference volume, and I'll be sure to post it when the pdf is available. For now, perhaps you'd be interested in a previous version? Other accounts can be found here (National Parks Traveler), here (National Fossil Day), and here (Capital Journal, Pierre, SD).

References cited:

Tweet, J. S. 2014. Smashed rodents, false preprints, and the BBC: the paleontology of Mississippi River and National Recreation Area, Minnesota. Dakoterra 6:107–118.

Sunday, May 11, 2014

Reference diagrams

Just a quick post...

I have a couple of diagrams that given the basics of the bedrock geology of the central Twin Cities. One covers all of the formations exposed as bedrock within MNRRA, and the other focuses on the St. Paul–Minneapolis bluffs (note that thicknesses and rock types differ elsewhere). They are based on a combination of information in Mossler and Tipping (2000), Mossler (2008, 2013), personal observations, and recommendations from the Minnesota Geological Survey. The patterns and symbols come from the USGS's standards (http://pubs.usgs.gov/tm/2006/11A02/), except for the little fossil cartoons, which came from photos run through a comic filter. They're admittedly schematic (my disconformities are nothing to write home about, and I just used arbitrary widths for susceptibility to erosion, with more resistant rock types sticking out farther), and I'm open to suggestions. I prepared them for MNRRA, so if you want to use them elsewhere, you should credit the park.

Sunday, May 4, 2014

Fossils in the St. Peter Sandstone 2: actual fossils


I'm not quite sure why, but "Fossils in the St. Peter Sandstone" is one of the more popular posts to date. Who am I to argue with the St. Peter Sandstone? Last fall I visited the paleontological collections of the University of Minnesota and took a number of photos. I've received permission to post examples (thank you, Dr. David Fox!), and among them are a few photos of actual St. Peter Sandstone fossils, as primarily collected by Sardeson.

Sunday, April 27, 2014

Where to see metro geology, part 3: Coldwater Spring

Picking up from where we left off last time...

Going south from Minnehaha Park on the bike trail network, specifically the Fort Snelling State Trail, we encounter Coldwater Spring. Coldwater Spring, also known as Camp Coldwater, is a small parcel situated between property of Minnehaha Park, Fort Snelling State Park, the Veterans Hospital, and other landowners (there's actually a number of small land parcels in this area, but this is a paleontology and geology blog, not a land ownership blog. If you're curious, there's a map here, with Coldwater as #8, Department of the Interior). The site is currently owned by the National Park Service as the only part of Mississippi National River and Recreation Area that is not an island. Before that, it hosted a Bureau of Mines complex. The complex was vacated during the 1990s after the bureau was closed by Congress, but the buildings still stood until 2011. In fact, if you are using the older version of Google Maps, the buildings reappear when you've zoomed in far enough to transition from flat to 45 degrees. All that's left of the complex today is a few chunks of foundation and the concrete ore storage bins. Before the Bureau of Mines, the titular spring was used by Fort Snelling, taking over what had been a squatter's camp in the 1820s and 1830s. Going back before the Fort, we get into the tribal period of use. The spring is in the Platteville Formation, which is not surprising given that the different members of the formation can promote spring outflows at the contacts (water flows through one member, then runs into another member which isn't as permeable).

Sunday, April 20, 2014

Watching the river flow

Nothing in particular, just a few observations:

I had some errands to do in St. Paul on Saturday and ended up showing my mother around some of the localities I'd been to last year for a project. There was the overlook north of the Ford Bridge, across from the Temple of Aaron, where I'd seen a shell bed in the Magnolia Member of the Platteville, but the site turned out to be a lot more interesting with a year of experience under my belt. This time, we could follow the shell bed around the outcrop, and I could pick out the overlying Carimona Member of the Decorah Shale.

The shell bed, highlighted by a helpful graffiti artist.

Sunday, April 13, 2014

Where to see metro geology, part 2: Minnehaha Regional Park

When we left off in Part 1, we were hanging around the observation area of Lock & Dam 1. Directly west of the observation area is Minnehaha Regional Park, famous as the home of Minnehaha Falls. Minnehaha Falls is one of a series of cataracts that have formed along the Mississippi in the Twin Cities. The basic processes went like this: each time the glaciers rolled through, they filled up the preexisting river system with glacial debris, and each time they retreated, the river system reestablished drainage. The last time the system was reset, the Minnesota–Mississippi network was grinding its way through the Platteville until it scoured into an old channel in the vicinity of Dayton's Bluff. It's a lot easier to wash out loose debris than it is to erode the Platteville, and a waterfall (proto-St. Anthony Falls) formed where the two met. Over the years, the waterfall eroded upriver, and every time the falls passed a tributary, a smaller waterfall ended up forming on that creek or river, too. This is how we got Hidden Falls, Shadow Falls, and a host of falls that are now mostly to well and truly extinct (human intervention in the drainage systems), as well as Minnehaha Falls. There is something of a cottage industry among Minnesota's geologists of reckoning the elapsed time since deglaciation by calculating the rate of retreat of St. Anthony Falls, using historical observations of its locations before the 1870s, the properties of the underlying formations, and the starting point, but that is for another time.

Sunday, April 6, 2014

Practical considerations and hazards

If you do choose to explore Twin Cities geology beyond the most convenient couple of places, it is worth knowing something about the terrain. Most practicalities are the same as you would use for any hiking trip: sturdy boots, sunscreen, insect repellent in the buggy times of year, a hat, and so forth. I recommend long pants and sleeves, to protect your arms and legs from banging against things and to give you less to worry about in terms of bloodsucking multi-legged friends, but I realize that this can get extremely uncomfortable in the summer, when the atmosphere transitions from hot and humid to hot and gelatinous. At any rate, choose clothes that you wouldn't mind getting ripped, roughed-up, or coated in mud. Have water on hand, too.

Saturday, March 29, 2014

Where to see metro geology, part 1: Lock and Dam No. 1

As the snow and ice begin to melt away and the temperature rises above freezing, it once more becomes possible to see the geology of the metro without outfitting a polar expedition. While there's something to be said for iced-over waterfalls and the peace and stillness of a fresh winterscape, it's darned hard to take field notes with choppers on or fogged-up glasses, and frankly if you're doing it to impress people, it won't work. Spring is not a bad time to do some exploring; you don't have to contend with the bugs, the generous Minnesota humidity isn't in full swing yet, and the ground vegetation hasn't obscured many areas (and given ticks places to loiter). The most obvious drawback to springtime geology is the saturation of the ground, particularly in places where the Decorah Shale is at or near the surface. The Decorah likes to form a thick gray-green mud that both cakes footwear and makes the ground admirably slippery, particularly on slopes where you'd just as soon prefer that it wasn't slippery. Throw in the leaf litter from the previous fall, and your April hike can get a lot more interesting. A less-obvious hazard is the insidious action of freeze and thaw cycles. In short, rocks that weren't fractured and liable to fall or slide in the autumn can get that way by the spring.

Sunday, March 23, 2014

Dinosaurs in limbo

Following paleontology can be a bit like getting presents on birthdays or Christmas or what-have-you. Sometimes you get completely knocked out by something, having had no idea it was on the way. Sometimes you know what's coming, and it's just a matter of waiting for the big day. Sometimes it gets held up in the mail, or the store's out and it's on back order, so you still know it's coming, but you don't know when. Finally, in a few cases it seems like the darn thing got lost somewhere. As of the time I am writing, March 22/23, the latest greatest dinosaur discovery in the news is the "chicken from hell", Anzu wyliei, a 3-m long distant relative of Oviraptor from, fittingly, the Hell Creek Formation of Montana ("Anzu" being a reference to a Sumerian demon). My first reaction was "Finally!" You see, Anzu had been floating around for years under various nicknames like the "Hell Creek Chirostenotes" or "Chirostenotes sp.". It was quite familiar to
the dinosaur paleontology community; it was just a question of when it would be described.

Sunday, March 16, 2014

On the Arctic Cretaceous

By now, those of you who follow paleontology news have probably heard of Nanuqsaurus hoglundi, the newly described genus and species of small Arctic tyrannosaur. The obligatory and nearly instantaneously produced Wikipedia article can be found here, and the scientific description can be found here. Nanuqsaurus comes from rocks of the North Slope of Alaska, and lived about 70 million years ago. It's just the "tip of the iceberg", so to speak, of the North Slope dinosaurs, which also include the hornless horned dinosaur Pachyrhinosaurus perotorum, a bonehead named Alaskacephale, the ubiquitous duckbill Edmontosaurus, and various small theropods. This is pretty typical for the latest Cretaceous of North America, give or take an armored dinosaur.

Sunday, March 9, 2014

Fossils in the St. Peter Sandstone

The St. Peter Sandstone, a Middle–Late Ordovician unit that deserves the appellation "sandstone" like few other formations, has proven itself a very useful formation. Its extremely pure quartz sand is prized for various industrial applications, like glassmaking. It is readily excavated, so digging sewers and burying utilities is simplified. It has a tendency to form caves, which coupled with the ease of excavating makes it an ideal substrate for underground storage, cheese aging, mushroom growing, some types of brewing, and so on. More frivolously, it has provided a vast natural canvas for people who like to carve their names in things, and it has rewarded generations of graduate students looking for thesis and dissertation topics. At 100+ feet (30 m+) of uniform sand with few apparent bedding structures, and an off-white color that weathers to a kind of sickly gray, it is also an excellent natural soporific if you are not interested in any of these things. This most useful of formations is very much a bust paleontologically, which seems like some kind of a metaphor, but I'm not going to push things.

Sunday, March 2, 2014

Ordovician microbial mats, featuring the Gopher Ordnance Works

Here's a little curiosity, bringing together a short-lived ordnance plant, Early Ordovician sea scum, and Clinton R. Stauffer, who seems to have become a patron saint of this blog through the first couple of months. Let's deal with the ordnance plant first.

Sunday, February 23, 2014

A road where the buffalo roamed

Personally, I don't have fond thoughts of I-35E. In my mind, it is indelibly associated with long back-ups at the interchange with I-94 in St. Paul, particularly I-94 eastbound in the evening rush hour. But enough of complaints; if the interstate could think and speak, doubtless it wouldn't be happy with traffic jams either. I-35E happens to run in an old river valley north of I-94. The drainage was known as Trout Brook, and it gradually disappeared from the surface between about the 1880s and the 1950s (an overview of the valley can be found here).

Sunday, February 16, 2014

Side Effects of a Misspent Youth

So, something on the lighter side, while I consider future directions for posts (see the last paragraph). Sometimes people relate one of their skills to a childhood interest, like someone who collected baseball cards developing an aptitude for math or statistics. These relationships are not always obvious, but I'm sure you can think back and say "I learned about [X] because I liked playing/reading/building/... [Y]." For me, I spent a lot of time reading dinosaur books, but I also managed to pick up a few other things, too. Here are some of them, in alphabetical order:

Sunday, February 9, 2014

Practical guide to MNRRA/metro-area bedrock geology

I can't believe I didn't put up a post like this earlier. Here is a thumbnail guide to the various bedrock formations exposed within MNRRA and, by extension, most of the Twin Cities metro. Further information can be found in Ojakangas and Matsch (1982) or Ojakangas (2009), if you'd prefer a nontechnical level of discourse, or Mossler (2008) if you want a technical overview. The maps published by Mossler and Tipping (2000) and Mossler (2013) (see previous post) are also useful.

The formations of interest are the Jordan Sandstone, Prairie du Chien Group, St. Peter Sandstone, Glenwood Formation, Platteville Formation, Decorah Shale, and Cummingsville Formation. We'll take it from the top, or rather, the bottom, going in ascending order from the oldest rocks that are exposed (the Jordan Sandstone; there are older rocks below it, but they aren't exposed within MNRRA or in the central Metro. You can find most of them along the St. Croix, though).

Thursday, February 6, 2014

A brief meditation on the joys of packrat middens

One more trip to the Quaternary, for a personal favorite...

Imagine someone has asked you to describe what an area was like hundreds, thousands, perhaps tens of thousands of years ago. They're interested in the ecology, the climate, and so forth. What could you use to accomplish this? If there are lakes and marshes, you might start by taking sediment cores and looking for pollen, which tell you what kinds of plants were present, and how the flora changed over time. If you're on the coast, you might look for deposits of shells, which are useful for describing the conditions of the water (salinity, temperature, how energetic the setting was) and for stable isotope analyses. If there's a lot of ancient wood, you might get into tree-ring data. In dry protected places of western North America, there is another type of paleoecological indicator: middens constructed by packrats.

Sunday, February 2, 2014

Metro mammoths

Many states have had inventories published of Pleistocene mammal finds; I'm putting together a file for a future post. The most recent such report for Minnesota was complied by Clinton R. Stauffer and published sometime in the late 1940s. It is often cited as Stauffer 1945, but he cites several finds from 1946 and 1948. The journal is a proceedings volume for 1945, which is where the usual date comes from, but the Minnesota Academy of Sciences must have had some trouble getting it out that year. Anyway, 1945, 1948, the immediate point is that it's been a while.

Wednesday, January 29, 2014

Little island mammoths of California

Doing my bit to encourage warm thoughts for those of us in the frozen north...

I present to you an island off the coast of what is now California, approximately 15,000 years ago. This island is called Santarosae (or Santa Rosae); as sea level rises following the melting of the great continental ice sheets, it will be dissected into the four northern Channel Islands (San Miguel, Santa Rosa, Santa Cruz, and Anacapa), which are eventually reunited as Channel Islands National Park (with Santa Barbara Island). These events, though, are in the future. For "now", we have one large island a handful of miles from the coast:

A. The modern northern Channel Islands. B. The geography of the islands at various times in the recent past. From Collins (2009).

Saturday, January 25, 2014

Platteville follies: a crushed giant rodent from Hidden Falls

I'd like to start off with a couple of photographs, to illustrate some facts of life concerning our old friend, the Platteville Formation:

An ever-so-slightly hazardous ledge along the road into Crosby Farm Regional Park.

Hidden Falls Regional Park: when good rocks go bad.
The Platteville Formation just loves to ledge out, particularly the lower part, which rests on the recessive Glenwood Formation, and once you get heavy rocks ledged out far enough... About ten thousand years ago, not very far from the second photo, there was a ledge of the Platteville Formation left jutting out in the figurative "wake" of the erosion of the Mississippi River system. At some point, a dog-sized rodent opted to go underneath it. Maybe this was its usual shelter, or maybe it was driven there by some circumstance; we'll never know, short of time travel. Unfortunately for the rodent, the slab failed, with predictable results. It would be covered by the debris until July of 1938, when a Works Progress Administration crew uncovered the site while widening what is now the north entrance road into Hidden Falls Park. Its skeleton, crushed and coated with calcite leached out of the slab, was recovered and eventually prepared, reconstructed, put on display at the Science Museum of Minnesota, and described scientifically as an example of the extinct mammal known as Castoroides ohioensis, a.k.a. the giant beaver.

From Powell (1948): the WPA project that led to the discovery (site with the superimposed white circled cross).
"Well," you say, "that was refreshingly concise." Ah, but there's always more to say.

Wednesday, January 22, 2014

Anchisaurus is older than you might think

Anchisaurus is kind of a second-tier dinosaur, not up there with Tyrannosaurus, Triceratops, Velociraptor, and their ilk, but it gets a fair amount of exposure, especially if you pull in the old synonym Yaleosaurus. It gets points for having a long history, having a few interesting anecdotes associated with it, being one of the first early dinosaurs known from good remains, and beginning with the letter "A"; this latter bit is important, because it means Anchisaurus ends up near the beginning of children's A-Z dinosaur books. (Is this why so many dinosaur names begin with "A"?)

Sunday, January 19, 2014

Divisions of the Platteville Formation

There comes a time when we must speak of the Platteville Formation in detail. If there wasn't a Platteville Formation, there would be no narrow gorge in the Twin Cities, no Minnehaha Falls or Hidden Falls, and most importantly no Saint Anthony Falls: if there's no Saint Anthony Falls, Minneapolis develops in a radically different way. No falls, no easy water power, no mills. The Twin Cities owe their existence to a 455 million year old carbonate bank and the vagaries of glacial and river erosion.

And today the Falls of St. Anthony are mostly artificial. Turns out that drilling holes through the Platteville into the St. Peter Sandstone near the edge of a cataract can be unsafe.

Wednesday, January 15, 2014

Bedrock Geology of the Twin Cities Ten-County Metropolitan Area, Minnesota

Just a quick midweek post...

I'd like to plug the Minnesota Geological Survey, in particular their fantastic collection of online publications. Everything published by the modern Survey or its 19th century incarnation is available for download as pdfs. Looking for, say, the fossil volume of The Geology of Minnesota monograph series? Parts One and Two. The geology of Anoka County? Right here. A publication on Minnesota brick and tile manufacturing? Here (and it's by a man named Grout, which just seems like some strange kind of destiny). Anyway, if you poke around the main list, found at the second link above, you'll find just about anything that can be written about Minnesota rocks. If you're not especially familiar with geology, I'd recommend starting with the "Minnesota At A Glance" documents under "Miscellaneous Publications", or the publications under "Educational Series".

I'd like to draw your attention to one of the newest publications, "Bedrock geology of the Twin Cities ten-county metropolitan area, Minnesota" by John H. Mossler. This is the newest in a line of geologic maps of the Twin Cities going back to the 19th century. The link I provided has three links at the bottom; unless you have GIS software, I'd recommend just going for the first link, "10 county map.pdf". To briefly explain if you haven't had much contact with geologic maps, this map shows the locations of various rock formations, as well as folds and faults (not that we're swarming with them in east-central Minnesota, but there are some). The rock formations are denoted by color and by a short letter code; for example, the Decorah Shale is represented by a teal color with Od, the "O" for the Ordovician Period and the "d" for the Decorah. (the map is a bit inconvenient in that several of the formations have been given similar shades of blue; fortunately, because the rocks in question are flat-lying with few folds and faults to break up the succession, it's usually not much of a problem to tell what is what once you are familiar with the order.) Older rocks are found where the younger rocks have been eroded, such as in the various modern and ancient river channels.

An important caveat is illustrated by the cross-section, which shows an otherwise un-mapped brown layer covering almost everything to the tune of a couple hundred feet (60+ m); this brown layer represents Quaternary deposits, mostly the stuff so generously left behind by glaciers. In other words, the main map is what you'd get if you vacuumed up all of the loose stuff on top. The terrain left behind would be kind of strange, because the glacial deposits cover a lot of old river channels (every time there was a glacial advance, the previous channels would be buried, and new channels would be excavated after the glaciers retreated; some of the older channels cut down significantly deeper than the modern channels – the modern Mississippi above Fort Snelling doesn't cut into "yellow" rocks [Jordan Sandstone] until it gets out of the central metro, for example). The majority of the map was made from subsurface data, such as well logs; the ubiquitous circles are water wells with logs. Areas where the bedrock is exposed at the surface (and which are large enough to be mapped at a scale of 1:125,000) are denoted by a dark gray color. Zooming down to 300x or 400x, where the street grids become comfortable to read, shows that most of these outcrops are near the modern river system. This is because the river have cut through the glacial deposits into the bedrock. Some of the large areas of dark gray pick out quarries, like the one on Grey Cloud Island. There are also thumbnail descriptions of the formations at the bottom, describing the thicknesses, what the formations are made of, and so forth.

References

Mossler, J. H. 2013. Bedrock geology of the Twin Cities ten-county metropolitan area, Minnesota. Minnesota Geological Survey, St. Paul, Minnesota. Miscellaneous Map Series 194. Scale 1:125,000.

Sunday, January 12, 2014

Scolecodonts and other signs of worms

Clinton R. Stauffer had one of the most convenient field areas it is possible for a geologist to have. He worked for the University of Minnesota from 1914 to 1944, producing a number of papers on paleontology and stratigraphy; they include a study of the Paleozoic of Minnesota (Stauffer and Thiel 1941), a list of Pleistocene mammal finds from the state (Stauffer 1945; an update would be greatly appreciated!), and several descriptions of microfossils (Stauffer 1930, 1933, 1935a, 1935b). He did a fair amount of collecting for the university, and a fair amount of collecting within the university. "Aha," you may say if you are familiar with the geography; "the campus is split by the river, with prominent and accessible bluffs." This is quite correct, but he did not limit his on-campus collecting to the bluffs. For example, during the construction of Northrop Auditorium in 1927, he obtained rocks from the excavation for the heating shaft (Stauffer 1930), and described a number of conodonts and other fossils from this material (Stauffer 1930, 1933, 1935a). If he wanted comparable material from other locations, it was only a matter of miles to southwestern St. Paul/southeastern Minneapolis, where he worked extensively in the Ford Plant/Fort Bridge/Minnehaha Creek/Lock & Dam 1 area (this was convenient both in terms of location and time; the dam, auto plant, and bridge were all completed during this time frame, so there was a lot of disturbed ground and excavated rock to pick through). It wasn't all roses and brachiopods, though; those bluffs on campus are not a place for anyone who have a healthy respect for gravity and large heavy rocks. The combination of a narrow footpath and overhanging rock makes the area about the most hazardous I have seen for Twin Cities geology.

The bluffs south of the Washington Avenue Bridge. Not recommended.

Wednesday, January 8, 2014

Monoplacophorans

There are some things in life that just don't have a handy name. Take for example the subject of this entry, an obscure group of mollusks known from a few modern deep-water species and a more robust fossil record. Various members of this group have labored under the terms "Monoplacophora", "Tergomya", and "Tryblidiida", all of which could be mistaken for a disease, a planet in a science fiction series, or a piece of anatomy you'd rather not know about. (You can combine all three: "I got monoplacophora in my tryblidiida after I visited Tergomya. It's as bad as it sounds.")  At one point someone suggested that their vernacular name should be "gastroverm", which you'll probably agree was no help at all. The reason for this multitude of names has to do with the rules of classification; visit here or here if you want details (and don't say I didn't warn you), but the basic bit is that Tryblidiida includes all the modern forms, and is classified in Tergomya, which is in turn part of Monoplacophora, and "Monoplacophora" is something of a problem because its traditional definition includes some things that weren't all that closely related. However, everyone was kind of used to Monoplacophora, so they kept it around, except now it can have a precise definition, or be a "state of mind" including various odd extinct things from the Cambrian, which I shall omit. If you want to be picky, this is about tergomyans.

Saturday, January 4, 2014

190+ years of Twin Cities geology/paleontology

Investigations of the geology and paleontology of the Twin Cities area of Minnesota go back a surprisingly long time. Several descriptions can be found from the decades before statehood (1858), included as parts of larger surveys (i.e. Keating [1824], Featherstonhaugh [1836], Nicollet [1843], and several publications by David Dale Owen [1847, 1848, 1852]). The earliest report I am familiar with was published by William H. Keating, concerning an 1823 expedition. Keating was something of a polymath who wore a number of different hats during his relatively short life (1799–1840), including three years' work in the schools and mines of Europe (Miles 1959). In 1823 he joined an expedition under the noted explorer Major Stephen H. Long, as the title of his 1824 publication makes clear (this was back when a title was also an abstract and introduction).