A Brief Digression on the Art of Identifying Fossils

If you let it get around that you have some knowledge of fossils, inevitably somebody is going to ask you to identify something. I'm sure everyone in this position has the usual gripes about "dinosaur eggs" or "dinosaur hearts" or "dinosaur skulls" that are really just regular humble rocks viewed through bifocals of hope and inexperience. The only skills and resources needed here are tact and diplomacy, to work the conversation in such a way that it comes to an expedient close without unnecessarily cheesing off the hopeful inquirer (and recognizing that sometimes it's just not possible to have a productive interaction with somebody who insists they have dinosaur eggs).

Then there's the real thing. I get a few requests for identification every month, sometimes through work, sometimes submitted by blog readers to my email. This can be a challenge, especially for work, since the National Park Service can boast an impressive sweep of geologic time and diversity of fossils. I can be looking at photos of Devonian marine invertebrates one week and Cenozoic plant fossils the next. Then, of course, there's dealing with the fossils I find; I've had several in the past few months that were clearly something of interest but were also outside of my experience. It's been a long, long time since someone could be familiar with every kind of described fossil. What is one to do?

If identifying fossils is something that interests you beyond picking up a few names, you can learn from fossil and rockhound communities (online and in person). You're also going to be in for some self-teaching. Fossil identification has never been a huge field and has dwindled (for one thing, biostratigraphy is no longer as important for industry). Whether identifying fossils for someone else or yourself, the first thing you'll want is references with lots of good pictures. A good field guide to fossils, like the National Audubon Society's version, is a handy starter to at least get you into the correct phylum. Many times, that's all you need or want; for groups that require thin sections to identify, or groups where you get a lot of internal casts, "bryozoan" or "snail" is often enough, maybe with some morphological jargon. Depending on how much attention people have given your local rocks, there may be specialist books (like this one), online guides, or both. A "Roadside Geology"-type book may also be helpful in providing background information on your rock formations, which is useful for figuring out more specialized publications. (Or sometimes not, if people can't agree on what to call the rocks!) Similarly, if you are interested in specific kinds of fossils (e.g., shark teeth), there may be dedicated references available.

A few other observations:

• A lot of things simply aren't identifiable very far: too weathered, too fragmented, too much covered by matrix, weird cross-sectional view, etc. That's just the breaks.
• Photos in field guides and other sources are generally of the best specimens, with museum-quality preparation. The average person is probably not going to be that lucky and probably doesn't have access to those skills. This is something that needs to be taken into account when making identifications. When I work on paleontological resource inventories, I like to include "typical" images of fossils so park staff will have a better idea of what to expect.
• Good photos and illustrations are not available for every species (especially older names in areas where not much work has been done), and what is out there will not generally cover every potential view.
• A further complication when hunting reference images is changes in taxonomy. For some groups (I'm thinking especially of brachiopods at the moment), species have switched genera several times. To further complicate things, not all authors will catch on, and some will simply disagree. Hardcore identification may require becoming familiar with name changes, because the images you need to find may be under an unexpected name. This is, needless to say, very frustrating.
• Unless you've gotten involved in high-stakes fossil identification, there's no shame in revising identifications as you get more experience. When you start off, you'll have a natural bias to identify things in terms of the first things you learned to identify. You may also tend to identify things as more rare or unusual options, or make identifications to genus or species when you'd be better off sticking at a higher level, or have other biases due to inexperience. When I started with Decorah fossils, I had a hard time with trilobites and basically pretended they didn't exist until I got an eye for them. (A little bit of the buried edge of a small ribbed brachiopod shell can look a lot like the margin of a buried pygidium, especially when you don't know what you're doing.) Similarly, despite what this blog might suggest, it took me a long time to get an eye for stromatolites.
• It's good to know about common types of pseudofossils, especially if your area has a particular specialty.

Uŋčí Makhá Park Revisited, Part 1: Freeze-Thaw

After I'd come across the new exposures at Uŋčí Makhá Park last fall, I was very curious about how a Minnesota winter and spring would treat them. After all, these were fresh, with no previous direct exposure to snow, ice, and freeze-thaw cycles. Would they rapidly degrade, or were they made of sterner material? Last week I had the opportunity to spend some quality time at the park, in preparation for and leading a training session for Mississippi National River & Recreation Area seasonals (and if any of the participants happen on this post, hello! I hope you had a good time!).

What were the results of this natural experiment? A few observations:

The Carimona Member of the Decorah (blue-gray upper interval), particularly the blocks used as landscaping, suffered appreciably more than the Magnolia Member of the Platteville (tan lower interval). I attribute this to the greater shale content of the Carimona.

This is a pretty illustrative comparison. The blue-gray block on the upper left is Carimona, and the tan block on the lower right is Magnolia. The Carimona block's upper surface is littered with small chips, while the only chips on the Magnolia block came from the Carimona block. (Note also the large burrow on the Magnolia block.)

More Carimona landscaping showing exfoliation.

This indicates that the Carimona blocks will weather faster than the Magnolia blocks; eventually, both lithologies will reach equilibrium with their new surroundings, but the "fucoidal" surfaces on the landscaping are going to go away faster than the shell beds.

Note the burrows popping off the surface in some places.

It wasn't all smooth sailing for the Magnolia, though. Although many blocks and beds seemed fine, others had definite signs of damage.

Here a thin bed is breaking up.

This isolated block appears to be shattered. (Colors are weird because when I took this photo, I'd forgotten to reset the lighting from tungsten bulbs.)

Unlike last fall, which was a time of drought, this spring we can also definitely see where the seeps are.

And they're concentrated at the bentonite layers in the Carimona.

Many fossils and features came through without particular damage, though. I included a photo of a bivalve in the fossil guide post. Here it is last week:

Dare I say that it's "happy as a clam"? (Ignore the color balance differences.)

With that out of the way, did we find other fossils I hadn't seen in the fall? Well, of course! Tune in next week for some less-typical fossils!

Quick Guide to Fossils at Uŋčí Makhá Park

So I went back to Uŋčí Makhá Park last weekend and spent a couple of hours taking photos of fossils, because it makes such an ideal place to see the upper Platteville fauna. After all, a winter of freezes and thaws may not leave these new exposures looking as nice as they do now. Here's a quick guide to what can be seen there. (Let's see how many photos I can squeeze into one post, and how many species I can misidentify!)

Determining where you are stratigraphically

First of all, I'd just like to reiterate the stratigraphy. Most of the vertical extent is in the Magnolia Member of the Platteville Formation, with the upper part composed of the Carimona Member of the Decorah Shale. I'm thinking more or less the entire extent of the Carimona is exposed, based on thickness; at any rate the next thing up would be the shaly part of the Decorah, and there isn't a trace of it to be seen. I'm suspicious because the difference is just so darn clear, but at this site there is an unmistakable color change between the two units: the Carimona is the upper blue-gray interval and the Magnolia is the light tan-gray interval below. The Deicke K-bentonite is the lower and thicker of the two bentonite gaps in the Carimona. (Note that the Carimona is sometimes supplemented or replaced by landscaping, but this is pretty obvious.) As you walk from south to north, the "floor" goes up stratigraphically, so it's not all one bedding plane but a gently rising series of planes, until by the exit you're close to the color change.

The color change is quite evident here. The Deicke K-bentonite is the cut-in about halfway up the blue-gray Carimona (above the scale bar in the center of the photo).

Here we've gone north, and the floor has risen. The Deicke is still the seam in the middle of the blue-gray rocks.

Rockfall

One of the characteristic aspects of the Mifflin Member of the Platteville Formation is its habit of planar jointing. The faces of outcrops often look like someone took a rock saw to them. Nor are they necessarily single flat planes; sometimes joints intersect to form sharp angles. The heavy thunderstorms the previous week inspired a large chunk of Mifflin outcrop to collapse along intersecting joints.

Tumbled down

The joint planes did not form overnight, which can be seen by the amount of roots and soil in the new outcrop faces. There were some pretty big roots in there as well, but whatever tree(s) had once produced them is long gone.

A view into the wedge more or less along one of the two joints.

This particular rockfall was about as polite as possible, occurring not at the top of a stereotypical 30-foot bluff but from a much lower bluff, adjacent to a bike path. The orientation of the wedged stack shows that it toppled out of its former position. The top of the stack is therefore farthest from the bluff. Perhaps it failed at the base first, due to poor support from the Pecatonica, then flopped over.

History going from left to right

Fates of collections

Despite our best intentions and planning, a lot of things can happen to a collection. We saw an extreme example of this recently in the devastating fire at the National Museum of Brazil on September 2. Many fossil collections have been partially or completely lost to fires since people began accumulating specimens for scientific purposes, and we can be sure that there will be losses to come from fires. Of course, fires are not the only way institutions have lost collections. Apart from occasional attrition (specimens becoming misplaced, damaged or destroyed through accidents, lost while on loans, or outright stolen), large portions of paleontological collections to entire collections have gone from their original institutions in a variety of ways.

Fire

Although fossils are, generally, basically rocks, fire can indeed cause damage to rocks. Water used in firefighting can also damage rocks, for example rocks composed of shrink-swell clays, and rocks with significant organics are vulnerable to both fire and water damage. (And if the specimens are late Quaternary paleoecological materials such as dung or middens? You've got a repeat of Rampart Cave in the museum.) Rocks can also be damaged by heavy objects falling on them during fires. Other issues may include, but are not limited to, being covered by melted materials and being subjected to explosive events. Furthermore, even if a given fossil survives a fire, it may be lost during recovery efforts.

Fires are not as common as they once were, thanks to improvements in fireproofing and fire suppression, although these advances cannot help if they are not implemented or are otherwise unavailable. For example, the National Museum of Brazil lacked sprinkler systems, and water for firefighting had to be brought to the scene. A significant cause of many late 19th century and early 20th century fires was early electrical systems.

Here are a few U.S. fires I've come across that affected fossil collections; it is certainly not exhaustive! It does cover nine decades and everything from two state capitols to a modest facility in the Big Bend of Texas:

• Academy of Science of St. Louis, May 1869: included some of Benjamin Franklin Shumard's collections;
• Minnesota State Capitol, St. Paul, March 1, 1881: this fire claimed the Minnesota Academy of Science collections, which among other things held mammoth or mastodon fossils from Stillwater;
• Texas State Capitol, Austin, November 9, 1881: this fire destroyed the remnants of Shumard's Texas Geological Survey specimens;
• Science Hall, University of Wisconsin–Madison, December 1, 1884: this building housed the Wisconsin State Collection, including some of R. P. Whitfield's St. Croix fossils;
• Academic Hall, University of Missouri, Columbia, January 9, 1892: another group of Shumard's fossils was lost in this blaze;
• Williston Hall, Mount Holyoke College, South Hadley, December 22, 1917: in dinosaur paleontology, this fire is best known for the loss of the holotype of Podokesaurus holyokensis;
• Chisos Basin Civilian Conservation Corps barracks, December 24, 1941: this building housed a small museum of Big Bend fossils;
• Williams Hall, Lehigh University, Bethlehem, February 1956: a fire in the third floor of this building is implicated in the disappearance of a collection of Ordovician fossils collected near Delaware Water Gap.

War

Many collections have been partially or wholly destroyed in wars, particularly at European institutions during the two World Wars. The poster child for these losses is the holotype of Spinosaurus aegyptiacus, lost along with other Egyptian fossils (including Aegyptosaurus baharijensis) when the Paleontological Museum in Munich was hit by bombs during a night raid, April 24–25, 1944. Specimens and larger collections have sometimes also been looted, for commercial value or as a kind of "scientific imperialism". Wars and other armed conflicts have not been a major issue for collections in the U.S. since the Civil War, when there were few significant collections. One exception was the Texas Geological Survey collection, left in limbo at the start of the Civil War. Almost all of the specimens amassed by Benjamin Franklin Shumard for the survey were lost during the war when the State Capitol was turned over to the manufacturing of percussion caps. (In case you're wondering, that makes three fires and one loss-by-neglect for Shumard, who simply could not catch a break.)

Disbursement or transfer

While you may be under the impression that your favorite museum accumulated all of its specimens on its own, maybe with some scattered donations thrown in, if you scratch the surface you will probably find that the museum has absorbed multiple substantial collections over the years. These may be personal collections (such as the collections of Edward Drinker Cope and James Hall at the American Museum of Natural History), corporate collections (think invertebrates and microfossils collected for oil companies), or collections from other institutions (for example, in recent decades the Natural History Museum of Los Angeles County has incorporated collections from UCLA, Cal Tech, CSUN, and USC). The fact is that many places have accumulated collections over the years, only to end up sending them elsewhere for various reasons: change in direction, loss of funding, streamlining of collections, retirement of key staff, lack of interest, etc. This kind of movement can involve entire collections or only parts of collections (paleobotany seems peculiarly vulnerable to this). Technically speaking, the specimens are not "lost", although relocation of a collection can result in loss or damage to specimens, and the collections can sometimes *seem* lost if you're trying to track them down years after the fact!

Although small institutions are probably most likely to send their collections elsewhere, even storied, historically significant collections have been transferred. Princeton gave their vertebrate paleontology collections to Yale in 1985 when the university decided to cut the paleontology program. The USGS collections in Washington and Menlo Park went to the Smithsonian and the University of California Museum of Paleontology, respectively, following political wrangling in the mid-1990s. Integrating established collections into their new homes can be a headache, and specimens from large added collections often retain some part of their original identity. For example, fossils from Princeton in the Yale collections include "PU" in their catalog identification.

Identifying invertebrate fossils

Pop quiz! (don't worry, it's not for credit)

Romance *and* brachiopods

Here we have an assortment of fossils, tastefully arranged in a holiday-appropriate setting. They're all the typical local Ordovician stuff, but many Paleozoic shallow marine formations will have a lot of the same general things. What are they, and how can you tell?

When to stay away from outcrops and exposures

Some recent events have provided photographic fodder for a brief unscheduled revisit of safety concerns in the rocks of the Twin Cities, but first I am going to plug the reborn Park Paleontology newsletter. I'll hit it some more this weekend in more detail, but I particularly want to call out Chapter 3 by Emily Thorpe, who was a Geoscientists in the Parks intern over the winter at Salinas Pueblo Missions National Monument. Among other discoveries, she's got the first vertebrate from the Yeso Group (Arroyo de Alamillo Formation), the part and counterpart articulated back half of a skeleton. We've had a lot of great projects from GIPs the past few years, and I'd strongly encourage college students in the geosciences to have a look when the next batch of positions comes out.

Meanwhile, back in the Ordovician...

You may remember the following photo from this post, or this post. Coincidentally, in both posts the photo is being used as an example of a hazard. It was taken back in June 2013 along the road into Crosby Farm Regional Park, before you get to Watergate Marina.

I wonder where this is going...

If you take that road today (May 2017), this is what you'll see:

...the answer appears to be "down".

This is why you should not stand too close to the walls of the bluffs, or to the edge on top.

Meanwhile, over at Shadow Falls, the Decorah Shale presents a different issue, one that can be expressed as a recipe titled "Reconstituted Ordovician Seafloor": take a hillslope of weathered marine shale, and over the course of six days add nearly five inches of rain. It's amazing!

Hiking boots? More like cleats.

The running water is Nature's subtle way of telling you to stay off.

It's not the mud itself that's the big problem (unless you hate mud, in which case you're really in the wrong place), but the slippery sloppy footing. If you go over into the ravine, it's not going to be easy to get you out!

Hash slabs

It is common for fossils in the wild to be found in beds of uncountable fragments, some identifiable to species, others only barely recognizable as fossils. These assemblages are often called "fossil hash", for obvious reasons. Although you can have conceivably make a hash out of just about any kind of body fossil and some kinds of more discrete trace fossils (it takes a bit of creativity here), the term is usually applied to invertebrate fossils. This leads to the phenomenon of "hash slabs" or "hash plates", a more portable portion of a bed of fossil hash. Hash slabs can make great display or educational pieces, and a good slab rewards continued study; you can never find everything the first time, and as you learn more, you are able to find more. [2017/05/08: why have I been using "hash slab" as opposed to "hash plate"? I don't know, except I seem to be the kind of person who just has to reinvent the wheel.]

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.