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.