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The Figure Makes the Fossil

As I wrap up revisions on a manuscript, as well as continuing the day to day work in “my” museum collection, I’ve been thinking a lot about what makes a good figure of a fossil. The thought is driven in part by wanting to illustrate the specimens we’re describing in detail, but it’s also driven by the need for my co-workers and me to be able to identify specimens as they come in from the field.

Illustrations, ideally, are used by more than just the few specialists on a group. Life at a museum makes me realize just how much collections staff* need good illustrations, too! It also makes me experience the complete inadequacy of the figures in the great majority of papers. Much of this inadequacy, I suspect, stems from historical space limitations in print journals…now that that is changing (for at least some journals), it’s a good time to talk about what makes a well-illustrated fossil.

*edit: and amateur collectors! I realized I had left this out in my initial post.

Multiple views of the skull of Nyanzachoerus khinzir, a fossil pig from Chad. CC-BY, from Boisserie et al., 2014.
Multiple views of a partial skull of Nyanzachoerus khinzir, a fossil pig from Chad. CC-BY, from Boisserie et al., 2014.

Lots of views
Most fossils are highly three-dimensional objects, so multiple views are essential to capture the anatomy. Unless we’re dealing with a heavily flattened fish or leaf imprint, multiple views are essential. An oblique view is nice too–sometimes that’s what it takes to better highlight a particular feature. Even better? 3D models. In ascending order of usefulness, this includes movies, 3D PDFs, and printable, freestanding 3D files (e.g., STL or PLY format).

Skeleton of the ankylosaur dinosaur Chuanqilong chaoyangensis, with photo and line drawing. CC-BY, from Han et al., 2014.
Skeleton of the ankylosaur dinosaur Chuanqilong chaoyangensis, with photo and interpretive line drawing. CC-BY, from Han et al., 2014.

Drawings
Every fossil needs some interpretation, particularly in the case of skulls and other complex fossils. A good drawing will indicate sutures, important holes, and other features that may not be easily visible on a photograph. [Note: this includes not just line drawings, but also other renderings–a skilled artist can work wonders with a fossil!]

Detail of a Cretaceous crocodilian tooth at maximum published resolution. CC-BY, modified from Pol et al. 2014.
Detail of a Cretaceous crocodilian tooth at maximum published resolution. “de” indicates a denticle. CC-BY, modified from Pol et al. 2014.

High resolution
This should be a no-brainer, but it is amazing how many journals require high-resolution figures at submission and then publish heavily down-sampled images. This is a waste of the authors’ time, and it reduces the utility of the image for the reader. That extra bit of zoom can be really valuable sometimes, particularly for multi-part figures!

This is what a sample size should look like! One block from the new pterosaur discovery site--scale bar equals 200 mm. From Manzig et al., 2014, CC-BY.
A fantastic color image of a pterosaur (flying reptile) mass accumulation. CC-BY, from Manzig et al., 2014.

Color
It isĀ incredible what things pop out in a color versus a grayscale image. Areas of reconstruction, crushing, and changing bone type are often far more easily seen when all of the color data are left intact. Thankfully, many journals now encourage color images, even if the printed copy remains in grayscale.

Scales of an ancient acanthodian fish, Nerepisacanthus, showing the fossil in full-color and the counterpart coated to enhance detail. CC-BY, from Burrow and Rudkin, 2014.
Scales of an ancient acanthodian fish, Nerepisacanthus, showing the fossil in full-color and the counterpart coated to enhance detail. CC-BY, modified from Burrow and Rudkin, 2014.

Grayscale / Color-Free
Yes, this goes against everything I just said above. Some specimens, depending upon preservation, are mottled to a point where it is difficult to pick out morphology. In this case, a color-free representation can be invaluable. This is best achieved by either coating specimens with an appropriate substance (as in the above image), or digital scans reconstructed without the obstructing colors.

Hand bones of Nimbadon, an extinct, arboreal wombat-like marsupial. CC-BY, from Black et al. 2012.
Hand bones of Nimbadon, an extinct, arboreal wombat-like marsupial. CC-BY, from Black et al. 2012.

Illustrate everything
Fossils rarely manifest as complete skulls or highly diagnostic elements. Sure, teeth are the most diagnostic part for many mammals, but what about the rest of the skeleton? Many collection drawers are filled with isolated and unidentified wrist and ankle bones, the durable blocky elements that fossilize so nicely. Unfortunately, they’re often very poorly illustrated in the literature! Good luck trying to “figure out” an entocuneiform or a navicular (pun only somewhat intended). Collections staff and researchers can spend a lot of time trying to identify common, complete, and clearly diagnostic elements that just don’t have comparable material widely figured in the literature (particularly in the absence of a good, identified comparative collection). This even applies to some quite common fossils. For instance, horse teeth are quite well illustrated, but it’s surprisingly difficult to find figures of individual vertebrae or some of the more obscure ankle bones.

Parting Thoughts
As scientists, we should strive to make our work as accessible, reproducible, and useful as possible. Comprehensive and clearly rendered figures are essential for achieving this goal.

Discussion
  1. Excellent points!
    in some cases it may even be a good idea to create a high-resolution 3D model and export a colour-free orhtophoto from it. That way, you can get rid of the annoying discolourations many fossils show, and additionally have an undistorted image to boot.

  2. Fun article with a lot of good points. I’m agreed on the horse anatomy point you make, although there are some excellent French b/w line illustrations of appendicular elements in “Atlas Osteologique.” They include all of the small bones as well, shown in multiple views. Unfortunately, the axial skeleton is not included, but I always found these books an invaluable resource and the only one illustrating the pesky small elements.

    These books only cover Quaternary herbivores and some carnivores but the quality of drawings is excellent.

  3. “It is amazing how many journals require high-resolution figures at submission and then publish heavily down-sampled images.”

    Yes! It’s absolutely ridiculous. One of the worst offenders, unfortunately, is the open-access palaeontology pioneer Palaeontologia Electronica. See for example Witton, Naish and Conway’s recent piece State of the Palaeoart, in which all the images are a weedy 400 pixels wide. That renders the skeletal sketches of Figure 2 all but invisible, and makes a mockery of the composite Figure 3, in which the seven composed art pieces range from 125×129 pixels down to an absurd 68×129 pixels. In a piece that is all about art, that is just inexcusable.

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