Introduction

As an experienced Cambrian trilobite worker, it is not uncommon for people to contact me asking what species they have and including a photograph of the specimen. These photos are commonly of un-whitened specimens, which make it difficult to make an accurate identification. Whitening the specimen with ammonium chloride sublimate or for larger specimens magnesium ribbon smoke is the preferred way of illustration. When the person sending me the photos are avocational collectors, I expect un-whitened photos, given most are unfamiliar with the process or have limited resources to do the whitening. However, there is a trend in professional publications to provide un-whitened specimens and this can be a serious problem.

Whitening provides a photograph of a specimen that shows most of its morphology needed for identification as well as the specimen flaws. For example, Figure 1 shows a silicified specimen of
Elrathina antiqua Palmer in Palmer and Halley, 1979 with different treatments. Figure 1.1 is the un-whitened, color picture of the specimen, which shows very little detailed morphology. Figure 1.2 is the same picture changed to black and white, with a few more details apparent, but still not very reveling as to the specimen’s morphology. Figure 1.3 and 1.4 illustrates the same specimen, now coated with ammonium chloride sublimate. Both the color (1.3) and black and white (1.4) now illustrate the detailed morphology of the entire shield (librigena are missing). Most trilobite workers would have little problem seeing the morphological features needed to identify the taxon. Figure 1.5 and 1.6 are again the same specimen, this time coated with colloidal graphite and then ammonium chloride sublimate. The use of colloidal graphite enhances contrast between the furrows and raised areas (e.g., glabella) and eliminates any color patterns on the specimen. This is my preferred way of illustrating trilobites because it does show the morphological details. For example, in the uncoated specimens you cannot see if there are either glabellar furrows, an ocular ridge or surface ornamentation. In the blackened and whitened specimen, you can see that there is no visible glabellar furrows or ocular ridges and the exoskeleton is smooth (no pits or granules).

When professional publications contain photographs of un-whitened specimens, critical details of the morphology are lost in color patterns (e.g., partial coating by limonite) and/or the fine details of the furrows, surface, articulating rings, course of sutures, etc. are not visible. This inhibits the reader the chance to compare the taxon to other similar taxa. As a reviewer of several trilobite papers for professional journals, I have seen authors use un-whitened specimens and find myself asking if I can really see the morphology that the authors are describing. Sometimes color photos of un-whitened specimens are needed (e.g., to show digestive track) and sometimes the specimen is well enough preserved so that just about every detail is visible. But most of the time, whitening is needed. Just because we can publish in color, we should ask: “Should we?”


Fred Sundberg

Show Low
, Arizona
sundbergfred@gmail.com

Reference
Palmer, A.R., and Halley, R.B., 1979, Physical stratigraphy and trilobite biostratigraphy of the Carrara Formation (Lower and Middle Cambrian) in the southern Great Basin: United States Geological Survey Professional Paper, v. 1047, 131 p.


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Figure 1. A single specimen of Elrathina antiqua Palmer in Palmer and Halley, 1979 from the middle Cambrian of Nevada illustrating the amount of morphological detail provided in 1) un-whitened color photo; 2) same photo as 1 converted to black and white; 3) specimen whitened, color photo; 4) specimen whitened, black and white photo; 5) specimen coated with colloidal graphite and then whitened, color photo; 5) specimen coated with colloidal graphite and then whitened, black and white photo. Specimen is mounted on an index card, silicified, and photographed with a ring light (no directional side light), disarticulated within the thorax, and missing the librigena.


Links

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The Trilobite Papers 20 are part of the PaleoNet system. Sponsorship of The Palaeontological Association is gratefully acknowledged.