JPT Nº20

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INTRODUCTION

Photography long ago proved itself an indispensable tool for paleontologists seeking to study fossil specimens and communicate their relevance for interpreting the history of life. The emergence of new digital imaging technologies (e.g., digital X-ray, X-ray computed tomography (CT), synchrotron radiation scanning, 3-D laser surface scanning, photogrammetry) and their application to the study of fossils stimulated an increased emphasis on the use of imagery as a tool to communicate scientific information. Each digital imaging technique comes with different strengths and weaknesses. Unfortunately, new technologies can contribute to the relative diminution in perceived importance of older or more traditional technologies and applications, sometimes before their full potential is explored and documented. Photography is a good example of this phenomenon.


Progressive Photonics is a suite of systematic, reproducible, simple, quick, and inexpensive digital imaging techniques using visible and invisible portions of the electromagnetic spectrum. Progressive Photonics techniques coupled with modern photographic and lighting equipment generate images that help distinguish biologic and geologic data from other data. The techniques can reveal subtle details such as soft tissues, micro-structures, and preparation artifacts that often are invisible to other methods of investigation and documentation (e.g., CT scanning, 3D surface scanning, photogrammetry, digital X-ray). The sequential imaging process and resultant images generated using Progressive Photonics significantly enhance scientific research and archival documentation of paleontological specimens. The importance, relevance, and ease of acquiring scientific images and their metadata (data the digital camera automatically saves plus light, filters, and other relevant data the camera does not save) is generally undervalued, as evidenced by their limited presence in paleontological literature.


Our use of the term ‘progressive’ has dual meanings. It suggests the methods and protocols described here constitute a significant improvement (i.e., progress) over status quo and inconsistent photographic approaches commonly used in paleontological research. More importantly, the term also describes the calculated and sequential progression of images through the electromagnetic spectrum that facilitate detailed comparison of the reactions of a specimen to those different stimuli. Our use of the term ‘forensic’ is intended to describe an organized and purposeful investigation of the history (natural or man-made) of a specimen. Our use of the term ‘forensic’ does not have any legal connotation.


The extraordinary variety of taphonomic settings under which fossilization may occur, the chemical and structural diversity of sediments that entomb fossils, and the biological properties of different lineages in the tree of Life render impossible any effort to adopt a purely formulaic approach to the study of fossils. The techniques outlined here are proven to be useful in various ways for imaging fossil specimens that are preserved under different conditions. They accommodate specimens with both simple and complicated taphonomic histories, including man-made alterations of various kinds.


Fossil specimens can take days, weeks, or months to prepare but a valuable and informative sequence of images can be taken in 15-20 minutes. For under $1200 any lab can acquire the basic tools needed to begin using this imaging formula (e.g., entry-level UV lamp, ring-light, camera body and lens, filters). We used these imaging techniques at approximately thirty institutions around the world and always were able to find a suitable space within each institution for effective imaging.


Progressive Photonics facilitates ready comparison of images generated by controlled, sequential changes in the electromagnetic spectrum using direct, oblique, and polarized visible light, as well as portions of the non-visible light spectrum. The use of non-visible ultraviolet (UV) light commonly generates a fluorescing reaction in different materials (biologic and man-made) that often is not observable in visible-light imaging or by naked eye. Fluorescing reactions can be virtually impossible to describe accurately in detail without the use of an image. Photography of the fluorescing reaction of fossils under UV illumination was documented in the 1920s (Tischlinger and Ariatta, 2013) although it has never been implemented as a standard tool for investigating and documenting paleontological specimens. UV-spectrum wavelengths have long been recognized as the ‘gold standard’ for generating fluorescent reactions primarily because the higher level of energy in UV spectrum waves versus visible wavelength energy. In visible-light fluorescence (e.g., mercury vapor, xenon, halogen, laser, LED) distinguishing visible illumination from true fluorescent reaction can be difficult and can be complicated by techniques that require post-processing with editing software that relies on subjective interpretation. It is important not to confuse the fluorescent reaction of specimens exposed to higher intensity visible light with the broader and distinctly different reactions generated from non-visible UV or IR illumination. The imaging methods outlined here reduce the potential for misinterpretation of specimen images. Our methods do not require post-production photo editing and, therefore, yield greater confidence in the data as well as a savings in time. Imaging under the standard protocols presented here facilitates both documentation of, and communication about, specimen reaction(s) so that observations are repeatable. Although excellent examples of disclosure of methods, filtering, and digital image manipulation exist in the paleontological literature (e.g., Haug et al., 2009, 2013), these are exceptions to a general lack of adequate documentation or disclosure.


The techniques we present here are applicable across many scales, from the largest specimens at outcrop scale to the microscopic. Depending on specimen characteristics or individual research questions, the techniques are easily adaptable and can be executed with a camera mounted on a studio stand, a tripod, a copy-stand, or through a microscope photo port.


The techniques also facilitate the interpretation of taphonomic histories, a separate area of inquiry we designate as Forensic Photonics. We recognize the fundamental distinction between the methods used to acquire images (Progressive Photonics) from the cognitive context under which those images are studied and interpreted (Forensic Photonics).

 

The techniques and equipment used in Progressive Photonics are outlined below. We also provide a brief overview of safety issues that must accompany use of ultraviolet light sources, and a range of applications through specimen-based case studies.

Institutional abbreviations

AMNH: American Museum of Natural History, New York, New York.
FLFO: Florissant Fossil Beds National Monument, Florissant, Colorado.
FOBU: Fossil Butte National Monument, Kemmerer, Wyoming.
LFPSE: Lauer Foundation for Paleontology, Science and Education, Wheaton, Illinois.
PEFO: Petrified Forest National Park, Arizona.
SMNS: Staatliches Museum für Naturkunde, Stuttgart, Germany.
TMM: Vertebrate Paleontology Laboratory, The University of Texas at Austin, Texas.
TTU: Texas Tech University, Lubbock, Texas.
UNSM: University of Nebraska State Museum, Lincoln, Nebraska.
USNM: National Museum of Natural History, Smithsonian Institution, Washington, D.C.
UW: University of Wyoming Geological Museum, Laramie, Wyoming.

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