DISCUSSION

The application of computed tomography (CT) and 3D laser scanners has become widespread, producing high quality 3D digital models used in accurate fossil restorations, mass estimations, biomechanical studies, and finite element analysis (Lyons et al. 2000, Motani 2005, Rayfield 2005, Polcyn et al. 2005, Boyd and Motani 2008, Smith and Strait 2008, Rybczynski et al. 2008, Falkingham et al. 2009). In paleoichnology, LIDAR (Light Detection and Ranging remote sensing system used to collect topographic data) and photogrammetry have been incorporated to capture high-resolution images from remote localities and sites with large concentrations of dinosaur footprints (Breithaupt et al. 2004, Bates et al. 2008).

This paper demonstrates the feasibility of using portable 3D laser scanners to capture field data and create high-resolution, interactive 3D models of at-risk natural history resources. A portable 3D laser scanner can be used as a method of capturing data while visiting institutions and collections, as well as producing facsimiles of material that is normally inaccessible, too large, or too fragile to mold and cast. Laser scanning is non-invasive, whereas in many molding and casting procedures, the molding material may damage specimens.

Dinosaur tracks and other trace fossils are geologic features and as such are subject to the same natural processes as other rock formations. Weathering and other geological processes can alter the track both after its initial formation and during its subsequent surface exposure as a trace fossil. In addition, the vertical placement of the type specimen of Eubrontes (?) glenrosensis Shuler (1935) in the bandstand wall introduces the effects of gravity to the weathering process. Chemical stabilizers applied to the surface of footprints can temporarily halt erosion; however, this typically consolidates only the outer surface layer of rock, causing spalling (the flaking of material) and accelerated erosion.

Using a high-resolution 3D model of an at risk specimens, erosional rates can be monitored to provide the needed information for future planning and conservation. By creating an accurate 3D digital model, the current condition of the type specimen of Eubrontes (?) glenrosensis Shuler (1935) can now be used as a baseline to monitor future erosion. Using established protocols, 3D scanning can be repeated periodically to quantify and graphically display track erosion (Figure 7.3).

Apart from removing the bandstand track from public display, the loss of this culturally and scientifically important fossil is inevitable, emphasizing a greater need for long-term preservation of the type specimen. 3D laser scanning, or digitizing by CT, allows for the creation of a digital equivalent of a plastotype (any artificial specimen molded and casted directly from the primary type, Morningstar 1924). We propose the term "digitype" to refer to this particular use of digital facsimile. Plastotypes are not currently recognized by the ICZN (International Commission on Zoological Nomenclature) and currently could not replace the actual specimen as an official representation of that taxon. However, illustration or description of a syntype as a lectotype can be treated as designation of the specimen, whether the specimen exists or not (ICZN. 1999, Article 74.4). In our opinion, this policy reflects a somewhat dated view; given the fidelity of current CT and laser scanning technology, digital vouchers should enjoy the same status.

As the technology to capture 3D data has become more commonplace, digital archives and online museums have become an important way for researchers to distribute data to peers, educators, and the public (Smith and Strait 2008). Database management and digital archives require long-term storage and means of retrieval of digital information (Chen 2001). As a result, the preservation of digital information has become increasingly more important as we expand our technical resources. Unlike physical specimens and casts, digital facsimiles demand periodic attention to handle rapid technical advances in media formats. Preservation becomes more then just the product of a program, but process as well (Chen 2001). In addition, technical advances demonstrate the need to develop standard formats to ensure data accessibility. Currently there is no single 3D format that is universally portable and accepted by all software manufacturers and researchers. Until there is, researchers can take advantage of commonly used file formats, such as Wavefront OBJ (Rose and Ramey 1993) and Stanford PLY Polygon (Turk 1998) formats, both which provide the ability to move 3D data between application, and allow dissemination of 3D data through the worldwide web, CD-ROMs, and DVD (McHenry and Bajcsy 2008).