Palaeontologia Electronica HIGH RESOLUTION THREE

Palaeontologia Electronica http://palaeo-electronica.org HIGH RESOLUTION THREE-DIMENSIONAL LASER-SCANNING OF THE TYPE SPECIMEN OF EUBRONTES (?) GLENROSENSIS SHULER, 1935, FROM THE COMANCHEAN (LOWER CRETACEOUS) OF TEXAS: IMPLICATIONS FOR DIGITAL ARCHIVING AND PRESERVATION Thomas L. Adams, Christopher Strganac, Michael J. Polcyn, and Louis L. Jacobs ABSTRACT The lower member of the Glen Rose Formation (Albian, Lower Cretaceous) in what is now Dinosaur Valley State Park preserves dinosaur trackways of theropods and sauropods. An excavated theropod track was built into the wall of the bandstand at the Somervell County Courthouse by the citizens of Glen Rose, Texas, in 1933 and later designated as the type specimen of the ichnospecies Eubrontes (?) glenrosensis. To this day, this unique paleontological and cultural resource attracts visitors. Over the past 74 years, exposure to the elements has caused erosional loss, altering the shape of the track impression, but to an unknown degree. In order to preserve the current state of the type specimen and provide a baseline for future analyses, 3D laser scanning was employed to perform in situ digitization of the track. The scans were post-processed to generate a high-resolution 3D digital model of the track. The model was rendered in various media formats for viewing, publication, and archival purposes. Raw scan data and industry-standard 3D object files formats are available for download. Portable 3D laser scanners capture original fossil morphology and texture, thus provid- ing a low cost, high fidelity alternative to traditional molding and casting. The results demonstrate the advantages of using portable laser scanners to capture field data and create high-resolution, interactive models that can be digitally archived and made accessible via the worldwide web for research and education. Thomas L. Adams. Roy M. Huffington Department of Earth Sciences, Southern Methodist University, Dallas, Texas 75275-0395 U.S.A. [email protected] Christopher Strganac. Roy M. Huffington Department of Earth Sciences, Southern Methodist University, Dallas, Texas 75275-0395 U.S.A. [email protected] Michael J. Polcyn. Roy M. Huffington Department of Earth Science, Southern Methodist University, Dallas, Texas 75275-0395 U.S.A. [email protected] Louis L. Jacobs. Roy M. Huffington Department of Earth Sciences, Southern Methodist University, Dallas, Texas 75275-0395 U.S.A. [email protected] KEY WORDS: 3D laser scanning, Eubrontes, digital archive, Lower Cretaceous, dinosaur track PE Article Number: 13.3.1T Copyright: Palaeontological Association November 2010 Submission: 16 November 2009. Acceptance: 14 September 2010 Adams, Thomas L., Strganac, Christopher, Polcyn, Michael J., and Jacobs, Louis L, 2010. High Resolution Three-Dimensional Laser- Scanning of the Type Specimen of Eubrontes (?) glenrosensis Shuler, 1935, from the Comanchean (Lower Cretaceous) of Texas: Implications for Digital Archiving and Preservation. Palaeontologia Electronica Vol. 13, Issue 3; 1T:11p; http://palaeo-electronica.org/2010_3/226/index.html ADAMS ET AL.: 3D GLEN ROSE TRACK INTRODUCTION rent state of the track surface as a 3D facsimile for archive and conservation, (2) provide a baseline The Glen Rose Formation represents the for study of future erosional damage, and (3) pro- transgression phase of a transgressive-regressive vide a low cost, accessible method of distribution sequence within the Lower Cretaceous Trinity for study and outreach. Group (Upper Aptian – Lower Albian) of Central Texas (Jacobs and Winkler 1998). The Glen Rose METHODS Formation, and indeed the entire Trinity Group, preserves a diverse vertebrate fauna represented Producing casts by traditional techniques, by body fossils (Winkler et al. 1990). At the type such as rubber or silicon molds, were rejected due locality in Somervell County, Texas, the Glen Rose to cost of material, labor, limited life span, storage Formation is approximately 75 m thick and is con- issues, and potential damage to the track. sidered earliest Albian in age (Rodgers 1967, Although casts have been used successfully for Young 1967, Perkins 1987, Winkler et al., 1989, replication and distribution of fossils, including Jacobs and Winkler 1998). The Glen Rose Forma- tracks, recent advances in 3D digitizing technology tion is subdivided into three members. The upper provide a high fidelity, low cost means of producing member consists of alternating limestones and facsimiles that can be used in a variety of ways. marls. The middle member is the most extensive unit, consisting of lime mudstones, wackestones, and calcarenites. The lower member consists of alternating arenaceous limestones and mudstones (Winkler et al. 1989). Sediments in the lower member formed on shallow subtidal to tidal flats (Haw- thorne 1990), preserving extensive tracks of theropods and sauropods, as well as rare ornitho- pod tracks (Farlow 1987, Pittman 1989, Hawthorne 1990). Since their discovery in the early part of the 20th Century, dinosaur tracks have been an inte- gral part of the human as well as geological history of North Central Texas (Bird 1985, Jacobs 1997, Jasinski 2008). In 1935, Shuler formally described the large theropod track embedded in the stone wall of the bandstand in the Somervell County Courthouse square in Glen Rose, Texas. Shuler (1935) tentatively assigned it to the ichnogenus Eubrontes (?) as a new ichnospecies Eubrontes (?) glenrosensis (Figure 1.1, Shuler 1935, Albritton 1942, Langston 1974, Farlow 1987). The specimen was originally from the “fourth crossing” (Hendrix- Ramfield crossing) of the Paluxy River, that now lies in Dinosaur Valley State Park, approximately 6 miles west of the town of Glen Rose (Shuler 1935, Jasinski 2008). As a type specimen, conservation FIGURE 1. The type specimen of the ichnospecies is important, but in this case less than optimum. Eubrontes (?) glenrosensis. 1.1 Track embedded in the The footprint, preserved as an impression in limestone wall of the bandstand in the Somervell County stone (Figure 1.2), is exposed to weather and has Courthouse square in Glen Rose, Texas; 1.2 Close up suffered visible erosion. However, given the cul- view of the type specimen. Notice eroded lower section tural and historical significance of the specimen, of the track. Fossil wood is from the Paluxy Formation, removal to an institutional collection is not feasible. which overlies the Glen Rose Formation. Scale bar equals 100 millimeters. Therefore, our goals were to: (1) preserve the cur- 2 PALAEO-ELECTRONICA.ORG FIGURE 2. Schematic flow chart illustrating the 3D digitizing process. Figure 2 provides an overview of the process with secondary surface images to create a photo- employed to achieve our aforementioned goals. realistic model. Other scanner technologies may require this additional step. Data Acquisition Data Processing and Archiving We employed a NextEngine™ HD Desktop 3D scanner and ScanStudio™ HD PRO software Raw scans were imported into Rapidform® (NextEngine™ 2008, Figure 3.1) running on a XOR2™ Redesign (INUS 2009) to align and merge standard Windows XP 32 laptop. The scanner and them into a single 3D model. The final 3D model pc were powered from outlets available on the was exported in Wavefront OBJ (Rose and Ramey bandstand. A tent was required to control lighting 1993) format that includes mesh, material, and tex- and maximize laser contrast (Figure 3.2). Based on ture files (*.obj, *.mtl, *.jpg). LightWave 3D® ver- the large size of the track (640 mm x 430 mm), pre- sion 9.3 software (NewTek 2007) was used to cision was set to wide mode for single scans, cap- render the 3D object into common web accessible turing a view approximately 250 by 330 mm. The media file formats (Figures 4, 5, Appendix 1). Raw optimum recording distance from the scanner to ScanStudio™ files, processed 3D object file the footprint was between 400 mm to 480 mm, (Appendix 2), and additional media formats were measured before each scan. To ensure the great- archived within the Shuler Museum of Paleontol- est resolution, the NextEngine™ was set to HD ogy at Southern Methodist University, Texas. (high definition), a tolerance of 0.13 mm, and a smoothing level of one. A surface attributes setting Erosional Analysis (light - dark) of 60% and matte surface were deter- Visual inspection reveals that the track-bear- mine experimentally to give optimum color fidelity ing limestone surface has undergone deterioration and surface capture. Data capture was focused pri- since its mounting in 1933 (Figure 1.2), but to an marily on the track impression and not on the unknown degree. Although theoretically possible, peripheral surface of the limestone block. Multiple we made no attempt to quantify the morphology scan angles were required to capture all internal present at the time of Shuler’s publication. Shuler track surfaces and minimize occluded surfaces. (1935, figures 2, 3) did make clay molds and plas- Scans were rough aligned within ScanStudio™. ter casts of the bandstand track; however, those Fifty-two overlapping scans (~2.0 GB in size) were and his original photographs and notes are now saved. The scanner captured both point cloud data lost; therefore, quantitative comparisons with first and RGB color textures during the scanning pro- generation facsimiles was not possible. To qualita- cess, removing the need to integrate scan data tively assess erosional loss, we made visual com- 3 ADAMS ET AL.: 3D GLEN ROSE TRACK depart, generating various reports that quantify the area and degree of divergence (Figure 7.3). Renderings of Digital Model A two-dimensional image of the color mapped 3D model was rendered in Lightwave 3D (Newtek) to replicate a similar camera view and shadowing to what is seen in Shuler’s (1935) figure 1 (Figure 6.2). The camera view and light origin were visually approximated based on shadows in Shuler’s (1935) figure 1, and we made no assumptions as to camera type, lens, or distortion introduced by either. A second false color image of the 3D model was rendered to illustrate the relief of the impression, with cool colors indicating the deeper areas of the track (Figure 6.3).

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