INTRODUCTION

Technological advances have given paleontological researchers a variety of new methods for collecting 3D data, drastically changing how data are acquired and permitting novel, sophisticated 3D morphological analyses. High-resolution digitizers and scanners are unique in that the data they produce can be used to collect 3D data points from complex morphology, such as mammalian molars or tarsals. The Reflex Microscope was the first commonly available instrument for collecting 3D data on small- to medium-sized specimens (e.g., Strait 1993a, 1993b, 2001; Reed 1997; Yamashita 1998). However, this method cannot be broadly applied, as the researcher has to individually select each point to be recorded. This method is useful for comparisons of discrete landmarks and features, but it is too cumbersome and time consuming to collect the thousands of points necessary for accurate 3D characterization of even a single mammalian tooth. Furthermore, the low accuracy and resolution of electromagnetic (i.e., Polhemus 3Draw Pro) or contact digitizers (Immersion Microscribe 3D) (Zucotti 1998; Ungar and Williamson 2000; Wilhite 2003) make them impractical for working on all but the largest mammals. Confocal microscopy has also been used for 3D model generation of mammalian dental specimens (Jernvall and Selanne 1999; Evans et al. 2001) and is an excellent choice for very small specimens. However, since this technology was designed for biomedical imaging of tissues, cells, and organelles, it has specimen size limitations. Although specimens as large as 6 mm have been reported, those above 1-2 mm need to be scanned in pieces and merged, considerably increasing the processing time (Jernvall and Selanne 1999) and potential error.

Two methods have proven most beneficial for 3D data collection of complex morphology, Computed Tomography (CT) and 3D laser scanning. High-resolution x-ray CT scanners have proven to be a valuable technology for producing morphological models of vertebrates from a broad range of specimen sizes (e.g., DigiMorph; Kobayashi et al. 2002; Silcox 2003; Clifford and Witmer 2004; Kay et al. 2004; Colbert 2005; Dumont et al. 2005, 2006; Claeson et al. 2006; Holliday et al. 2006; Rayfield and Milner, 2006; Ridgely and Witmer 2006; Macrini et al. 2006). CT data can be very accurate (the degree of accuracy depends inherently on the CT scanning system) and is the only technology for obtaining internal data since it actually acquires sectional data through specimens. For collection of surface feature data laser scanners can also be used (3Dmuseum; Lyons et al. 2000; Motani 2005; Boyd and Motani 2006; Delson et al. 2006; Evans et al. 2006, 2007; Motani et al. 2006; Penkrot 2006; Rybczynski et al. 2006; Smith and Strait 2006; Strait and Smith 2006; Wilson et al. 2006). Just like CT scanners, the precision of the models is scanner dependent but can produce surface models as equally detailed and accurate and are comparably time efficient when both scanning and processing are considered. The primary advantage of high-resolution laser scanners over CT scanners is that they are less expensive and require less technical expertise to operate and maintain.

Growing alongside the technology to produce 3D models is the computing power necessary to manipulate 3D data and the potential to make these models readily accessible via the Internet. The development of more online databases has also been driven by funding agencies, with increasing emphasis on the ability of researchers to disseminate data to peers, educators, and the general public. As a result, online databases have become increasingly important tools in biological and paleontological research, teaching, and outreach. Existing sites include compilations of vast amounts of data, in unique formats that are almost instantaneously accessible on the web (e.g., Carrasco et al. 2005; O'Leary and Kaufman 2007; North American Fossil Mammal Systematics Database 2002; The Paleobiology Database 1998; Maddison and Schulz 2007). Additionally, with the introduction of CT and laser scanners to paleontological studies, websites are also now available that feature 3D models of fossils. Sites such as 3D Museum provide visualization of a host of fossil taxa, and the Digital Morphology Library houses many CT based models of extant and fossil vertebrates. The MorphoBrowser database specializes in vertebrate dental remains and includes a shape search function, to locate taxa of similar morphology (Evans et al. 2005). PaleoView3D is devoted to publishing 3D models and associated metadata of late Paleocene and early Eocene mammals (Strait and Smith 2006).

PaleoView3D is the first online site whose primary goal is not just to display 3D models of fossil organisms, but to allow users to download 3D data for their own research. During the development of PaleoView3D, several major issues had to be addressed: 1) how to standardize model production for consistency from model to model, 2) how to expedite the production of a large number of models, and 3) how to evaluate model accuracy. Standardization of methodology included consistent coating of specimens prior to scanning and during the scanning process and the use of a consistent step-size (distance the laser travels between scan-lines) and sensor exposure settings. New methods were explored for expediting scanning and modeling included the development of a multiscan platform permitting multiple specimens to be scanned and registered in unison and designing an autosurfacing macro to facilitate image processing uniformity. Error studies were performed on objects of known dimension to assess model accuracy. Finally, since by necessity many of the PaleoView3D models were based on casts as opposed to original specimens, an error study was designed to compare models based on casts versus the originals.

While online 3D databases provide tremendous opportunity for paleontological analyses, certain precautions must be taken before incorporating 3D data from multiple sources. Unfortunately, not all 3D models are created equal due to the variety of aforementioned acquisition and modeling techniques. In order to comparatively analyze 3D models from PaleoView3D and other databases, users must have confidence in the accuracy of those models, and should be informed of the process used to generate those data. Therefore, rigorous testing and documentation of the modeling process is necessary prior to dissemination of these data, so that the user can make an informed decision on how best to utilize the models. The goal of this study was to standardize and document the novel modeling process used to generate models for PaleoView3D, in particular, with a broader implication of showing the necessity for the explication of model production and accuracy for all online databases.