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JPT Nº18

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INTRODUCTION

 

Numerous small fossil teeth from vertebrates were collected during a paleontological resource surface survey in southwest Utah. The major dimension of most of the teeth is less than 12 mm, and this makes detailed examination of the teeth impossible without the aid of magnification. One method for facilitating examination of the teeth, and for sharing details of their shapes and surface features is photogrammetry. Photogrammetry is becoming increasingly valuable for documenting and archiving fossils (Breithaupt et al., 2004; Matthews, 2008; Falkingham, 2012; Mallison and Wings, 2014; Matthews et al., 2016). For instance, the ability to use photogrammetry on small, centimeter-scale specimens was demonstrated (Falkingham, 2012), but its application to specimens too small to be examined in detail without the aid of magnification is not common. This is due in part to complexities associated with photographing small specimens in a way that is compatible with further processing for photogrammetry.

 

A significant challenge in applying photogrammetry to small specimens is managing the relationship between magnification and depth of field in the source images. Photogrammetry can only reasonably reproduce details that are clearly visible in the images input for analysis. Consequently, getting photogrammetry models of small specimens with good fidelity of important features requires that they be photographed at higher magnifications than those commonly used in conventional photography. However, a by-product of increased magnification is reduced depth of field so that individual images of magnified subjects that are not flat may not be completely in-focus. This can be problematic for acceptable photogrammetry processing. A specific challenge, therefore, for using photogrammetry for small, contoured specimens like teeth is being able to produce suitably magnified images that are fully focused.


his work outlines an approach being used to apply photogrammetry for documenting, archiving, and sharing information about small, vertebrate fossil teeth. The general approach draws from work being done on modern insect specimens (Nguyen et al., 2014), and from various sources of information on applied photogrammetry available on the internet (Cognysis-Inc.com; Porter et al., 2016; Minnesota Anthropology). The details of the photography set-up and the processing needed to prepare images of the teeth for photogrammetry are presented. The ability to capture and magnify the shape and surface details of small fossil teeth are demonstrated with two specific examples of isolated specimens collected from the Silty Facies of the Kayenta Formation in southwest Utah.
 

 

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