808


Journal of Paleontology 92(5):804–837


this study. A small number of additional cone snail fossils col- lected from YN020 prior to July 2015 are also included in this study. All studied specimen lots from YN020 are listed in Supplementary data set 1.


Specimen preparation.—Prior to study, most specimens were scrubbed clean in water and, in most cases, soaked overnight in diluted (~50%) Clorox® bleach, which sometimes favors the process by which ultraviolet light reveals original coloration patterns (see detailed overview in Krueger, 1974). Following the bleach treatment, shells were again rinsed in water and allowed to dry overnight.


Digital photography and photo processing.—Digital photo- graphy of specimens under ultraviolet light followed the approach described recently in detail by Hendricks (2015). Most images were captured using a Nikon D7100 camera and two Raytech LS-7CB lamps were used for longwave UV illumina- tion. Because brightly fluorescing regions of the shell (e.g., Fig. 1.2) correspond to regions that would have been pigmented during life, Adobe Photoshop was used to create inversed images (e.g., Fig. 1.3) in order to reconstruct the appearance of the original coloration pattern; thus, fluorescing regions become darkened. Importantly, this approach does not reconstruct the actual pigment color of the shell of the once-living animal. These inversed color images are useful, however, for recogniz- ing different elements of coloration patterning. Besides being used to create inverse images, Adobe Photoshop was utilized for uniformly adjusting the white balance of images (often applying the default “shade” setting to photographs taken under UV light and the “auto” setting to photographs taken under regular light), as well as their levels (which were adjusted manually). Some small shell features were digitally photographed at multiple focal levels using a Nikon SMZ1500 stereoscopic zoom microscope in concert with a Nikon Digital Sight DS-Fi2 Camera Head and DS-U3 Digital Camera Control Unit. The resulting image series were then merged into single composite focus stacked images using the software Helicon Focus (v. 6.2.2; Kozub et al., 2014).


Morphological terminology.—Most of the terminology used here for cone snail shell morphology follows that of Röckel et al. (1995), Hendricks (2009, 2015), and Kohn (2014). Consistent with these past studies, four simple measurements were col- lected in most cases using digital calipers from well-preserved specimens in order to quantify shell form (in some cases, how- ever, measurements were captured from digital images). These are illustrated on Figure 2.1 and include maximum shell length (SL), maximum diameter (MD), aperture height (AH), and height of maximum diameter (HMD). Three ratios were derived from these linear measurements and were used to assign quali- tative descriptors to different aspects cone snail shell shape following Röckel et al. (1995). These ratios include relative diameter (RD), position of maximum diameter (PMD), and the relative height of the spire (RSH).


RD=MD=AH PMD=HMD=AH


(1) (2)


RSH= SLAH ðÞ=SL (3) While landmark- (e.g., Cunha et al., 2008; Cruz et al.,


2012; Tenorio et al., 2012) and outline-based (e.g., Smith and Hendricks, 2013) geometric morphometric techniques have previously been applied to the shells of Conidae, these three simple ratios and their descriptors have been widely applied to many modern and fossil species (e.g., Röckel et al., 1995; Hendricks, 2009, 2015; Kohn, 2014; Harzhauser and Landau, 2016; Helwerda, 2017) and allow for straightforward compar- isons to be made between species. It is important to recognize, however, that measurements of RD and PMD (and related ratios) are not necessarily homologous across species (also see Smith and Hendricks, 2013; Harzhauser and Landau, 2016). The shell shoulder (defined here as the intersection of the abaxial margin of the sutural ramp with the last whorl) is sometimes positioned at the HMD, especially in species with sharply angled shoulders. In other species, the HMD may be beneath (i.e., anterior to) the shoulder. Even so, these simple metrics are useful for characterizing shell shape, assessing intraspecific variation, and have the advantage—unlike outline- based geometric morphometric approaches—of being collect- able from imperfectly preserved fossil specimens. Shell measurement data for individual specimens are presented in Supplementary data set 2. Additionally, reports of typical shell size follow the approach of Kohn (2014, p. 45), who reported “the median length of shells larger than one-half the maximum size, in order to minimize the effect of varying proportions of juvenile shells in the samples.” Smith (1930) recognized the importance of the shape of the


subsutural flexure (SSF) for differentiating cone snail species (also see Hendricks, 2009). The SSF traces the growing edge of the shell across the sutural ramp and may be shallow to deep in


depth, and symmetrical to asymmetrical in shape. While the final interval of growth is often damaged on fossil cone snail shells, earlier growth lines very often preserve the shape of the SSF, especially where shell production temporarily ceased, leaving high-relief traces of past growth (e.g., Fig. 2.2). For this study, three simple measurements were collected


from digital images to quantify the shape of the SSF for individual species. Prior to photography, shells were positioned with the apex pointed towards the camera lens, with the axis of coiling oriented perpendicular to it. Following photography, the resulting images were digitally rotated such that the adaxial region of the SSF (i.e., where it intersects the previous whorl) was positioned directly beneath the apex of the shell (see dashed line on Fig. 2.2). Measurements were then collected as indicated in Figure 2.3 and include: (1) the depth of the subsutural flexure (SSFD); (2) the width from the origin point to the position of maximum SSF depth, which is usually the point of maximum curvature (SSFW1); and (3) the width from the position of maximum depth to the abaxial margin of the sutural ramp (SSFW2). From these measurements, two ratios were used to quantify


the general morphology of the SSF. First, the depth-to-width ratio of the SSF (DWSSF) was calculated as follows.


DWSSF =SSFD = SSFW1 +SSFW2 ðÞ (4)


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