A new high-resolution 3-D quantitative method for analysing small morphological features: an example using a Cambrian trilobite

Abstract

Taphonomic processes play an important role in the preservation of small morphological features such as granulation or pits. However, the assessment of these features may face the issue of the small size of the specimens and, sometimes, the destructiveness of these analyses, which makes impossible carrying them out in singular specimen, such as holotypes or lectotypes. This paper takes a new approach to analysing small-morphological features, by using an optical surface roughness (OSR) meter to create a high-resolution three-dimensional digital-elevation model (DEM). This non-destructive technique allows analysing quantitatively the DEM using geometric morphometric methods (GMM). We created a number of DEMs from three populations putatively belonging to the same species of trilobite (Oryctocephalus indicus) that present the same cranidial outline, but differ in the presence or absence of the second and third transglabellar furrows. Profile analysis of the DEMs demonstrate that all three populations show similar preservation variation in the glabellar furrows and lobes. The GMM shows that all populations exhibit the same range of variation. Differences in preservation are a consequence of different degrees of cementation and rates of dissolution. Fast cementation enhances the preservation of glabellar furrows and lobes, while fast dissolution hampers preservation of the same structures.

Nature and significance of intraspecific variation in the early Cambrian oryctocephalid trilobiteOryctocephalites palmeriSundberg and McCollum, 1997

“…These findings suggest that, in compacted material, the presence and/or depth of some transverse or longitudinal glabellar furrows should be considered more reliable for taxonomic identification than the presence and/or depth of others. Zhao et al (2008) and Esteve et al (2017Esteve et al ( , 2018 asserted that Oryctocephalus reticulatus (Lermontova, 1940;see Sundberg et al, 2011) and Oryctocephalus americanus Sundberg and McCollum, 2003b are synonymous with Oryctocephalus indicus, which is the index fossil for the Wuliuan Stage, Miaolingian Series (Zhao et al, 2019). All three species are very similar in cranidial shape (see Esteve et al, 2017) but differ in the number of transglabellar furrows, with only one furrow in O. reticulatus and O. americanus and three in O. indicus.…”

“…All three species are very similar in cranidial shape (see Esteve et al, 2017) but differ in the number of transglabellar furrows, with only one furrow in O. reticulatus and O. americanus and three in O. indicus. Zhao et al (2015) and Esteve et al (2017Esteve et al ( , 2018 suggested that this might be the result of taphonomy or biological variation. The study of compaction in Oryctocephalites palmeri described herein suggests that the differences in the number of transglabellar furrows in Oryctocephalus is reliable and synonymy of the three species of Oryctocephalus is doubtful.…”

Morphometric measurements of bedrock rivers at different spatial scales and applications to geomorphological heritage research

“…Fort et al 2012;Vazquez-Calvo et al 2012) and only more recently on geological heritage (e.g. Esteve et al 2018). However, to this day, they have not been used in geomorphological analysis nor in the valorisation of geoheritage.…”

On the Combination of Remote Sensing and Geophysical Methods for the Digitalization of the San Lázaro Middle Paleolithic Rock Shelter (Segovia, Central Iberia, Spain)

“…Taphonomical analyses of the archaeological findings: a process in which the materials unearthed in the site are studied to know the processes they suffered [32][33][34][35][36][37][38].…”