Quantifying the Denticle Multiverse: A Standardized Coding System to Capture Three Dimensional Morphological Variations for Quantitative Evolutionary and Ecological Studies of Elasmobranch Denticles.

Abstract

Dermal denticles-microscopic tooth-like scales-are a major defining feature of elasmobranch skin, and are of interest to a wide array of fields, including paleontology, evolutionary biology, developmental biology, functional morphology, and bio-inspired design. While dermal denticle research is a growing field, there is currently no standardized vocabulary or framework to compare denticle morphology across research fields, siloing, and limiting denticle research efforts. Here, we present a morphological framework, which includes a character code that comprehensively captures denticle morphology from a wide diversity of denticle sampling types and imaging methods, and is backed by an easy-to-use google sheets-based coding tool and R package for replicating disparity analyses. The code is based on a wide-spread literature review of published denticle images, scanning electron microscope (SEMs), and computed tomography (CT) scans of extant shark denticles, and a review of tens of thousands of fossil denticles from pelagic ocean sediments dating back over 100 million years. The code's flexibility and replicability facilitate comparison across studies and independent research teams, and the addition of novel character categories. Denticle morphotypes are defined as denticles with unique combinations of character traits. This coding system facilitates morphologically backed disparity analyses of denticle morphological diversity, whether through deep time, across the body of a shark, or across a time-series of development, providing a more detailed, quantitative, and universal tool for analyzing denticle morphology across studies.