A Comparative Study on the Microstructures, Mineral Content, and Mechanical Properties of Non-Avian Reptilian Eggshells
Journal
Biology
Journal Volume
12
Journal Issue
5
Pages
Article number 688
Date Issued
2023-05-07
Author(s)
Wu, Hsio-Jou
Tseng, Yu-Chien
Tsao, Shu-Han
Chiang, Pei-Lin
Tai, Wei-Yu
Hsieh, Hsin-I
Juang, Jia-Yang
Abstract
We analyze 214 freshly laid eggs belonging to 16 species across three orders of Class Reptilia. Using mechanical compression tests, we measure each egg's absolute stiffness (K, unit: N m-1) and relative stiffness (C number). The effective Young's modulus, E, was obtained by combining experimental and numerical methods. The mineral (CaCO3) content was measured by acid-base titration, the microstructures by scanning electron microscopy (SEM), and the crystallography by electron backscatter diffraction (EBSD). We find that the C number of reptilian eggs is, on average, higher than that of bird eggs, indicating that reptilian eggs are stiffer with respect to the egg mass than birds. However, Young's moduli of the reptilian eggshells (32.85 ± 3.48 GPa) are similar to those of avian eggshells (32.07 ± 5.95 GPa), even though those eggshells have different crystal forms, microstructures, and crystallography. Titration measurement shows that the reptilian eggshells are highly mineralized (>89% for nine Testudines species and 96% for Caiman crocodilus). Comparing the species with aragonite and calcite crystals, we find that calcite shells, including those of the Kwangsi gecko (inner part) and spectacled caiman (outer part), generally have larger grains than the aragonite ones. However, the grain size is not correlated to the effective Young's modulus. Also, as measured by the C number, the aragonite shells are, on average, stiffer than the calcite ones (except for the Kwangsi gecko), primarily due to their thicker shells.
Subjects
aragonite; calcite; mechanical properties; microstructure; reptilian eggshell
SDGs
Publisher
MDPI
Type
journal article