Shell strength of freshwater molluscs and its implication on preservation potential

PAULA A. CRISTINI; JOSEFINA BALLARRE; FRONTINI, P.M.

Historical Biology

Taylor and Francis Ltd.michael.wagreich@univie.ac.at

Año: 2020

Shell strength of the modern freshwater molluscs Heleobia parchappii, Biomphalaria peregrina, Uncancylusconcentricus, Musculium argentinum, Physa acuta, Succinea meridionalis and Pomacea canaliculata wasquantified through load measurements and analysed using Weibull distribution, a statistical method usedfor brittle materials. In this study, we defined shell strength as the maximum compressive force required tobreak a shell per unit of resistant area, which is known as mechanical tension or stress. Intrinsic properties ofshells were also measured through mineralogical and morphological characterisation. Shells were mainlycomposed of aragonite and varied in size and shell thickness, being P. canaliculata (biovolume = 104 mm3)the largest and H. australis and H. parchappii (3.35 and 7.93 mm3, respectively) the smallest ones. Thedominant microstructure was cross-lamellar, with layers that varied between one and four. The organicmatter of the matrix varied between 1.58% and 4.24%. Shell strength differs among mollusc species. Smallestspecies have higher shell strength than larger ones because they have a smaller resistant area on which theload is applied, and therefore the resulting value of fracture stress increases abruptly. This may explain thedominance of H. parchappii in death and fossil assemblages from Pampa sediments.