The record of CaCO₃ biominerals serves as a valuable repository documenting Earth's evolutionary history and environmental changes. An in-depth understanding of the mineralogical diversity within calcifying organisms is essential for interpreting the evolutionary record of CaCO₃ and evaluating the adaptability of biomineralizers to past and future environmental change. To offer insights into the relative importance of environment vs. phylogenetic history in determining mineralogy, this study explores the modern-day global distribution of mineralogies in cheilostome bryozoans.

Cheilostome bryozoans vary considerably in their mineral composition: in our dataset 65% of the species possess purely calcite skeletons, 15% exclusively employ aragonite, and 20% exhibit mixed (i.e., calcite and aragonite) mineralogies. Temperature is the predominant measured environmental factor influencing bryozoan skeletal mineralogy, accounting for 20% of its variability across species, when phylogenetic relatedness is unaccounted for. Bryozoans in lower latitudes, characterized by higher seawater temperatures, have higher aragonite concentrations. By accounting for phylogenetic structure using a subset of 87 species for which we have topological information, 40% of the observed mineralogical variability could be attributed to present-day temperature. In contrast, depth and salinity played minor roles, explaining less than 1% of the mineralogical variation each.

This study emphasizes the influence of evolutionary history on the mineralogical variability of calcifying organisms, even when it can be shown that a single environmental factor (temperature) explains a substantial amount of this variability. When confronted with changing temperature, calcifiers such as bryozoans are likely to respond in diverse ways, depending on the species, given their phylogenetic relatedness and the external conditions they meet.

We employed X-ray diffraction (XRD) to analyze the skeletal mineral composition of 872 individual colonies, representing 437 bryozoan species, in terms of calcite/aragonite ratios. We integrated this data with equivalent published data, thus reaching 981 species, and applied linear models (LMs), generalized linear models (GLMs), and phylogenetic generalized least squares models (PGLSs), to investigate the influences of temperature, salinity, depth, and phylogenetic history on the mineralogy of nearly 1,000 cheilostome bryozoan species.