Evolutionary history biases inferences of ecology and environment from δ¹³C but not δ¹⁸O values

Closely related taxa are, on average, more similar in terms of their physiology, morphology and ecology than distantly related ones. How this biological similarity affects geochemical signals, and their interpretations, has yet to be tested in an explicitly evolutionary framework. Here, we compile and analyze planktonic foraminiferal size-specific stable carbon and oxygen isotope values (δ13C and δ18O) spanning the last 107 million years. After controlling for dominant drivers of size-δ13C and δ18O trends, such as geological preservation, presence of algal photosymbionts and global environmental trends, we identify that shared evolutionary history has shaped the evolution of species-specific “vital effects” in δ13C, but not in δ18O. Our results lay the groundwork for using a phylogenetic approach to ‘correct’ species δ13C vital effects through time, thereby reducing systematic biases in interpretations of long-term δ13C records – a key measure of holistic organismal biology and of the global carbon cycle.