Stable strontium isotopes of Late Devonian conodonts from Kowala (Poland) reveal genus-level signatures

Conodonts are extinct early vertebrates whose apatite oral elements provide one of the most extensive vertebrate fossil records widely used in biostratigraphy and paleoceanography. However, their trophic ecology and physiological differentiation remain poorly constrained. Here we investigate stable strontium isotope compositions (delta Sr-88) in six conodont genera from a well-preserved latest Famennian (Upper Devonian) succession at the Kowala Quarry (Holy Cross Mountains, Poland), spanning three conodont biozones. After detailed assessment of diagenetic preservation using crystallographic, elemental, and radiogenic Sr isotope data (Sr-87/Sr-86), we show that conodont bioapatite retains a primary biological delta Sr-88 signal. Statistically significant genus-level differences in delta Sr-88 are observed and persist after correction for stratigraphic trends. The studied genera cluster into two distinct groups, with Palmatolepis, Bispathodus, and Pandorinellina showing higher delta Sr-88 values than Branmehla, Mehlina, and Idioprioniodus. These differences are consistent with biologically driven isotope fractionation and likely reflect trophic niche differentiation and/or digestive physiology (vital effects) rather than diagenetic overprinting. Comparison with apparatus architecture indicates that delta Sr-88 variations correlate most strongly with P-1 element morphology: taxa with blade-like P-1 elements display lower delta Sr-88 values than those with platform-, icrion-, or expanded basal cavity morphologies. Our results demonstrate that stable Sr isotopes provide a novel proxy for reconstructing trophic structure and ecological differentiation in extinct marine vertebrate communities.