Environmental differentiation reflected in the vertebrate fauna diversity in the Lower Devonian of the Holy Cross Mountains, Poland

The Lower Devonian of the Holy Cross Mountains is well-known in the field of vertebrate palaeontology but remains unrecognized as regards palaeoenvironmental reconstructions. We therefore analysed the spatial distribution and relative abundance of fossil vertebrates in this area within one time interval. The fauna from an Early Devonian (Emsian) siliciclastic bone-bearing breccia (the “Placoderm Sandstone”) exposed in four sections of the Łysogóry region and five sections of the Kielce region was analysed with respect to the frequency of the remains and their taxonomic affinity. The relative abundances of agnathans, acanthodians, placoderms, osteichthyans and chondrichthyans suggest more open marine conditions in the Łysogóry region and more terrestrial-influenced in the Kielce region during the Emsian. The results show that the average agnathan and acanthodian content of the Łysogóry region is significantly larger than that in the Kielce region. On the other hand, there are relatively fewer osteichthyans in the Łysogóry region and a significantly higher proportion of bony fishes was recorded in the fauna of the Kielce region. Placoderms are characterized by their generally similar frequency in both regions and from site to site in each of them, though a greater abundance was noted from the Kielce region. Likewise differences in the proportions of particular groups in the Kielce region suggest a large variety of marginal-marine environments under the influence of factors that might have included marine currents and variable conditions around a river mouth.