Unveiling Medusozoan Fossil patterns: A statistical and spatial study of the lower Cambrian Site in Constantina, Spain

Abstract

A new approach, applying different statistical methods to the early Cambrian medusozoan site of Constantina (Seville, Spain), has allowed the establishment of new biometric parameters for the specimens, a more precise determination of the number of imprints—both subumbrellar and exumbrellar forms—and the deduction of their main taphonomic characteristics. A total of 275 specimens have been identified, with exumbrellar forms (morphotype B) being the most frequent (92%) and having the smallest average length (24.91 cm), while subumbrellar forms (morphotype A) are larger on average (38.29 cm). This new registry represents a record three times greater than previously considered, with the sample characterised by specimens with an average length of 25.93 cm. The analysis of the length/width ratio shows a very strong and statistically significant correlation, implying isometric growth of the medusozoans, consistent with their adult stage. Most specimens exhibit a clear NW-SE orientation, which is parallel to the dominant direction of the palaeocurrents, suggesting that they were reoriented as they were pushed toward the coast before deposition. Additionally, most fossils are clustered in two distinct areas of the surface with very high density, indicating the presence of a common accumulation agent for the entire assemblage. Finally, the analysis of the expanded spatial window through spatial modelling has led to the identification of up to 16 additional specimens that had not been confirmed or were of uncertain identification.