Niche partitioning among the Mesozoic echinoderms: biotic vs abiotic traits

Abstract

Although niche partitioning is distinctly difficult to be quantitatively measured, the fossil record can provide the necessary archive for detecting and measuring niche differentiation at different spatial and temporal scales. The consequences of the evolution of the durophagous predators in the Mesozoic Era are well documented among many invertebrates such as mollusks and brachiopods. However, they are less characterized among the echinoderms. In order to assess the consequence of increased predation on the echinoderms and to find the causality between their diversity/dispersion and the sea level variations, the echinoderm occurrence data from the Paleobiology Database was spatiotemporally analyzed. The results indicated that life habit, diet, and locomotion of the echinoderm communities have undergone a major shift. Indeed, a steady trend of increasing the mobile and infaunal taxa, which is a well-known predator-resistant life mode, was observed. In addition, a significant positive correlation was found between carnivores and both of mobile and infaunal taxa (R = 0.70 and 0.56 respectively, p < 0.001), which indicates that mobility and infaunalization provide the opportunity to avoid predation. Moreover, there was a temporal shift in the latitudinal diversity gradient where the diversity peak occurs mainly between 10 and 40 N. Furthermore, there is a general concordance between the echinoderm diversity and the Mesozoic sea level curve. Cluster analyses and nonmetric multidimensional scaling (nMDS) indicated that with increasing sea level, the fauna which was distinct among the different geographic provinces in the Triassic became more similar during the Cretaceous. The latter suggests that sea level is a major factor controlling the biogeographic pattern of the benthic invertebrates.