Palaeontological and molecular arguments for the origin of silica-secreting marine organisms

The morphological resemblance of some primitive Early Palaeozoic Radiolaria with siliceous sponges has raised the intriguing question of their possible phylogenetic affinity. Here, we address this question through the analysis of available molecular evidence for a number of silica-secreting marine organisms. The obtained phylogenetic tree does not support the above hypothesis, but it suggests the monophyly of Acantharian and Polycystine Radiolaria. The record of the oldest known siliceous fossils provides a time calibration of the molecular dendrograms and allows us to suggest likely ages for the origin of several non-fossilizable groups.