The reconstruction of the ancestral sequence of steroid receptors is sensitive to taxonomic sampling. The ancestral sequence of ER and NR3C was inferred using either a complete dataset (AncSRa) or a partial dataset (AncSRb) where 5 mollusk ER sequences as well as amphiER and amphiNR3C were omitted. The position of those sequences within the phylogenetic tree calculated with the complete dataset was compared. The position of a previously described ancestor (AncSR1) is indicated as well. Triangles represent the different NR clades. For the complete tree, presenting all the 80 sequences present in the tree, see Additional file 7.