Contrasting phylogenetic hypotheses of stem-group Sauropterygia and relationships of Nothosaurus . A, In the analysis of Holmes et al. , the putative pachypleurosaur Keichosaurus plots as a basal nothosauroid, and Pachypleurosauria and Nothosauroidea form a monophyletic taxon, resulting in the loss of the node Eusauropterygia; B, The classical view  with the Pachypleurosauria as the sister-group of Eusauropterygia including Nothosauroidea and Pistosauroidea; C, Phylogeny of the Nothosauridae [modified from 16] with the sampled species indicated in bold. Nothosaurus winterswijkensis and N. marchicus are more basal species than N. giganteus. N. mirabilis is one of the most derived nothosaur species.