In the tidal-flat organism lineage, two possible explanations fit the morphology: either 'reinforced strut' evolved once in the ancestor of Calamollis and Deromollis, or a similar structure evolved independently in two separate branches. Fossil Fossil R-170 has the early form of the trait, and the orthologous DNA marker 10 distances are Brimollis-Calamollis: 18; Brimollis-Deromollis: 9; Brimollis-Elimollis: 12; Calamollis-Deromollis: 2; Calamollis-Elimollis: 18; Deromollis-Elimollis: 9. Which relationship requires the fewest unsupported assumptions?