Fig. 6

The generated tree shows the inferred phylogenetic relationships for 25 genera of hyoliths, obtained from a strict consensus tree generated from TNT v. 1.5 [35] on the left and the strict consensus generated from PAUP* version 4.0b10 [34] on the right. numbered nodes a–e (in circles) represent key synapomorphic characters. a: Slender dorsally curved conical conch; b: Presence of folds along both ventral and dorsal margin of operculum; c: Conch dorsi-ventral differentiation with angulated cross section; d: Externally fitting operculum with distinct cardinal and conical shields; e: Presence of helens or have relative features, such as lateral sinuses and rooflets. The sketchs on the right showing the evolutionary changes of the skeletal components and structures between hyolithids and orthothecids