Fig. 3. Ossification patterns of the carpus and tarsus in the primitive salamander clade Panhynobia.

Specimens are arranged with catalog numbers placed between the carpus (top row) and tarsus (bottom row) in each specimen. Each of the five crown (A, B, and E to G) and two stem (C and D) panhynobians are arranged from left to right to show increased ossification of the mesopodium over ontogeny (not to scale). Most specimens are shown in dorsal view, except three specimens (FMNH 285321, CIB 72893, and CIB 17597) are shown in ventral view to better visualize the mesopodials. Mesopodials are color-coded following Fig. 2, with the preaxial side of the limb denoted by digit II in gold color. The digital arch mesopodials (distal carpals/tarsals and the postminimus) ossify following the preaxial dominance from the basale commune to the postminimus, if any. By contrast, ossifications in nondigital arch mesopodials are characterized by the postaxial dominance, with the preaxial column (element y and radiale/tibiale or their fusions) remaining as the last part to ossify. Along the proximodistal axis, central and preaxial columns generally ossify from distally to proximally with a reversed ossification sequence in the preaxial column present in Liua shihi (B) and Pseudohynobius flavomaculatus (G). Note that species with names colored in blue have carpus ossified earlier than tarsus and that species with names colored in yellow have carpus ossified later than tarsus.