Fig. 5. Evolution of the developmental patterns (early and late skeletogenesis) of the autopodium in tetrapods.

Taxa with names framed in purple rectangles have typical salamander preaxial dominance across the mesopodium, those in orange have typical amniote/anuran postaxial dominance across the mesopodium, and those in green have a mixed “intermedium” mode with preaxial dominance in the digital arch and postaxial dominance in nondigital arch mesopodium. Taxa with names not framed in colorful rectangles have unknown developmental patterns (labeled by colorful solid circles with white “?” in the middle) in the mesopodium, or the mesopodium is absent or remains permanently cartilaginous (collectively by “?” in black). The preaxial side of the autopodium is denoted by metapodial II in gold, and color-coded arrows are used to manifest the developmental polarities along the anteroposterior axis in digits (light blue), digital arch (purple), and nondigital arch (red horizontal) mesopodials and that along the proximodistal axis (red vertical) in preaxial and central columns.