Fig. 6 in Quadrupedal dinosaurs did not evolve fully pronated forearms: New evidence from the ulna

Fig. 6. Comparison of true standardized views of forearm pronation in tetrapods that have evolved a fully pronated manus, in flexor (A1–C1) and distal (A2–C2) views. A. A representative metatherian mammal (marsupial), Virginia opossum Didelphis virginiana Kerr, 1792 (FMNH 166984), oriented in a fully pronated orientation. B. A representative chameleon, Furcifer pardalis (Cuvier, 1829) (FMNH 250433). C. A representative anuran (toad), Bufo blombergi Myers and Funkhouser, 1951 (FMNH 210096). Flexor views are scaled to equal radial length; distal views are not to scale. The reader should note that the distal radial epiphyses of small therians and chameleons are often not located at exactly 180° of pronation relative to their ulnae, as it may not be necessary due to a crouching forelimb posture with moderately abducted elbows (Hutson 2010). Note also that, when present, the full pronation of an anuran manus is accomplished via carpal, not radial torsion (see Schwarz 1935: fig. 10), while the distal radial epiphysis remains in full contact with the plesiomorphically semi-pronated articulation (Ecker and Wiedersheim 1896).