Fig. 1.

Skeletal domains (patterns) in fins and limbs. The proximal end of the appendages is to the left in all pictures. (A–D) Pectoral fin skeletons of the paddlefish (A), zebrafish (B), bamboo shark (C) and dogfish (D). In these actinopterygians (A,B) and chondrichthyans (C,D), there is a radial domain (consisting of several radial bones, proximal to the red broken line) and a fin-ray region (lepidotrichia or ceratotrichia, distal to the red broken line). (E–H) Pectoral fin skeletons of Sauripterus (E), Eustenopteron (F), Panderichthys (G), and Tiktaalik (H). These sarcopterygian fish have the three parts of the endoskeletal domain (stylopod, zeugopod, and multi-patterned radial bones in the distal domain: roughly separated by blue lines) and a fin-ray region (distal to the red broken line). (I–K) Forelimb skeletons of Acanthostega (I), chicken (J), and mouse (K). The distal-most endoskeletal domain is the autopod domain (distal to the right blue line), and there is no fin-ray region. (A–C) were redrawn from Dahn et al. (2007), (D) from an article (Yonei-Tamura et al. 2008), (E) and (I) from a review (Raff, 2007), and (F–H) from an article (Boisvert et al. 2008).