Posteriorized Catshark Fins (IMAGE) Center for Genomic Regulation Caption Figure 2: These are "posteriorized" catshark fins. In control fins (left), Hand2 is expressed in the posterior margin, and three basal bones (ppr, pmr, pmt) are connected to the pectoral girdle. Whereas in "posteriorised" fins (middle), expression of Hand2 is extended anteriorly (arrowheads). In the severe case, a single basal bone is connected to the body trunk and number of distal radials is reduced. Interestingly, a fossil sarcopterygian Tiktaalik also had a single basal bone (humerus). Credit Mikiko Tanaka, Tokyo Institute of Technology Usage Restrictions None License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.