Wrists, ankles and digits distinguish tetrapod limbs from fins, but direct evidence on the origin of these features has been unavailable. Here we describe the pectoral appendage of a member of the sister group of tetrapods, Tiktaalik roseae, which is morphologically and functionally transitional between a fin and a limb. The expanded array of distal endochondral bones and synovial joints in the fin of Tiktaalik is similar to the distal limb pattern of basal tetrapods. The fin of Tiktaalik was capable of a range of postures, including a limb-like substrate-supported stance in which the shoulder and elbow were flexed and the distal skeleton extended. The origin of limbs probably involved the elaboration and proliferation of features already present in the fins of fish such as Tiktaalik.
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The illustrations are the work of K. Monoyios. Specimen preparation was performed by C. F. Mullison and B. Masek. NUFV 108 was discovered and quarried by S. Gatesy. Permits to conduct this research were granted by the Nunavut Ministry of Culture, Languages, Elders and Youth (D. Stenton and J. Ross), the Grise Fiord Hamlet, and the Iviq Hunters and Trappers Association. Field operations received logistical support from the Polar Continental Shelf Project (B. Hyrcyk, D. Maloley, J. MacEachern, W. Benoit, G. Benoit, N. Couture, H. Gordon, D. Clouthier and D. Mueller) and collections support from the Canadian Museum of Nature (S. Cumbaa and K. Shepherd). The elders of the Inuit Qaujimajatuqangit Katimajiit of the Government of Nunavut provided the generic name for the new taxon. M. Shuvinai coordinated the naming effort. A. Embry and U. Mayr provided guidance at the inception of the field project. M. Coates commented on a draft of the manuscript. Field assistance (1999–2004) was provided by W. Amaral, B. Atagootak, J. Conrad, M. Davis, J. Downs, S. Gatesy, S. Madsen, K. Middleton, K. Monoyios, C. Schaff, M. Shapiro, R. Shearman and C. Sullivan. This research was supported by a patron of our research, the Academy of Natural Sciences, the Putnam Expeditionary Fund (Harvard University), the University of Chicago, the National Science Foundation and the National Geographic Society Committee for Research and Exploration. Author Contributions N.H.S. and E.B.D. conceived and co-directed the project. F.A.J. Jr collaborated on all phases of the research.
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Nature Reviews Genetics (2017)