P1.98 Wednesday, Jan. 4 Comparative analysis of the functional relationship between the endochondral and dermal elements of the pectoral fin among fossil and living sarcopterygian fishes TAFT, Natalia*; LEMBERG, Justin; DAESCHLER, Edward; SHUBIN, Neil; University of Chicago; University of Chicago; Academy of Natural Sciences; University of Chicago email@example.com
In this study we incorporate data from the relationship of the endochondral and dermal pectoral fin skeletons among key fossil taxa, Eusthenopteron, Sauripterus and Tiktaalik with data on the musculature from the extant lungfish Neoceratodus to generate a more complete picture of pectoral fin function in the water to land transition in tetrapods. Several morphological changes in the dermal skeleton (fin rays) of Tiktaalik support the hypothesis that Tiktaalik used its pectoral fin for routine substrate contact more than other tetrapodomorph fishes. First, the pectoral fin rays were much shorter than those of the other fossil taxa, particularly on the anterior fin surface. Second, for all taxa the anterior fin rays are more robust than the posterior fin rays. Both of these characters are associated with the use of the pectoral fins for substrate contact in living benthic fishes. Third, evidence from multiple specimens suggests that the fin rays of Tiktaalik exhibit a uniquely asymmetrical distribution on the dorsal and ventral fin surfaces. Dorsally, the lepidotrichia extend proximally to the distal edge of the ulnare in all three fossil taxa examined. In Tiktaalik, the lepidotrichia are restricted to the distal edges of the fin ventrally. We hypothesize that this reduction of lepidotrichia resulted in a fleshy, flexible ventral lobe that could conform to a complex substrate. In addition, data on the pectoral fin musculature from the extant Neoceratodus provides new data on how the overlapping dermal and endochondral skeletons are integrated as a functional unit in sarcopterygian fishes.