111-3 Sat Jan 2 The evolutionary change of morphogenesis of dinosaur-type femoral head Egawa, S*; Bishop, PJ; Pintore, R; Griffin, CT; Tsai, HP; Botelho, JF; Smith-Paredes, D; Kuratani, S; Norell, MA; Nesbitt, SJ; Hutchinson, JR; Bhullar, BAS; Yale Peabody Museum, USA; RIKEN BDR, Japan; Royal Veterinary College, UK; Royal Veterinary College, UK; Virginia Tech, USA; Missouri State University, USA; Yale Peabody Museum, USA; Pontificia Universidad Católica, Chile; Yale Peabody Museum, USA; RIKEN BDR, Japan; American Museum of Natural History, USA; Virginia Tech, USA; Royal Veterinary College, UK; Yale Peabody Museum, USA shiro.egawa@riken.jp https://egawashiro.wixsite.com/shiroegawaphd
Dinosaurian femoral heads are distinguished by considerable medial extension or overhang of the proximal end. This morphology has been central to discussions of form and function of the locomotor apparatus. Here, we reconstructed the morphogenetic (developmental) evolution of the proximal end of the dinosaurian femur. Embryology of extant close relatives (neontology) suggests acquisition by gradual medial growth of the proximal end. On the other hand, the fossil record (paleontology) suggests acquisition by torsion of the proximal end about the long axis. We resolve this apparent conflict by showing that medial overhang of the dinosaur femoral head was initially acquired by torsion, which was then superseded by growth of the medial region. Subtle anatomical shifts support this hypothesis; and their biomechanical implications and phylogenetic timing are congruent with the general consensus regarding broader morphofunctional evolution on the avian stem.
