Meeting Abstract
P2-267 Saturday, Jan. 5 15:30 – 17:30 The Avian Pelvis Possesses Ancestral Dinosaurian Character StatesEearly in Development GRIFFIN, C*; BOTELHO, J; HANSON, M; FABBRI, M; BHULLAR, A; Virginia Tech; Yale University; Yale University; Yale University; Yale University ctgriff@vt.edu
The avian body plan is unique among all other vertebrate groups and was assembled in stages over millions of years. The avian pelvis in particular is conspicuously different from the ancestral reptilian condition, providing adaptations suited to the biomechanical demands of flight (e.g. anteroposteriorly expanded ilium and sacrum, backward-facing pubis, shifts in hindlimb muscle sizes and uses), and so the evolution of this region is key to the origin of Aves. However, whereas the evolution of this region is recorded by extinct forms, how development has influenced the formation of the avian body plan is poorly constrained, leaving a major knowledge gap that precludes an integrated understanding of avian evolution. The avian pelvis could be constructed in one of two ways: 1) the derived avian condition could be present at the outset of morphogenesis, as in the avian beak; 2) the beginning of morphogenesis could resemble the ancestral condition, with derived character states accumulating during prenatal development. Here, we use a new method of imaging embryonic tissues in three dimensions—immunostaining cleared embryos and stacking the resulting confocal microscope images in computed tomography software—to demonstrate that the avian pelvis possesses ancestral archosaurian and dinosaurian conditions (e.g., forward-facing pubis, short ilium, anteriorly directed obturator muscle, shorter abdominals), progressively gaining the derived avian character states during development. Therefore, unlike some portions of the avian body, the beginning of pelvic morphogenesis resembles the ancestral condition of many key characters. In addition to the fossil record, the means of transitioning from typically ‘dinosaurian’ to avian locomotion can be studied through development.
