The Origin and Evolutionary Consequences of Skeletal Traits Shaped by Embryonic Muscular Activity, from Basal Theropods to Modern Birds

摘要: Embryonic muscular activity (EMA) is involved in the development of several distinctive traits birds. Modern avian diversity and fossil record dinosaur-bird transition allow special insight into their evolution. Traits shaped by EMA result from mechanical forces acting at post-morphogenetic stages, such that genes often play a very indirect role. Their origin seldom suggests direct selection for trait, but side-effect other changes as musculo-skeletal rearrangements, heterochrony skeletal maturation, or increased incubation temperature (which increases EMA). EMA-shaped like sesamoids may be inconstant, highly conserved, even disappear then reappear Some become increasingly influenced evolution genetic-molecular mechanisms (genetic assimilation). There also ample evidence evolutionary transitions to bony eminences tendon insertion sites, vice-versa. This can explained newfound similarities earliest both kinds structures, which suggest these are likely triggered EMA. Other require formation will not necessarily undergo genetic assimilation, still conserved over tens hundreds millions years, allowing reduction loss elements. Upon origin, directly genetic, nor immediately adaptive. Nevertheless, key role innovation, have consequences subsequent direction change. Its more important ubiquitous than currently suspected.