An integrative approach to understanding bird origins

Abstract

Recent discoveries of spectacular dinosaur fossils overwhelmingly support the hypothesis that birds are descended from maniraptoran theropod dinosaurs, and furthermore, demonstrate that distinctive bird characteristics such as feathers, flight, endothermic physiology, unique strategies for reproduction and growth, and a novel pulmonary system originated among Mesozoic terrestrial dinosaurs. The transition from ground-living to flight-capable theropod dinosaurs now probably represents one of the best-documented major evolutionary transitions in life history. Recent studies in developmental biology and other disciplines provide additional insights into how bird characteristics originated and evolved. The iconic features of extant birds for the most part evolved in a gradual and stepwise fashion throughout archosaur evolution. However, new data also highlight occasional bursts of morphological novelty at certain stages particularly close to the origin of birds and an unavoidable complex, mosaic evolutionary distribution of major bird characteristics on the theropod tree. Research into bird origins provides a premier example of how paleontological and neontological data can interact to reveal the complexity of major innovations, to answer key evolutionary questions, and to lead to new research directions. A better understanding of bird origins requires multifaceted and integrative approaches, yet fossils necessarily provide the final test of any evolutionary model.

Dinosaur incubation periods directly determined from growth-line counts in embryonic teeth show reptilian-grade development

“…Dinosaur eggs and attending parents (if present) (1, 33-36, 43) would have been exposed to prolonged risks (e.g., predation, starvation, and stochastic environmental events) (43,45,70,71). This exposure likely contributed to their tendency to lay large clutches with relatively smaller eggs as a means to counter high-mortality rates (43,72) within the egg (45, 46) and after hatching (73,74). As in extant birds (13), prolonged nesting cycles may have made some environments improbable for successful reproduction and production of extra broods by some taxa, especially large dinosaurs whose incubation spanned the better part of a year.…”

Topographical mapping of α- and β-keratins on developing chicken skin integuments: Functional interaction and evolutionary perspectives

“…Novel morphogenetic processes have evolved, leading to the complex feather morphology and make feathers and scales distinct in their mature structures (16)(17)(18). Recently, molecular networks for the multistep evolution of novel pathways, which exist in feather but not scale morphogenesis, have been identified and reviewed (19). They involved the recruitment of signaling pathways such as the FGF (fibroblast growth factor), BMP (bone morphogenetic protein) and Wnt (wingless-integration) pathways as well as adhesion…”

Avian genomics: fledging into the wild!

“…Avian evolutionary patterns can, however, be studied not only by genomics, and therefore, an integrative approach to understanding bird origins was highlighted as well (Xu et al 2014), in addition to stating clearly the value of classical and modern (i.e., including biobanks) natural history collections (Kress 2014). Neither do the avian genome project data (Zhang et al 2014a) stand isolated with regard to other major genome sequencing projects.…”