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Session Schedule & Abstracts

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Saturday 2nd July, 2016

Plenary Session 4: Luis Chiappe

Room: Salon D–E   8:15 am–9:30 am

Moderator(s): A. Chinsamy-Turan
PLN4-1  8:15 am  Assembling the bird: morphological evidence from Mesozoic fossils elucidates the evolution of the avian body plan and systems. Chiappe LM*, Natural History Museum of Los Angeles County
Abstract: Worldwide discoveries of Mesozoic fossils provide unprecedented anatomical information for understanding when and how key traits related to the life history, physiology, ecology, and locomotion of birds first evolved. Bone microstructural studies reveal the evolution of growth patterns and other life history traits. These studies show how early in their evolution, birds transitioned from interrupted to uninterrupted growth, thereby revealing how birds that ancestrally grew over multiple years evolved modern patterns in which somatic maturity is reached within the first year. These studies also document that sexual maturity predated somatic maturity in early birds and how the opposite pattern, typical of modern birds, originated later in the group's evolution. Fossils preserving soft tissues and intestinal contents clarify the evolution of the digestive and reproductive systems of birds. They demonstrate that the bauplan of the digestive tract of present-day birds evolved at least 125 million years ago. They also illustrate how the avian pattern of sequential maturation of follicles and ovulation was acquired early in their evolution and in a piecemeal fashion. The diversity of body plans and ecomorphological traits of Mesozoic birds alludes to the evolution of many different lifestyles, some resembling those of their modern counterparts. Fossils preserving plumage allow for the characterization of aerodynamic parameters (wing surface area, aspect ratio, and others) that, together with quantitative predictions from extant birds, provide information about the basic flight modes of primitive birds, thus rendering evidence of when modern flight modes first appeared. In all, a wealth of Mesozoic fossils clarifies how unique adaptations of the avian body—rapid growth, large egg volume, endothermy, and flight modalities, among others—developed through variably complex and stepwise patterns during the early stages of the evolutionary history of birds.

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