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Session Schedule & Abstracts

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Thursday 30th June, 2016

Plenary Session 2: Alexander Vargas

Room: Salon D–E   8:15 am–9:30 am

Moderator(s): J. E. Moustakas-Verho
PLN2-1  8:15 am  Embryos of living dinosaurs: A path to uncover the evolution of development. Vargas AO*, Universidad de Chile
Abstract: Several historical debates on the evolution of birds demonstrate that combining developmental and paleontological data can be quite challenging. Paleontologists and embryologists may provide different identifications for the same avian body parts, and claims have been made that the development of the wing and ankle of birds does not support a dinosaur ancestor. New techniques have revealed many debated structures actually show dinosaur-like development, but in some cases, both paleontology and development provide sound data, that nevertheless appears contradictory. Given the accumulated evidence the dinosaur-bird link, these cases are now interpreted as pointing to previously unsuspected evolutionary changes in developmental pathways. A well-known case is the likely occurrence of a homeotic transformation of digit identity in the evolution from dinosaur hands to bird wings. The wrist provides another example. Dinosaurs most closely related to birds ("raptors") did not have a pisiform bone in their wrist, yet birds have added a large bone with unmistakable pisiform-like development. Past arguments against the dinosaur-bird link have included "Dollo's law", the alleged impossibility of re-evolving structures once lost in evolution. The case of the pisiform would urge us to revise this law, but even today, evolutionary reversions are controversial and subject to high demands of evidence. Differences to ancient structures are argued to show that "reversion" is actually neomorphism, and any ancestral resemblance is coincidental. Evidence of ancient molecular-genetic mechanisms can also be demanded as ultimate proof of reversion. I will discuss cases in birds (both natural and experimental) to argue that reversion need not be absolute: differences may evolve, but resemblances to ancestors involve the co-option of ancient developmental systems. Further, these ancient developmental systems can be largely epigenetic, leaving little or no molecular-genetic signature.

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