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Session Schedule & Abstracts

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Friday 1st July, 2016

Symposium: Palate development, function and evolution 2

Room: Salon G   11:30 am–12:45 pm

Moderator(s): J. Richman, C. M. Holliday, & J. Abramyan
PLT2-1  11:30 am  Structure and strain in the chondrichthyan palatoquadrate. Wilga C.D.*, University of Alaska Anchorage; Diniz S.E., University of Rhode Island; Tutu E.O., University of Rhode Island; Summers A.P., University of Washington
Abstract: Functional morphology of the palatoquadrate in several species of chondrichthyan fishes was compared horizontally in adults and ontogenetically in selected species. Meckel's cartilage was also compared due to its morphological coupling to the palatoquadrate and their key role in feeding and ventilation. Shape change in these elements over ontogeny and across species was analyzed using geometric morphometric analyses, percent mineralization, cross-sectional area, and second moment of area. Similarly, functional changes were analyzed using mechanical stiffness, Poisson's ratio, and Young's Modulus. Interspecific shape changes were greater in the palatoquadrate than Meckel's cartilage. Ontogenetic shape changes varied with elements showing isometric or negative allometry. Cross-sectional area and percent mineralization also varies leading to consistent stiffness over ontogeny. An inflection point exists in the stress-strain curve that may indicate mechanical property changes in tesserae-ligament interactions during compression. Tessellated cartilage has a complex heterogeneous structure that varies among species leading to functional differences that may be correlated with feeding style and diet.

PLT2-2  12:00 pm  Relative kinetic competency in the palatal complexes of birds and other diapsids. Cost I. N.*, University of Missouri; Spates A., University of Missouri; Sellers K. C., University of Missouri; Davis J. L., University of Southern Indiana; Middleton K. M., University of Missouri; Witmer L. M., Ohio University; Holliday C. M., University of Missouri
Abstract: Cranial kinesis, or flexibility among intracranial joints, defines many clades of birds and other reptiles. Numerous evolutionary and functional transitions occurred during avian cranial evolution where the primitive, vertically-thin palate of non-avian theropods was modified into either a flat, sutured, weakly-flexible assembly in palaeognaths or a strut-like, often highly-flexible palate in neognaths. Palatal elements and their braincase articulations are key features of the kinetic feeding apparatus as they must promote or restrain movements of the facial skeleton such as in propalinal (rostrocaudal) or pleurokinetic (mediolateral) excursions. However, kinetic movements remain challenging to assess without in vivo data or among extinct taxa such as non-avian dinosaurs. Here we share an experimental methodology designed to test hypotheses of kinetic excursions and ultimately of the evolution of avian kinesis. We developed 3D finite element models of birds and other diapsids (e.g., Tyrannosaurus, Edmontosaurus, Gekko) which differ markedly in palatal morphology as well as known kinetic behaviors. Palatal complexes (pterygoids, palatines, quadrates) were repositioned in three different postures (neutral, propalinal, pleurokinetic) in each taxon to represent hypothetical excursions of palatal kinesis. Jaw and protractor muscles were mapped onto the models, 3D moments about multiple joints were calculated using BoneLoad, muscle orientations were tracked among the different postures, and force propagation through the models were evaluated using finite element analysis. We found palatal posture to greatly influence muscle orientation and loading environment among our sample. These methods are powerful for reconstructing and understanding the complex biomechanical environment of the skulls of kinetic species as well as vertebrates in general. This research was funded by the National Science Foundation (NSF IOS-1457319), Missouri Research Board, Missouri Research Council and the Dept. of Pathology and Anatomical Sciences.

PLT2-3  12:15 pm  The significance of novel palatal joints in the adaptive radiations of archosaurs. Holliday CM*, University of Missouri; Bailleul AM, University of Missouri; Cost IN, University of Missouri; Sellers KC, University of Missouri; Witmer LM, Ohio University; Vickaryous MK, University of Guelph
Abstract: From the origin of the mammalian temporomandibular joint, to the iterative evolution of piscine intramandibular joints, to the Paleozoic rise of gnathostomes, vertebrate adaptive radiations often accompany major innovations in linkages of the feeding apparatus. Here we explore equally significant, arthrological adaptations evolved by crocodyliforms and dinosaurs using imaging, histology, biomechanics, and comparative approaches. Although both extant archosaur clades underwent significant transformations in palatal articulations, they did so in divergent ways. Crocodyliforms evolved hard-biting, akinetic crania further stabilized by their characteristic pterygomandibular joint. Avian clades frequently develop novel articulations to either better canalize kinetic movements (e.g., ducks, parrots) or to stiffen the skull (e.g, woodpeckers). These novel, secondary articulations are mediated by a spectrum of skeletal tissues including secondary cartilage, chondroid bone, vestiges of the palatoquadrate cartilage, fibrous entheses and flexion zones all of which reflect a fascinating interplay of developmental origins, loading environment and phylogenetic history during the radiations of archosaurs.

PLT2-4  12:30 pm  Why (and how) the long face? The evolutionary and developmental bases of Anolis facial diversity. Sanger TJ*, Loyola University in Chicago; Johnson MA, Trinity University; Sherratt E, Australian National University
Abstract: Evolved differences in craniofacial form and function have been critical to the success and diversification of vertebrates. To obtain an understanding of the factors that have constrained and/or facilitated the production of this diversity evolutionary biologists must embrace an organismal approach to the study of anatomy, integrating developmental, ecological, and behavioral perspectives. We have taken this broad approach to the study of craniofacial variation in Anolis lizards, a textbook model of adaptive diversification. Despite decades of research on this diverse genus, few studies have addressed variation in head shape until recently. Previously we showed that the most striking changes in craniofacial shape among anoles are associated with differences in male facial length. Our behavioral observations in field have not yet revealed ecological differences that can explain this variation, but have led us to propose hypotheses based on sexual selection. Through comparative developmental analyses we have shown that variation in facial length is the result of modifications in facial growth rates, not changes in patterning as observed in other lineages. Our analysis of anoles illustrates that the mechanisms driving facial outgrowth are distinct from those in birds and mice. The ongoing collaborative research among our labs is aimed at understanding how these mechanisms have been modified in anoles with different facial morphologies.

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