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Functional cranial joint histology in Anas platyrhynchos : a window to understand avian cranial kinesis
Author(s) -
Bailleul Alida M,
Holliday Casey M
Publication year - 2016
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.30.1_supplement.1038.6
Subject(s) - anatomy , biology , symphysis , synovial joint , pathology , articular cartilage , medicine , alternative medicine , osteoarthritis
Many of the cranial joints of birds allow significant cranial kinesis, a phenomenon in part responsible for the remarkable diversity of avian feeding adaptations. Whereas some morphological and biomechanical features of cranial kinesis have been studied, little is known about joint structure at the microscopic scale. Consequently, it is still unclear: 1) how the skeletal tissues found at these joints mediate intracranial movements; 2) how these cranial joints vary among different reptile clades; and 3) if specific tissues coincide with particular loading environments. These data are key to understanding the structural basis of kinesis, how secondary articulations form and the origins of the avian feeding apparatus. Here we investigated the functional joint histology of the duck ( Anas platyrhynchos) . Ducks have derived adaptations for herbivory and are model organisms in developmental biology and biomechanics. A total of five specimens (three adults and two hatchlings) were histologically sampled. Two other specimens were CT‐scanned using contrast‐enhancing techniques to build 3D anatomical and biomechanical models. Five intracranial joints were sampled: three diarthroses (jaw joint, otic joint and palatobasal joint) and two syndesmoses (mandibular symphysis and craniofacial hinge). CT data were registered with histological slides to better compare 3D structure. The jaw, otic and palatobasal joints are all synovial, with a synovial cavity encasing cartilage on each articular surface. The prokinetic hinge is a complex joint: laterally it is synovial, whereas medially it is a synostosis. The mandibular symphysis is a synostosis. Upon comparisons with functionally homologous, albeit structurally analogous joints in lizards and crocodylians, major differences in tissue organization occur within the otic and palatobasal joints, as well as in portions of the craniofacial hinge, likely reflecting each clade's developmental and phylogenetic trajectories. These clade‐specific differences in joint microstructure are possibly responsible for the wide range of skull morphologies and cranial kinesis in reptiles. The results of this study have significant implications to understanding the origins of avian cranial kinesis in a broader phylogenetic context (i.e., within non‐avian dinosaurs). Support or Funding Information This study was funded by: NSF‐IOS 1457319; Department of Pathology and Anatomical Sciences.