Title page for ETD etd-04192012-173641


Type of Document Dissertation
Author Dubansky, Brooke Hopkins
Author's Email Address bhopki1@tigers.lsu.edu
URN etd-04192012-173641
Title The Functional Morphology of the Intermandibulo-cervical Envelope of the American Alligator (Alligator mississippiensis)
Degree Doctor of Philosophy (Ph.D.)
Department Biological Sciences
Advisory Committee
Advisor Name Title
Homberger, Dominique Committee Chair
Bragulla, Hermann Committee Member
Hafner, Mark Committee Member
Teruyama, Ryoichi Committee Member
Hawke, John Dean's Representative
Keywords
  • crocodilians
  • integument
  • feeding
  • morphology
  • evolution
Date of Defense 2012-04-17
Availability unrestricted
Abstract
Alligators appear to swallow prey items that are large relative to their head size. Therefore, the intermandibulo-cervical envelope (i.e., the skin, Fascia superficialis, and constrictor musculature) was expected to be expandable. The three main layers of the intermandibulo-cervical envelope expand and recoil in tandem, but through different mechanisms. In the skin, which consists of hard-cornified scales and soft-cornified interscale skin segments, only the latter are expandable. Therefore, the width and orientation of the interscale skin segments determine the extent and direction of expansion of the skin. Whereas the intermandibular skin region is very expandable and enables the manipulation and crushing of large prey items in the mouth cavity, the gular and cervical skin regions can expand longitudinally, but have very limited circumferential expansibility. Elastic fibers in the dermis and Fascia superficialis provide the resilience needed to return the skin to its resting condition. The trilaminate Fascia superficialis expands by changing the orientation of its helically arranged collagen fibers. The three main skin regions, which are also characterized by particular scale and interscale skin patterns, are in congruence with the three parts of the underlying constrictor musculature. The expansibility of the constrictor muscles is determined by their proportion of muscle length to tendon length, because muscle fibers can lengthen passively, whereas collagenous tendon fibers resist lengthening. The expansibility of the constrictor muscles diminishes from rostral to caudal. Whereas the longitudinal expansibility of the intermandibulo-cervical envelope allows lateral and dorso-ventral movements of the head and neck, the limited circumferential expansibility of the gular and cervical regions constrains the size of prey items that can pass through the throat and matches the narrow isthmus of the thoracic inlet. Hence, the functional-morphological data of the intermandibulo-cervical envelope require a reinterpretation of feeding mechanics and prey choice of alligators.
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