Testudines

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  • Testudines
    • Diagnostics
      • Massive breaks covered in sharp keratinous ridges
        • No teeth
      • Pectoral and pelvic girdles situated inside the rib cage
        • Fan-shaped ribs
      • Retractable neck
        • Enlarged otic capsules
      • Shell
        • Dorsal carapace and ventral plastron forming an armour
      • Ectothermic
        • Some with high metabolic rates
      • Anapsid skull, with posterior emargination
        • No side openings behind the orbit
    • Leatherback Sea Turtle Adaptations
      • brown fat tissue
      • muscle-generated heat
      • Countercurrent heat exchange mechanisms
        • I.e. in flippers and around trachea
      • Body temp. higher than that of the surrounding water
      • 3m long
        • Giant sea turtles Archelon and Protostega were even larger
    • Neck retraction
      • Cryptodira
      • Pleurodira
        • Withdraw neck sideways into the shell
        • Only two extant families
    • Bony elements
      • Dorsal carapace and ventral plastron
      • Vertebraw and ribs fused to dermal plates beneath skin which interlock to form a hard shell
      • Exteriorly, the bony shell is covered by keratinous scutes
      • Plastron is made up of 9 bones
        • 2 epiplastra are homologous to the other clavicles of other tetrapods
        • remaining plastral bones are homologous to abdominal ribs in other tetrapods
      • pectoral and pelvic girdles are inside the rib cage
        • Shoulder girdle has a triradiate configuration: consists of 2 scapula processes and 1 coracoid process
        • Pelvic girdle is compact with stout ilia, ischia and *****
          • Paired large openings (thyroid fenestrae) on the ventral surface of the pelvis
      • Elongation of the trunk vertebrae
    • Skull Morphology
      • Extensive plate-like bones
      • Anapsid type
      • Absent of skull fenestrations
      • Palate
        • Maxilla forming a medial bony sheet fused with vomer and palatine
    • Sight
      • Well developed
      • Colour vision
      • Oil droplets occur in sensory cells of retina
      • Blue, green, red, and double cone cells are present
    • Smell
      • Well developed
      • jacob's organ present
      • Gular pumping is thought to facilitate passage of air particles over the Jacob's organ
      • Olfactory bulbs
    • Internal Anatomy
      • Massive lungs extending anteroposteriorly below carapace (attached to underside)
    • Breathing
      • paired transverse abdominis (TA) muscles wrapped around posterior portion of lungs
        • Exhalation: compress the lungs when they contract
      • Cup-shaped oblique abdominis (OA) muscles
        • Inhalation: flatten, which causes an expansion of the inguinal flank posteriorly, ventrally and laterally
      • Air forced out of lungs when head and limbs are retracted into the shell
    • Hearing
      • Cartilaginous tympanic disc, overlaying epidermis
        • 'ear drum'
      • lower sounds 100-60Hz
    • Eunotosaurus
      • Ribs: wide and flat, forms broad plates similar to a primitive turtle shell
      • ribs t-shaped in cross section, each w/ broad, flat surface on top and narrow ridge running along its length on bottom
      • most ribs fused to vert.
      • babies show a diapsid skull
    • Pappochelys
      • wide body, small skull, long tail
      • skull pointed, large eye sockets
      • Several turtle-like features: expanded ribs and tightly packed gastralia
        • Each rib flattened into broad-blade like structure w/ bumps and ridges covering outer surface and a ridge running down inner surface forming T in cross section; also diapsid skull
    • Odontochelys
      • teeth embedded in its upper and lower jaws
      • Plastron, NO carapace
      • wide ribs like modern turtle embryos (before developing ossified plates of carapace)
      • Long-pointed skull and elongate tail
      • evidence plastron evolved before carapace (indicates aquatic origin)
    • How Shells came to be
      • Carapacial ridge develops in lateral aspect of the flanks of the turtle embryo and will give rise to a carapacial margin
      • The ribs are arrested in the dorsal part of body growing toward the carapacial ridge (amniotes: ribs grow ventrally)
      • Serratus anterior muscles ventral to ribs because of the folding of the lateral body wall
      • Ribs grow laterally and are confined dorsally
      • Muscle plate eventually becomes folded at a level coinciding with tip of ribs- runs inside the scapula as in other amniotes

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