BIOL 3114 Lecture Notes - Lecture 11: Cervical Vertebrae, Dermal Bone, Turtle
20 Oct 2016
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Chapter 12 order testudines the turtles. Body plan is highly distinctive and recognizable. Key synapomorphies of turtles: body covered in a bony shell. Ventral plastron: shell composed of dermal bone plates fused to expanded ribs (carapace) and clavicles and gastralia (plastron, bony shell covered with epidermal keratinized scutes, ribs external to limb girdles! Synapomorphies: no teeth jaws covered by horny beak, cervical vertebrae modified for flexibility. Many species can withdraw head entirely within shell: anterior and/or posterior portion of plastron may be hinged. Oldest fully-shelled fossil late triassic, 205 mya: proganochelys germany, similar to modern turtles but extensive dermal armor on neck, tail couldn"t withdraw head. Odontochelys (late triassic, 220 mya: well-developed plastron, carapace had only neural plates, ribs were thickened but separate, small peg-like teeth, long tail. Historically, viewed as parareptiles related to extinct pareiasaurs: based on shared anapsid skull. Recent molecular and morphological based phylogenies suggest turtles more closely related to diapsida.
