BIOL 330 Lecture Notes - Lecture 11: Tetrapod, Extinction Event, Mesozoic
24 Mar 2017
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Extant turtles 13 families; about 313 species. Much less diversity in life-histories: all oviparous, no parental care. Morphological specializations (terrestrial, freshwater and marine habitats) Reduced lower shells; more agile (active predators) Reduced ossification of the shell makes them lighter. Dermal bone, 59 centers of ossification; fused to vertebral column and ribs. Ribs are external to girdles (unique) (cid:858)tra(cid:374)sfor(cid:373)atio(cid:374)ist(cid:859) theor(cid:455) (cid:894)sele(cid:272)tio(cid:374) is ke(cid:455)(cid:895) Small bony plates (found in many reptiles) developed into larger plates that coalesced, forming a covering; fusion of plates with underlying ribs (cid:858)e(cid:373)erge(cid:374)tist(cid:859) theor(cid:455) Turtle embryos have disk-shaped thickening of the skin on the back that is the precursor to the carapace; ribs then grow into this disk. Cannot use rib cage (fused to shell) Large lungs ventilated with muscular activity: exhalation viscera pulls. Ectotherms (but largest marine species achieve considerable endothermy; ex. sea turtles) Basking in the sun (activating vitamin d in calcium deposition) Many species have a large body size slows rate of heating/cooling (thermal inertia)
