Module II.docx - L8 Cont Limb modification in tetrapods...

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L8 Cont. 03/21/2017 ° Limb modification in tetrapods: depending on the live style of animal, the limbs are different In bird forearm, there’s a decrease in number of bones by fusing them together, this makes the skeleton lighter for flight. In chicken foot, tarsals and metatarsals fuse to form tarsometatarsus (one bone) that articulates with digits. The digit number is reduced Horse foot: reduction in number of digits. Fossil horse has 3 digits. Modern horse only has one digit. Cat hindlimb: the series tarsals bones o Fibulare articulate with fibula shank o Tibiale articulate with tibia In human food: fibulare is the bone of your heel. o Calcanum is large in human for walking ° Pectoral girdle modification: Forelimb attaches to pectoral girdle that’s to the axial skeleton In early vertebrate, the attachment is stronger because pectoral girdle is attach to the skull Theory that girdle develop from gill arches. Pectoral girdle is a combination of dermal and endochondral bones Variety of pectoral girdle throughout evolution: o Dermal element is higher than endochondral in early vertebrates o Later, dermal elements are reduced, where endochondral element because more emphasized in girdle o In mammals, dermal bone is only present in clavicles. Scapula is endochondral. o Procoracoid becomes coracoid in later tetrapods. In mammals, coracoid fuse with scapula and become coracoid process o Clavicle in mammals is very tiny; only dermal origin ° Pelvic girdle: there was never any dermal elements in it. Attach fin to skeleton in early vertebrates In tetrapod , illium, pubis and ischium make up the pelvic girdle o Illium is a bone in that attachés the pelvic girdle to the skeleton
Pelvic area in males and females are different; in males, the pubic bone is more narrow; in female, the pubic bone is wider to create child-bearing area Turtle axial skeleton: Appendicular skeleton lies inside the rib cage, different from most other tetrapods Rib cage has a protective shell around the girdles. All the insides are covered. Evolutionarily, the change which turn girdle inside the shell happen very suddenly. They couldn’t find any intermediate fossils The shell is made up of dorasal carapace (dermal scale) and ventral plastron (bony structure): Expanded ribs and vertebrae. And on top of it is the dermal bones Clavicle is fused with plastron. Pubis, ischium and illium make up the pelvic girdle. ° Endochondral bone: Dermal bones appear from dermis and not from cartilages Endochondral bone made out of cartilage as precursor. Then the cartilage ossifies. The outer shell of the endocohondral bone is very strong. Inner part of bone is very spongy, which creates lightness Sponginess of bird bones are higher than terrestrial animals; adaptation for flight Embryologically: the bone is made out of lateral plate mesoderm o Mesenchymal cells migrate and accumulate to create cartiliage.

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