L8 Cont.03/21/2017°Limb modification in tetrapods: depending on the live style of animal, the limbs are differentIn 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 reducedHorse foot: reduction in number of digits. Fossil horse has 3 digits. Modern horse only has one digit.Cat hindlimb: the series tarsals bonesoFibulare articulate with fibula shankoTibiale articulate with tibiaIn human food: fibulare is the bone of your heel. oCalcanum is large in human for walking°Pectoral girdle modification:Forelimb attaches to pectoral girdle that’s to the axial skeletonIn early vertebrate, the attachment is stronger because pectoral girdle is attach to the skullTheory that girdle develop from gill arches. Pectoral girdle is a combination of dermal and endochondral bonesVariety of pectoral girdle throughout evolution:oDermal element is higher than endochondral in early vertebratesoLater, dermal elements are reduced, where endochondral element because more emphasized in girdleoIn mammals, dermal bone is only present in clavicles. Scapulais endochondral. oProcoracoid becomes coracoid in later tetrapods. In mammals, coracoid fuse with scapula and become coracoid processoClavicle in mammals is very tiny; only dermal origin°Pelvic girdle: there was never any dermal elements in it.Attach fin to skeleton in early vertebratesIn tetrapod, illium, pubis and ischiummake up the pelvic girdleoIllium 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 areaTurtle axial skeleton:Appendicular skeleton lies inside the rib cage, different from most other tetrapodsRib cage has a protective shell around the girdles. All the insides arecovered.Evolutionarily, the change which turn girdle inside the shell happen very suddenly. They couldn’t find any intermediate fossilsThe 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 bonesClavicle is fused with plastron. Pubis, ischium and illium make up the pelvic girdle.°Endochondral bone:Dermal bones appear from dermis and not from cartilagesEndochondral 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 lightnessSponginess of bird bones are higher than terrestrial animals; adaptation for flightEmbryologically: the bone is made out of lateral plate mesodermoMesenchymal cells migrate and accumulate to create cartiliage.