appendages

appendages - 10/20/2011 EVOLUTION OF APPENDAGES 3 theories...

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10/20/2011 1 EVOLUTION OF APPENDAGES 3 theories of appendage evolution: Gill Arch Theory Fin Fold Theory Fin Spine Theory None are entirely supported!! Paired appendages likely evolved more than once EVOLUTION OF APPENDAGES Paired Fins - 3 types Lobe Fin : Sarcopterygian fish Axis = central skeletal base Preaxials = extend from the anterior portion of the axis Postaxials = extend from the posterior portion of the axis Finfold Fin : Chondrichthyian fish Base composed of Pro - Meso - and Metapterygium Radials extend outward from the base Ray Fin : Actinopterygian fish Basalia : series of bones forming the base on primitive bony fish Radialia : secondary series of support bones Lepidotrichia : parallel fin rays supporting main body of fin Pectoral fins generally more important Pelvic fins less important and may be: lost or greatly reduced positioned in a variety of different places adapted as accessory reproductive organs
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10/20/2011 2 Pectoral Girdle Provides support for the anterior appendages Duplex structure including both dermal and endochondral elements Dermal elements for strength Endochondral elements for articulation of the limb (glenoid fossa) Pectoral Girdle Dermal Elements Cleithrum Primitively the main structural element Clavicle Joins two sides together Supracleithrum Connects girdle to back of skull Pectoral Girdle Endochrondral Elements Scapula Main bone for articulation of the limb Coracoid Like the clavicle connects two sides together Suprascapula Additional point for muscle attachment Major trend is for the reduction of dermal elements and attachment to the sternum (axial skeleton)
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10/20/2011 3 Pelvic Girdle Entirely endochrondral Initially just a means of joining two posterior fins together Ischiopubic bar -> basipterygium Tetrapods - adapted to support the weight of posterior portion of the body Attachment of limb to sacrum (axial skeleton) Ventral cartilage plate develops in all tetrapods Two points of ossification = ischium & pubis Dorsal plate develops independently Single point of ossification = ilium All three bones fuse together to form the
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appendages - 10/20/2011 EVOLUTION OF APPENDAGES 3 theories...

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