10 Girdle, Fins, Limbs, And Locomotion

Comparative Anatomy of the Vertebrates:

[CHAPTER 10:

Girdles, Fins Limbs and Locomotion ]

OUTLINE I. Pectoral Girdle a. Ostracoderms b. Teleost c. Chondrichthyes d. Early Tetrapods - clavicles - coracoid plate - coracoid process - scapula e. Mammals II. Pelvic Girdle - pelvic plate - sacroiliac joint - prepubic cartilage - epipubic and hypoischial bone - innominate bone - relaxin III. Fins A. Fin Rays B. Skeletal Base of Fin Rays C. Paired Fins D. Medial Fins E. Caudal Fins F. Origin of Paired Fins IV. Tetrapod Limbs A. Manus B. Pes C. Origin of Limbs D. Locomotion on Land without Limbs

APPENDICULAR SKELETON – girdles, fins and limbs Limb buds – where tetrapod limbs arise during embryogenesis – may be transitory, incomplete or functionless vestiges which bespeaks an ancestor with functional tetrapod limbs Fin folds – where fins arise during embryogenesis I. PECTORAL GIRDLES – dermal + replacement bones a.) OSTRACODERMS – with pectoral appendages; girdles remain unclear b.) TELEOSTS – cleithrum as the major bone of the girdle – no clavicle – scapulocoracoid (coracoid+scapula)

c.) d.)

CHONDRICHTHYES– components

calcified

endoskeletal

EARLY TETRAPODS – interclavicle (addn’l membrane bone) – no posttemporal (braced the girdle against the skull in fishes) – supracleithrum is missing

*Please refer to The Skeletal System 4 Handout for the tabulated components of pectoral girdle in representative vertebrates. CLAVICLES – fate is correlated with that of the coracoid – clavicle and/or coracoid and procoracoid brace the scapula against the sternum – long bones of furculum (wishbone) in birds CORACOID PLATE – 2 ossification centers: a. Anterior – gives rise to procoracoids b. Posterior – gives rise to coracoids CORACOID PROCESS OF THE SCAPULA – vestige of the procoracoids and coracoids in Eutheria SCAPULA – present in all tetrapods that retain any vestiges of anterior limbs – bears part or all of the glenoid fossa for articulation of the girdle with the head of the humerus e.) MAMMALIAN SCAPULA (Recall scapula of cat!): 1. Scapular spine 2. Supraspinous fossa 3. Infraspinous fossa 4. Acromion process Mammalian clavicle – large in monotremes, insectivores and primates – in bats, brace the scapula against the sternum – no clavicle in cats (to withstand the shock of landing upright on their forelimbs), ungulates (facilitates grazing) and ungulates Observation: Dermal bones predominate in the pectoral girdle of bony fishes, whereas replacement bones predominate in tetrapods.

Comparative Anatomy of the Vertebrates:

[CHAPTER 10:

Girdles, Fins Limbs and Locomotion ]

II. PELVIC GIRDLES – no dermal bones 1. PELVIC (ISCHIOPUBIC) PLATES – paired (brace for the pelvic fins) that meet in the midventral pelvic symphysis in fishes – fused as one structure in chondrichthyes and lungfishes – with 2 ossification centers to form a pubis and an ischium in tetrapods acetabulum – for articulation of head of femur ilium – from blastema dorsal to the pelvic plate pubic, ischial and ishiopubic symphyses – absent in birds to provide a wider outlet from the pelvic cavity for laying eggs pelvis – sacrum + girdle (amniotes); encircles caudal end of the coelom pelvic cavity – contains the urogenital organs; terminal portion of large intestine 2. SACROILIAC JOINT – junction b/n sacrum and ilium; shock absorber; immobile

2. LEPIDOTRICHIA – bony; teleosts Actinotrichia – distal to the fin rays; stiffen the fin rays B. SKELETAL BASE OF FIN RAYS 1. BASALIA – absent in specialized teleosts 2. RADIALIA – vestiges in specialized teleosts Archipterygium – ancestral fin type C. PAIRED FINS 1. LOBED FINS – sarcopterygians (actinistians and rhipidistians); fleshy proximal lobe and membranous distal portion 2. FIN FOLD FINS – chondrichthyans; with broad base; basalia: propterygia, mesopterygia, metapterygia 3. RAY FINS – actinopterygians (most like tuna have no pelvic fins for streamlinings); very flexible (teleosts) 4. SPINY FINS – acanthodians; supported by hollow spines (not fin rays) Biserial – fin with two series of radials; e.g. dipnoan Neoceratodus Claspers – modified basalia in male chondrichthyans

3. PREPUBIC (YPSILOID) CARTILAGE – urodeles; for attachment of respiratory muscles 4. EPIPUBIC AND HYPOISCHIAL BONE – reptiles, monotremes and marsupials; epipubic bone is marsupial bone (supports marsupium) in marsupials Archaeopteryx – no synsacrum 5. INNOMINATE (COXAL) BONE – ankylosed ilium, ischium and pubis in mammals 6. RELAXIN – ovarian hormone which softens the fibrocartilage of pelvic symphyses during parturition III. FINS Functions: 1. steering devices for changing direction 2. stabilizers to prevent the body from rolling 3. control of body inclination when swimming away from the horizontal 4. serve as brakes to decrease forward motion A. FIN RAYS 1. CERATOTRICHIA – keratinized; elasmobranchs

D. MEDIAN FINS 1. DORSAL FINS – act as keels, keeping motionless fishes from rolling to the left and right; may be used for locomotion in rare cases; impt in Rajiformes (inc. number), lampreys and bony eels (elongated) 2. ANAL FINS – modified as gonopodia (analogous to claspers) in some viviparous teleosts E. CAUDAL FINS 1. HETEROCERCAL – notochord turns upward; placoderms, Paleozoic and modern sharks, some acanthodians, and chondrosteans (sturgeons and spoonbills) 2. HYPOCERCAL – vertebral column turns downward; ichthyosaurs (result of evolutionary convergence) 3. DIPHYCERCAL – externally symmetrical, vertebral column ends with a little upbending; dipnoans and Latimeria 4. HOMOCERCAL – notochord turns far dorsad; teleosts *Heterocercal condition – most primitive; the rest are modifications of it

Comparative Anatomy of the Vertebrates:

[CHAPTER 10:

Girdles, Fins Limbs and Locomotion ]

*Similaities in morphologic features of caudal fins – may be the result of convergent evolution F. ORIGIN OF PAIRED FINS 1. FIN FOLD HYPOTHESIS – paired fins are derived from a pair of continuous fleshy folds of lateral body wall analogous to the metapleural folds of an amphioxus; no evidence; of historical interest only 2. GILL ARCH HYPOTHESIS – pectoral and pelvic girdles are modified gill arches, and the skeleton within the fin is an expansion of the gill rays 3. FIN SPINE HYPOTHESIS – membranes in 2 pairs develop in rays supported by radial elements *Pelvic fins appear to be a gnathostome feature. *Spines in acanthodians – derived feature

IV. TETRAPOD LIMBS *Early tetrapods – first segment is horizontal from the trunk; second segment perpendicular to the first, directed downward; among amphibians and basal lizards THREE SEGMENTS: 1. PROPODIUM – upper arm, thigh 2. EPIPODIUM – forearm, shank 3. AUTOPODIUM – manus, modifications

pes;

most

PATELLA (KNEECAP) – sesamoid bone; in birds and mammals; protects the joint from the abrasive action of the tendon PENTADACTYL LIMB – five-digit limb A. MANUS 1. CARPUS – wrist with 3 rows of bones: a. Proximal Carpals  radiale  intermediale  ulnare  pisiform – sesamoid bone; in most reptiles and mammals b. centralia – 3 or more bones c. distal carpals – 5 th th  hamate – fused 4 and 5 distal carpals 2. METACARPUS – skeleton of the palm 3. PHALANGES – bones of the digits; 2-3-4-5-3 (generalized phalangeal

formula); 2-3-3-3-3 in late therapsids and mammals with pentadactyl limbs PREPOLLEX – elongated carpal; can be seen in a panda POLLEX – thumb MODIFICATIONS OF MANUS: 1. reduction in the number of bones by evolutionary loss or fusion 2. disproportionate lengthening or shortening of some of the bones 3. increase in the number of phalanges ADAPTATIONS OF MANUS: 1. Flight  CARPOMETACARPUS – fused three distal carpals and three metacarpals; in birds  ALULA – first finger in brids; for braking  PATAGIUM – wing membrane; pterosaurs, bats, gliding lemurs; a result of convergent evolution if present in unrelated mammals 2. For life in the ocean – became flippers 3. For swift-footedness  PLANTIGRADE – common in mammals with pentadactyl limbs (monotremes, marsupials, insectivores, bears, arboreal raccoons and primates); primitive tetrapod stance  DIGITIGRADE – rabbits, rodents and most carnivores; increased speed and agility and more silent than plantigrade  UNGULIGRADE – stance that is wellsuited for running a. PARAXONIC FEET – body weight borne on two parallel axes; artiodactyls b. MESAXONIC FEET – body weight borne on the middle digit; perissodactyls 4. For grasping – accomplished by flexing the fingers at each interphalangeal joint; primates, rodents; opposable thumb B. PES 1. TARSALS – wrist with 3 rows of bones: a. proximal tarsals  fibulare  intermediale  tibiale b. centralia – 3 or more bones

Comparative Anatomy of the Vertebrates:

[CHAPTER 10:

Girdles, Fins Limbs and Locomotion ]

c. distal tarsals – 5  cuboid – fused 4th and 5th tarsals 2. METATARSALS – skeleton of the palm 3. PHALANGES – bones of the digits 2-3-4-5-4 (Sphenodon); 2-3-4-4-0 (alligator); 2-3-4-4-0 (turtles); 2-3-4-5-4 (generalized for reptiles); and 2-3-3-3-3 in early therapsids and mammals PREHALLUX – vestiges of a tarsal or metatarsal HALLUX – great toe ASTRAGALOCALCANEUS – fused proximal tarsals and a centrale; in lizards TIBIOFIBULA – fused of tibia and fibula (frogs); splinter in birds; lost in deer and other ungulates TIBIOTARSUS – fused of tibia and proximal tarsals (birds) TARSOMETATARSUS – fused distal tarsals and metatarsals *There is an intratarsal joint between the tibiotarsus and tarsometatarsus and a joint between the tarsometatarsus and toes. ZYGODACTYLY – X; woodpeckers and parrots *Mammals have a hinge joint instead of an intratarsal joint. The tibiale is the principal weight-bearing bone of the ankle. METATARSAL arch – in hominoids; distributes the body weight over four solid bases; absorbs some of the shock generated by bipedal locomotion; provides “spring” for walking and running *In wriggling seals, walruses, cetaceans and sirenians, the anterior flippers are for maneuvering. Wirggling seals move using their posterior flippers and with lateral undulations of the trunk. Walruses, cetaceans and sirenians move by dorsal and ventral undulations. C. HYPOTHESES (ORIGIN OF THE LIMBS): 1. MODIFICATION OF EXISTING STRUCTURES (supported by fossil record)  Rhipidistian pectoral fin with basal bone articulates proximally with scapula and distally with a pair of radials  Loss of fin rays and modifications of distal radials could have produced the skeleton of the tetrapod limb



Preaxial and postaxial radials could have formed the digits 2. FORMATION OF NEW FEATURES (based on developmental studies)  Initial cell proliferations develop the limb buds at the sides of the trunk of the body  Second period of cell proliferation occurs at right angles to the limb axis (distal to the wrist) giving rise to the digits D. LOCOMOTION ON LAND WITHOUT LIMBS 1. SERPENTINE or LATERAL UNDULATION – by forming loops; limbless lizards and snakes 2. RECTILINEAR LOCOMOTION – gliding forward on the substrate while keeping the entire body in a straight line; depends on generating friction between sections of the ventral skin and the substrate 3. SIDEWINDING – rattlesnakes and snakes (desert) 4. CONCERTINA MOVEMENT – modified serpentine movements; bracing S-shaped loops against the burrow wall and exerting horizontal force while thrusting the head and forebody forward