SKELETAL SYSTEM: APPENDICULAR SKELETON

1. SKELETAL SYSTEM: APPENDICULAR SKELETON Mrs. Ofelia Solano Saludar Department of Natural Sciences University of St. La Salle Bacolod City

2. Appendages and supporting girdles: pectoral and pelvic

3. The appendicular skeleton has a different embryonic origin than the axial skeleton. • Somatic mesoderm of the lateral plate contributes to the limb bud mesenchyme. • Initially, mesenchyme of the limb bud consists solely of this lateral plate origin. • As the basic skeletal plan is laid out, mesenchymal cells from the somitesmigrate in to form muscle cells, and neural crest cells migrate in to form both nerves and pigment cells.

4. ORIGIN OF PAIRED APPENDAGES Gill arch hypothesis - fins derived from the last 2 gill arches Fin spine hypothesis - fins derived from tissue attached to spines that may have evolved to provide protection from predators (Acanthodians) Fin-fold hypothesis- continuous finfolds became discontinuous from loss

5. EVIDENCES FOR THE FIN-FOLD HYPOTHESIS: • Development and early structure of paired & unpaired fins are identical • In Acanthodians, the fin fold became discontinuous with each segment supported by a rigid spine; placodermshad a pair in the front of the body, and a pair at the rear. • Ammocoetes larva had continuous dorsocaudal fin folds • Ventrolateral fin folds found in jawless ostracoderms helped stabilize body position during swimming.

6. *The number of muscle buds & nerve branches to the embryonic paired fins involve more segments than in the adult *Shape of the fins & parallelism of fin rays suggest origin from a continuous fin fold.

7. FINS • Steering, braking, controlling inclination while horizontal swimming, & as stabilizers that prevent rolling; forward thrust by lateral undulation of body • Pterygiophores (bone or cartilage) provide base support for fin rays: • Basalia- enlarged, proximal; 3 types: pro, meso, metapterygia • Radialia- slender, distal • Found in all fishes except Agnathans where there are no paired fins • Slight development of pectoral fins, small musculature & absence of jaws are features of bottom-dwelling forms.

8. Fins are stiffened by dermal rays: Lepidotrichia- jointed bony dermal scales; teleosts Ceratotrichia- cartilaginous unsegmented rays; chondrichthyes Actinotrichia- delicate distal rays; found in both types

9. Archipterygial fins are symmetrical along the central axis (modern fishes); supporting skeleton and musculature are inside the body wall of the fish. Metapterygialfins are assym- metrical along the central axis; the skeletal and muscular support are outside of the body wall; were preadaptedto bear weight and used for locomotion by fishes wallowing in shallow mud flats or temporary water bodies.

10. PAIRED FINS • 1. Pectoral & Pelvic fins: • Lobed fins- fleshy proximal lobe consisting of fin skeleton, muscles, fin rays; sarcopterygians • Fin folds- broad base; basalia of pelvic fins are modified as claspers to transfer sperm to the female in male chondrichthyans • Ray fins- lost basals, flexible; teleosts

11. 2. Median fins: Dorsal fins used as keels, rarely used for locomotion Anal fins- modified as gonopodium; analogous to claspers 3. Caudal fins: Heterocercal placoderms, sharks Homocercal teleosts Diphycercal Dipnoans & Latimeria

12. OSTEICHTHYES Dorsal fins Caudal fin Pectoral fin Anal fin Pelvic fin

14. Fins on opposite sides of the body attach to GIRDLES that in turn attach the fins to the axial skeleton and to each other.

15. PECTORAL GIRDLE Other than locomotion, it also shields the heart, forms the back of the oral cavity and acts as an attachment site for jaw musculature. Membrane bones: cleithrum, supracleithrum, postcleithrum, posttemporal (anchors to skull), clavicle, interclavicle Replacement bones: Coracoid, Scapula

16. PECTORAL GIRDLES: FROM FISH TO TETRAPOD • PLACODERMS- first to have girdles. Pectoral girdle was the scapulocoracoidwith an articularfossa that received basal pterygiophores of fins. Pelvic girdle was a single endoskeletal element. • SARCOPTERYGIANS- scapulocoracoid, cleithrum, post- temporal, clavicle & interclavicle bones • CROSSOPTERYGIANS: clavicle, cleithrum, scapulocoracoid

17. FISHES: scapula & coracoid receive the forces transmitted to the trunk; posttemporal braces the girdles against the caudal angles of the skull; clavicle braces against its opposite in a midventralsymphysis

18. CHONDRICHTHYES • Primitive sharks had pectoral & pelvic fins consisting of basals & tightly packed radials • Girdles consisted of a single enlarged basal element similar to placoderms.

19. In modern sharks the paired basal components extend to the body midline which fuse to form a U-shaped scapulocoracoid bar for the pectoral girdle and a puboischiadicbar for the pelvic girdle.

20. The pectoral girdle is cartilaginous, with no dermal elements: coracoid, scapula, suprascapula (scapulacoracoid) • It does not connect to axial skeleton, but fused at midline

21. TETRAPODS: • Clavicle- missing in limbless forms; present in most mammals; furculum (wishbone) of birds • Coracoids- procoracoids & coracoids ossify in coracoid plate; assist or replace the clavicles in bracing against the reptilian & avian sternum; vestigial coracoid process of the scapula in eutherians • Scapula- present in all tetrapods; suprascapula typically fuses with scapula Dermal bones predominate in the pectoral girdle of bony fishes; replacement bones predominate in tetrapods. • Tetrapods never brace their pectoral girdles against the skull or vertebral column.

22. AMPHIBIANS: • Acquired interclavicle (episternum in tetrapods), lost posttemporal, supracleithrum & cleithrum • Replacement bones: coracoid, scapula & suprascapula • Urodeleshave no membrane bones • Anurans have clavicle, no interclavicle • REPTILES: • Scapula, coracoid, sometimes clavicle, & interclavicle • Crocodiles have reduced clavicle • Turtles have interclavicle fused with shell • Snakes have no girdle • Lizards have a significant clavicle, interclavicle

23. BIRDS: 2 clavicles plus interclavicle form furcula; bladelike scapula; procoracoid articulates with sternum

24. MAMMALS • A new coracoid is formed. • The scapula enlarges & the coracoid is reduced as the coracoid process. • The interclavicle bone persists in therapsid reptiles & monotremes, but is lost in marsupials and eutherians.

25. The clavicle is large in digging, climbing, or flying forelimbs • Reduced or absent in felines (leaping dissipates impact on muscles), cetaceans (fishlike), ungulates (facilitates grazing)

26. THERAPSIDS, MONOTREMES:clavicle, procoracoid, coracoid, scapula • EUTHERIAN MAMMALS: scapula is divided by scapular spine into supraspinous & infraspinousfossae to accommodate origins of strong muscles that insert on humerus; acromion process articulates with clavicle

27. P ECTORAL GI RDLE PHYLOGENY

28. PECTORAL GIRDLES OF SELECTED VERTEBRATES

29. FISHES • Consists of 2 cartilaginous or bony plates (ischiopubic plates) that articulate with the pelvic fins ) • Usually meet ventrally in a symphysis, or form a median bar in sharks & lungfishes

30. PELVIC GIRDLE • Arose from pterygiophores supporting fins • Brace posterior paired appendages & enclose pelvic cavity organs • No dermal components (unlike pectoral girdle) • Sarcopterygians: one bone embedded in the body wall. The left & right pelvic girdles do not meet at midline & there is no connection to the axial skeleton • Crossopterygians: single element with processes

31. Ichthyostega, an amphibian in the fossil record, had 3 fused bones in the pelvic girdle: pubis, ischium& the ilium, attached to vertebral column by sacral ribs. • In frogs & toads, the ilia are elongated & extend from sacral vertebra to urostyle; sacroiliac joint between ilium & sacral vertebra is freely moveable & moves when a frog or toad jumps

32. REPTILES Stronger sacroiliac joint; ilium & ischium are expanded to accommodate musculature for more muscle attachment & stability needed for bipedal locomotion

33. BIRDS: • Girdles braced against lumbar & sacral vertebrae • Pubic bones are typically long & thin • Synsacrum– Ilium is braced against fused vertebrae • Limited pubic symphysis provides a larger outlet for eggs

34. MAMMALS • Ilium, ischium, and pubis unite to form the innominate bone (coxa) • Encompass a pelvic cavity • Epipubic bone in marsupials is unique for pouch support

35. P ELV I C GI RDLE PHYLOGENY

36. TRANSITION TO LAND: Terrestial vertebrates need stronger girdles and limbs. • Pectoral girdle became detached from the skull providing a neck region for better head mobility • Limbs plus lateral undulations, should provide points of pivot for trunk to move

37. ANCESTRAL TETRAPOD LIMBS The Labyrinthodont amphibians probably evolved from a Crossopterygian ancestor. When the fresh water pools in which these fish lived became stagnant, they may have crawled up the bank to breath air using primitive lungs. As the lobed fins of these fish evolved into stronger limbs, the first tetrapods appeared.

38. EARLY TETRAPOD LIMBS ARE MODIFICATIONS OF RHIPIDISTIAN FINS: • Loss of fin rays and distal radials produced the first tetrapod limb. • Digits are a novel feature of tetrapodsand are not modifications of radials. • Girdles remained fishlike.

39. In the pectoral fins of rhipidistian crossopterygians, a single basal bone (humerus), articulates with the scapula and distally with a pair of radials (radius & ulna).

40. In early tetrapods, limbs were short & first segment extended straight out from the body. As such, their primitive gaits include: • Trot- diagonally opposite feet meet the ground, the center of mass lies on the line connecting the 2 pts. of support; a 3rd point of support on a long tail further stabilizes gait. • Lateral-sequence gait- center of mass inside triangle of support • Limb rotation- muscles rotate long bones to retract feet & propel body forward.

41. From a sprawled position, tetrapods can change their position by drawing limbs under the body. The sprawled posture brings a medially directed force towards the pectoral girdle. As limbs are brought under the body, forces shift vertically, accounting for phylogenetic loss of some pectoral elements.

42. This change in limb posture results from torsion of the distal ends of long bones so that they are nearly parallel the vertebral column. This brings the digits forward and in line with direction of travel.

43. TETRAPOD LIMBS • Some have lost one or both pairs; in others, one pair is modified as arms, wings, or paddles; typically have 5 segments: • Stylopodium: proximal • Zeugopodium: middle • Mesopodium: carpals & tarsals • Metapodium: metacarpals & metatarsals • Phalanges: bones of the digits (fingers, toes, claws)

44. PROPODIUM or Anterior Limb: • Brachium (upper arm) – humerus • Antebrachium(forearm) - radius & ulna • Carpus(wrist) – proximal row: radiale, ulnare, intermedium, & pisiform ; middle row: 3 centrals;distal row: starting on radial side: 1-5 distals • Metacarpus (palm) – metacarpals • Digits or phalanges - general formula starting at thumb: 2,3,4,5,3 • Manus, autopodium, forefoot orhand: includes mesopodium, metapodium, phalanges

45. SELECTED VERTEBRATES FOREL IMBS OF

46. EPIPODIUM or Posterior limb femur (thigh) - femur crus (shank) - tibia & fibula tarsus (ankle) - tarsals metatarsus (instep) - metatarsals digits - phalanges Pes, autopodium, hindfootor foot: includes mesopodium, metapodium, phalanges

47. Some lack both pairs of limbs: caecilians (apodans), most snakes; snake-like lizards • Some have forelimbs only: manatees & dugongs, dolphins; cetaceans, sirenians have vestigial elements embedded in body wall

48. A reduced number of ankle bones in birds have fused with the tibia & metatarsals to add an elongated segment to the hindlimbs. • An intratarsal joint adds to the flexibility of the pes. • Digit 2 is long digit of wing • Phalangeal formula for foot is 2,3,4,5,0

49. PES OF SELECTED VERTEBRATES

50. TYPES OF TERRESTIAL LOCOMOTION • Walking, running, cursorial (terrestrial, usually quadrupedal) • Many specialized for moving quickly in a terrestrial habitat • Pattern of footfalls depends on species and speed of travel • Humans are the only truly bipedal species