Limb Posture and Girdles

1. Limb Posture and Girdles • Early tetrapods had sprawling posture • Forces directed toward medial elements • Still used by many tetrapods Fig. 9.32 Digits oriented laterally Fig. 9.35

2. Sprawling Posture

3. Sprawling Posture

4. Limb Posture and Girdles • Movement of limbs under body shifted forces to be vertical • Led to reduction/loss of medial elements and increase in scapula prominence Digits also re-oriented to face forward Fig. 9.32 Fig. 9.35

5. Cursorial locomotion = rapid running • Dog: http://www.youtube.com/watch?v=LeErz1pI_mc • Horse: http://www.youtube.com/watch?v=OcD1_jvhc_g • Cheetah: http://www.youtube.com/watch?v=iarsmqA3dck

6. Are hippos the ancestors of whales and dolphins? Durodon

7. Cranial Skeleton

8. The Vertebrate Cranium • Composed of three parts: • Chondrocranium – endochondral bone • Splanchnocranium– endochondral bone • Dermatochranium– dermal bone • Each has separate evolutionary origin

9. The Vertebrate Cranium Chondrochranium Splanchnochranium Contributions of each vary greatly among species! Fig. 7.2 Dermatochranium

10. Chondrocranium • Acts as a platform supporting the brain • Encases the brain in Elasmobranchii • Mostly embryonic in other vertebrates • Contributes to occipital, ethmoid, and sphenoid bones in mammals • See Table 7.1 (but don’t memorize it!) • Posterior portion likely from ancient vertebral segments

11. Chondrocranium Cartilage Bone What ossifies or remains cartilage depends on species Foramen magnum forms in this portion of cranium Occipital condyle also derived from this portion Fig. 7.3

12. Splanchnocranium • Neural crest cells move into the walls of the pharynx and differentiate into branchialarches (= pharyngealarches = gill arches) • Phylogenetically from filter feeding elements • Composed of five articulated elements: • Pharyngobranchialdorsal • Epibranchial • Ceratobranchial • Hypobranchial • Basibranchialventral

13. Splanchnocranium Fig. 7.5

14. Origin of Jaws • Jaws arose from anterior branchial arches • Serial “theory” = jaws from one arch • Composite “theory” = jaws from > 1 adjacent arches Fig. 7.8

15. Comparison of dorsoventralpatterning gene expression in the developing zebrafish and lamprey pharyngeal skeletons. 1st arch development Branchial arch development Expressed in ventral pharynx of developing lamprey Cerny R et al. PNAS 2010;107:17262-17267

16. Jaw Suspension • See pp. 246-247 and Fig. 7.8 • Know how splanchnocranium elements are involved with jaw attachment to rest of skull Fig. 7.8

17. Dermatocranium • Phylogenetically from armor of integument in early fishes • “Sank inward” to attach to chondrocranium and splanchnocranium • Composed of 6 series of bones (see Table 7.3) • These elements reduced (lost or fused) in fishes and amphibians • Predominates amniote cranium, making most of braincase and jaw

18. Dermatocranium Series • Facial • Orbital • Temporal • Vault • Palatal • Mandibular Fig. 7.10

19. Dermatocranium Series • Facial – encircles nares and forms snout • Orbital – encircles eyes • Temporal – posterior part of braincase • Vault – “roofing bones” cover brain on top • Palatal – roof of the mouth • Mandibular – lower jaw Fig. 7.10

20. Cranium is Composed of Diverse Bones with Diverse Origins Chondrochranium Different vertebrate groups differ in the contribution of each of these 3 parts Splanchnochranium Dermatochranium