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Support from the axial skeleton
- Early forms - notochord, no vertebrae.
- -neural crest absent.
- Locomotor muscles bilarteral - dorsoventrally asymetrical (epaxial and hypaxial)
- Tunicate larvae - notochords and segmental muscles flex body.
- Amphioxus notochord - specialized contractile muscle fibers stiffen hydrostatic skeleton (flatten notochord).
- -Prevents anteroposterior collapse fo burrowing animal.
- Myosepta divide lateral muscles into myomeres.
- Aquatic vertebrates:
- Jawless fish lack vertebral column.
- Lamprey's - cartilaginous blocks along notochord (lacking in hagfishes)
- Early jawless fish cranial skeleton - dermal, chondrocranial and pharyngeal supports.
- Most early skeletons lack bone; present in a few animals.
- Fossil lampreys - cartilaginous cranial elements.
- Lampreys - similar bilarteral muscle arrangement as in Amphioxus.
Gnathostome axial skeletal elements.
- Three tail segments shown.
- Vertebral elements - pleurocentrum, intercentrum, dorsal and ventral arches.
Body support - jawed vertebrates
- Water provides some support.
- Axial skeleton - attachment for locomotor muscles.
- Cartilaginous or bony vertebrae resist anteroposterior compressive forces.
- Spinal flexibility from intervertebral joints.
- Ribs unify locomotor muscle function - act as levers during locomotion.
- Fishes - trunk and caudal vertebrae.
- Other vertebrates vertebra differentiate into up to five types.
- Rhipidisteans and early tetrapods: parts ossify but remain separate.
- Lepospondyl: all elements fused; usually centrum from a pleurocentrum.
Vertebral end shapes differ
- Acoelous - flat for compression
- Amphicoelous - both ends concave
- Procoelous - anterior concave
- Opisthocoelous - posterior end concave
- Heterocoelous - saddle like end articulations
All flat vertebrae are bad
- Laterally undulatory movements of swimming fishes and tetrapods, separate acoelous vertebral faces - leave a gap to pinch or stretch nerve cord. (this is not good)
- Curved ends allow spinal flexion, with no nerve cord damage.
Dorsal and ventral ribs
- Dorsal ribs form at myoseptum and horizontal septum intersections.
- Ventral ribs form where myosepta meet coelomic cavity.
- Serially homologous with caudal vertebral hemal arches.
- Ventral ribs lost in tetrapods; dorsal ribs persist.
- True ribs articulate with sternum.
- False ribs articulate with common costal cartilage.
- Floating ribs lack articulation.
- ventral bone or cartilage plate to which ribs join.
- Site of chest muscle origin.
- Sternum and ribs=rib cage - protects thoracic structures.
- differentation of embryonic regions into somites.
- Somites become associated with other cells and notochord to form slcerotome which becomes segmental vertebrae.
up to four pairs in primitive fishes contribute to vertebrae from mesenchymal cells that gathered around notochord in embryology.
Bertebral formation in mammals
- Primary sclerotomes divide and regroup to form vertebrae.
- Pericordal tube grows upward and round nerve cord, forming neural spine and arches.
Patterns of axial skeletons in sharks
- Vertebral elements enlarge, surpassing the notochord.
- Note regional differences in vertebral form.
- Spaces between axial elements - for notochord.
Review questions so far
- 1. Define - amphicoelous vertebra
- 2. How does such a vertebra present damage to the nerve cord when the animal bends?
- 3. What elements make up a vertebra?
- 4. What is a sclerotome?
- 5. Why do animals have ribs and what do they do?
- 6. How do ribs develop?
tail allows the animal to keep the head up easily.
- Explain how a heterocercal tail helps the animal to keep its head up while swimming.
- What kind of animal is Eusthenopteron?
- -A fossil rhipidistean
Fusion and reductions in the first few vertebrae
- results in distinctive pattern of first few cervicals in mammals.
- Describe how these changes occur.
How a turtle skeleton functions as a unit and allows great neck flexibility and movement
- How do turtle cervical vertebrae move?
- Where are turtle ribs?
- Where are turtle limb girdles in comparison to the ribs?
- Describe how limb movement in a turtle must differ from that of an animal that lacks a shell.
Snake vertebrae questions
- Wha are the zygantrum and zygosphene - what do they do?
- Where are they located on these drawings?
- Why does an animal need such structures?
List and explain the significance of adaptations that allow this animal to fly and how these skeletal features differ from those of non flying animals.
Synsacrum of a bird
- How does this feature form?
- How does it differ from pelvis of other animals?
Body support in water and on land
- Using the previous slide, explain how body support differs between aquatic and terrestrial animals.
- How do tails, long necks and heavy heads of different terrestrial animals affect their ability to balance on their vertebral columns?
- How is this ability affected if the animals stand bipedally instead of quadrupedally?
- Use the previous and next several slides to answer these questions.
These are an arched bridge and a similarly constructed animal.
- What happens to the animal's body posture if the nuchal ligament was damaged or missing?
- How would loss or damage to the abdominal muscles affect posture?
- protect spinal cord but also serve as muscle attachment sites - shape, orientation and size=related to these muscle activities.
- Describe how these muscles work in the examples shown.
- Neural spines support nuchal ligament and therefore the weight of head of animal.
- Unfortunately, bison nuchal ligament does not attach to nerual spines.
- What is going on with these spines anyway?
Identify animals - correlate locomotor habits with their movement patterns and determine why they have the vertebral types you see here. Classify these animals and identify when they lived and to whom they are related.
Evolutionary series of whale body forms.
- Determine evolutionary pressures.
- Explain how these pressures caused these anatomical changes.
- Identify when each animal lived.
Bird vertebral column
Identify how the different vertebral regions in birds function. Some areas (which?) are heavily fused - others have great mobility. Why does this occur for each region? How does it occur for each region?
- Human bipediality differs from that of primates. Explain why and the correlated anatomical changes that go with each form of bipedal locomotion.
- Human ligaments and muscles reoriented to allow a different support pattern than in quadrupeds.
- This rigging pattern is similar to that of a tall ship mast and spars.
- Pelvic differences between a chimp that walks bipedally occasionally and a human who does it habitually.
- Describe these differences and determine functional significance for each.
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