CVA Notes: Postcranial

Axial Skeleton:

  • Axial skele defines & supports longitudinal axis of the body

  • Notochord: long, cont.s rod of fibrous conn. tissue

    • Older vs. vertebral column but replaced by it in development in most vertebrates

  • Vertebral column: discrete but repeating series of cartilaginous or bony elements

    • originated as block-like elements in early vertebrates (ie. Haikouella)

    • V. column evolution complicated, because various elements arose or were lost multiple times

    • Impossible to examine embryos of early vertebrates which limits our understanding

Vertebral Anatomy:

  • Dorsal arches:

    • Neural: spinal cord passes through this

    • Interneural

  • Ventral arches:

    • Hemal

    • Interhemal

  • Centra: bases of ventral arches enlarged @ notochord

    • Intercentrum: base of hemal arch. Dom in temnospodyls (anamniotes)

    • Pleurocentrum: base of interhemal arch. Dom in amniotes

  • Vertebral segment: up to 2 dorsal arches, 2 ventral arches, and 2 centra

    *dashed lines represent body segments

Phylogeny:

  • Maj. Patterns:

    • Greater ossification from ancestral pattern; consolidation of segment components

    • Vertebral column: straight →arched

    • Ribs: more ribs surr. viscera →fewer ribs surr. thoracic cavity

      (ribs, however, are larger/thicker to compensate)

  • Adaptations for life on land:

    • Arches for support

    • Zygopophyses: little projection b/w each vertebrate that prevent torsion/ twisting

    • Cervical vertebrae allow head movement (neck turning)

Agnathan Axial Skele:

  • Notochord large and prominent

  • Vertebral elements hard to document in fossil forms…or, weren’t present

  • Living agnathans:

    • hagfish have notochord only as adults

    • Lamprey possess some small cartilaginous vertebral elements but notochord dominates

Ancient gnathostomes:

  • (a) Acanthodians & Placoderms: notochord prominent; no vertebral centra; some arches present

  • (b) Ancient Chondrichthyes: prominent notochord, arches present

Chondrichthyes (modern):

  • Modern: vertebrae prominent; notochord remnant w/in vertebral column (amphicoelous intervertebral joints)

Osteichthyes:

  • Primitive Ost. (ie Sturgeons & paddlefishes): vertebral column dominant but secondarily unossified, notochord retained

  • Adv. Ost (incl. Teleosts): Vertebra dominant & column ossified, no notochord present


  • Sarcopterygian: Ancient forms generally more ossified than modern forms

Amphibians:

  • 3 lineages of 4pods evolved from Rhipidistians:

    • Temnospondyl: intercentrum dominant, leading to modern amphibians, hemal arch forms the body (…→ Urodeles → Anurans)

    • Anthracosaur: pleurocentrum dominant, leading to modern amniotes, interhemal arch forms the body

    • Ichthyostegids: lil dusion of vertebral elements, extinct

  • Urodeles (Salamanders):

    • Vertebral column straight and fish-like

    • 1x midventral sternal plate that articulates w/ shoulder girdle

  • Anurans (Frogs):

    • Vertebral column arched and 4pod-like

    • 1x xiphisternum, sometimes w/ xiphoid cartilage or another element called omosternum

Sauropsids:

  • Modern anthracosaurs (our ancestors)

  • Head-neck articulation: Atlas and axis: 1st 2 cervical vertebrae, allowing movement of head

  • Adaptations:

    • Snake: extra zygapophyses to manage twisting

    • Testudines: vertebrae fused w/ shell

    • Gastralia: dermal bony “ribs” in abdominal region

    • Birds: uncinate processes for fight muscle attachment, pringle/ saddle like built

Mammals:

  • Limbs are now below the body and not to its side, which is a big deal when conserving energy just to stands or lift body upward.

  • Typically 7 cervical vertebrae (neck)

  • Thoracic vertebrae: c.12, w/ ribs

  • Lumbar: c.7, w/out ribs

  • Sacrum of fused vertebrae, usually 2-3, humans have 5

  • Caudal vertebrae much simpler, reduced compared to reptilian caudal vertebrae…few to many but lacking ribs

  • Innominate bone: fused public, ischial, and iliac bones

    dog skele