CVA Notes: Postcranial

Axial Skeleton

Defines and supports the longitudinal axis of the body.

Notochord

Long, continuous rod of fibrous connective tissue, older than vertebral column but replaced by it in development in most vertebrates.

Vertebral Column

A discrete but repeating series of cartilaginous or bony elements, evolved from block-like elements in early vertebrates; its evo complicated due to various elements arose or were lost multiple times

Dorsal Arches

Structures in vertebral anatomy that include neural and interneural arches.

Ventral Arches

Structures in vertebral anatomy, composed of hemal and interhemal arches.

Centra

Bases of ventral arches enlarged @ notochord.

Intercentrum

base of hermal arch. Dom in temnospodyls

Pleurocentrum

base of interhemal arch. Dom in amniotes

Vertebral Segment

Consists of up to 2 dorsal arches, 2 ventral arches, and 2 centra.

More ribs surrounding viscera →

fewer ribs surr. thoracic cavity (ribs are larger/ thicker to compensate)

Cervical vertebrae allow for...

head movement (neck turning)

Living agnathans

Hagfish have notochord only as adults;

Lampreys possess some small cartilaginous vertebral elements, but notochord dominates

Zygopophyses

Little projections between each vertebra that prevent torsion or twisting.

Agnathan Axial Skeleton

Characterized by a prominent/ large notochord and hard-to-document vertebral elements in fossil forms.

Ancient gnathostomes: Acanthodians & Placoderms

notochord prominent; no vertebral centra; some arches present

Ancient gnathostomes: Ancient Chondrichthyes

prominent notochord, arches present

Chondrichthyes (modern): Modern

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

Chondrichthyes (modern): Osteichthyes

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

Chondrichthyes (modern): Adv. Ost. (incl. Teleosts)

Vertebra dom & column ossified but no notochord present

Chondrichthyes (modern): Sarcopterygian

Ancient forms generally more ossified than modern forms

Amphibians: Temnospondyl

One of 3 lineages of 4pods evolved from Rhipidistians: intercentrum dom., leading to modern amphibians, hemal arch forms the body (…→Urodeles → Anurans)

Amphibians: Anthracosaur

1 of 3 lineages of 4pods evolved from Rhipidistians: An ancient lineage leading to modern amniotes, pleurocentrum dom., interhaemal arch forms the body.

Amphibians: Ichthyostegids

Diffuse arrangement of vertebral elements and are now extinct.

Amphibians: Urodeles (salamanders)

Vertebral column arched and 4pod-like;

1x midventral sternal plate that articulates w/ shoulder girdle

Amphibians: Anurans (Frogs)

Vertebral column arched and 4pod-like;

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

Sauropsids are...

modern anthracosaurs (our ancestors)

Head-neck articulation

atlas and axis: 1st 2 cervical vertebrae, allowing movement of head

Snake’s Adaptations

extra zygopophyses to manage twisting

Testudines

vertebrae fused w/ shell

Bird Adaptations

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

Gastralia

Dermal bony 'ribs' found in the abdominal region of crocs only

Innominate bone

The fused pelvic bones including public, ischial, and iliac bones.

Thoracic vertebrae

c. 12, w/ ribs

Cervical Vertebrae

Typically 7 vertebrae in mammals, allowing for neck movement.

Sacrum

A group of fused vertebrae, usually 2-3 in mammals, with humans having 5.

Caudal Vertebrae

The simplified and reduced vertebrae at the tail end of vertebrates, lacking ribs.

Mammal’s adaptation for Life on Land

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.