Chapter 8 Part 2: Axial Skeleton Flashcards
describe the fishy axial skeleton of agnathans
Only a few cartilaginous vertebral elements are present
Example: Placoderm Coccosteus, with prominent notochord supporting dorsal and ventral vertebral elements
Example: Acanthodian Acanthodes, with neural and hemal arches that presumably rode upon a notochord
How is the modern chondrichthyan axial skeleton different?
Primitive Chrondrichthyans: Chain of neural arches presumably riding upon a notochord that extended into the tail
Modern: The vertebral elements tend to enlarge in elasmobranchs, surpassing the notochord as the major mechanical support for the body in modern forms
Describe the axial skeleton of primitive Actinopterygians
Vertebral column is unossified - several elements of the vertebrae are present in each segment
Describe the axial skeleton of Neopterygians
characterized by very ossified vertebrae
How is the teleost axial skeleton different?
- Vertebral column typically is ossified and its centra more prominent to replace the notochord as the major mechanical support for the body
- Neural spines and ribs become more developed, as do accessory bony elements that help internally stabilize some of the unpaired fins
The rhipidistians axial skeleton is made of rhachitomous vertebrae – what does that mean?
Vertebral elements usually ossified and rachitomous; Exhibited rachitomous vertebrae - each vertebra consisted of three separate vertebral elements:
a neural arch
a hoop- or crescent-shaped intercentrum
paired pleurocentra
Notochord runs through Circular shape seen in the middle
What is the difference between an aspidospondyl vertebra and a holospondyl vertebra?
Aspidospondyly: the three elements (intercentrum, pleurocentrum, and neural arch/spine), either paired or single, remain as separate ossified elements
Holospondyly: all vertebral elements in a segment are fused into a single piece
Which part of the original rhachitomous vertebra evolved into the centrum in modern amphibians
the intercentrum evolved into the centrum for modern amphibians
- Which part of the original rhachitomous vertebra evolved into the centrum in modern amniotes?
the pleurocentrum evolved into the centrum in modern amniotes
Acoelous
Suited to receive and distribute compressive forces within the vertebral column
Amphicoelous
Each surface is concave - allows limited motion of axial skeleton in most directions
Procoelous
Concave anteriorly and convex posteriorly
Convex articular surface of one centrum fits into the concave surface of the next to form a kind of ball-and-socket joint, permitting extensive motion in most directions without stretching the nerve cord
Opisthocelous
Convex articular surface of one centrum fits into the concave surface of the next to form a kind of ball-and-socket joint, permitting extensive motion in most directions without stretching the nerve cord
Concave posteriorly and convex anteriorly
Heterocoelous
Saddle-shaped articular surfaces at both ends
Allow great lateral and vertical flexion, prevent wringing or rotation of the vertebral column about its long axis
Name 3 types of tail fins
Heterocercal, Diphycercal, and Homocercal
