COMPARATIVE VERTEBRATE ANATOMY BIOL 021 1 OCTOBER 2012 CRANIAL

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LECTURE 1

Comparative Vertebrate Anatomy, BIOL 021, 1 October 2012



Cranial Skeleton – three components


The head skeleton is comprised of dermatocranium (dermal skull bones), splanchnocranium (branchial or ‘gill arch’ skeleton), and neurocranium (endoskeletal braincase, sensory capsules).


Cranial Skeleton – splanchnocranium


The mandibular and hyoid arches are modified brachial arches. The stapes of the mammalan middle ear is homologous with the hyomandibula, an element of the hyoid arch. Consider the functional evolution of the element. What is its function in primarily aquatic gnathostomes? in early limbed sarcopterygians? in amphibians? in reptiles? in mammals?


The original vertebrate jaws are part of the endoskeletal splanchnocranium. The mammalian lower jaw is comprised of a single dermal bone, the dentary. The mammalian upper jaw is a single dermal bone, the maxilla. How did dermal bones come to replace the endoskeletal jaws? In what ways, if any, may the mammalian lower jaws be considered homologous with the original, endoskeletal jaws of gnathostomes.


intracranial kinesis


What is intracranial kinesis and how does it differ from cranial mobility? Consider the reduction in intracranial kinesis across the vertebrate transition to land? Why is a highly mobile skull advantageous in aquatic environments [consider its role in fish respiration] and explain why a less kinetic skull may have been advantageous for the earliest terrestrial vertebrates? What happens across this transition to improve cranial mobility?


Comparative anatomy – cranial skeleton


In chondrichthyans, upper and lower jaws swing forward during biting. Of what advantage might be mobile upper jaws?


In actinopterygians, intracranial kinesis enables the pumping required to pull water into the mouth and out across the gill curtain. Consider how, during pumping, the hyomandibula functions in coordinating the motions of different parts of the head skeleton.


Vocabulary

dermatocranium

chondrocranium/neurocranim

trabeculae

parachodrals

occipitals

ethmoid plate

basal plate

occipital arch

splanchnocranium

mandibular arch

palatoquadrate

Meckel’s cartilage

hyoid arch

hyomandibula

malleus (of mammals)

incus (of mammals)

stapes (of tetrapods)

hyoid bone/apparatus

intracranial kinesis



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