DON'T FORGET: LAB EXAM IS NEXT WEEK!

Treat skulls with care, especially lower jaws. Keep hand under jaw.

Wash hand afterwards.

Hyostylic - shark and perch

Autostylic - all tetrapods

Amphistylic - no examples in lab

Look at pages 6, 7, 8

Trend of decrease in number of skull bones, number of sutures

increases strength, lightness of bones

ID underlined bones.

On exam: Know cat and hyomandibular and jaw articulation bones on other skulls.

Note: exoccipital, basioccipital, quadratojugal, stapes, incus, malleus

(Look at sea turtle.)

Palatal complex: palate and upper jaw

Neurocranium: brain case (next to brain)

Dermal roof: top & sides of skull

Anapsid condition: solid dermal roof

Green sea turtle good example

Jaw muscles enclosed within dermal roof

little area for jaw muscle attachment or enlargement

Snapping turtle - Otic notch at back of skull allows anterior expansion of jaw muscles.

‘Modified anapsid’ condition increases power of bite.

Holes arose in dermal roof, muscles pass through roof to attach on outside of skull.

Moose is ‘true synapsid’ skull.

Temporal fossa separated from anterior orbit by post-orbital bar.

Black bear is ‘modified synapsid’ skull.

Temporal fossa is continuous with orbit.

Carnivores, some omnivores, with enlarged jaw muscles, show decrease in size of post-orbital bar.

Modified to increase power of bite.

Sagittal crest also may be increased to provide increased surface area for muscle attachment.

Single opening, high on skull

eg. plesiosaurs, ichthyosaurs

no examples in lab

Diapsid

2 temporal fossae, separated from orbit

eg alligator, crocodile, dinosaur

In ‘modified diapsid’ condition, bar between two temporal fossae may be lost. Weight of skull is reduced with loss of bars.

1. Lizard has space on side of skull, reflecting loss of second temporal fossa.

Has one fossa, one arch

2. Bird has one large cavern, with all bars between orbit and temporal fossae lost.

i. Decrease in number of bones comprising lower jaw

In mammal, dentary is single bone on each side of the lower jaw.

ii. With loss of bones, switch to bones articulating hinge between upper and lower jaw.

Amphibian, reptile: quadrate (upper) and articular (lower) jaw form hinge.

2 small bones form hinge: not very strong

In mammals, dentary - squamosal hinge is much stronger, involved larger bones

iii. Fate of jaw bones

hyomandibular -> stapes

quadrate -> incus

articular -> malleus

angular -> tympanic