ZOO 2090 Lecture Notes - Lecture 4: Cleithrum, Articular Processes, Chondrichthyes

• School: University of Guelph
• Department: Zoology
• Course: ZOO 2090
• Professor: Jinzhong Fu

Document Summary

Agnathan skull: anaspid without without armour, pteraspidomorph with dermal bone, armour in red. Placoderm skull: view on left is without dermatocranium. Trend toward increased number of skull bones in actinopterygians. Early gnathostomes had wide mouths, far back hinge and an upper jaw fused with the braincase. Teleosts have narrow mouth, hinge moved forward, and both the upper and lower jaws can move forward independently of the braincase. Suction driven by volume change of the buccal cavity: despite the great diversity of teleosts(cid:198)basic pattern of skull bones is preserved. Early fishes: euautostylic: upper jaw braced against braincase directly, hyomandibula not involved (independent from hyomandibula, oldest, placoderms, acanthodians, amphistylic: upper jaw supported by hyomandibula and an anterior ligament connection with braincase (two primary articulation) Two principal trends: hyostyly(cid:198)contact with chondrocranium (otic capsule) principally through hyomandibula. Evolved: autostyly(cid:198)quadrate attaches chrondrocranium and jaw directly, with no support from hyomandibula, not evolved.