ZOO 2090 Lecture Notes - Lecture 5: Agnatha, Chondrichthyes, Dermal Bone

• School: University of Guelph
• Department: Zoology
• Course: ZOO 2090
• Professor: Fred Laberge

Document Summary

Describe how bone and jaws enabled fished to expand their ecological niches. Mouth present, but no biting apparatus derives from pharyngeal arches. Groups were already highly specialized by 330 mya and display features likely representative of two extant groups: hagfish and lamprey (together often referred to as cyclostomes) ancestral agnathans. Use round mouth to cling to live prey while sucking blood, others use their mouth to cling to substrate characteristics: metamorphosis of ammocoete larva, single nostril, seven gill openings, cartilage associated with notochord lack bone. Displayed a lateral line system and an outer exoskeleton made up of dermal bone plates. Armous innovation good fossils they appeared in the ordovician, radiated most in the silurian and were extinct by the end of the. Devonian (>100 mya) four major groups are recognized: pteraspiodomorphs (extinct) Most had a head shield made of fused bone plates the caudal exoskeleton was made up of small plates and scales, allowing movement of their single caudal fin.