Gnathostomes- "Jawed Fishes"

1. Gnathostomes- "Jawed Fishes" • Appearance of Jaws- Silurian (410-430 million years ago); before agnathan radiation • value of jaws: • greater feeding opportunities- new types of food; mechanical digestion • defense • manipulate objects

2. origin of jaws • information from studies of comparative morphology/embryology • gill arches & jaws arise from neural crest tissue • palatoquadrate- upper jaw; braces jaws against brain case • mandible- lower jaw

5. Acanthidians • first jawed vertebrates • Silurian-Permian (430-260 MYA) • diagnostic features: a. mostly small (10-15 cm) b. streamlined c. ganoid scales- dermal bony scales d. large forward facing eyes e. sharp teeth f. rows of ventral paired fins g. active swimmers

6. Acanthidian

7. Placoderms- "plate-skinned" 1. Silurian-Devonian (410-350 MYA) 2. diagnostic features: a. medium-large (~30 cm) b. heavy dermal plates c. medial jaw musculature d. lack teeth e. braincase ossified f. primitive vertebral column g. dorso-ventrally flattened 3. dead end group

8. Placoderm