jawless verts & the origin of jawed verts

where did vertebrates evolve

• earliest vertebrate fossils are from marine sediment

• invertebrate deuterostomes are exclusively marine and have the same osmolal concentration as surroundings

  • echinoderms, cephalochordates, urochordate

• hagfish are isosmotic with surrounding sea water

cyclostome synapomorphies

• single, medial nostril

• gills supported by brachial basket

• gill arch lateral to gill tissue

• velum- membranous flap in pharynx that pumps water over gills

• tongue with keratinous teeth

• periocular trunk muscles (myomeres)

• unique immune system

• vertebral elements

hagfish

• ~75 species

• cartilaginous vertebral structures (arcualia)

• deep sea scavengers

• highly skewed sex ratios (100:1)

• some hermaphroditic

• isosmotic

• degenerate eyes

• keratin teethlike projections

• one semicircular canal

  • helps with balance & cooridination

• slime glands

lamprey

• ~40 species

• arcualia

• large well-developed eyes

• pineal body

• two semicircular canals

• seven gill pouches & openings

• dorsal fin

• chloride cells in gills & well-developed kidneys

• parasitic

ohio native lamprey

• parasitic

  • silver lamprey

  • ohio lamprey

• nonparasitic (adults do not feed)

  • american brook lamprey

  • least brook lamprey

  • mountain brook lamprey

  • northern brook lamprey

gnathostome synapomorphies

• jointed gill arches

• jaws with true teeth

• two dorsal fins

• pectoral & pelvic fins

• w-shaped axial muscles

• second hox gene duplication

• vertebrae with centrum

• ribs

• paired nostrils

• three semicircular canals

origin of fins

• adjust body position

• hydrofoils

  • help generate lift

• provide thrust

• defense (spiny fins)

• mate attraction

• pitch- up and down

• yaw- side to side

• roll

what is the selective value of jaws?

• allows for better oxygen extraction

• more aggressive lifestyles