31.3 Vertebrates

Vertebrate Intro Have all 4 chordate characteristics at some point of development Embryonic notochord generally replaced by vertebral column Generally a high level of cephalization (brain and nervous system) with complex sense organs Closed circulatory system

Vertebrate Intro (cont’d) Jaw evolution allowed for easier predation Strong endoskeleton allows for large terrestrial organisms Complete digestive tract Generally, sexes are separate (not hermaphrodites) Sexual reproduction typical

Vertebrate Intro (cont’d) Evolution of amnion (extraembryonic membrane that encloses a fluid filled sac) Some lay shelled eggs Others are placental (e.g. mammals) and development of offspring occurs in female uterus

Fishes Evolutionary development: (from least to most evolved) 1.Jawless fishes (superclass Agnatha) a)About 63 species b)Cylindrical c)Up to 1 meter long d)Include hagfish and lampreys e)Some are parasitic

Fishes (cont’d) 2.Cartilaginous fishes (class Chondrichthyes) a)About 850 species b)Include rays, sharks and skates c)Have jaws (adapted gill arches – structure that supports gills) d)Skeletons made of cartilage (not bone) e)Well-developed senses make good predators: a)Ability to sense electric currents in water b)Have lateral line system that allows them to sense pressure changes in water from movement nearby c)Keen sense of smell

Fishes (cont’d) 3.Bony fishes (class Osteichthyes) a)About species b)Most diverse class of all vertebrates c)Types of bony fishes: I.Ray-finned fishes i.Include fish we commonly eat: trout, cod, salmon ii.Have a pair of fins with thin bodies iii.Often have a swim-bladder, which regulates buoyancy iv.Water passes into mouth and out through gill slits: oxygen is absorbs and carbon dioxide given off v.Heart is simple pump with two chambers (one atrium and one ventricle)

Fishes (cont’d) II.Lobe-finned fishes i.Evolved into amphibians ii.Had fleshy appendages that were adapted to limbs for terrestrial life iii.Had a lung used for respiration iv.E.g. coelacanth, though extinct years ago was discovered off the coasts of Eastern Africa