31.3 Vertebrates

Vertebrate IntroHave 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

predationStrong endoskeleton allows for

large terrestrial organismsComplete digestive tractGenerally, 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 eggsOthers are placental (e.g.

mammals) and development of offspring occurs in female uterus

FishesEvolutionary development:

(from least to most evolved)1. Jawless fishes (superclass Agnatha)

a) About 63 speciesb) Cylindricalc) Up to 1 meter longd) Include hagfish and lampreyse) Some are parasitic

Fishes (cont’d)2. Cartilaginous fishes (class

Chondrichthyes)a) About 850 speciesb) Include rays, sharks and skatesc) 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 waterb) Have lateral line system that allows them to sense

pressure changes in water from movement nearbyc) Keen sense of smell

Fishes (cont’d)3. Bony fishes (class Osteichthyes)

a) About 20 000 speciesb) Most diverse class of all vertebratesc) Types of bony fishes:

I. Ray-finned fishesi. Include fish we commonly eat: trout, cod, salmonii. Have a pair of fins with thin bodiesiii. Often have a swim-bladder, which regulates

buoyancyiv. Water passes into mouth and out through gill slits:

oxygen is absorbs and carbon dioxide given offv. Heart is simple pump with two chambers (one

atrium and one ventricle)

Fishes (cont’d)II. Lobe-finned fishes

i. Evolved into amphibiansii. Had fleshy appendages that were adapted

to limbs for terrestrial lifeiii. Had a lung used for respirationiv. E.g. coelacanth, though extinct 20 000

years ago was discovered off the coasts of Eastern Africa