All chordates share four key characteristics: a notochord, hollow nerve cord, pharyngeal slits, and post-anal tail. In vertebrates, the notochord disintegrates and is replaced by a backbone with vertebrae made of cartilage or bone. The evolution of hinged jaws allowed vertebrates to eat a wide variety of prey. Gills function through diffusion, with oxygen diffusing from the higher concentrated water into the lower concentrated blood capillaries. Bony fishes have a stiff calcium-reinforced skeleton while cartilaginous fishes like sharks and rays have a cartilage skeleton that allows smooth movement.

1. Notochord – flexible rod that extends down the length of the body Invertebrate chordates – notochord becomes skeleton Vertebrate chordates – notochord disintegrates Chordates are named after a structure that is found in all chordate embryos

2. All chordates have: 1. Notochord 2. Hollow nerve cord – develops into brain and spinal cord 3. Pharyngeal slits – become gills in fish; not present in the adults of reptiles, birds, and mammals 4. Post-anal tail

3. Characteristics of Vertebrates Skull – protect brain Backbone – protect nerve cord Vertebrae – skeletal segments that compose the backbone Vertebrae can be made up of cartilage (sharks) or a combination of bone and cartilage (humans)‏ shark vertebrae human vertebrae

4. The evolution of hinged jaws enabled vertebrates to capture and eat a wide variety of prey

5. How do Gills Function? Hemoglobin is a protein in blood that binds readily with oxygen The blood moving in the capillaries in the blood is very low in oxygen There is a higher concentration of oxygen in the surrounding water than in the capillaries Diffusion! Oxygen diffuses across the membranes of the gills into the capillaries

6. Fishes with Bony Skeletons Bony fishes have a stiff skeleton reinforced by calcium compounds Operculum – protective flap which covers the gills; movement of the flap flushes water over the gills Internal Air Sac – makes the animal more buoyant

7. Fishes with Cartilaginous Skeletons Cartilage – tough, elastic connective tissue that allows smooth movement Sharks & Rays are cartilaginous fishes *Shark dissection the week after Spring Break! Rays are bottom-dwellers that use their jaws to crush mollusks and crustaceans Tail is used for defense